Single-atom-resolved fluorescence imaging of an atomic Mott insulator

DEFF Research Database (Denmark)

Sherson, Jacob; Weitenberg, Christof; Andres, Manuel

2010-01-01

in situ images of a quantum fluid in which each underlying quantum particle is detected. Here we report fluorescence imaging of strongly interacting bosonic Mott insulators in an optical lattice with single-atom and single-site resolution. From our images, we fully reconstruct the atom distribution...

Superconductivity induced by extremely high pressures in organic Mott-insulator β'-(BEDT-TTF)2IBrCl

International Nuclear Information System (INIS)

Kano, M; Uchiyama, K; Taniguchi, H; Hedo, M; Matsubayashi, K; Uwatoko, Y

2009-01-01

Previous research revealed that, at a pressure of 8.2 GPa, β'-(BEDT-TTF)2ICl2 possesses the highest transition temperature (T C ) among the organic conductors[1]. In the present work, transport studies under extremely high pressure of up to 10.0 GPa, using a cubic anvil press are reported for a related material, β'-(BEDT-TTF)2IBrCl which is an organic Mott-insulator in ambient pressure. Superconductivity with the highest T c (8.5 K, onset) was observed at P = 8.6 GPa.

Two-magnon scattering in spin–orbital Mott insulator Ba2IrO4

International Nuclear Information System (INIS)

Tsuda, Shunsuke; Uji, Shinya; Okabe, Hirotaka; Isobe, Masaaki

2016-01-01

A spin–orbit induced Mott insulator Ba 2 IrO 4 with the pseudo-spin J eff = 1/2, showing an antiferromagnetic order (T N = 240 K), has been investigated by Raman spectroscopy. A broad peak with the B 1g symmetry is found in a wide temperature region up to 400 K, which is ascribed to the two-magnon scattering. From the peak position and width, the exchange coupling and the antiferromagnetic correlation length are estimated to be 590 cm −1 and 45 Å at 90 K, respectively. The results are compared with the antiferromagnet La 2 CuO 4 with the spin S = 1/2. We conclude that there is no significant difference in the short wavelength spin-excitation between the S = 1/2 and J eff = 1/2 systems. (author)

Two-Magnon Scattering in Spin-Orbital Mott Insulator Ba2IrO4

Science.gov (United States)

Tsuda, Shunsuke; Okabe, Hirotaka; Isobe, Masaaki; Uji, Shinya

2016-02-01

A spin-orbit induced Mott insulator Ba2IrO4 with the pseudo-spin Jeff = 1/2, showing an antiferromagnetic order (TN = 240 K), has been investigated by Raman spectroscopy. A broad peak with the B1g symmetry is found in a wide temperature region up to 400 K, which is ascribed to the two-magnon scattering. From the peak position and width, the exchange coupling and the antiferromagnetic correlation length are estimated to be 590 cm-1 and 45 Å at 90 K, respectively. The results are compared with the antiferromagnet La2CuO4 with the spin S = 1/2. We conclude that there is no significant difference in the short wavelength spin-excitation between the S = 1/2 and Jeff = 1/2 systems.

Angle Resolved Photoemission Spectroscopy Studies of the Mott Insulator to Superconductor Evolution in Ca2-xNaxCuO2Cl2

Energy Technology Data Exchange (ETDEWEB)

Shen, Kyle Michael

2005-09-02

It is widely believed that many of the exotic physical properties of the high-T{sub c} cuprate superconductors arise from the proximity of these materials to the strongly correlated, antiferromagnetic Mott insulating state. Therefore, one of the fundamental questions in the field of high-temperature superconductivity is to understand the insulator-to-superconductor transition and precisely how the electronic structure of Mott insulator evolves as the first holes are doped into the system. This dissertation presents high-resolution, doping dependent angle-resolved photoemission (ARPES) studies of the cuprate superconductor Ca{sub 2-x}Na{sub x}CuO{sub 2}Cl{sub 2}, spanning from the undoped parent Mott insulator to a high-temperature superconductor with a T{sub c} of 22 K. A phenomenological model is proposed to explain how the spectral lineshape, the quasiparticle band dispersion, and the chemical potential all progress with doping in a logical and self-consistent framework. This model is based on Franck-Condon broadening observed in polaronic systems where strong electron-boson interactions cause the quasiparticle residue, Z, to be vanishingly small. Comparisons of the low-lying states to different electronic states in the valence band strongly suggest that the coupling of the photohole to the lattice (i.e. lattice polaron formation) is the dominant broadening mechanism for the lower Hubbard band states. Combining this polaronic framework with high-resolution ARPES measurements finally provides a resolution to the long-standing controversy over the behavior of the chemical potential in the high-T{sub c} cuprates. This scenario arises from replacing the conventional Fermi liquid quasiparticle interpretation of the features in the Mott insulator by a Franck-Condon model, allowing the reassignment of the position of the quasiparticle pole. As a function of hole doping, the chemical potential shifts smoothly into the valence band while spectral weight is transferred

Exploring the doping dependence of the Mott transition on X-ray irradiated crystals of {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Cl

Energy Technology Data Exchange (ETDEWEB)

Koehler, Sebastian; Tutsch, Ulrich; Naji, Ammar; Lang, Michael [Physikalisches Institut, Goethe-Universitaet Frankfurt (Germany); Sasaki, Takahiko [Institute for Materials Research, Tohoku University, Aoba-ku, Sendai, Miyagi (Japan)

2011-07-01

The quasi two-dimensional organic charge-transfer salt {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Cl exhibits a rich pressure vs. temperature phase diagram, including Mott-insulating and metallic phases separated by a first order transition line. By applying moderate pressures of {proportional_to}30 MPa (300 bar), the ratio of the kinetic energy to the onsite Coulomb repulsion t/U can be changed sufficiently to cross this phase transition line. Our objective is to study the effect of carrier doping and the accompanying changes of the first-order transition line and its second-order critical endpoint. We used X-ray irradiation to introduce charge carriers into the material, doping it away from half filling. We present resistivity data for the temperature range 5 KET){sub 2}Cu[N(CN){sub 2}]Cl crystals at various doping levels and discuss the accompanied changes in the p-T-phase diagram.

Quasi-continuous transition from a Fermi liquid to a spin liquid in κ-(ET)2Cu2(CN)3.

Science.gov (United States)

Furukawa, Tetsuya; Kobashi, Kazuhiko; Kurosaki, Yosuke; Miyagawa, Kazuya; Kanoda, Kazushi

2018-01-22

The Mott metal-insulator transition-a manifestation of Coulomb interactions among electrons-is known as a discontinuous transition. Recent theoretical studies, however, suggest that the transition is continuous if the Mott insulator carries a spin liquid with a spinon Fermi surface. Here, we demonstrate the case of a quasi-continuous Mott transition from a Fermi liquid to a spin liquid in an organic triangular-lattice system κ-(ET) 2 Cu 2 (CN) 3 . Transport experiments performed under fine pressure tuning have found that as the Mott transition is approached, the Fermi liquid coherence temperature continuously falls to the scale of kelvins, with a divergent quasi-particle decay rate on the metal side, and the charge gap continuously closes on the insulator side. A Clausius-Clapeyron analysis provides thermodynamic evidence for the extremely weak first-order nature of the transition. These results provide additional support for the existence of a spinon Fermi surface, which becomes an electron Fermi surface when charges are delocalized.

An Angle Resolved Photoemission Study of a Mott Insulator and Its Evolution to a High Temperature Superconductor

Energy Technology Data Exchange (ETDEWEB)

Ronning, Filip

2002-03-19

One of the most remarkable facts about the high temperature superconductors is their close proximity to an antiferromagnetically ordered Mott insulating phase. This fact suggests that to understand superconductivity in the cuprates we must first understand the insulating regime. Due to material properties the technique of angle resolved photoemission is ideally suited to study the electronic structure in the cuprates. Thus, a natural starting place to unlocking the secrets of high Tc would appears to be with a photoemission investigation of insulating cuprates. This dissertation presents the results of precisely such a study. In particular, we have focused on the compound Ca{sub 2-x}Na{sub x}CuO{sub 2}Cl{sub 2}. With increasing Na content this system goes from an antiferromagnetic Mott insulator with a Neel transition of 256K to a superconductor with an optimal transition temperature of 28K. At half filling we have found an asymmetry in the integrated spectral weight, which can be related to the occupation probability, n(k). This has led us to identify a d-wave-like dispersion in the insulator, which in turn implies that the high energy pseudogap as seen by photoemission is a remnant property of the insulator. These results are robust features of the insulator which we found in many different compounds and experimental conditions. By adding Na we were able to study the evolution of the electronic structure across the insulator to metal transition. We found that the chemical potential shifts as holes are doped into the system. This picture is in sharp contrast to the case of La{sub 2-x}Sr{sub x}CuO{sub 4} where the chemical potential remains fixed and states are created inside the gap. Furthermore, the low energy excitations (ie the Fermi surface) in metallic Ca{sub 1.9}Na{sub 0.1}CuO{sub 2}Cl{sub 2} is most well described as a Fermi arc, although the high binding energy features reveal the presence of shadow bands. Thus, the results in this dissertation provide a

Two-dimensional orbital ordering in d{sup 1} Mott insulator Sr{sub 2}VO{sub 4}

Energy Technology Data Exchange (ETDEWEB)

Viennois, R; Giannini, E; Teyssier, J; Elia, J; Van der Marel, D [DPMC, Universite de Geneve, 24 quai Ernest Ansermet, CH-1211 Geneve (Switzerland); Deisenhofer, J, E-mail: Romain.Viennois@unige.c [Institute of Physics, University of Augsburg, Augsburg (Germany)

2010-01-15

The Mott insulator Sr{sub 2}VO{sub 4} is a unique d{sup 1} two-dimensional compound exhibiting an orbital ordering transition. In addition to the orbital ordering transition at about 100 K, we discovered a ferromagnetic transition below 10 K, thus confirming the predictions of recent band structure calculations. The magnetic properties proved to be strongly sensitive to the material purity, the actual oxygen stoichiometry and the crystallographic parameters. An additional transition is observed at 125 K, which is believed to be due to structural modifications.

On the Mott transition and the new metal-insulator transitions in doped covalent and polar crystals

International Nuclear Information System (INIS)

Dzhumanov, S.; Begimkulov, U.; Kurbanov, U.T.; Yavidov, B.Y.

2001-10-01

The Mott transition and new metal-insulator transitions (MIT's) and their distinctive features in doped covalent semiconductors and polar compounds are studied within the continuum model of extrinsic carrier self-trapping, the Hubbard impurity band model (with on-site Coulomb repulsion and screening effects) and the extrinsic (bi)polaronic band model (with short- and long-range carrier-impurity, impurity-phonon and carrier-phonon interactions and intercarrier correlation) using the appropriate tight-binding approximations and variational methods. We have shown the formation possibility of large-radius localized one- and two-carrier impurity (or defect) states and narrow impurity bands in the band gap and charge transfer gap of these carrier-doped systems. The extrinsic Mott-Hubbard and (bi)polaronic insulating gaps are calculated exactly. The proper criterions for Mott transition, extrinsic excitonic and (bi)polaronic MIT's are obtained. We have demonstrated that the Mott transition occurs in doped covalent semiconductors (i.e. Si and Ge) and some insulators with weak carrier-phonon coupling near the large-radius dopants. While, in doped polar compounds (e.g. oxide high-T c superconductors (HTSC) and related materials) the MIT's are new extrinsic (or intrinsic) (bi)polaronic MIT's. We have found that the anisotropy of the dielectric (or (bi)polaronic) properties of doped cuprate HTSC is responsible for smooth (or continuous) MIT's, stripe formation and suppression of high-T c superconductivity. Various experimental results on in-gap states, bands and MIT's in doped covalent semiconductors, oxide HTSC and related materials are in good agreement with the developed theory of Mott transition and new (bi)polaronic MIT's. (author)

Dimensional crossover and cold-atom realization of gapless and semi-metallic Mott insulating phases

Science.gov (United States)

Orth, Peter P.; Scheurer, Mathias; Rachel, Stephan

2014-03-01

We propose a realistic cold-atom setup which allows for a dimensional crossover from a two-dimensional quantum spin Hall insulating phase to a three-dimensional strong topological insulator phase by simply tuning the hopping between the layers. We further employ cluster slave-rotor mean-field theory to study the effect of additional Hubbard onsite interactions that give rise to various spin liquid-like phases such as gapless and semi-metallic Mott insulating states.

Mott-insulating phases and magnetism of fermions in a double-well optical lattice

International Nuclear Information System (INIS)

Wang, Xin; Zhou, Qi; Das Sarma, S.

2011-01-01

We theoretically investigate, using nonperturbative strong correlation techniques, Mott-insulating phases and magnetic ordering of two-component fermions in a two-dimensional double-well optical lattice. At filling of two fermions per site, there are two types of Mott insulators, one of which is characterized by spin-1 antiferromagnetism below the Neel temperature. The superexchange interaction in this system is induced by the interplay between the interband interaction and the spin degree of freedom. A great advantage of the double-well optical lattice is that the magnetic quantum phase diagram and the Neel temperature can be easily controlled by tuning the orbital energy splitting of the two-level system. Particularly, the Neel temperature can be one order of magnitude larger than that in standard optical lattices, facilitating the experimental search for magnetic ordering in optical lattice systems.

Site-resolved imaging of a bosonic Mott insulator using ytterbium atoms

Science.gov (United States)

Miranda, Martin; Inoue, Ryotaro; Tambo, Naoki; Kozuma, Mikio

2017-10-01

We demonstrate site-resolved imaging of a strongly correlated quantum system without relying on laser cooling techniques during fluorescence imaging. We observe the formation of Mott shells in the insulating regime and realize thermometry in an atomic cloud. This work proves the feasibility of the noncooled approach and opens the door to extending the detection technology to new atomic species.

Mott-insulating phases in unidimensional multi-components fermionic cold atoms

International Nuclear Information System (INIS)

Nonne, Heloise

2011-01-01

This thesis is devoted to the investigation of the Mott insulating phases arising in one-dimensional multicomponent fermionic cold atoms systems. The first part of this work is the study of a model with alkaline-earth cold atoms with nuclear spin I = 1/2. Those atoms enjoy an additional orbital degree of freedom, due to the presence of a metastable excited state; they thus have a total of four components. Our investigation is carried at half-filling, at strong and at weak couplings by means of analytic methods (conformal theory, bosonization, refermionization, renormalisation group). We found that the zero temperature phase diagram of the system is very rich: it contains seven Mott insulating phases, among which three are particularly interesting, since they display a hidden order, related to the Haldane physics of the antiferromagnetic spin-1 Heisenberg chain. Our conclusions are checked against numerical simulations, that were carried out with the density matrix renormalization group (DMRG) algorithm for intermediate couplings. The comparison shows an adiabatic continuity between the different regimes. A similar study for a model of cold atoms with hyperfine spin-3/2 highlights the Haldane physics in the charge sector of the degrees of freedom, with an effective model given by an antiferromagnetic pseudo-spin-1 chain. This analysis provides us an opportunity to investigate the zero temperature properties of the SO(5) bilinear-bi-quadratic Heisenberg chain. We show the presence of two gapped phases: one is dimerized, the other has a hidden symmetry (Z 2 x Z 2 ) 2 and spin-3/2 edge states, and they are separated by a critical point that belongs to the SO(5) 1 universality class. Finally, we investigate half-integer hyperfine spin cold atoms systems with 2N components which generalized the results obtained for the hyperfine spin-3/2 model. This leads us to find an even/odd effect according to the parity of N, very similar to the even/odd effect of spin chains

Realization of a Hole-Doped Mott Insulator on a Triangular Silicon Lattice

Science.gov (United States)

Ming, Fangfei; Johnston, Steve; Mulugeta, Daniel; Smith, Tyler S.; Vilmercati, Paolo; Lee, Geunseop; Maier, Thomas A.; Snijders, Paul C.; Weitering, Hanno H.

2017-12-01

The physics of doped Mott insulators is at the heart of some of the most exotic physical phenomena in materials research including insulator-metal transitions, colossal magnetoresistance, and high-temperature superconductivity in layered perovskite compounds. Advances in this field would greatly benefit from the availability of new material systems with a similar richness of physical phenomena but with fewer chemical and structural complications in comparison to oxides. Using scanning tunneling microscopy and spectroscopy, we show that such a system can be realized on a silicon platform. The adsorption of one-third monolayer of Sn atoms on a Si(111) surface produces a triangular surface lattice with half filled dangling bond orbitals. Modulation hole doping of these dangling bonds unveils clear hallmarks of Mott physics, such as spectral weight transfer and the formation of quasiparticle states at the Fermi level, well-defined Fermi contour segments, and a sharp singularity in the density of states. These observations are remarkably similar to those made in complex oxide materials, including high-temperature superconductors, but highly extraordinary within the realm of conventional s p -bonded semiconductor materials. It suggests that exotic quantum matter phases can be realized and engineered on silicon-based materials platforms.

Non-destructive reversible resistive switching in Cr doped Mott insulator Ca2RuO4: Interface vs bulk effects

Science.gov (United States)

Shen, Shida; Williamson, Morgan; Cao, Gang; Zhou, Jianshi; Goodenough, John; Tsoi, Maxim

2017-12-01

A non-destructive reversible resistive switching is demonstrated in single crystals of Cr-doped Mott insulator Ca2RuO4. An applied electrical bias was shown to reduce the DC resistance of the crystal by as much as 75%. The original resistance of the sample could be restored by applying an electrical bias of opposite polarity. We have studied this resistive switching as a function of the bias strength, applied magnetic field, and temperature. A combination of 2-, 3-, and 4-probe measurements provide a means to distinguish between bulk and interfacial contributions to the switching and suggests that the switching is mostly an interfacial effect. The switching was tentatively attributed to electric-field driven lattice distortions which accompany the impurity-induced Mott transition. This field effect was confirmed by temperature-dependent resistivity measurements which show that the activation energy of this material can be tuned by an applied DC electrical bias. The observed resistance switching can potentially be used for building non-volatile memory devices like resistive random access memory.

Non-destructive reversible resistive switching in Cr doped Mott insulator Ca2RuO4: Interface vs bulk effects

KAUST Repository

Shen, Shida

2017-12-29

A non-destructive reversible resistive switching is demonstrated in single crystals of Cr-doped Mott insulator Ca2RuO4. An applied electrical bias was shown to reduce the DC resistance of the crystal by as much as 75%. The original resistance of the sample could be restored by applying an electrical bias of opposite polarity. We have studied this resistive switching as a function of the bias strength, applied magnetic field, and temperature. A combination of 2-, 3-, and 4-probe measurements provide a means to distinguish between bulk and interfacial contributions to the switching and suggests that the switching is mostly an interfacial effect. The switching was tentatively attributed to electric-field driven lattice distortions which accompany the impurity-induced Mott transition. This field effect was confirmed by temperature-dependent resistivity measurements which show that the activation energy of this material can be tuned by an applied DC electrical bias. The observed resistance switching can potentially be used for building non-volatile memory devices like resistive random access memory.

Mott transitions in the periodic Anderson model

International Nuclear Information System (INIS)

Logan, David E; Galpin, Martin R; Mannouch, Jonathan

2016-01-01

The periodic Anderson model (PAM) is studied within the framework of dynamical mean-field theory, with particular emphasis on the interaction-driven Mott transition it contains, and on resultant Mott insulators of both Mott–Hubbard and charge-transfer type. The form of the PAM phase diagram is first deduced on general grounds using two exact results, over the full range of model parameters and including metallic, Mott, Kondo and band insulator phases. The effective low-energy model which describes the PAM in the vicinity of a Mott transition is then shown to be a one-band Hubbard model, with effective hoppings that are not in general solely nearest neighbour, but decay exponentially with distance. This mapping is shown to have a range of implications for the physics of the problem, from phase boundaries to single-particle dynamics; all of which are confirmed and supplemented by NRG calculations. Finally we consider the locally degenerate, non-Fermi liquid Mott insulator, to describe which requires a two-self-energy description. This is shown to yield a number of exact results for the associated local moment, charge, and interaction-renormalised levels, together with a generalisation of Luttinger’s theorem to the Mott insulator. (paper)

Inhomogeneous field induced magnetoelectric effect in Mott insulators

Energy Technology Data Exchange (ETDEWEB)

Boulaevskii, Lev N [Los Alamos National Laboratory; Batista, Cristian D [Los Alamos National Laboratory

2008-01-01

We consider a Mott insulator like HoMnO{sub 3} whose magnetic lattice is geometrically frustrated and comprises a 3D array of triangular layers with magnetic moments ordered in a 120{sup o} structure. We show that the effect of a uniform magnetic field gradient, {gradient}H, is to redistribute the electronic charge of the magnetically ordered phase leading to a unfirom electric field gradient. The resulting voltage difference between the crystal edges is proportional to the square of the crystal thickness, or inter-edge distance, L. It can reach values of several volts for |{gradient}H| {approx} 0.01 T/cm and L {approx_equal} 1mm, as long as the crystal is free of antiferromagnetic domain walls.

Mottness

International Nuclear Information System (INIS)

Phillips, Philip

2006-01-01

We review several of the normal state properties of the cuprates in an attempt to establish an organizing principle from which pseudogap phenomena, broad spectral features, T-linear resistivity, and spectral weight transfer emerge. We first show that standard field theories with a single critical length scale cannot capture the T-linear resistivity as long as the charge carriers are critical. What seems to be missing is an additional length scale, which may or may not be critical. Second, we prove a generalised version of Luttinger's theorem for a Mott insulator. In particular, we show that for Mott insulators, regardless of the spatial dimension, the Fermi surface of the non-interacting system is converted into a surface of zeros of the single-particle Green function when the underlying band structure has particle-hole symmetry. Only in the presence of particle-hole symmetry does the volume of the surface of zeros equal the particle density. The surface of zeros persists at finite doping and is shown to provide a framework from which pseudogaps, broad spectral features, spectral weight transfer on the Mott gap scale, and the additional length scale required to capture T-linear resistivity can be understood

Impurity band Mott insulators: a new route to high Tc superconductivity

Directory of Open Access Journals (Sweden)

Ganapathy Baskaran

2008-01-01

Full Text Available Last century witnessed the birth of semiconductor electronics and nanotechnology. The physics behind these revolutionary developments is certain quantum mechanical behaviour of 'impurity state electrons' in crystalline 'band insulators', such as Si, Ge, GaAs and GaN, arising from intentionally added (doped impurities. The present article proposes that certain collective quantum behaviour of these impurity state electrons, arising from Coulomb repulsions, could lead to superconductivity in a parent band insulator, in a way not suspected before. Impurity band resonating valence bond theory of superconductivity in boron doped diamond, recently proposed by us, suggests possibility of superconductivity emerging from impurity band Mott insulators. We use certain key ideas and insights from the field of high-temperature superconductivity in cuprates and organics. Our suggestion also offers new possibilities in the field of semiconductor electronics and nanotechnology. The current level of sophistication in solid state technology and combinatorial materials science is very well capable of realizing our proposal and discover new superconductors.

A Mott-like State of Molecules

International Nuclear Information System (INIS)

Duerr, S.; Volz, T.; Syassen, N.; Bauer, D. M.; Hansis, E.; Rempe, G.

2006-01-01

We prepare a quantum state where each site of an optical lattice is occupied by exactly one molecule. This is the same quantum state as in a Mott insulator of molecules in the limit of negligible tunneling. Unlike previous Mott insulators, our system consists of molecules which can collide inelastically. In the absence of the optical lattice these collisions would lead to fast loss of the molecules from the sample. To prepare the state, we start from a Mott insulator of atomic 87Rb with a central region, where each lattice site is occupied by exactly two atoms. We then associate molecules using a Feshbach resonance. Remaining atoms can be removed using blast light. Our method does not rely on the molecule-molecule interaction properties and is therefore applicable to many systems

Self-energy behavior away from the Fermi surface in doped Mott insulators.

Science.gov (United States)

Merino, J; Gunnarsson, O; Kotliar, G

2016-02-03

We analyze self-energies of electrons away from the Fermi surface in doped Mott insulators using the dynamical cluster approximation to the Hubbard model. For large onsite repulsion, U, and hole doping, the magnitude of the self-energy for imaginary frequencies at the top of the band ([Formula: see text]) is enhanced with respect to the self-energy magnitude at the bottom of the band ([Formula: see text]). The self-energy behavior at these two [Formula: see text]-points is switched for electron doping. Although the hybridization is much larger for (0, 0) than for [Formula: see text], we demonstrate that this is not the origin of this difference. Isolated clusters under a downward shift of the chemical potential, [Formula: see text], at half-filling reproduce the overall self-energy behavior at (0, 0) and [Formula: see text] found in low hole doped embedded clusters. This happens although there is no change in the electronic structure of the isolated clusters. Our analysis shows that a downward shift of the chemical potential which weakly hole dopes the Mott insulator can lead to a large enhancement of the [Formula: see text] self-energy for imaginary frequencies which is not associated with electronic correlation effects, even in embedded clusters. Interpretations of the strength of electronic correlations based on self-energies for imaginary frequencies are, in general, misleading for states away from the Fermi surface.

Excitonic metal-insulator phase transition of the Mott type in compressed calcium

Science.gov (United States)

Voronkova, T. O.; Sarry, A. M.; Sarry, M. F.; Skidan, S. G.

2017-05-01

It has been experimentally found that, under the static compression of a calcium crystal at room temperature, it undergoes a series of structural phase transitions: face-centered cubic lattice → body-centered cubic lattice → simple cubic lattice. It has been decided to investigate precisely the simple cubic lattice (because it is an alternative lattice) with the aim of elucidating the possibility of the existence of other (nonstructural) phase transitions in it by using for this purpose the Hubbard model for electrons with half-filled ns-bands and preliminarily transforming the initial electronic system into an electron-hole system by means of the known Shiba operators (applicable only to alternative lattices). This transformation leads to the fact that, in the new system of fermions, instead of the former repulsion, there is an attraction between electrons and holes. Elementary excitations of this new system are bound boson pairs—excitons. This system of fermions has been quantitatively analyzed by jointly using the equation-of-motion method and the direct algebraic method. The numerical integration of the analytically exact transcendental equations derived from the first principles for alternative (one-, two-, and three-dimensional) lattices has demonstrated that, in systems of two-species (electrons + hole) fermions, temperature-induced metal-insulator phase transitions of the Mott type are actually possible. Moreover, all these crystals are in fact excitonic insulators. This conclusion is in complete agreement with the analytically exact calculations of the ground state of a one-dimensional crystal (with half-filled bands), which were performed by Lieb and Wu with the aim to find out the Mott insulator-metal transition of another type.

Antiferromagnetism and d-wave superconductivity in (doped) Mott insulators: A wave function approach

OpenAIRE

Weng, Z. Y.; Zhou, Y.; Muthukumar, V. N.

2003-01-01

We propose a class of wave functions that provide a unified description of antiferromagnetism and d-wave superconductivity in (doped) Mott insulators. The wave function has a Jastrow form and prohibits double occupancies. In the absence of holes, the wave function describes antiferromagnetism accurately. Off diagonal long range order develops at finite doping and the superconducting order parameter has d-wave symmetry. We also show how nodal quasiparticles and neutral spin excitations can be ...

Effects of Disorder on the Pressure-Induced Mott Transition in κ-(BEDT-TTF2Cu[N(CN2]Cl

Directory of Open Access Journals (Sweden)

Elena Gati

2018-01-01

Full Text Available We present a study of the influence of disorder on the Mott metal-insulator transition for the organic charge-transfer salt κ -(BEDT-TTF 2 Cu[N(CN 2 ]Cl. To this end, disorder was introduced into the system in a controlled way by exposing the single crystals to X-ray irradiation. The crystals were then fine-tuned across the Mott transition by the application of continuously controllable He-gas pressure at low temperatures. Measurements of the thermal expansion and resistance show that the first-order character of the Mott transition prevails for low irradiation doses achieved by irradiation times up to 100 h. For these crystals with a moderate degree of disorder, we find a first-order transition line which ends in a second-order critical endpoint, akin to the pristine crystals. Compared to the latter, however, we observe a significant reduction of both, the critical pressure p c and the critical temperature T c . This result is consistent with the theoretically-predicted formation of a soft Coulomb gap in the presence of strong correlations and small disorder. Furthermore, we demonstrate, similar to the observation for the pristine sample, that the Mott transition after 50 h of irradiation is accompanied by sizable lattice effects, the critical behavior of which can be well described by mean-field theory. Our results demonstrate that the character of the Mott transition remains essentially unchanged at a low disorder level. However, after an irradiation time of 150 h, no clear signatures of a discontinuous metal-insulator transition could be revealed anymore. These results suggest that, above a certain disorder level, the metal-insulator transition becomes a smeared first-order transition with some residual hysteresis.

Pertinence et limitations de la loi de Mott dans les isolants désordonnés

Science.gov (United States)

Ladieu, François; Sanquer, Marc

Twenty five years ago, Mott's law was established in order to describe electrical transport in disordered insulators at low temperature. In this review, we briefly summarize the different theoretical steps involved in the rigourous derivation of Mott's law. We stress upon the fact that Mott's law gives the mean conductance of an ensemble of macroscopic samples as long as electron-electron interactions remain negligible. We then study what happens when at least one of the key assumptions of Mott's law no longer holds. We first focus on systems whose size — at least in one dimension — is not macroscopic: the optimization involved in Mott's law is no longer relevant for the measured conductance. Eventually, we try to gather different works dealing with electron-electron interactions. It is now established that interactions generally produce a stronger divergence for the electrical resistance than the one predicted by Mott's law at the lowest temperatures. But the exact shape of this divergence, as well as its interpretation, remain debated. We try to make a link between Efros and Shklovskii 's work and their famous "Coulomb gap" and a more recent work about granular media. In this latter work, the size of the grains is the key parameter for the shape of the divergence of the resistance at low temperature. We suggest this could indicate a way for a model accounting for the different shapes of divergence of the electrical resistance at the lowest temperatures. Furthermore this framework of granular media allows us to deal with non linear regime: we explain the main differences between the predictions of the hot electrons model and the ones recently derived for a d -dimensional network of grains. Il y a déjà un quart de siècle que la loi de Mott a été établie afin de décrire le transport dans les milieux isolants désordonnés à basse température. Dans cet article de revue, nous rappelons brièvement les diverses étapes théoriques nécessaires à l

Thermally assisted ordering in Mott insulators

Science.gov (United States)

Sims, Hunter; Pavarini, Eva; Koch, Erik

2017-08-01

Landau theory describes phase transitions as the competition between energy and entropy: The ordered phase has lower energy, while the disordered phase has larger entropy. When heating the system, ordering is reduced entropically until it vanishes at the critical temperature. This picture implicitly assumes that the energy difference between the ordered and disordered phases does not change with temperature. We show that for orbital ordering in the Mott insulator KCuF3, this assumption fails qualitatively: entropy plays a negligible role, while thermal expansion energetically stabilizes the orbitally ordered phase to such an extent that no phase transition is observed. To understand this strong dependence on the lattice constant, we need to take into account the Born-Mayer repulsion between the ions. It is the latter, and not the Jahn-Teller elastic energy, which determines the magnitude of the distortion. This effect will be seen in all materials where the distortion expected from the Jahn-Teller mechanism is so large that the ions would touch. Our mechanism explains not only the absence of a phase transition in KCuF3, but even suggests the possibility of an inverted transition in closed-shell systems, where the ordered phase emerges only at high temperatures.

Resolving the chicken-and-egg problem in VO2: a new paradigm for the Mott transition

Science.gov (United States)

Najera, Oscar; Civelli, Marcello; Dobrosavljevi, Vladimir; Rozenberg, Marcelo

We consider a minimal model to investigate the metal-insulator transition in VO2. We adopt a Hubbard model with two orbital per unit cell, which captures the competition between Mott and singlet-dimer localization. We solve the model within Dynamical Mean Field Theory, characterizing in detail the metal-insulator transition and finding new features in the electronic states. We compare our results with available experimental data obtaining good agreement in the relevant model parameter range. Crucially, we can account for puzzling optical conductivity data obtained within the hysteresis region, which we associate to a novel metallic state characterized by a split heavy quasiparticle band. Our results show that the thermal-driven insulator-to-metal transition in VO2 is entirely compatible with a Mott electronic mechanism, solving a long standing ''chicken-and-egg'' debate and calling for further research of ``Mottronics'' applications of this system. This work was partially supported by public Grants from the French National Research Agency (ANR), project LACUNES No ANR-13-BS04-0006-01, the NSF DMR-1005751 and DMR-1410132.

Mott Transition of Fermionic Atoms in a Three-Dimensional Optical Trap

International Nuclear Information System (INIS)

Helmes, R. W.; Rosch, A.; Costi, T. A.

2008-01-01

We study theoretically the Mott metal-insulator transition for a system of fermionic atoms confined in a three-dimensional optical lattice and a harmonic trap. We describe an inhomogeneous system of several thousand sites using an adaptation of dynamical mean-field theory solved efficiently with the numerical renormalization group method. Above a critical value of the on-site interaction, a Mott-insulating phase appears in the system. We investigate signatures of the Mott phase in the density profile and in time-of-flight experiments

Temperature dependence of hole mobility in Mott insulators: Normal-state resistivity of high-T/sub c/ superconductors

International Nuclear Information System (INIS)

Kumar, N.

1989-01-01

We consider the diffusion of a hole injected in a Mott insulator described by a one-band Hubbard Hamiltonian at half-filling and in the atomic limit. The diffusion coefficient turns out to be temperature independent exactly giving 1/T dependence for the drift mobility via the Einstein relation. This is in marked disagreement with the (1/T)/sup 1/2/ dependence obtaining in the self-retracing path approximation at low temperatures. We note the possible relevance of our result to the linear T dependence of the normal-state resistivity observed in the high-T/sub c/ oxide superconductors

Mott glass from localization and confinement

Science.gov (United States)

Chou, Yang-Zhi; Nandkishore, Rahul M.; Radzihovsky, Leo

2018-05-01

We study a system of fermions in one spatial dimension with linearly confining interactions and short-range disorder. We focus on the zero-temperature properties of this system, which we characterize using bosonization and the Gaussian variational method. We compute the static compressibility and ac conductivity, and thereby demonstrate that the system is incompressible, but exhibits gapless optical conductivity. This corresponds to a "Mott glass" state, distinct from an Anderson and a fully gapped Mott insulator, arising due to the interplay of disorder and charge confinement. We argue that this Mott glass phenomenology should persist to nonzero temperatures.

Mean-Field Scaling of the Superfluid to Mott Insulator Transition in a 2D Optical Superlattice.

Science.gov (United States)

Thomas, Claire K; Barter, Thomas H; Leung, Tsz-Him; Okano, Masayuki; Jo, Gyu-Boong; Guzman, Jennie; Kimchi, Itamar; Vishwanath, Ashvin; Stamper-Kurn, Dan M

2017-09-08

The mean-field treatment of the Bose-Hubbard model predicts properties of lattice-trapped gases to be insensitive to the specific lattice geometry once system energies are scaled by the lattice coordination number z. We test this scaling directly by comparing coherence properties of ^{87}Rb gases that are driven across the superfluid to Mott insulator transition within optical lattices of either the kagome (z=4) or the triangular (z=6) geometries. The coherent fraction measured for atoms in the kagome lattice is lower than for those in a triangular lattice with the same interaction and tunneling energies. A comparison of measurements from both lattices agrees quantitatively with the scaling prediction. We also study the response of the gas to a change in lattice geometry, and observe the dynamics as a strongly interacting kagome-lattice gas is suddenly "hole doped" by introducing the additional sites of the triangular lattice.

Fingerprints of spin-orbital polarons and of their disorder in the photoemission spectra of doped Mott insulators with orbital degeneracy

Science.gov (United States)

Avella, Adolfo; Oleś, Andrzej M.; Horsch, Peter

2018-04-01

We explore the effects of disordered charged defects on the electronic excitations observed in the photoemission spectra of doped transition metal oxides in the Mott insulating regime by the example of the R1 -xCaxVO3 perovskites, where R = La, ⋯, Lu. A fundamental characteristic of these vanadium d2 compounds with partly filled t2 g valence orbitals is the persistence of spin and orbital order up to high doping, in contrast to the loss of magnetic order in high-Tc cuprates at low defect concentration. We study the disordered electronic structure of such doped Mott-Hubbard insulators within the unrestricted Hartree-Fock approximation and, as a result, manage to explain the spectral features that occur in photoemission and inverse photoemission. In particular, (i) the atomic multiplet excitations in the inverse photoemission spectra and the various defect-related states and satellites are qualitatively well reproduced, (ii) a robust Mott gap survives up to large doping, and (iii) we show that the defect states inside the Mott gap develop a soft gap at the Fermi energy. The soft defect-states gap, which separates the highest occupied from the lowest unoccupied states, can be characterized by a shape and a scale parameter extracted from a Weibull statistical sampling of the density of states near the chemical potential. These parameters provide a criterion and a comprehensive schematization for the insulator-metal transition in disordered systems. Our results provide clear indications that doped holes are bound to charged defects and form small spin-orbital polarons whose internal kinetic energy is responsible for the opening of the soft defect-states gap. We show that this kinetic gap survives disorder fluctuations of defects and is amplified by the long-range electron-electron interactions, whereas we observe a Coulomb singularity in the atomic limit. The small size of spin-orbital polarons is inferred by an analysis of the inverse participation ratio and by

Coherence and pairing in a doped Mott insulator: application to the cuprates.

Science.gov (United States)

Senthil, T; Lee, Patrick A

2009-08-14

The issues of single particle coherence and its interplay with singlet pairing are studied within the slave boson gauge theory of a doped Mott insulator. Prior work by one of us [T. Senthil, Phys. Rev. B 78, 045109 (2008)10.1103/PhysRevB.78.045109] showed that the coherence scale below which Landau quasiparticles emerge is parametrically lower than that identified in the slave boson mean field theory. Here we study the resulting new non-Fermi liquid intermediate temperature regime characterized by a single particle scattering rate that is linear in temperature (T). In the presence of a d-wave pair amplitude, this leads to a pseudogap state with T-dependent Fermi arcs near the nodal direction. Implications for understanding the cuprates are discussed.

Spectral properties near the Mott transition in the two-dimensional Hubbard model

Science.gov (United States)

Kohno, Masanori

2013-03-01

Single-particle excitations near the Mott transition in the two-dimensional (2D) Hubbard model are investigated by using cluster perturbation theory. The Mott transition is characterized by the loss of the spectral weight from the dispersing mode that leads continuously to the spin-wave excitation of the Mott insulator. The origins of the dominant modes of the 2D Hubbard model near the Mott transition can be traced back to those of the one-dimensional Hubbard model. Various anomalous spectral features observed in cuprate high-temperature superconductors, such as the pseudogap, Fermi arc, flat band, doping-induced states, hole pockets, and spinon-like and holon-like branches, as well as giant kink and waterfall in the dispersion relation, are explained in a unified manner as properties near the Mott transition in a 2D system.

Wide gap Chern Mott insulating phases achieved by design

Science.gov (United States)

Guo, Hongli; Gangopadhyay, Shruba; Köksal, Okan; Pentcheva, Rossitza; Pickett, Warren E.

2017-12-01

Quantum anomalous Hall insulators, which display robust boundary charge and spin currents categorized in terms of a bulk topological invariant known as the Chern number (Thouless et al Phys. Rev. Lett. 49, 405-408 (1982)), provide the quantum Hall anomalous effect without an applied magnetic field. Chern insulators are attracting interest both as a novel electronic phase and for their novel and potentially useful boundary charge and spin currents. Honeycomb lattice systems such as we discuss here, occupied by heavy transition-metal ions, have been proposed as Chern insulators, but finding a concrete example has been challenging due to an assortment of broken symmetry phases that thwart the topological character. Building on accumulated knowledge of the behavior of the 3d series, we tune spin-orbit and interaction strength together with strain to design two Chern insulator systems with bandgaps up to 130 meV and Chern numbers C = -1 and C = 2. We find, in this class, that a trade-off between larger spin-orbit coupling and strong interactions leads to a larger gap, whereas the stronger spin-orbit coupling correlates with the larger magnitude of the Hall conductivity. Symmetry lowering in the course of structural relaxation hampers obtaining quantum anomalous Hall character, as pointed out previously; there is only mild structural symmetry breaking of the bilayer in these robust Chern phases. Recent growth of insulating, magnetic phases in closely related materials with this orientation supports the likelihood that synthesis and exploitation will follow.

Electrostatic doping of a Mott insulator in an oxide heterostructure: the case of LaVO{sub 3}/SrTiO{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Mueller, Andreas; Pfaff, Florian; Sing, Michael; Claessen, Ralph [Physikalisches Insititut and Roentgen Research Center for Complex Material Systems, Universitaet Wuerzburg, D-97074 Wuerzburg (Germany); Boschker, Hans; Kamp, Martin; Koster, Gertjan; Rijnders, Guus [Faculty of Science and Technology and MESA-plus Institute for Nanotechnology, University of Twente, 7500 AE Enschede (Netherlands)

2012-07-01

The discovery of a quasi-two-dimensional electron system at the interface between the two band insulators LaAlO{sub 3} and SrTiO{sub 3} has triggered intense investigations of oxide heterostructures with other material combinations. The hope is that by combining a polar overlayer with a non-polar substrate electronic reconstruction will lead to highly mobile interface charge carriers with special properties. The formation of a conducting interface layer in epitaxial LaVO{sub 3}/SrTiO{sub 3}, where LaVO{sub 3} is a Mott insulator, is studied by transport measurements and hard X-ray photoelectron spectroscopy. We identify an insulator-to-metal transition above a critical LaVO{sub 3} thickness with transport properties similar to those recently reported for LaAlO{sub 3}/SrTiO{sub 3} interfaces. Interestingly, our photoemission measurements give evidence that electronic charge is transferred exclusively to the LaVO{sub 3}-side of the interface caused by an electronic reconstruction within the film itself. This opens the opportunity to study a band-filling controlled Mott transition induced by a purely electrostatic mechanism.

Device Performance of the Mott InsulatorDevice Performance of the Mott Insulator LaVO3 as a Photovoltaic Material

KAUST Repository

Wang, Lingfei; Li, Yongfeng; Bera, Ashok; Ma, Chun; Jin, Feng; Yuan, Kaidi; Yin, Wanjian; David, Adrian; Chen, Wei; Wu, Wenbin; Prellier, Wilfrid; Wei, Suhuai; Wu, Tao

2015-01-01

in solar cells in conjunction with carrier transporters and evaluate its device performance. Our complementary experimental and theoretical results on such prototypical solar cells made of Mott-Hubbard transition-metal oxides pave the road for developing

Mott-Hubbard transition and Anderson localization: A generalized dynamical mean-field theory approach

International Nuclear Information System (INIS)

Kuchinskii, E. Z.; Nekrasov, I. A.; Sadovskii, M. V.

2008-01-01

The DOS, the dynamic (optical) conductivity, and the phase diagram of a strongly correlated and strongly disordered paramagnetic Anderson-Hubbard model are analyzed within the generalized dynamical mean field theory (DMFT + Σ approximation). Strong correlations are taken into account by the DMFT, and disorder is taken into account via an appropriate generalization of the self-consistent theory of localization. The DMFT effective single-impurity problem is solved by a numerical renormalization group (NRG); we consider the three-dimensional system with a semielliptic DOS. The correlated metal, Mott insulator, and correlated Anderson insulator phases are identified via the evolution of the DOS and dynamic conductivity, demonstrating both the Mott-Hubbard and Anderson metal-insulator transition and allowing the construction of the complete zero-temperature phase diagram of the Anderson-Hubbard model. Rather unusual is the possibility of a disorder-induced Mott insulator-to-metal transition

Competition entre supraconductivite et magnetisme au voisinage de la transition de Mott dans le conducteur organique quasi-bidimensionnel k-(BEDT-TTF)2copper[N(CN)2]bromine

Science.gov (United States)

Fournier, David

Les conducteurs organiques quasi-bidimensionnels kappa-ET2X presentent d'importantes similitudes avec les SCHT telles qu'une phase isolant de Mott, un regime de pseudogap et un etat supraconducteur. L'etude de leurs proprietes apparait donc complementaire. Parmi les interrogations persistantes concernant la physique de ces systemes, l'origine du (ou des) processus exotique d'appariement, responsable de la supraconductivite est le sujet suscitant l'interet le plus marque dans la communaute. L'hypothese d'un mecanisme lie a la proximite d'un etat antiferromagnetique est privilegiee. Une etape importante dans la resolution de cette problematique est l'identification de la symetrie du parametre d'ordre. D'apres de nombreux travaux sur les systemes fortement correles, la sonde ultrasonore, de par sa sensibilite aux excitations de quasiparticule a basse temperature, est consideree comme particulierement adaptee a l'etude de cette propriete. Cependant, son emploi necessite l'utilisation d'un compose metallique a basse temperature et completement supraconducteur. Le compose metallique organique kappa-ET 2Cu[N(CN)2]Br presente toutes les caracteristiques necessaires a l'etude de cette propriete. En effet, il est situe loin de la transition du premier ordre de Mott et est completement supraconducteur. De facon surprenante, ce systeme semble se coupler fortement avec le reseau ce qui augmente significativement la sensibilite de cette sonde aux proprietes du gaz electronique. Cependant, des difficultes techniques importantes, liees a la nature intrinseque de ce materiau, doivent etre surmontees pour proceder a des mesures suivant differentes polarisations. La presente etude a profondement modifie notre comprehension de ce systeme. En effet, ces mesures ont permis de constater que le kappa-ET2Cu[N(CN)2]Br est un compose qui est situe en bordure de la zone de coexistence entre la supraconductivite et le magnetisme, ce qui constitue un resultat totalement inattendu. De plus, la

Polymorphous band structure model of gapping in the antiferromagnetic and paramagnetic phases of the Mott insulators MnO, FeO, CoO, and NiO

Science.gov (United States)

Trimarchi, Giancarlo; Wang, Zhi; Zunger, Alex

2018-01-01

The existence of band gaps in both the antiferromagnetic (AFM) and paramagnetic (PM) phases of the classic NaCl-structure Mott insulators MnO, FeO, CoO, and NiO is traditionally viewed and taught as a manifestation of strong correlation whereby insulation results from electrons moving across the lattice forming states with doubly occupied d orbitals on certain atomic sites and empty d orbitals on other sites. Within such theories, the gap of the AFM and PM phases of these oxides emerges even in the absence of spatial symmetry breaking. The need for such a correlated picture is partially based on the known failure of the commonly used band models for the PM phase that assume for such a spin disordered state the macroscopically averaged NaCl structure, where all transition metal (TM) sites are symmetry-equivalent (a monomorphous description), producing a gapless PM state with zero magnetic moments, in sharp conflict with experiment. Here, we seek to understand the minimum theoretical description needed to capture the leading descriptors of ground state Mott insulation in the classic, 3 d monoxide Mott systems—gapping and moment formation in the AFM and PM phase. As noted by previous authors, the spin-ordered AFM phase in these materials already shows in band theory a significant band gap when one doubles the NaCl unit cell by permitting different potentials for transition-metal atoms with different spins. For the spin-disordered PM phase, we allow analogously larger NaCl-type supercells where each TM site can have different spin direction and local bonding environments (i.e., disordered), yet the total spin is zero. Such a polymorphous description has the flexibility to acquire symmetry-breaking energy-lowering patterns that can lift the degeneracy of the d orbitals and develop large on-site magnetic moments without violating the global, averaged NaCl symmetry. Electrons are exchanged between spin-up and spin-down bands to create closed-shell insulating

Prospect of quantum anomalous Hall and quantum spin Hall effect in doped kagome lattice Mott insulators.

Science.gov (United States)

Guterding, Daniel; Jeschke, Harald O; Valentí, Roser

2016-05-17

Electronic states with non-trivial topology host a number of novel phenomena with potential for revolutionizing information technology. The quantum anomalous Hall effect provides spin-polarized dissipation-free transport of electrons, while the quantum spin Hall effect in combination with superconductivity has been proposed as the basis for realizing decoherence-free quantum computing. We introduce a new strategy for realizing these effects, namely by hole and electron doping kagome lattice Mott insulators through, for instance, chemical substitution. As an example, we apply this new approach to the natural mineral herbertsmithite. We prove the feasibility of the proposed modifications by performing ab-initio density functional theory calculations and demonstrate the occurrence of the predicted effects using realistic models. Our results herald a new family of quantum anomalous Hall and quantum spin Hall insulators at affordable energy/temperature scales based on kagome lattices of transition metal ions.

Impact ionization processes in the steady state of a driven Mott-insulating layer coupled to metallic leads

Science.gov (United States)

Sorantin, Max E.; Dorda, Antonius; Held, Karsten; Arrigoni, Enrico

2018-03-01

We study a simple model of photovoltaic energy harvesting across a Mott-insulating gap consisting of a correlated layer connected to two metallic leads held at different chemical potentials. We address, in particular, the issue of impact ionization, whereby a particle photoexcited to the high-energy part of the upper Hubbard band uses its extra energy to produce a second particle-hole excitation. We find a drastic increase of the photocurrent upon entering the frequency regime where impact ionization is possible. At large values of the Mott gap, where impact ionization is energetically not allowed, we observe a suppression of the current and a piling up of charge in the high-energy part of the upper Hubbard band. Our study is based on a Floquet dynamical mean-field theory treatment of the steady state with the so-called auxiliary master equation approach as impurity solver. We verify that an additional approximation, taking the self-energy diagonal in the Floquet indices, is appropriate for the parameter range we are considering.

Metal-insulator transitions in IZO, IGZO, and ITZO films

Energy Technology Data Exchange (ETDEWEB)

Makise, Kazumasa, E-mail: makise@nict.go.jp [National Institute of Information and Communications Technology, Kobe 651-2492 (Japan); Hidaka, Kazuya; Ezaki, Syohei; Asano, Takayuki; Shinozaki, Bunju [Department of Physics, Kyushu University, Fukuoka 810-8560 (Japan); Tomai, Shigekazu; Yano, Koki; Nakamura, Hiroaki [Central Research Laboratories, Idemitsu Kosan Co. Ltd, Chiba 299-0293 (Japan)

2014-10-21

In this study, we measured the low-temperature resistivity of amorphous two- and three-dimensional (2D and 3D) indium-zinc oxide, indium-gallium-zinc oxide, and indium-tin-zinc oxide films with a wide range of carrier densities. To determine their critical characteristics at the metal-insulator transition (MIT), we used the Ioffe–Regel criterion. We found that the MIT occurs in a narrow range between k{sub F}ℓ =0.13 and k{sub F}ℓ =0.25, where k{sub F} and ℓ are the Fermi wave number and electron mean free path, respectively. For films in the insulating region, we analyzed ρ(T) using a procedure proposed by Zabrodskii and Zinov'eva. This analysis confirmed the occurrence of Mott and Efros–Shklovskii (ES) variable-range hopping. The materials studied show crossover behavior from exp(T{sub Mott}/T){sup 1/4} or exp(T{sub Mott}/T){sup 1/3} for Mott hopping conduction to exp(T{sub ES}/T){sup 1/2} for ES hopping conduction with decreasing temperature. For both 2D and 3D materials, we found that the relationship between T{sub Mott} and T{sub ES} satisfies T{sub ES}∝T{sub Mott}{sup 2/3}.

Insulating phase in Sr{sub 2}IrO{sub 4}: An investigation using critical analysis and magnetocaloric effect

Energy Technology Data Exchange (ETDEWEB)

Bhatti, Imtiaz Noor; Pramanik, A.K., E-mail: akpramanik@mail.jnu.ac.in

2017-01-15

The nature of insulating phase in 5d based Sr{sub 2}IrO{sub 4} is quite debated as the theoretical as well as experimental investigations have put forward evidences in favor of both magnetically driven Slater-type and interaction driven Mott-type insulator. To understand this insulating behavior, we have investigated the nature of magnetic state in Sr{sub 2}IrO{sub 4} through studying critical exponents, low temperature thermal demagnetization and magnetocaloric effect. The estimated critical exponents do not exactly match with any universality class, however, the values obey the scaling behavior. The exponent values suggest that spin interaction in present material is close to mean-field model. The analysis of low temperature thermal demagnetization data, however, shows dual presence of localized- and itinerant-type of magnetic interaction. Moreover, field dependent change in magnetic entropy indicates magnetic interaction is close to mean-field type. While this material shows an insulating behavior across the magnetic transition, yet a distinct change in slope in resistivity is observed around T{sub c}. We infer that though the insulating phase in Sr{sub 2}IrO{sub 4} is more close to be Slater-type but the simultaneous presence of both Slater- and Mott-type is the likely scenario for this material. - Highlights: • Critical analysis shows Sr{sub 2}IrO{sub 4} has ferromagnetic ordering temperature T{sub c}~225 K. • Obtained critical exponents imply spin interaction is close to mean-field model. • Analysis of magneto-entropy data also supports mean-field type interaction. • However, the presence of both itinerant and localized spin interaction is evident. • Sr{sub 2}IrO{sub 4} has simultaneous presence of both Slater- and Mott-type insulating phase.

Thouless energy as a unifying concept for Josephson junctions tuned through the Mott metal-insulator transition

Science.gov (United States)

Tahvildar-Zadeh, A. N.; Freericks, J. K.; Nikolić, B. K.

2006-05-01

The Thouless energy was introduced in the 1970s as a semiclassical energy for electrons diffusing through a finite-sized conductor. It turns out to be an important quantum-mechanical energy scale for many systems ranging from disordered metals to quantum chaos to quantum chromodynamics. In particular, it has been quite successful in describing the properties of Josephson junctions when the barrier is a diffusive normal-state metal. The Thouless energy concept can be generalized to insulating barriers by extracting an energy scale from the two-probe Kubo conductance of a strongly correlated electron system (metallic or insulating) via a generalized definition of the quantum-mechanical level spacing to many-body systems. This energy scale is known to determine the crossover from tunneling to Ohmic (thermally activated) transport in normal tunnel junctions. Here we use it to illustrate how the quasiclassical picture of transport in Josephson junctions is modified as the strongly correlated barrier passes through the Mott transition. Surprisingly, we find the quasiclassical form holds well beyond its putative realm of validity.

Uniaxial-Strain-Orientation Dependence of the Competition between Mott and Charge Ordered Phases and their Corresponding Superconductivity of β-(BDA-TTP)2I3

Science.gov (United States)

Nuruzzaman, Md.; Yokogawa, Keiichi; Yoshino, Harukazu; Yoshimoto, Haruo; Kikuchi, Koichi; Kaihatsu, Takayuki; Yamada, Jun-ichi; Murata, Keizo

2012-12-01

We studied the electronic transport properties of the charge transfer salt β-(BDA-TTP)2I3 [BDA-TTP: 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene] by applying uniaxial strains along the three crystallographic axes, and obtained three corresponding temperature-pressure phase diagrams. Three phase diagrams were quite dependent on the direction of compression. Following the preceding paper by Kikuchi et al., we speculate that the insulating states are of 1/2-filled Mott insulators for the a- and b-axes compressions, and of 1/4-filled charge ordered states for the c-axis compression as well as hydrostatic pressure. The superconducting phase under uniaxial strain was realized with Tc = 5 K at 1.9 GPa along the a-axis and with Tc = 5.6 K at 1.75 GPa along the b-axis. Superconductivity was also reproduced with a Tc of 9.5 K at 1.0 GPa for the c-axis compressions in the range of 0.85 to 1.53 GPa as previously reported. We studied tentative measurement on upper critical fields, Bc2's of these superconductivities and found that the extrapolated values, Bc2(0)'s, exceeded Pauli-limit by about 2--3 times. However, at least in terms of Bc2, the difference in superconductivity associated with two different insulating states was not clear.

Core-level photoemission revealing the Mott transition

International Nuclear Information System (INIS)

Kim, Hyeong-Do; Noh, Han-Jin; Kim, K.H.; Oh, S.-J.

2005-01-01

Ru 3d core-level X-ray photoemission spectra of various ruthenates are examined. They show in general two-peak structures, which can be assigned as the screened and unscreened peaks. The screened peak is absent in a Mott insulator, but develops into a main peak as the correlation strength becomes weak. This spectral behavior is well explained by the dynamical mean-field theory calculation for the single-band Hubbard model with the on-site core-hole potential using the exact diagonalization method. The new mechanism of the core-level photoemission satellite can be utilized to reveal the Mott transition phenomenon in various strongly correlated electron systems

Mott Transition In Strongly Correlated Materials: Many-Body Methods And Realistic Materials Simulations

Science.gov (United States)

Lee, Tsung-Han

improved DMFT to describe a Mott insulator containing spin-propagating and chargeless fermionic excitations, spinons. We found the spinon Fermi-liquid, in the Mott insulating phase, is immiscible to the electron Fermi-liquid, in the metallic phase, due to the strong scattering between spinons in a metal. Third, we proposed a new approach within the slave-boson (Gutzwiller) framework that allows to describe both the low energy quasiparticle excitation and the high energy Hubbard excitation, which cannot be captured within the original slave-boson framework. In the second part, we applied LDA+RISB to realistic materials modeling. First, we tested the accuracy of LDA+RISB on predicting the structure of transition metal compounds, CrO, MnO, FeO, CoO, CoS, and CoSe. Our results display remarkable agreements with the experimental observations. Second, we applied LDA+RISB to analyze the nature of the Am-O chemical bonding in the CsAm(CrO 4)2 crystal. Our results indicate the Am-O bonding has strongly covalent character, and they also address the importance of the correlation effects to describe the experimentally observed electronic structure. In summary, we proposed three extensions within DMFT and RISB framework, which allow to investigate the domain wall structure in metal-Mott insulator coexistence regime, the metal-to-Mott-insulator transition with spinons excitation in the Mott-insulating phase, and the Hubbard excitation within RISB approach. Furthermore, we demonstrated that LDA+RISB is a reliable approximation to the strongly correlated materials by applying it to the transition metal compounds and the Americian chromate compounds.

A pure Hubbard model with demonstrable pairing adjacent to the Mott-insulating phase

International Nuclear Information System (INIS)

Champion, J D; Long, M W

2003-01-01

We introduce a Hubbard model on a particular class of geometries, and consider the effect of doping the highly spin-degenerate Mott-insulating state with a microscopic number of holes in the extreme strong-coupling limit. The geometry is quite general, with pairs of atomic sites at each superlattice vertex, and a highly frustrated inter-atomic connectivity: the one-dimensional realization is a chain of edge-sharing tetrahedra. The sole model parameter is the ratio of intra-pair to inter-pair hopping matrix elements. If the intra-pair hopping is negligible then introducing a microscopic number of holes results in a ferromagnetic Nagaoka groundstate. Conversely, if the intra-pair hopping is comparable with the inter-pair hopping then the groundstate is low spin with short-ranged spin correlations. We exactly solve the correlated motion of a pair of holes in such a state and find that, in 1d and 2d, they form a bound pair on a length scale that increases with diminishing binding energy. This result is pertinent to the long-standing problem of hole motion in the CuO 2 planes of the high-temperature superconductors: we have rigorously shown that, on our frustrated geometry, the holes pair up and a short-ranged low-spin state is generated by hole motion alone

Antiferromagnetic Mott insulating state in the single-component molecular material Pd(tmdt)2

Science.gov (United States)

Takagi, Rina; Sari, Dita Puspita; Mohd-Tajudin, Saidah Sakinah; Ashi, Retno; Watanabe, Isao; Ishibashi, Shoji; Miyagawa, Kazuya; Ogura, Satomi; Zhou, Biao; Kobayashi, Akiko; Kanoda, Kazushi

2017-12-01

A family of compounds built by a single molecular species, M (tmdt) 2, with a metal ion, M , and organic ligands, tmdt, affords diverse electronic phases due to M -dependent interplays between d electrons in M , and π electrons in tmdt. We investigated the spin state in Pd (tmdt) 2 , a π -electron system without a d -electron contribution, through 1H nuclear magnetic resonance (NMR) and muon-spin resonance experiments. The temperature profiles of the NMR linewidth, relaxation rate, and asymmetry parameter in muon decay show an inhomogeneous antiferromagnetic order with moments distributed around ˜0.1 μB that onsets at above 100 K. This result provides an example of the antiferromagnetic order in a pure π -electron system in M (tmdt) 2, and it demonstrates that correlation among the π electrons is so strong as to give the Néel temperature over 100 K. The small and inhomogeneous moments are understandable as the crucial disorder effect in correlated electrons situated near the Mott transition.

The Mott localization and magnetic properties in condensed fermions systems

International Nuclear Information System (INIS)

Wojcik, W.

1995-01-01

In the present thesis the Mott localization and magnetic properties in condensed fermions system are considered. The Hubbard model has been used to strongly correlated electron systems and the Skyrme potential to a dense neutron matter with small concentration of protons. A variational approach to the metal-insulator transition is proposed which combines the Mott and Gutzwiller-Brinkman-Rice aspects of the localization. Magnetic properties of strongly correlated electrons are analyzed within the modified spin-rotation-invariant approach in the slow-boson representation. The theoretical prediction for considered systems are presented. 112 refs, 39 figs

Magnetism and the low-energy electronic structure of Mott insulators K{sub 2}CoF{sub 4} and SrMnO{sub 3} perovskites

Energy Technology Data Exchange (ETDEWEB)

Nalecz, D.M., E-mail: sfnalecz@cyf-kr.edu.pl [Institute of Physics, Pedagogical University, 30-084, Krakow (Poland); Radwanski, R.J. [Institute of Physics, Pedagogical University, 30-084, Krakow (Poland); Center of Solid State Physics, S" n" t Filip 5, 31-150, Krakow (Poland); Ropka, Z. [Center of Solid State Physics, S" n" t Filip 5, 31-150, Krakow (Poland)

2016-09-01

For Mott insulators, K{sub 2}CoF{sub 4} and SrMnO{sub 3}, we have calculated, in the purely ionic model, the low-energy electronic structure both in the paramagnetic and magnetic state as well as zero-temperature magnetic moment, its direction and its temperature dependence. We have calculated the octahedral crystal-field strength 10Dq to be 0.98 and 2.25 eV. We claim that for an adequate theoretical description of magnetic properties even small local distortions and the intra-atomic relativistic spin-orbit coupling have to be taken into account. Our studies have revealed a strong interplay of the magnetism, the orbital moment in particular, with the local crystallographic structure. The calculated orbital moment in K{sub 2}CoF{sub 4} is very large, 1.06 μ{sub B}, giving 30% contribution to the total moment - this result points the necessity to “unquench” the orbital magnetism in 3d compounds. We consistently described magnetic and some optical properties of these compounds, containing atoms with incomplete 3d shell, in agreement with their insulating ground state. - Highlights: • The octahedral crystal-field 10Dq amounts to 0.98 and 2.25 eV in K{sub 2}CoF{sub 4} and SrMnO{sub 3}. • The low-energy electronic structures in the magnetic state is displayed. • There is a strong interplay of the magnetism and the local crystal structure. • Temperature dependence of the Mn{sup 4+}- ion magnetic moment has been described. • Relativistic spin-orbit coupling is indispensable for description of 3d magnetism.

Superconductivity, Mott-Hubbard states, and molecular orbital order in intercalated fullerides

CERN Document Server

Iwasa, Y

2003-01-01

This article reviews the current status of chemically doped fullerene superconductors and related compounds, with particular focus on Mott-Hubbard states and the role of molecular orbital degeneracy. Alkaline-earth metal fullerides produce superconductors of several kinds, all of which have states with higher valence than (C sub 6 sub 0) sup 6 sup - , where the second lowest unoccupied molecular orbital (the LUMO + 1 state) is filled. Alkali-metal-doped fullerides, on the other hand, afford superconductors only at the stoichiometry A sub 3 C sub 6 sub 0 (A denotes alkali metal) and in basically fcc structures. The metallicity and superconductivity of A sub 3 C sub 6 sub 0 compounds are destroyed either by reduction of the crystal symmetry or by change in the valence of C sub 6 sub 0. This difference is attributed to the narrower bandwidth in the A sub 3 C sub 6 sub 0 system, causing electronic instability in Jahn-Teller insulators and Mott-Hubbard insulators. The latter metal-insulator transition is driven by...

Electronic structure properties of UO2 as a Mott insulator

Science.gov (United States)

Sheykhi, Samira; Payami, Mahmoud

2018-06-01

In this work using the density functional theory (DFT), we have studied the structural, electronic and magnetic properties of uranium dioxide with antiferromagnetic 1k-, 2k-, and 3k-order structures. Ordinary approximations in DFT, such as the local density approximation (LDA) or generalized gradient approximation (GGA), usually predict incorrect metallic behaviors for this strongly correlated electron system. Using Hubbard term correction for f-electrons, LDA+U method, as well as using the screened Heyd-Scuseria-Ernzerhof (HSE) hybrid functional for the exchange-correlation (XC), we have obtained the correct ground-state behavior as an insulator, with band gaps in good agreement with experiment.

Chaotic dynamics in nanoscale NbO2 Mott memristors for analogue computing

Science.gov (United States)

Kumar, Suhas; Strachan, John Paul; Williams, R. Stanley

2017-08-01

At present, machine learning systems use simplified neuron models that lack the rich nonlinear phenomena observed in biological systems, which display spatio-temporal cooperative dynamics. There is evidence that neurons operate in a regime called the edge of chaos that may be central to complexity, learning efficiency, adaptability and analogue (non-Boolean) computation in brains. Neural networks have exhibited enhanced computational complexity when operated at the edge of chaos, and networks of chaotic elements have been proposed for solving combinatorial or global optimization problems. Thus, a source of controllable chaotic behaviour that can be incorporated into a neural-inspired circuit may be an essential component of future computational systems. Such chaotic elements have been simulated using elaborate transistor circuits that simulate known equations of chaos, but an experimental realization of chaotic dynamics from a single scalable electronic device has been lacking. Here we describe niobium dioxide (NbO2) Mott memristors each less than 100 nanometres across that exhibit both a nonlinear-transport-driven current-controlled negative differential resistance and a Mott-transition-driven temperature-controlled negative differential resistance. Mott materials have a temperature-dependent metal-insulator transition that acts as an electronic switch, which introduces a history-dependent resistance into the device. We incorporate these memristors into a relaxation oscillator and observe a tunable range of periodic and chaotic self-oscillations. We show that the nonlinear current transport coupled with thermal fluctuations at the nanoscale generates chaotic oscillations. Such memristors could be useful in certain types of neural-inspired computation by introducing a pseudo-random signal that prevents global synchronization and could also assist in finding a global minimum during a constrained search. We specifically demonstrate that incorporating such

Orbital-selective Mott phase of Cu-substituted iron-based superconductors

International Nuclear Information System (INIS)

Liu, Yang; Zhao, Yang-Yang; Song, Yun

2016-01-01

We study the phase transition in Cu-substituted iron-based superconductors with a new developed real-space Green’s function method. We find that Cu substitution has strong effect on the orbital-selective Mott transition introduced by the Hund’s rule coupling. The redistribution of the orbital occupancy which is caused by the increase of the Hund’s rule coupling, gives rise to the Mott–Hubbard metal-insulator transition in the half-filled d xy orbital. We also find that more and more electronic states appear inside that Mott gap of the d xy orbital with the increase of Cu substitution, and the in-gap states around the Fermi level are strongly localized at some specific lattice sites. Further, a distinctive phase diagram, obtained for the Cu-substituted Fe-based superconductors, displays an orbital-selective insulating phase, as a result of the cooperative effect of the Hund’s rule coupling and the impurity-induced disorder. (paper)

Collective excitations and the nature of Mott transition in undoped gapped graphene

International Nuclear Information System (INIS)

Jafari, S A

2012-01-01

The particle-hole continuum (PHC) for massive Dirac fermions provides an unprecedented opportunity for the formation of two collective split-off states, one in the singlet and the other in the triplet (spin-1) channel, when the short-range interactions are added to the undoped system. Both states are close in energy and are separated from the continuum of free particle-hole excitations by an energy scale of the order of the gap parameter Δ. They both disperse linearly with two different velocities, reminiscent of spin-charge separation in Luttinger liquids. When the strength of Hubbard interactions is stronger than a critical value, the velocity of singlet excitation, which we interpret as a charge composite boson, becomes zero and renders the system a Mott insulator. Beyond this critical point the low-energy sector is left with a linearly dispersing triplet mode - a characteristic of a Mott insulator. The velocity of the triplet mode at the Mott criticality is twice the velocity of the underlying Dirac fermions. The phase transition line in the space of U and Δ is in qualitative agreement with our previous dynamical mean field theory calculations. (paper)

Characteristics of the Mott transition and electronic states of high-temperature cuprate superconductors from the perspective of the Hubbard model

Science.gov (United States)

Kohno, Masanori

2018-04-01

A fundamental issue of the Mott transition is how electrons behaving as single particles carrying spin and charge in a metal change into those exhibiting separated spin and charge excitations (low-energy spin excitation and high-energy charge excitation) in a Mott insulator. This issue has attracted considerable attention particularly in relation to high-temperature cuprate superconductors, which exhibit electronic states near the Mott transition that are difficult to explain in conventional pictures. Here, from a new viewpoint of the Mott transition based on analyses of the Hubbard model, we review anomalous features observed in high-temperature cuprate superconductors near the Mott transition.

Observation of a Slater-type metal-to-insulator transition in Sr$_2$IrO$_4$ from time-resolved photo-carrier dynamics

OpenAIRE

Hsieh, D.; Mahmood, F.; Torchinsky, D. H.; Cao, G.; Gedik, N.

2012-01-01

We perform a time-resolved optical study of Sr$_2$IrO$_4$ to understand the influence of magnetic ordering on the low energy electronic structure of a strongly spin-orbit coupled $J_{eff}$=1/2 Mott insulator. By studying the recovery dynamics of photo-carriers excited across the Mott gap, we find that upon cooling through the N\\'{e}el temperature $T_N$ the system evolves continuously from a metal-like phase with fast ($\\sim$50 fs) and excitation density independent relaxation dynamics to a ga...

Spin-Orbital Excitations in Ca2RuO4 Revealed by Resonant Inelastic X-Ray Scattering

DEFF Research Database (Denmark)

Das, L.; Forte, F.; Fittipaldi, R.

2018-01-01

The strongly correlated insulator Ca2RuO4 is considered as a paradigmatic realization of both spin-orbital physics and a band-Mott insulating phase, characterized by orbitally selective coexistence of a band and a Mott gap. We present a high resolution oxygen K-edge resonant inelastic x-ray scatt......-Mott scenario. The high-energy excitations correspond to intra-atomic singlet-triplet transitions at an energy scale set by Hund's coupling. Our findings give a unifying picture of the spin and orbital excitations in the band-Mott insulator Ca2RuO4.......The strongly correlated insulator Ca2RuO4 is considered as a paradigmatic realization of both spin-orbital physics and a band-Mott insulating phase, characterized by orbitally selective coexistence of a band and a Mott gap. We present a high resolution oxygen K-edge resonant inelastic x......-ray scattering study of the antiferromagnetic Mott insulating state of Ca2RuO4. A set of low-energy (about 80 and 400 meV) and high-energy (about 1.3 and 2.2 eV) excitations are reported, which show strong incident light polarization dependence. Our results strongly support a spin-orbit coupled band...

DWPF Stage 2: precipitation test program at Mott

International Nuclear Information System (INIS)

Schmitz, M.A.

1981-01-01

This memorandum covers the results of the test program conducted at Mott Metallurgical to determine cross-flow filter performance on potassium/cesium tetraphenylborate (K/Cs TPB)-sodium titanate slurries. The test program was designed to provide essential basic operating data to supplement the 1000-gallon cold process tests planned at TNX and the shielded cell tests with actual waste supernate planned by Chemical Technology. The specific Mott Metallurgical test objectives are outlined in DPST-81-722. During the Mott Metallurgical test program an average filtrate flow rate of approximately 0.05 gpm/ft 2 was repeatedly demonstrated over an 8-hr run with 0.5 micron filter elements. Initial Fe/Al sludge concentrations up to 150 ppM did not affect filter performance. Rheologies of the K/Cs TPB-sodium titanate slurries up to 13% by weight, the maximum concentration achieved, are summarized. Several recommendations are made to act as a guide for optimal filter performance

Electric field-triggered metal-insulator transition resistive switching of bilayered multiphasic VOx

Science.gov (United States)

Won, Seokjae; Lee, Sang Yeon; Hwang, Jungyeon; Park, Jucheol; Seo, Hyungtak

2018-01-01

Electric field-triggered Mott transition of VO2 for next-generation memory devices with sharp and fast resistance-switching response is considered to be ideal but the formation of single-phase VO2 by common deposition techniques is very challenging. Here, VOx films with a VO2-dominant phase for a Mott transition-based metal-insulator transition (MIT) switching device were successfully fabricated by the combined process of RF magnetron sputtering of V metal and subsequent O2 annealing to form. By performing various material characterizations, including scanning transmission electron microscopy-electron energy loss spectroscopy, the film is determined to have a bilayer structure consisting of a VO2-rich bottom layer acting as the Mott transition switching layer and a V2O5/V2O3 mixed top layer acting as a control layer that suppresses any stray leakage current and improves cyclic performance. This bilayer structure enables excellent electric field-triggered Mott transition-based resistive switching of Pt-VOx-Pt metal-insulator-metal devices with a set/reset current ratio reaching 200, set/reset voltage of less than 2.5 V, and very stable DC cyclic switching upto 120 cycles with a great set/reset current and voltage distribution less than 5% of standard deviation at room temperature, which are specifications applicable for neuromorphic or memory device applications. [Figure not available: see fulltext.

Filling-driven Mott transition in SU(N ) Hubbard models

Science.gov (United States)

Lee, Seung-Sup B.; von Delft, Jan; Weichselbaum, Andreas

2018-04-01

We study the filling-driven Mott transition involving the metallic and paramagnetic insulating phases in SU (N ) Fermi-Hubbard models, using the dynamical mean-field theory and the numerical renormalization group as its impurity solver. The compressibility shows a striking temperature dependence: near the critical end-point temperature, it is strongly enhanced in the metallic phase close to the insulating phase. We demonstrate that this compressibility enhancement is associated with the thermal suppression of the quasiparticle peak in the local spectral functions. We also explain that the asymmetric shape of the quasiparticle peak originates from the asymmetry in the dynamics of the generalized doublons and holons.

Finite-temperature dynamics of the Mott insulating Hubbard chain

Science.gov (United States)

Nocera, Alberto; Essler, Fabian H. L.; Feiguin, Adrian E.

2018-01-01

We study the dynamical response of the half-filled one-dimensional Hubbard model for a range of interaction strengths U and temperatures T by a combination of numerical and analytical techniques. Using time-dependent density matrix renormalization group computations we find that the single-particle spectral function undergoes a crossover to a spin-incoherent Luttinger liquid regime at temperatures T ˜J =4 t2/U for sufficiently large U >4 t . At smaller values of U and elevated temperatures the spectral function is found to exhibit two thermally broadened bands of excitations, reminiscent of what is found in the Hubbard-I approximation. The dynamical density-density response function is shown to exhibit a finite-temperature resonance at low frequencies inside the Mott gap, with a physical origin similar to the Villain mode in gapped quantum spin chains. We complement our numerical computations by developing an analytic strong-coupling approach to the low-temperature dynamics in the spin-incoherent regime.

Filling- and interaction-driven Mott transition. Quantum cluster calculations within self-energy-functional theory; Fuellungs- und wechselwirkungsabhaengiger Mott-Uebergang. Quanten-Cluster-Rechnungen im Rahmen der Selbstenergiefunktional-Theorie

Energy Technology Data Exchange (ETDEWEB)

Balzer, Matthias

2008-07-01

The central goal of this thesis is the examination of strongly correlated electron systems on the basis of the two-dimensional Hubbard model. We analyze how the properties of the Mott insulator change upon doping and with interaction strength. The numerical evaluation is done using quantum cluster approximations, which allow for a thermodynamically consistent description of the ground state properties. The framework of self-energy-functional theory offers great flexibility for the construction of cluster approximations. A detailed analysis sheds light on the quality and the convergence properties of different cluster approximations within the self-energy-functional theory. We use the one-dimensional Hubbard model for these examinations and compare our results with the exact solution. In two dimensions the ground state of the particle-hole symmetric model at half-filling is an antiferromagnetic insulator, independent of the interaction strength. The inclusion of short-range spatial correlations by our cluster approach leads to a considerable improvement of the antiferromagnetic order parameter as compared to dynamical mean-field theory. In the paramagnetic phase we furthermore observe a metal-insulator transition as a function of the interaction strength, which qualitatively differs from the pure mean-field scenario. Starting from the antiferromagnetic Mott insulator a filling-controlled metal-insulator transition in a paramagnetic metallic phase can be observed. Depending on the cluster approximation used an antiferromagnetic metallic phase may occur at first. In addition to long-range antiferromagnetic order, we also considered superconductivity in our calculations. The superconducting order parameter as a function of doping is in good agreement with other numerical methods, as well as with experimental results. (orig.)

Boson localization and the superfluid-insulator transition

International Nuclear Information System (INIS)

Fisher, M.P.A.; Weichman, P.B.; Grinstein, G.; Fisher, D.S.; Condensed Matter Physics 114-36, California Institute of Technology, Pasadena, California 91125; IBM Research Division, Thomas J. Watson Research Center, Yorktown Heights, New York 10598; Joseph Henry Laboratory of Physics, Jadwin Hall, Princeton University, Princeton, New Jersey 08544)

1989-01-01

The phase diagrams and phase transitions of bosons with short-ranged repulsive interactions moving in periodic and/or random external potentials at zero temperature are investigated with emphasis on the superfluid-insulator transition induced by varying a parameter such as the density. Bosons in periodic potentials (e.g., on a lattice) at T=0 exhibit two types of phases: a superfluid phase and Mott insulating phases characterized by integer (or commensurate) boson densities, by the existence of a gap for particle-hole excitations, and by zero compressibility. Generically, the superfluid onset transition in d dimensions from a Mott insulator to superfluidity is ''ideal,'' or mean field in character, but at special multicritical points with particle-hole symmetry it is in the universality class of the (d+1)-dimensional XY model. In the presence of disorder, a third, ''Bose glass'' phase exists. This phase is insulating because of the localization effects of the randomness and analogous to the Fermi glass phase of interacting fermions in a strongly disordered potential

Strain engineering and one-dimensional organization of metal-insulator domains in single-crystal vanadium dioxide beams.

Science.gov (United States)

Cao, J; Ertekin, E; Srinivasan, V; Fan, W; Huang, S; Zheng, H; Yim, J W L; Khanal, D R; Ogletree, D F; Grossman, J C; Wu, J

2009-11-01

Correlated electron materials can undergo a variety of phase transitions, including superconductivity, the metal-insulator transition and colossal magnetoresistance. Moreover, multiple physical phases or domains with dimensions of nanometres to micrometres can coexist in these materials at temperatures where a pure phase is expected. Making use of the properties of correlated electron materials in device applications will require the ability to control domain structures and phase transitions in these materials. Lattice strain has been shown to cause the coexistence of metallic and insulating phases in the Mott insulator VO(2). Here, we show that we can nucleate and manipulate ordered arrays of metallic and insulating domains along single-crystal beams of VO(2) by continuously tuning the strain over a wide range of values. The Mott transition between a low-temperature insulating phase and a high-temperature metallic phase usually occurs at 341 K in VO(2), but the active control of strain allows us to reduce this transition temperature to room temperature. In addition to device applications, the ability to control the phase structure of VO(2) with strain could lead to a deeper understanding of the correlated electron materials in general.

Spin-Orbital Excitations in Ca_{2}RuO_{4} Revealed by Resonant Inelastic X-Ray Scattering

Directory of Open Access Journals (Sweden)

L. Das

2018-03-01

Full Text Available The strongly correlated insulator Ca_{2}RuO_{4} is considered as a paradigmatic realization of both spin-orbital physics and a band-Mott insulating phase, characterized by orbitally selective coexistence of a band and a Mott gap. We present a high resolution oxygen K-edge resonant inelastic x-ray scattering study of the antiferromagnetic Mott insulating state of Ca_{2}RuO_{4}. A set of low-energy (about 80 and 400 meV and high-energy (about 1.3 and 2.2 eV excitations are reported, which show strong incident light polarization dependence. Our results strongly support a spin-orbit coupled band-Mott scenario and explore in detail the nature of its exotic excitations. Guided by theoretical modeling, we interpret the low-energy excitations as a result of composite spin-orbital excitations. Their nature unveils the intricate interplay of crystal-field splitting and spin-orbit coupling in the band-Mott scenario. The high-energy excitations correspond to intra-atomic singlet-triplet transitions at an energy scale set by Hund’s coupling. Our findings give a unifying picture of the spin and orbital excitations in the band-Mott insulator Ca_{2}RuO_{4}.

Filling- and interaction-driven Mott transition. Quantum cluster calculations within self-energy-functional theory

International Nuclear Information System (INIS)

Balzer, Matthias

2008-01-01

The central goal of this thesis is the examination of strongly correlated electron systems on the basis of the two-dimensional Hubbard model. We analyze how the properties of the Mott insulator change upon doping and with interaction strength. The numerical evaluation is done using quantum cluster approximations, which allow for a thermodynamically consistent description of the ground state properties. The framework of self-energy-functional theory offers great flexibility for the construction of cluster approximations. A detailed analysis sheds light on the quality and the convergence properties of different cluster approximations within the self-energy-functional theory. We use the one-dimensional Hubbard model for these examinations and compare our results with the exact solution. In two dimensions the ground state of the particle-hole symmetric model at half-filling is an antiferromagnetic insulator, independent of the interaction strength. The inclusion of short-range spatial correlations by our cluster approach leads to a considerable improvement of the antiferromagnetic order parameter as compared to dynamical mean-field theory. In the paramagnetic phase we furthermore observe a metal-insulator transition as a function of the interaction strength, which qualitatively differs from the pure mean-field scenario. Starting from the antiferromagnetic Mott insulator a filling-controlled metal-insulator transition in a paramagnetic metallic phase can be observed. Depending on the cluster approximation used an antiferromagnetic metallic phase may occur at first. In addition to long-range antiferromagnetic order, we also considered superconductivity in our calculations. The superconducting order parameter as a function of doping is in good agreement with other numerical methods, as well as with experimental results. (orig.)

The Mott localization and magnetic properties in condensed fermions systems; Lokalizacja Motta i wlasnosci magnetyczne skondensowanych ukladow fermionowych

Energy Technology Data Exchange (ETDEWEB)

Wojcik, W. [Politechnika Krakowska, Cracow (Poland)

1995-12-31

In the present thesis the Mott localization and magnetic properties in condensed fermions system are considered. The Hubbard model has been used to strongly correlated electron systems and the Skyrme potential to a dense neutron matter with small concentration of protons. A variational approach to the metal-insulator transition is proposed which combines the Mott and Gutzwiller-Brinkman-Rice aspects of the localization. Magnetic properties of strongly correlated electrons are analyzed within the modified spin-rotation-invariant approach in the slow-boson representation. The theoretical prediction for considered systems are presented. 112 refs, 39 figs.

The Mott localization and magnetic properties in condensed fermions systems; Lokalizacja Motta i wlasnosci magnetyczne skondensowanych ukladow fermionowych

Energy Technology Data Exchange (ETDEWEB)

Wojcik, W [Politechnika Krakowska, Cracow (Poland)

1996-12-31

In the present thesis the Mott localization and magnetic properties in condensed fermions system are considered. The Hubbard model has been used to strongly correlated electron systems and the Skyrme potential to a dense neutron matter with small concentration of protons. A variational approach to the metal-insulator transition is proposed which combines the Mott and Gutzwiller-Brinkman-Rice aspects of the localization. Magnetic properties of strongly correlated electrons are analyzed within the modified spin-rotation-invariant approach in the slow-boson representation. The theoretical prediction for considered systems are presented. 112 refs, 39 figs.

Ba2NiOsO6 : A Dirac-Mott insulator with ferromagnetism near 100 K

International Nuclear Information System (INIS)

Feng, Hai L.; Calder, Stuart

2016-01-01

In this study, the ferromagnetic semiconductor Ba 2 NiOsO 6 (T mag ~ 100 K) was synthesized at 6 GPa and 1500 °C. It crystallizes into a double perovskite structure [Fm - 3m; a = 8.0428 (1) Å], where the Ni 2+ and Os 6+ ions are perfectly ordered at the perovskite B site. We show that the spin-orbit coupling of Os 6+ plays an essential role in opening the charge gap. The magnetic state was investigated by density functional theory calculations and powder neutron diffraction. The latter revealed a collinear ferromagnetic order in a > 21 kOe magnetic field at 5 K. The ferromagnetic gapped state is fundamentally different from that of known dilute magnetic semiconductors such as (Ga,Mn)As and (Cd,Mn)Te (T mag < 180 K), the spin-gapless semiconductor Mn 2 CoAl (T mag ~ 720 K), and the ferromagnetic insulators EuO (T mag ~ 70 K) and Bi 3 Cr 3 O 11 (T mag ~ 220 K). It is also qualitatively different from known ferrimagnetic insulators and semiconductors, which are characterized by an antiparallel spin arrangement. Our finding of the ferromagnetic semiconductivity of Ba 2 NiOsO 6 should increase interest in the platinum group oxides, because this alternative class of materials should be useful in the development of spintronic, quantum magnetic, and related devices.

Electronic Correlations, Jahn-Teller Distortions and Mott Transition to Superconductivity in Alkali-C60 Compounds

Directory of Open Access Journals (Sweden)

Alloul H.

2012-03-01

Full Text Available The discovery in 1991 of high temperature superconductivity (SC in A3C60 compounds, where A is an alkali ion, has been rapidly ascribed to a BCS mechanism, in which the pairing is mediated by on ball optical phonon modes. While this has lead to consider that electronic correlations were not important in these compounds, further studies of various AnC60 with n=1, 2, 4 allowed to evidence that their electronic properties cannot be explained by a simple progressive band filling of the C60 six-fold degenerate t1u molecular level. This could only be ascribed to the simultaneous influence of electron correlations and Jahn-Teller Distortions (JTD of the C60 ball, which energetically favour evenly charged C60 molecules. This is underlined by the recent discovery of two expanded fulleride Cs3C60 isomeric phases which are Mott insulators at ambient pressure. Both phases undergo a pressure induced first order Mott transition to SC with a (p, T phase diagram displaying a dome shaped SC, a common situation encountered nowadays in correlated electron systems. NMR experiments allowed us to study the magnetic properties of the Mott phases and to evidence clear deviations from BCS expectations near the Mott transition. So, although SC involves an electron-phonon mechanism, the incidence of electron correlations has an importance on the electronic properties, as had been anticipated from DMFT calculations.

Strong Energy-momentum Dispersion of Phonon Dressed Carriers in the Lightly Doped Band Insulator SrTiO3

International Nuclear Information System (INIS)

Meevasana, Warawat

2010-01-01

Much progress has been made recently in the study of the effects of electron-phonon (el-ph) coupling in doped insulators using angle resolved photoemission (ARPES), yielding evidence for the dominant role of el-ph interactions in underdoped cuprates. As these studies have been limited to doped Mott insulators, the important question arises how this compares with doped band insulators where similar el-ph couplings should be at work. The archetypical case is the perovskite SrTiO 3 (STO), well known for its giant dielectric constant of 10000 at low temperature, exceeding that of La 2 CuO 4 by a factor of 500. Based on this fact, it has been suggested that doped STO should be the archetypical bipolaron superconductor. Here we report an ARPES study from high-quality surfaces of lightly doped SrTiO 3 . Comparing to lightly doped Mott insulators, we find the signatures of only moderate electron-phonon coupling: a dispersion anomaly associated with the low frequency optical phonon with a λ(prime) ∼ 0.3 and an overall bandwidth renormalization suggesting an overall λ(prime) ∼ 0.7 coming from the higher frequency phonons. Further, we find no clear signatures of the large pseudogap or small polaron phenomena. These findings demonstrate that a large dielectric constant itself is not a good indicator of el-ph coupling and highlight the unusually strong effects of the el-ph coupling in doped Mott insulators.

Pressure-Induced Confined Metal from the Mott Insulator {\mathrm{Sr}}_3{\mathrm{Ir}}_{\mathrm{<span\; class="hlt">2</span>}}{{O}}_7

Energy Technology Data Exchange (ETDEWEB)

Ding, Yang; Yang, Liuxiang; Chen, Cheng-Chien; Kim, Heung-Sik; Han, Myung Joon; Luo, Wei; Feng, Zhenxing; Upton, Mary; Casa, Diego; Kim, Jungho; Gog, Thomas; Zeng, Zhidan; Cao, Gang; Mao, Ho-kwang; van Veenendaal, Michel

2016-05-24

The spin-orbit Mott insulator Sr₃Ir₂O₇ provides a fascinating playground to explore insulator-metal transition driven by intertwined charge, spin, and lattice degrees of freedom. Here, we report high-pressure electric resistance and resonant inelastic x-ray scattering measurements on single-crystal Sr₃Ir₂O₇ up to 63-65 GPa at 300 K. The material becomes a confined metal at 59.5 GPa, showing metallicity in the ab plane but an insulating behavior along the c axis. Such an unusual phenomenon resembles the strange metal phase in cuprate superconductors. Since there is no sign of the collapse of spin-orbit or Coulomb interactions in x-ray measurements, this novel insulator-metal transition is potentially driven by a first-order structural change at nearby pressures. Our discovery points to a new approach for synthesizing functional materials.

Pressure-driven phase transitions in TiOCl and the family (Ca, Sr, Ba)Fe2As2

International Nuclear Information System (INIS)

Zhang YuZhong; Opahle, Ingo; Jeschke, Harald O; ValentI, Roser

2010-01-01

Motivated by recent experimental measurements on pressure-driven phase transitions in Mott insulators as well as the new iron pnictide superconductors, we show that first principles Car-Parrinello molecular dynamics calculations are a powerful method to describe the microscopic origin of such transitions. We present results for (i) the pressure-induced insulator to metal phase transition in the prototypical Mott insulator TiOCl as well as (ii) the pressure-induced structural and magnetic phase transitions in the family of correlated metals AFe 2 As 2 (A = Ca, Sr, Ba). Comparison of our predictions with existing experimental results yields very good agreement.

Dynamical cluster approximation plus semiclassical approximation study for a Mott insulator and d-wave pairing

Science.gov (United States)

Kim, SungKun; Lee, Hunpyo

2017-06-01

Via a dynamical cluster approximation with N c = 4 in combination with a semiclassical approximation (DCA+SCA), we study the doped two-dimensional Hubbard model. We obtain a plaquette antiferromagnetic (AF) Mott insulator, a plaquette AF ordered metal, a pseudogap (or d-wave superconductor) and a paramagnetic metal by tuning the doping concentration. These features are similar to the behaviors observed in copper-oxide superconductors and are in qualitative agreement with the results calculated by the cluster dynamical mean field theory with the continuous-time quantum Monte Carlo (CDMFT+CTQMC) approach. The results of our DCA+SCA differ from those of the CDMFT+CTQMC approach in that the d-wave superconducting order parameters are shown even in the high doped region, unlike the results of the CDMFT+CTQMC approach. We think that the strong plaquette AF orderings in the dynamical cluster approximation (DCA) with N c = 4 suppress superconducting states with increasing doping up to strongly doped region, because frozen dynamical fluctuations in a semiclassical approximation (SCA) approach are unable to destroy those orderings. Our calculation with short-range spatial fluctuations is initial research, because the SCA can manage long-range spatial fluctuations in feasible computational times beyond the CDMFT+CTQMC tool. We believe that our future DCA+SCA calculations should supply information on the fully momentum-resolved physical properties, which could be compared with the results measured by angle-resolved photoemission spectroscopy experiments.

Electron-optical systems for Mott polarimeters

International Nuclear Information System (INIS)

Fishkova, T.Ya.; Mamaev, Yu.A.; Ovsyannikova, I.P.; Petrov, V.N.; Shpak, E.V.

1994-01-01

Electron-optical systems, forming polarized electron beams from solid and gaseous sources at a Mott detector with operating potentials of 20 and 50 kV, have been theoretically investigated. The integral EOS creates a beam <2.6 nm in diameter at the target of the Mott detector for secondary electrons with energies of 1-20 eV and exit angles of 0 -60 . The differential EOS provides an energy resolution of 2-6% within the range of 3-2000 eV, the illumination being 5-13% for a 4π angle; at the target of the Mott detector it creates a beam of 1-6 mm in diameter. Both systems have been constructed at the laboratory of Spin-polarized Electron Spectroscopy (Department of Experimental Physics) at St. Petersburg State Technical University. ((orig.))

Excitons in insulators

International Nuclear Information System (INIS)

Grasser, R.; Scharmann, A.

1983-01-01

This chapter investigates absorption, reflectivity, and intrinsic luminescence spectra of free and/or self-trapped (localized) excitons in alkali halides and rare gas solids. Introduces the concepts underlying the Wannier-Mott and Frenkel exciton models, two extreme pictures of an exciton in crystalline materials. Discusses the theoretical and experimental background; excitons in alkali halides; and excitons in rare gas solids. Shows that the intrinsic optical behavior of wide gap insulators in the range of the fundamental absorption edge is controlled by modified Wannier-Mott excitons. Finds that while that alkali halides only show free and relaxed molecular-like exciton emission, in rare gas crystals luminescence due to free, single and double centered localized excitons is observed. Indicates that the simultaneous existence of free and self-trapped excitons in these solid requires an energy barrier for self-trapping

Variable range hopping in TiO2 insulating layers for oxide electronic devices

Directory of Open Access Journals (Sweden)

Y. L. Zhao

2012-03-01

Full Text Available TiO2 thin films are of importance in oxide electronics, e.g., Pt/TiO2/Pt for memristors and Co-TiO2/TiO2/Co-TiO2 for spin tunneling devices. When such structures are deposited at a variety of oxygen pressures, how does TiO2 behave as an insulator? We report the discovery of an anomalous resistivity minimum in a TiO2 film at low pressure (not strongly dependent on deposition temperature. Hall measurements rule out band transport and in most of the pressure range the transport is variable range hopping (VRH though below 20 K it was difficult to differentiate between Mott and Efros-Shklovskii's (ES mechanism. Magnetoresistance (MR of the sample with lowest resistivity was positive at low temperature (for VRH but negative above 10 K indicating quantum interference effects.

Quantum Critical “Opalescence” around Metal-Insulator Transitions

Science.gov (United States)

Misawa, Takahiro; Yamaji, Youhei; Imada, Masatoshi

2006-08-01

Divergent carrier-density fluctuations equivalent to the critical opalescence of gas-liquid transition emerge around a metal-insulator critical point at a finite temperature. In contrast to the gas-liquid transitions, however, the critical temperatures can be lowered to zero, which offers a challenging quantum phase transition. We present a microscopic description of such quantum critical phenomena in two dimensions. The conventional scheme of phase transitions by Ginzburg, Landau, and Wilson is violated because of its topological nature. It offers a clear insight into the criticalities of metal-insulator transitions (MIT) associated with Mott or charge-order transitions. Fermi degeneracy involving the diverging density fluctuations generates emergent phenomena near the endpoint of the first-order MIT and must shed new light on remarkable phenomena found in correlated metals such as unconventional cuprate superconductors. It indeed accounts for the otherwise puzzling criticality of the Mott transition recently discovered in an organic conductor. We propose to accurately measure enhanced dielectric fluctuations at small wave numbers.

Probing the spin-orbit Mott state in Sr3Ir2O7 by electron doping

Science.gov (United States)

Hogan, Thomas C.

Iridium-based members of the Ruddlesden-Popper family of oxide compounds are characterized by a unique combination of energetically comparable effects: crystal-field splitting, spin-orbit coupling, and electron-electron interactions are all present, and the combine to produce a Jeff = 1/2 ground state. In the bilayer member of this series, Sr3Ir2O7, this state manifests as electrically insulating, with unpaired Ir4+ spins aligned along the long axis of the unit cell to produce a G-type antiferromagnet with an ordered moment of 0.36 uB. In this work, this Mott state is destabilized by electron doping via La3+ substitution on the Sr-site to produce (Sr1-x Lax)3Ir2O7. The introduction of carriers initially causes nano-scale phase-separated regions to develop before driving a global insulator-to-metal transition at x=0.04. Coinciding with this transition is the disappearance of evidence of magnetic order in the system in either bulk magnetization or magnetic scattering experiments. The doping also enhances a structural order parameter observed in the parent compound at forbidden reciprocal lattice vectors. A more complete structural solution is proposed to account for this previously unresolved distortion, and also offers an explanation as to the anomalous net ferromagnetism seen prior in bulk measurements. Finally, spin dynamics are probed via a resonant x-ray technique to reveal evidence of spin-dimer-like behavior dominated by inter-plane interactions. This result supports a bond-operator treatment of the interaction Hamiltonian, and also explains the doping dependence of high temperature magnetic susceptibility.

Superfluid and insulating phases in an interacting-boson model: mean-field theory and the RPA

International Nuclear Information System (INIS)

Sheshadri, K.; Pandit, R.; Krishnamurthy, H.R.; Ramakrishnan, T.V.

1993-01-01

The bosonic Hubbard model is studied via a simple mean-field theory. At zero temperature, in addition to yielding a phase diagram that is qualitatively correct, namely a superfluid phase for non-integer fillings and a Mott transition from a superfluid to an insulating phase for integer fillings, this theory gives results that are in good agreement with Monte Carlo simulations. In particular, the superfluid fraction obtained as a function of the interaction strength U for both integer and non-integer fillings is close to the simulation results. In all phases the excitation spectra are obtained by using the random phase approximation (RPA): the spectrum has a gap in the insulating phase and is gapless (and linear at small wave vectors) in the superfluid phase. Analytic results are presented in the limits of large U and small superfluid density. Finite-temperature phase diagrams and the Mott-insulator-normal-phase crossover are also described. (orig.)

MeV Mott polarimetry at Jefferson Lab

International Nuclear Information System (INIS)

Steigerwald, M.

2001-01-01

In the recent past, Mott polarimetry has been employed only at low electron beam energies (≅100 keV). Shortly after J. Sromicki demonstrated the first Mott scattering experiment on lead foils at 14 MeV (MAMI, 1994), a high energy Mott scattering polarimeter was developed at Thomas Jefferson National Accelerator Facility (5 MeV, 1995). An instrumental precision of 0.5% was achieved due to dramatic improvement in eliminating the background signal by means of collimation, shielding, time of flight and coincidence methods. Measurements for gold targets between 0.05 μm and 5 μm for electron energies between 2 and 8 MeV are presented. A model was developed to explain the depolarization effects in the target foils due to double scattering. The instrumental helicity correlated asymmetries were measured to smaller than 0.1%

Interplay of long-range and short-range Coulomb interactions in an Anderson-Mott insulator

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Baćani, Mirko; Novak, Mario; Orbanić, Filip; Prša, Krunoslav; Kokanović, Ivan; Babić, Dinko

2017-07-01

In this paper, we tackle the complexity of coexisting disorder and Coulomb electron-electron interactions (CEEIs) in solids by addressing a strongly disordered system with intricate CEEIs and a screening that changes both with charge carrier doping level Q and temperature T . We report on an experimental comparative study of the T dependencies of the electrical conductivity σ and magnetic susceptibility χ of polyaniline pellets doped with dodecylbenzenesulfonic acid over a wide range. This material is special within the class of doped polyaniline by exhibiting in the electronic transport a crossover between a low-T variable range hopping (VRH) and a high-T nearest-neighbor hopping (NNH) well below room temperature. Moreover, there is evidence of a soft Coulomb gap ΔC in the disorder band, which implies the existence of a long-range CEEI. Simultaneously, there is an onsite CEEI manifested as a Hubbard gap U and originating in the electronic structure of doped polyaniline, which consists of localized electron states with dynamically varying occupancy. Therefore, our samples represent an Anderson-Mott insulator in which long-range and short-range CEEIs coexist. The main result of the study is the presence of a crossover between low- and high-T regimes not only in σ (T ) but also in χ (T ) , the crossover temperature T* being essentially the same for both observables over the entire doping range. The relatively large electron localization length along the polymer chains results in U being small, between 12 and 20 meV for the high and low Q , respectively. Therefore, the thermal energy at T* is sufficiently large to lead to an effective closing of the Hubbard gap and the consequent appearance of NNH in the electronic transport within the disorder band. ΔC is considerably larger than U , decreasing from 190 to 30 meV as Q increases, and plays the role of an activation energy in the NNH.

Reliability of the one-crossing approximation in describing the Mott transition

International Nuclear Information System (INIS)

Vildosola, V; Roura-Bas, P; Pourovskii, L V; Manuel, L O

2015-01-01

We assess the reliability of the one-crossing approximation (OCA) approach in a quantitative description of the Mott transition in the framework of the dynamical mean field theory (DMFT). The OCA approach has been applied in conjunction with DMFT to a number of heavy-fermion, actinide, transition metal compounds and nanoscale systems. However, several recent studies in the framework of impurity models pointed out serious deficiencies of OCA and raised questions regarding its reliability. Here we consider a single band Hubbard model on the Bethe lattice at finite temperatures and compare the results of OCA to those of a numerically exact quantum Monte Carlo (QMC) method. The temperature-local repulsion U phase diagram for the particle-hole symmetric case obtained by OCA is in good agreement with that of QMC, with the metal–insulator transition captured very well. We find, however, that the insulator to metal transition is shifted to higher values of U and, simultaneously, correlations in the metallic phase are significantly overestimated. This counter-intuitive behaviour is due to simultaneous underestimations of the Kondo scale in the metallic phase and the size of the insulating gap. We trace the underestimation of the insulating gap to that of the second moment of the high-frequency expansion of the impurity spectral density. Calculations of the system away from the particle-hole symmetric case are also presented and discussed. (paper)

Reliability of the one-crossing approximation in describing the Mott transition

Science.gov (United States)

Vildosola, V.; Pourovskii, L. V.; Manuel, L. O.; Roura-Bas, P.

2015-12-01

We assess the reliability of the one-crossing approximation (OCA) approach in a quantitative description of the Mott transition in the framework of the dynamical mean field theory (DMFT). The OCA approach has been applied in conjunction with DMFT to a number of heavy-fermion, actinide, transition metal compounds and nanoscale systems. However, several recent studies in the framework of impurity models pointed out serious deficiencies of OCA and raised questions regarding its reliability. Here we consider a single band Hubbard model on the Bethe lattice at finite temperatures and compare the results of OCA to those of a numerically exact quantum Monte Carlo (QMC) method. The temperature-local repulsion U phase diagram for the particle-hole symmetric case obtained by OCA is in good agreement with that of QMC, with the metal-insulator transition captured very well. We find, however, that the insulator to metal transition is shifted to higher values of U and, simultaneously, correlations in the metallic phase are significantly overestimated. This counter-intuitive behaviour is due to simultaneous underestimations of the Kondo scale in the metallic phase and the size of the insulating gap. We trace the underestimation of the insulating gap to that of the second moment of the high-frequency expansion of the impurity spectral density. Calculations of the system away from the particle-hole symmetric case are also presented and discussed.

The Statistical Fragmentation Theory of N. F. Mott

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Grady, Dennis

2004-07-01

For a brief period during the height of World War II, Neville F. Mott left his position at the University of Bristol and headed up a concerted theoretical effort at Fort Halstead, UK, to investigate the operational science of weapons and armor technology. The seminal achievements resulting from the efforts of the participating scientists are extraordinary and have provided the basis for much of the continuing research in this field over the intervening six decades. N. F. Mott chose to study the phenomenon of the explosive-driven fragmentation of exploding shell cases. The approaches pursued by Mott are documented in several interim reports and open literature publications and offer a fascinating look into the insightful thinking and scientific methods of one of the preeminent physicists of the last century. This presentation offers a perspective into the several theoretical approaches pursued by Mott. In particular, the hallmark relation for the representation of exploding munitions fragmentation data to the present day is the Mott distribution. The efforts of Mott leading to this distribution are explored and a judgment is offered as to whether Mott himself would use this distribution today.

Effective field theory and integrability in two-dimensional Mott transition

International Nuclear Information System (INIS)

Bottesi, Federico L.; Zemba, Guillermo R.

2011-01-01

Highlights: → Mott transition in 2d lattice fermion model. → 3D integrability out of 2D. → Effective field theory for Mott transition in 2d. → Double Chern-Simons. → d-Density waves. - Abstract: We study the Mott transition in a two-dimensional lattice spinless fermion model with nearest neighbors density-density interactions. By means of a two-dimensional Jordan-Wigner transformation, the model is mapped onto the lattice XXZ spin model, which is shown to possess a quantum group symmetry as a consequence of a recently found solution of the Zamolodchikov tetrahedron equation. A projection (from three to two space-time dimensions) property of the solution is used to identify the symmetry of the model at the Mott critical point as U q (sl(2)-circumflex)xU q (sl(2)-circumflex), with deformation parameter q = -1. Based on this result, the low-energy effective field theory for the model is obtained and shown to be a lattice double Chern-Simons theory with coupling constant k = 1 (with the standard normalization). By further employing the effective filed theory methods, we show that the Mott transition that arises is of topological nature, with vortices in an antiferromagnetic array and matter currents characterized by a d-density wave order parameter. We also analyze the behavior of the system upon weak coupling, and conclude that it undergoes a quantum gas-liquid transition which belongs to the Ising universality class.

Transport of electric charge in insulators

International Nuclear Information System (INIS)

Lopez C, E.

1979-01-01

In this work a review is made of important concepts in the study of the transport of electric charge in insulators. These concepts are: electrical contacts, transport regimes as viewed in the I-V characteristics, and photoinjection processes by internal photemission of holes or electrons from metals or semiconductors into insulators or by a virtual electrode using strongly absorbed light. Experimental results of photoinjection of holes and electrons into sulfur single crystals are analyzed using these concepts. The observation of the Mott-Gurney transition is reported for the first time. This is the transition between the region of space charge limited currents (SCLC) and the region of saturation of the current as a function of the applied voltage. A modified Mott-Gurney theoretical model is presented that is able to explain the whole I-V characteristic for uv and the internal photoemission of hopes and uv photoinjection of electrons. For the case of internal photoemission of electrons the conventional space charge limited current theory for an exponential distribution of traps is able to explain the experimental data. It is found that the crystals are of high purity since the total density of traps, as calculated from their exponential distribution, is Nsub(t) equals 1.8 X 10 14 cm -3 . (author)

Mott-Schottky analysis of thin ZnO films

International Nuclear Information System (INIS)

Windisch, Charles F. Jr.; Exarhos, Gregory J.

2000-01-01

Thin ZnO films, both native and doped with secondary metal ions, have been prepared by sputter deposition and also by casting from solutions containing a range of precursor salts. The conductivity and infrared reflectivity of these films are subsequently enhanced chemically following treatment in H 2 gas at 400 degree sign C or by cathodic electrochemical treatment in a neutral (pH=7) phosphate buffer solution. While Hall-type measurements usually are used to evaluate the electrical properties of such films, the present study investigated whether a conventional Mott-Schottky analysis could be used to monitor the change in concentration of free carriers in these films before and after chemical and electrochemical reduction. The Mott-Schottky approach would be particularly appropriate for electrochemically modified films since the measurements could be made in the same electrolyte used for the post-deposition electrochemical processing. Results of studies on sputtered pure ZnO films in ferricyanide solution were promising. Mott-Schottky plots were linear and gave free carrier concentrations typical for undoped semiconductors. Film thicknesses estimated from the Mott-Schottky data were also reasonably close to thicknesses calculated from reflectance measurements. Studies on solution-deposited films were less successful. Mott-Schottky plots were nonlinear, apparently due to film porosity. A combination of dc polarization and atomic force microscopy measurements confirmed this conclusion. The results suggest that Mott-Schottky analysis would be suitable for characterizing solution-deposited ZnO films only after extensive modeling was performed to incorporate the effects of film porosity on the characteristics of the space-charge region of the semiconductor. (c) 2000 American Vacuum Society

Semiconductor of spinons: from Ising band insulator to orthogonal band insulator.

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Farajollahpour, T; Jafari, S A

2018-01-10

We use the ionic Hubbard model to study the effects of strong correlations on a two-dimensional semiconductor. The spectral gap in the limit where on-site interactions are zero is set by the staggered ionic potential, while in the strong interaction limit it is set by the Hubbard U. Combining mean field solutions of the slave spin and slave rotor methods, we propose two interesting gapped phases in between: (i) the insulating phase before the Mott phase can be viewed as gapping a non-Fermi liquid state of spinons by the staggered ionic potential. The quasi-particles of underlying spinons are orthogonal to physical electrons, giving rise to the 'ARPES-dark' state where the ARPES gap will be larger than the optical and thermal gap. (ii) The Ising insulator corresponding to ordered phase of the Ising variable is characterized by single-particle excitations whose dispersion is controlled by Ising-like temperature and field dependences. The temperature can be conveniently employed to drive a phase transition between these two insulating phases where Ising exponents become measurable by ARPES and cyclotron resonance. The rare earth monochalcogenide semiconductors where the magneto-resistance is anomalously large can be a candidate system for the Ising band insulator. We argue that the Ising and orthogonal insulating phases require strong enough ionic potential to survive the downward renormalization of the ionic potential caused by Hubbard U.

Semiconductor of spinons: from Ising band insulator to orthogonal band insulator

Science.gov (United States)

Farajollahpour, T.; Jafari, S. A.

2018-01-01

We use the ionic Hubbard model to study the effects of strong correlations on a two-dimensional semiconductor. The spectral gap in the limit where on-site interactions are zero is set by the staggered ionic potential, while in the strong interaction limit it is set by the Hubbard U. Combining mean field solutions of the slave spin and slave rotor methods, we propose two interesting gapped phases in between: (i) the insulating phase before the Mott phase can be viewed as gapping a non-Fermi liquid state of spinons by the staggered ionic potential. The quasi-particles of underlying spinons are orthogonal to physical electrons, giving rise to the ‘ARPES-dark’ state where the ARPES gap will be larger than the optical and thermal gap. (ii) The Ising insulator corresponding to ordered phase of the Ising variable is characterized by single-particle excitations whose dispersion is controlled by Ising-like temperature and field dependences. The temperature can be conveniently employed to drive a phase transition between these two insulating phases where Ising exponents become measurable by ARPES and cyclotron resonance. The rare earth monochalcogenide semiconductors where the magneto-resistance is anomalously large can be a candidate system for the Ising band insulator. We argue that the Ising and orthogonal insulating phases require strong enough ionic potential to survive the downward renormalization of the ionic potential caused by Hubbard U.

Nevill Mott reminiscences and appreciations

CERN Document Server

Davis, E A

1998-01-01

Sir Nevill Mott was Britain''s last Winner of the Nobel Prize for Physics. This is a tribute to the life and work of Nobel Laureate Nevill Mott, a hugely admired and appreciated man, and one of this countries greatest ever scientists. It includes contributions from over 80 of his friends, family and colleagues, full of anecdotes and appreciations for this collossus of modern physics.

Peierls instability as the insulating origin of the Na/Si(111)-(3 × 1) surface with a Na coverage of 2/3 monolayers

Science.gov (United States)

Kang, Myung Ho; Kwon, Se Gab; Jung, Sung Chul

2018-03-01

Density functional theory (DFT) calculations are used to investigate the insulating origin of the Na/Si(111)-(3 × 1) surface with a Na coverage of 2/3 monolayers. In the coverage definition, one monolayer refers to one Na atom per surface Si atom, so this surface contains an odd number of electrons (i.e., three Si dangling-bond electrons plus two Na electrons) per 3 × 1 unit cell. Interestingly, this odd-electron surface has been ascribed to a Mott-Hubbard insulator to account for the measured insulating band structure with a gap of about 0.8 eV. Here, we instead propose a Peierls instability as the origin of the experimental band gap. The concept of Peierls instability is fundamental in one-dimensional metal systems but has not been taken into account in previous studies of this surface. Our DFT calculations demonstrate that the linear chain structure of Si dangling bonds in this surface is energetically unstable with respect to a × 2 buckling modulation, and the buckling-induced band gap of 0.79 eV explains well the measured insulating nature.

Electronic Identification of the Parental Phases and Mesoscopic Phase Separation of K_{x}Fe_{2-y}Se_{2} Superconductors

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F. Chen

2011-12-01

Full Text Available The nature of the parent compound of a high-temperature superconductor (HTS often plays a pivotal role in determining its superconductivity. The parent compounds of the cuprate HTSs are antiferromagnetically ordered Mott insulators, while those of the iron-pnictide HTSs are metals with spin-density-wave order. Here we report the electronic identification of two insulating parental phases and one semiconducting parental phase of the newly discovered family of K_{x}Fe_{2-y}Se_{2} superconductors. The two insulating phases exhibit Mott-insulator-like signatures, and one of the insulating phases is even present in the superconducting and semiconducting K_{x}Fe_{2-y}Se_{2} compounds. However, it is mesoscopically phase-separated from the superconducting or semiconducting phase. Moreover, we find that both the superconducting and semiconducting phases are free of the magnetic and vacancy orders present in the insulating phases, and that the electronic structure of the superconducting phase could be developed by doping the semiconducting phase with electrons. The rich electronic properties discovered in these parental phases of the K_{x}Fe_{2-y}Se_{2} superconductors provide the foundation for studying the anomalous behavior in this new class of iron-based superconductors.

Orthorhombic fulleride (CH3NH2)K3C60 close to Mott-Hubbard instability: Ab initio study

Science.gov (United States)

Potočnik, Anton; Manini, Nicola; Komelj, Matej; Tosatti, Erio; Arčon, Denis

2012-08-01

We study the electronic structure and magnetic interactions in methylamine-intercalated orthorhombic alkali-doped fullerene (CH3NH2)K3C60 within the density functional theory. As in the simpler ammonia intercalated compound (NH3)K3C60, the orthorhombic crystal-field anisotropy Δ lifts the t1u triple degeneracy at the Γ point and drives the system deep into the Mott-insulating phase. However, the computed Δ and conduction electron bandwidth W cannot alone account for the abnormally low experimental Néel temperature, TN=11 K, of the methylamine compound, compared to the much higher value TN=40 K of the ammonia one. Significant interactions between CH3NH2 and C603- are responsible for the stabilization of particular fullerene-cage distortions and the ensuing low-spin S=1/2 state. These interactions also seem to affect the magnetic properties, as interfullerene exchange interactions depend on the relative orientation of deformations of neighboring C603- molecules. For the ferro-orientational order of CH3NH2-K+ groups we find an apparent reduced dimensionality in magnetic exchange interactions, which may explain the suppressed Néel temperature. The disorder in exchange interactions caused by orientational disorder of CH3NH2-K+ groups could further contribute to this suppression.

Two-Magnon Raman Scattering and Pseudospin-Lattice Interactions in Sr_{2}IrO_{4} and Sr_{3}Ir_{2}O_{7}.

Science.gov (United States)

Gretarsson, H; Sung, N H; Höppner, M; Kim, B J; Keimer, B; Le Tacon, M

2016-04-01

We have used Raman scattering to investigate the magnetic excitations and lattice dynamics in the prototypical spin-orbit Mott insulators Sr_{2}IrO_{4} and Sr_{3}Ir_{2}O_{7}. Both compounds exhibit pronounced two-magnon Raman scattering features with different energies, line shapes, and temperature dependencies, which in part reflect the different influence of long-range frustrating exchange interactions. Additionally, we find strong Fano asymmetries in the line shapes of low-energy phonon modes in both compounds, which disappear upon cooling below the antiferromagnetic ordering temperatures. These unusual phonon anomalies indicate that the spin-orbit coupling in Mott-insulating iridates is not sufficiently strong to quench the orbital dynamics in the paramagnetic state.

Mg-doped VO2 nanoparticles: hydrothermal synthesis, enhanced visible transmittance and decreased metal-insulator transition temperature.

Science.gov (United States)

Zhou, Jiadong; Gao, Yanfeng; Liu, Xinling; Chen, Zhang; Dai, Lei; Cao, Chuanxiang; Luo, Hongjie; Kanahira, Minoru; Sun, Chao; Yan, Liuming

2013-05-28

This paper reports the successful preparation of Mg-doped VO2 nanoparticles via hydrothermal synthesis. The metal-insulator transition temperature (T(c)) decreased by approximately 2 K per at% Mg. The Tc decreased to 54 °C with 7.0 at% dopant. The composite foils made from Mg-doped VO2 particles displayed excellent visible transmittance (up to 54.2%) and solar modulation ability (up to 10.6%). In addition, the absorption edge blue-shifted from 490 nm to 440 nm at a Mg content of 3.8 at%, representing a widened optical band gap from 2.0 eV for pure VO2 to 2.4 eV at 3.8 at% doping. As a result, the colour of the Mg-doped films was modified to increase their brightness and lighten the yellow colour over that of the undoped-VO2 film. A first principle calculation was conducted to understand how dopants affect the optical, Mott phase transition and structural properties of VO2.

Photoinduced Coherent Spin Fluctuation in Primary Dynamics of Insulator to Metal Transition in Perovskite Cobalt Oxide

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Arima T.

2013-03-01

Full Text Available Coherent spin fluctuation was detected in the photoinduced Mott insulator-metal transition in perovskite cobalt oxide by using 3 optical-cycle infrared pulse. Such coherent spin fluctuation is driven by the perovskite distortion changing orbital gap.

Tuning metal-insulator behavior in LaTiO3/SrTiO3 heterostructures integrated directly on Si(100) through control of atomic layer thickness

Science.gov (United States)

Ahmadi-Majlan, Kamyar; Chen, Tongjie; Lim, Zheng Hui; Conlin, Patrick; Hensley, Ricky; Chrysler, Matthew; Su, Dong; Chen, Hanghui; Kumah, Divine P.; Ngai, Joseph H.

2018-05-01

We present electrical and structural characterization of epitaxial LaTiO3/SrTiO3 heterostructures integrated directly on Si(100). By reducing the thicknesses of the heterostructures, an enhancement in carrier-carrier scattering is observed in the Fermi liquid behavior, followed by a metal to insulator transition in the electrical transport. The insulating behavior is described by activated transport, and its onset occurs near an occupation of 1 electron per Ti site within the SrTiO3, providing evidence for a Mott driven transition. We also discuss the role that structure and gradients in strain could play in enhancing the carrier density. The manipulation of Mott metal-insulator behavior in oxides grown directly on Si opens the pathway to harnessing strongly correlated phenomena in device technologies.

B-cell lymphoma with Mott cell differentiation in two young adult dogs.

Science.gov (United States)

Stacy, Nicole I; Nabity, Mary B; Hackendahl, Nicole; Buote, Melanie; Ward, Jennifer; Ginn, Pamela E; Vernau, William; Clapp, William L; Harvey, John W

2009-03-01

Two young adult dogs with gastrointestinal signs were each found to have an intra-abdominal mass based on physical examination and diagnostic imaging. On exploratory laparotomy, small intestinal masses and mesenteric lymphadenopathy were found in both dogs; a liver mass was also found in dog 1. Cytologic and histologic examination of intestinal and liver masses and mesenteric lymph nodes revealed 2 distinct lymphoid cell populations: lymphoblasts and atypical Mott cells. With Romanowsky stains, the atypical Mott cells contained many discrete, clear to pale blue cytoplasmic inclusions consistent with Russell bodies that were positive by immunohistochemistry for IgM and CD79a in both dogs and for IgG in dog 2. The Mott cells and occasional lymphoblasts stained strongly positive with periodic acid-Schiff. Using flow cytometric immunophenotyping in dog 1, 60% of peripheral blood mononuclear cells and 85% of cells in an affected lymph node were positive for CD21, CD79a, IgM, and MCH II, indicative of B-cells. With electron microscopy, disorganized and dilated endoplasmic reticulum was seen in Mott cells in tumors from both dogs. Antigen receptor gene rearrangement analysis of lymph node and intestinal masses indicated a clonal B-cell population. Based on cell morphology, tissue involvement, and evidence for clonal B-cell proliferation, we diagnosed neoplasms involving Mott cells. To the authors' knowledge, this is the second report of Mott cell tumors or, more appropriately, B-cell lymphoma with Mott cell differentiation, in dogs. More complete characterization of this neoplasm requires further investigation of additional cases. This lymphoproliferative disease should be considered as a differential diagnosis for canine gastrointestinal tumors.

Metal-insulator transition in SrTi1−xVxO3 thin films

International Nuclear Information System (INIS)

Gu, Man; Wolf, Stuart A.; Lu, Jiwei

2013-01-01

Epitaxial SrTi 1−x V x O 3 (0 ≤ x ≤ 1) thin films were grown on (001)-oriented (LaAlO 3 ) 0.3 (Sr 2 AlTaO 6 ) 0.7 (LSAT) substrates using the pulsed electron-beam deposition technique. The transport study revealed a temperature driven metal-insulator transition (MIT) at 95 K for x = 0.67. The films with higher vanadium concentration (x > 0.67) were metallic corresponding to a Fermi liquid system. In the insulating phase (x < 0.67), the resistivity behavior was governed by Mott's variable range hopping mechanism. The possible mechanisms for the induced MIT are discussed, including the effects of electron correlation, lattice distortion, and Anderson localization

Strongly correlated impurity band superconductivity in diamond: X-ray spectroscopic evidence

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G. Baskaran

2006-01-01

Full Text Available In a recent X-ray absorption study in boron doped diamond, Nakamura et al. have seen a well isolated narrow boron impurity band in non-superconducting samples and an additional narrow band at the chemical potential in a superconducting sample. We interpret the beautiful spectra as evidence for upper Hubbard band of a Mott insulating impurity band and an additional metallic 'mid-gap band' of a conducting 'self-doped' Mott insulator. This supports the basic framework of a recent theory of the present author of strongly correlated impurity band superconductivity (impurity band resonating valence bond, IBRVB theory in a template of a wide-gap insulator, with no direct involvement of valence band states.

The electronic structure and metal-insulator transitions in vanadium oxides

International Nuclear Information System (INIS)

Mossanek, Rodrigo Jose Ochekoski

2010-01-01

The electronic structure and metal-insulator transitions in vanadium oxides (SrVO_3, CaVO_3, LaVO_3 and YVO_3) are studied here. The purpose is to show a new interpretation to the spectra which is coherent with the changes across the metal-insulator transition. The main experimental techniques are the X-ray photoemission (PES) and X-ray absorption (XAS) spectroscopies. The spectra are interpreted with cluster model, band structure and atomic multiplet calculations. The presence of charge-transfer satellites in the core-level PES spectra showed that these vanadium oxides cannot be classified in the Mott-Hubbard regime. Further, the valence band and core-level spectra presented a similar behavior across the metal insulator transition. In fact, the structures in the spectra and their changes are determined by the different screening channels present in the metallic or insulating phases. The calculated spectral weight showed that the coherent fluctuations dominate the spectra at the Fermi level and give the metallic character to the SrVO_3 and CaVO_3 compounds. The vanishing of this charge fluctuation and the replacement by the Mott-Hubbard screening in the LaVO_3 and YVO_3 systems is ultimately responsible for the opening of a band gap and the insulating character. Further, the correlation effects are, indeed, important to the occupied electronic structure (coherent and incoherent peaks). On the other hand, the unoccupied electronic structure is dominated by exchange and crystal field effects (t2g and eg sub-bands of majority and minority spins). The optical conductivity spectrum was obtained by convoluting the removal and addition states. It showed that the oxygen states, as well as the crystal field and exchange effects are necessary to correctly compare and interpret the experimental results. Further, a correlation at the charge-transfer region of the core-level and valence band optical spectra was observed, which could be extended to other transition metal oxides

Mott transition in Ga-doped Mg{sub x}Zn{sub 1-x}O: A direct observation

Energy Technology Data Exchange (ETDEWEB)

Wei Wei; Nori, Sudhakar [Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC (United States); Jin Chunming [Department of Biomedical Engineering, University of North Carolina and North Carolina State University, Campus Box 7115, Raleigh, NC 27695-7115 (United States); Narayan, Jagdish [Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC (United States); Narayan, Roger J., E-mail: roger_narayan@unc.edu [Department of Biomedical Engineering, University of North Carolina and North Carolina State University, Campus Box 7115, Raleigh, NC 27695-7115 (United States); Ponarin, Dmtri; Smirnov, Alex [Department of Chemistry, North Carolina State University, Raleigh, NC (United States)

2010-07-25

This paper reports the direct evidence for Mott transition in Ga-doped Mg{sub x}Zn{sub 1-x}O thin films. Highly transparent Ga-doped Mg{sub x}Zn{sub 1-x}O thin films were grown on c-plane sapphire substrates using pulsed laser deposition. 0.1 at.%, 0.5 at.% and 1 at.% Ga-doped Mg{sub 0.1}Zn{sub 0.9}O films were selected for resistivity measurements in the temperature range from 250 K to 40 mK. The 0.1 at.% Ga-doped Mg{sub 0.1}Zn{sub 0.9}O thin film showed typical insulator-like behavior and the 1 at.% Ga-doped Mg{sub 0.1}Zn{sub 0.9}O thin film showed typical metal-like behavior. The 0.5 at.% Ga-doped Mg{sub 0.1}Zn{sub 0.9}O film showed increasing resistivity with decreasing temperature; resistivity was saturated with a value of 1.15 x 10{sup -2} {Omega} cm at 40 mK, which is characteristic of the metal-insulator transition region. Temperature-dependent conductivity {sigma}(T) in the low temperature range revealed that the electron-electron scattering is the dominant dephasing mechanism. The inelastic scattering time is found to vary as T{sup -3/2}.

Evaluation of the density of the charge trapped in organic ferroelectric capacitors based on the Mott-Schottky model

Energy Technology Data Exchange (ETDEWEB)

Kim, Won-Ho [Samsung Display Co. Ltd., Yongin (Korea, Republic of); Kwon, Jin-Hyuk; Park, Gyeong-Tae; Kim, Jae-Hyun; Bae, Jin-Hyuk [Kyungpook National University, Daegu (Korea, Republic of); Zhang, Xue; Park, Jae-Hoon [Hallym University, Chuncheon (Korea, Republic of)

2014-09-15

Organic ferroelectric capacitors were fabricated using pentacene and poly (vinylidene fluoride trifluoroethylene) (PVDF-TrFE) as an organic semiconductor and a ferroelectric material, respectively. A paraelectric poly(vinyl cinnamate) layer was adopted as an interlayer between the PVDFTrFE layer and the bottom electrode. The paraelectric interlayer induced a depolarization field opposite to the direction of the polarization formed in the ferroelectric PVDF-TrFE insulator, thereby suppressing spontaneous polarization. As a result, the Mott-Schottky model could be used to evaluate, from the extracted flat-band voltages, the density of the charge trapped in the organic ferroelectric capacitors.

Propagation of quantum correlations after a quench in the Mott-insulator regime of the Bose-Hubbard model

International Nuclear Information System (INIS)

Krutitsky, Konstantin V.; Navez, Patrick; Schuetzhold, Ralf; Queisser, Friedemann

2014-01-01

We study a quantum quench in the Bose-Hubbard model where the tunneling rate J is suddenly switched from zero to a finite value in the Mott regime. In order to solve the many-body quantum dynamics far from equilibrium, we consider the reduced density matrices for a finite number of lattice sites and split them up into on-site density operators, i.e., the mean field, plus two-point and three-point correlations etc. Neglecting three-point and higher correlations, we are able to numerically simulate the time-evolution of the on-site density matrices and the two-point quantum correlations (e.g., their effective light-cone structure) for a comparably large number of lattice sites. (orig.)

Metal-insulator transitions

Science.gov (United States)

Imada, Masatoshi; Fujimori, Atsushi; Tokura, Yoshinori

1998-10-01

Metal-insulator transitions are accompanied by huge resistivity changes, even over tens of orders of magnitude, and are widely observed in condensed-matter systems. This article presents the observations and current understanding of the metal-insulator transition with a pedagogical introduction to the subject. Especially important are the transitions driven by correlation effects associated with the electron-electron interaction. The insulating phase caused by the correlation effects is categorized as the Mott Insulator. Near the transition point the metallic state shows fluctuations and orderings in the spin, charge, and orbital degrees of freedom. The properties of these metals are frequently quite different from those of ordinary metals, as measured by transport, optical, and magnetic probes. The review first describes theoretical approaches to the unusual metallic states and to the metal-insulator transition. The Fermi-liquid theory treats the correlations that can be adiabatically connected with the noninteracting picture. Strong-coupling models that do not require Fermi-liquid behavior have also been developed. Much work has also been done on the scaling theory of the transition. A central issue for this review is the evaluation of these approaches in simple theoretical systems such as the Hubbard model and t-J models. Another key issue is strong competition among various orderings as in the interplay of spin and orbital fluctuations. Experimentally, the unusual properties of the metallic state near the insulating transition have been most extensively studied in d-electron systems. In particular, there is revived interest in transition-metal oxides, motivated by the epoch-making findings of high-temperature superconductivity in cuprates and colossal magnetoresistance in manganites. The article reviews the rich phenomena of anomalous metallicity, taking as examples Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Ru compounds. The diverse phenomena include strong spin and

Electronic Structure of the Pyrochlore-Type Ru Oxides through the Metal--Insulator Transition

International Nuclear Information System (INIS)

Okamoto, J.; Fujimori, S.I.; Okane, T.; Fujimori, A.; Abbate, M.; Yoshii, S.; Sato, M.

2003-01-01

The electronic structures of the pyrochlore-type Ru oxides Sm 2-x Ca x Ru 2 O 7 and Sm 2-x Bi x Ru 2 O 7 , which show metal-insulator transition with increasing Ca or Bi concentration, have been studied by ultraviolet photoemission spectroscopy. Spectral changes near the Fermi level are different but reflect the tendency of their transport properties in both systems. The Sm 2-x Ca x Ru 2 O 7 system shows an energy shift, which is expected from the increase of hole in the Ru 4d t 2g band and the Sm 2 - x Bi x Ru 2 O 7 system shows spectral weight transfer within the Ru 4d t 2g band, which is expected to be observed in bandwidth-control Mott-Hubbard system. (author)

MUTIL, Asymmetry Factor of Mott Cross-Sections for Electron, Positron Scattering

International Nuclear Information System (INIS)

Idoeta, R.; Legarda, F.

2002-01-01

1 - Description of program or function: The asymmetry factor S of Mott's differential cross section for the scattering of electrons and positrons by point nuclei without screening is calculated for any energy, atomic number and angle of scattering. 2 - Method of solution: We have summed the conditionally convergent series, F and G, appearing in the asymmetry factor using two consecutive transformations: The one of Yennie, Ravenhall and Wilson and that of Euler till we have seven times six significant figures repeated in the factor S. 3 - Restrictions on the complexity of the problem: Those appearing in the use of Mott's cross section for unscreened point nuclei

Metal-insulator transition in SrTi{sub 1−x}V{sub x}O{sub 3} thin films

Energy Technology Data Exchange (ETDEWEB)

Gu, Man [Department of Physics, University of Virginia, 382 McCormick Rd., Charlottesville, Virginia 22904 (United States); Wolf, Stuart A. [Department of Physics, University of Virginia, 382 McCormick Rd., Charlottesville, Virginia 22904 (United States); Department of Materials Science and Engineering, University of Virginia, 395 McCormick Rd., Charlottesville, Virginia 22904 (United States); Lu, Jiwei [Department of Materials Science and Engineering, University of Virginia, 395 McCormick Rd., Charlottesville, Virginia 22904 (United States)

2013-11-25

Epitaxial SrTi{sub 1−x}V{sub x}O{sub 3} (0 ≤ x ≤ 1) thin films were grown on (001)-oriented (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}AlTaO{sub 6}){sub 0.7} (LSAT) substrates using the pulsed electron-beam deposition technique. The transport study revealed a temperature driven metal-insulator transition (MIT) at 95 K for x = 0.67. The films with higher vanadium concentration (x > 0.67) were metallic corresponding to a Fermi liquid system. In the insulating phase (x < 0.67), the resistivity behavior was governed by Mott's variable range hopping mechanism. The possible mechanisms for the induced MIT are discussed, including the effects of electron correlation, lattice distortion, and Anderson localization.

Wannier-Mott Excitons in Nanoscale Molecular Ices

Science.gov (United States)

Chen, Y.-J.; Muñoz Caro, G. M.; Aparicio, S.; Jiménez-Escobar, A.; Lasne, J.; Rosu-Finsen, A.; McCoustra, M. R. S.; Cassidy, A. M.; Field, D.

2017-10-01

The absorption of light to create Wannier-Mott excitons is a fundamental feature dictating the optical and photovoltaic properties of low band gap, high permittivity semiconductors. Such excitons, with an electron-hole separation an order of magnitude greater than lattice dimensions, are largely limited to these semiconductors but here we find evidence of Wannier-Mott exciton formation in solid carbon monoxide (CO) with a band gap of >8 eV and a low electrical permittivity. This is established through the observation that a change of a few degrees K in deposition temperature can shift the electronic absorption spectra of solid CO by several hundred wave numbers, coupled with the recent discovery that deposition of CO leads to the spontaneous formation of electric fields within the film. These so-called spontelectric fields, here approaching 4 ×107 V m-1 , are strongly temperature dependent. We find that a simple electrostatic model reproduces the observed temperature dependent spectral shifts based on the Stark effect on a hole and electron residing several nm apart, identifying the presence of Wannier-Mott excitons. The spontelectric effect in CO simultaneously explains the long-standing enigma of the sensitivity of vacuum ultraviolet spectra to the deposition temperature.

Atomically resolved spectroscopic study of Sr.sub.2./sub.IrO.sub.4./sub.: Experiment and theory

Czech Academy of Sciences Publication Activity Database

Li, Q.; Cao, G.; Okamoto, S.; Yi, J.; Lin, W.; Sales, B.C.; Yan, J.; Arita, R.; Kuneš, Jan; Kozhevnikov, A.V.; Eguiluz, A.G.; Imada, M.; Gai, Z.; Pan, M.; Mandrus, D.G.

2013-01-01

Roč. 3, OCT (2013), s. 1-7 ISSN 2045-2322 R&D Projects: GA ČR GA13-25251S Institutional support: RVO:68378271 Keywords : Sr 2 IrO 4 * scanning tunneling microscopy * Mott insulator * Slater insulator Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 5.078, year: 2013 http://www.nature.com/srep/2013/131029/srep03073/full/srep03073.html

Quantum criticality around metal-insulator transitions of strongly correlated electron systems

Science.gov (United States)

Misawa, Takahiro; Imada, Masatoshi

2007-03-01

Quantum criticality of metal-insulator transitions in correlated electron systems is shown to belong to an unconventional universality class with violation of the Ginzburg-Landau-Wilson (GLW) scheme formulated for symmetry breaking transitions. This unconventionality arises from an emergent character of the quantum critical point, which appears at the marginal point between the Ising-type symmetry breaking at nonzero temperatures and the topological transition of the Fermi surface at zero temperature. We show that Hartree-Fock approximations of an extended Hubbard model on square lattices are capable of such metal-insulator transitions with unusual criticality under a preexisting symmetry breaking. The obtained universality is consistent with the scaling theory formulated for Mott transitions and with a number of numerical results beyond the mean-field level, implying that preexisting symmetry breaking is not necessarily required for the emergence of this unconventional universality. Examinations of fluctuation effects indicate that the obtained critical exponents remain essentially exact beyond the mean-field level. It further clarifies the whole structure of singularities by a unified treatment of the bandwidth-control and filling-control transitions. Detailed analyses of the criticality, containing diverging carrier density fluctuations around the marginal quantum critical point, are presented from microscopic calculations and reveal the nature as quantum critical “opalescence.” The mechanism of emerging marginal quantum critical point is ascribed to a positive feedback and interplay between the preexisting gap formation present even in metals and kinetic energy gain (loss) of the metallic carrier. Analyses of crossovers between GLW type at nonzero temperature and topological type at zero temperature show that the critical exponents observed in (V,Cr)2O3 and κ-ET -type organic conductors provide us with evidence for the existence of the present marginal

Interaction effects and quantum phase transitions in topological insulators

International Nuclear Information System (INIS)

Varney, Christopher N.; Sun Kai; Galitski, Victor; Rigol, Marcos

2010-01-01

We study strong correlation effects in topological insulators via the Lanczos algorithm, which we utilize to calculate the exact many-particle ground-state wave function and its topological properties. We analyze the simple, noninteracting Haldane model on a honeycomb lattice with known topological properties and demonstrate that these properties are already evident in small clusters. Next, we consider interacting fermions by introducing repulsive nearest-neighbor interactions. A first-order quantum phase transition was discovered at finite interaction strength between the topological band insulator and a topologically trivial Mott insulating phase by use of the fidelity metric and the charge-density-wave structure factor. We construct the phase diagram at T=0 as a function of the interaction strength and the complex phase for the next-nearest-neighbor hoppings. Finally, we consider the Haldane model with interacting hard-core bosons, where no evidence for a topological phase is observed. An important general conclusion of our work is that despite the intrinsic nonlocality of topological phases their key topological properties manifest themselves already in small systems and therefore can be studied numerically via exact diagonalization and observed experimentally, e.g., with trapped ions and cold atoms in optical lattices.

Winding Up of the Wave-Function Phase by an Insulator-to-Superfluid Transition in a Ring of Coupled Bose-Einstein Condensates

International Nuclear Information System (INIS)

Dziarmaga, Jacek; Meisner, Jakub; Zurek, Wojciech H.

2008-01-01

We study phase transition from the Mott insulator to superfluid in a periodic optical lattice. Kibble-Zurek mechanism predicts buildup of winding number through random walk of BEC phases, with the step size scaling as a third root of transition rate. We confirm this and demonstrate that this scaling accounts for the net winding number after the transition

Magnetic states, correlation effects and metal-insulator transition in FCC lattice

Science.gov (United States)

Timirgazin, M. A.; Igoshev, P. A.; Arzhnikov, A. K.; Irkhin, V. Yu

2016-12-01

The ground-state magnetic phase diagram (including collinear and spiral states) of the single-band Hubbard model for the face-centered cubic lattice and related metal-insulator transition (MIT) are investigated within the slave-boson approach by Kotliar and Ruckenstein. The correlation-induced electron spectrum narrowing and a comparison with a generalized Hartree-Fock approximation allow one to estimate the strength of correlation effects. This, as well as the MIT scenario, depends dramatically on the ratio of the next-nearest and nearest electron hopping integrals {{t}\\prime}/t . In contrast with metallic state, possessing substantial band narrowing, insulator one is only weakly correlated. The magnetic (Slater) scenario of MIT is found to be superior over the Mott one. Unlike simple and body-centered cubic lattices, MIT is the first order transition (discontinuous) for most {{t}\\prime}/t . The insulator state is type-II or type-III antiferromagnet, and the metallic state is spin-spiral, collinear antiferromagnet or paramagnet depending on {{t}\\prime}/t . The picture of magnetic ordering is compared with that in the standard localized-electron (Heisenberg) model.

arXiv Gauge Topological Nature of the Superconductor-Insulator Transition

CERN Document Server

Diamantini, M.C.; Lukyanchuk, I.; Vinokur, V.M.

It has long been believed that, at absolute zero, electrons can form only one quantum coherent state, a superconductor. Yet, several two dimensional superconducting systems were found to harbor the superinsulating state with infinite resistance, a mirror image of superconductivity, and a metallic state often referred to as Bose metal, characterized by finite longitudinal and vanishing Hall resistances. The nature of these novel and mysterious quantum coherent states is the subject of intense study.Here, we propose a topological gauge description of the superconductor-insulator transition (SIT) that enables us to identify the underlying mechanism of superinsulation as Polyakov's linear confinement of Cooper pairs via instantons. We find a criterion defining conditions for either a direct SIT or for the SIT via the intermediate Bose metal and demonstrate that this Bose metal phase is a Mott topological insulator in which the Cooper pair-vortex liquid is frozen by Aharonov-Bohm interactions.

Mott scattering as a probe of long range QCD

International Nuclear Information System (INIS)

Bertulani, C.A.; Balantekin, A.B.

1993-12-01

We investigate the possibility of using the Mott scattering between identical nuclei to assess the existence of long range QCD, e.g., a color Van der Waals interaction, as suggested recently. Among other effects which were not considered before, the tail of the nuclear potential, emission of radiation by Bremsstrahlung, atomic screening, emission of delta-electrons, and the quasi-molecule binding are included in our calculations. We show that the sum of these effects can explain the observed shift in the Mott oscillations in a recent experiment. (orig.)

Developing Topological Insulator Fiber Based Photon Pairs Source for Ultrafast Optoelectronic Applications

Science.gov (United States)

2016-04-01

of a thin layer of topological insulator Bi2Se3 with the transmission of T = 50%. We apply magnetic field B=3 tesla normal to the sample and parallel...nonlinear induced by magnetic field in the Topological Insulator Bi2Se3 and Molybdenum Disulfide MoS2. The nonlinear effect is pulse broadening...Topological Insulator Q- Switched Erbium-Doped Fiber Laser”, IEEE J. Sel. Top. Quant. Electron., 20, 0900508 (2014). [2]. Shuqing Chen et al, “Stable Q

Insulator layer formation in MgB2 SIS junctions

International Nuclear Information System (INIS)

Shimakage, H.; Tsujimoto, K.; Wang, Z.; Tonouchi, M.

2005-01-01

The dependence of current-voltage characteristics on thin film deposition conditions was investigated using MgB 2 /AlN/NbN SIS junctions. By increasing the substrate temperature in AlN insulator deposition, the current density decreased and the normal resistance increased. The results indicated that an additional insulator layer between the MgB 2 and AlN formed, either before or during the AlN deposition. The thickness of the additional insulator layer was increased with an increase in the AlN deposition temperature. From the dependence of current density on the thickness of AlN in low temperature depositions, the thickness of the additional insulator layer was estimated to be 1-1.5 nm when the AlN insulator was deposited from 0.14 to 0.7 nm. Moreover, with the current density of MgB 2 /AlN/MgB 2 SIS junctions, further insulator layer formation was confirmed

Universal Quantum Criticality in the Metal-Insulator Transition of Two-Dimensional Interacting Dirac Electrons

Directory of Open Access Journals (Sweden)

Yuichi Otsuka

2016-03-01

Full Text Available The metal-insulator transition has been a subject of intense research since Mott first proposed that the metallic behavior of interacting electrons could turn to an insulating one as electron correlations increase. Here, we consider electrons with massless Dirac-like dispersion in two spatial dimensions, described by the Hubbard models on two geometrically different lattices, and perform numerically exact calculations on unprecedentedly large systems that, combined with a careful finite-size scaling analysis, allow us to explore the quantum critical behavior in the vicinity of the interaction-driven metal-insulator transition. Thereby, we find that the transition is continuous, and we determine the quantum criticality for the corresponding universality class, which is described in the continuous limit by the Gross-Neveu model, a model extensively studied in quantum field theory. Furthermore, we discuss a fluctuation-driven scenario for the metal-insulator transition in the interacting Dirac electrons: The metal-insulator transition is triggered only by the vanishing of the quasiparticle weight, not by the Dirac Fermi velocity, which instead remains finite near the transition. This important feature cannot be captured by a simple mean-field or Gutzwiller-type approximate picture but is rather consistent with the low-energy behavior of the Gross-Neveu model.

First-order metal-insulator transitions in the extended Hubbard model due to self-consistent screening of the effective interaction

Science.gov (United States)

Schüler, M.; van Loon, E. G. C. P.; Katsnelson, M. I.; Wehling, T. O.

2018-04-01

While the Hubbard model is the standard model to study Mott metal-insulator transitions, it is still unclear to what extent it can describe metal-insulator transitions in real solids, where nonlocal Coulomb interactions are always present. By using a variational principle, we clarify this issue for short- and long-range nonlocal Coulomb interactions for half-filled systems on bipartite lattices. We find that repulsive nonlocal interactions generally stabilize the Fermi-liquid regime. The metal-insulator phase boundary is shifted to larger interaction strengths to leading order linearly with nonlocal interactions. Importantly, nonlocal interactions can raise the order of the metal-insulator transition. We present a detailed analysis of how the dimension and geometry of the lattice as well as the temperature determine the critical nonlocal interaction leading to a first-order transition: for systems in more than two dimensions with nonzero density of states at the Fermi energy the critical nonlocal interaction is arbitrarily small; otherwise, it is finite.

Electronic structure and insulating gap in epitaxial VO2 polymorphs

Directory of Open Access Journals (Sweden)

Shinbuhm Lee

2015-12-01

Full Text Available Determining the origin of the insulating gap in the monoclinic V O2(M1 is a long-standing issue. The difficulty of this study arises from the simultaneous occurrence of structural and electronic transitions upon thermal cycling. Here, we compare the electronic structure of the M1 phase with that of single crystalline insulating V O2(A and V O2(B thin films to better understand the insulating phase of VO2. As these A and B phases do not undergo a structural transition upon thermal cycling, we comparatively study the origin of the gap opening in the insulating VO2 phases. By x-ray absorption and optical spectroscopy, we find that the shift of unoccupied t2g orbitals away from the Fermi level is a common feature, which plays an important role for the insulating behavior in VO2 polymorphs. The distinct splitting of the half-filled t2g orbital is observed only in the M1 phase, widening the bandgap up to ∼0.6 eV. Our approach of comparing all three insulating VO2 phases provides insight into a better understanding of the electronic structure and the origin of the insulating gap in VO2.

Importance of space-time fluctuations and non-linearities for the transport inside insulating glasses; Importance des fluctuations spatio-temporelles et des non linearites pour le transport dans les verres isolants

Energy Technology Data Exchange (ETDEWEB)

Ladieu, F

2003-07-01

This work deals with transport in insulating glasses. In such solids, the discrete translational symmetry is lost, which means that the plane wave analysis is not a priori the right 'starting point'. As a result, the transport is more difficult to handle, and a huge amount of works have been devoted to many aspects of transport in disordered systems, especially since the seventies. Here we focus on three specific questions: (i) the heat transport in glasses submitted to micro-beams and the associated irreversible vaporization; (ii) the electronic d.c. transport, below 1 Kelvin, in Mott-Anderson insulators, i.e. in 'electron glasses' where both disorder and electron-electron interactions are relevant; (iii) the low frequency dielectric constant in 'structural glasses' (i.e. 'ordinary glasses') which, below 1 Kelvin, is both universal (i.e. independent on the chemical composition) and very different of that of crystals. For each topic, we present both original experiments and the new theoretical concepts that we have elaborated so as to understand the main experimental features. Eventually, it appears that, in any case, transport in insulating glasses is strongly dominated by quite a small part of the 'glass-applied field' ensemble and that the nonlinear response is a relevant tool to get informations on this 'sub-part' which dominates the transport in the whole system. (author)

A Review on Disorder-Driven Metal–Insulator Transition in Crystalline Vacancy-Rich GeSbTe Phase-Change Materials

Science.gov (United States)

Wang, Jiang-Jing; Xu, Ya-Zhi; Mazzarello, Riccardo; Wuttig, Matthias; Zhang, Wei

2017-01-01

Metal–insulator transition (MIT) is one of the most essential topics in condensed matter physics and materials science. The accompanied drastic change in electrical resistance can be exploited in electronic devices, such as data storage and memory technology. It is generally accepted that the underlying mechanism of most MITs is an interplay of electron correlation effects (Mott type) and disorder effects (Anderson type), and to disentangle the two effects is difficult. Recent progress on the crystalline Ge1Sb2Te4 (GST) compound provides compelling evidence for a disorder-driven MIT. In this work, we discuss the presence of strong disorder in GST, and elucidate its effects on electron localization and transport properties. We also show how the degree of disorder in GST can be reduced via thermal annealing, triggering a disorder-driven metal–insulator transition. The resistance switching by disorder tuning in crystalline GST may enable novel multilevel data storage devices. PMID:28773222

16 CFR 460.2 - What is home insulation.

Science.gov (United States)

2010-01-01

... 16 Commercial Practices 1 2010-01-01 2010-01-01 false What is home insulation. 460.2 Section 460.2 Commercial Practices FEDERAL TRADE COMMISSION TRADE REGULATION RULES LABELING AND ADVERTISING OF HOME..., semirigid, flexible, or loose-fill form. Home insulation is for use in old or new homes, condominiums...

The Mott transition in the strong coupling perturbation theory

Science.gov (United States)

Sherman, A.

2015-01-01

Using the strong coupling diagram technique a self-consistent equation for the electron Green's function is derived for the repulsive Hubbard model. Terms of two lowest orders of the ratio of the bandwidth Δ to the Hubbard repulsion U are taken into account in the irreducible part of the Larkin equation. The obtained equation is shown to retain causality and reduces to Green's function of uncorrelated electrons in the limit U → 0. Calculations were performed for the semi-elliptical initial band. It is shown that the approximation describes the Mott transition, which occurs at Uc =√{ 3 } Δ / 2. This value coincides with that obtained in the Hubbard-III approximation. At half-filling, for 0 self-energy is nonzero at the Fermi level, which indicates that the obtained solution is not a Fermi liquid. At small deviations from half-filling the density of states shifts along the frequency axis without perceptible changes in its shape. For larger deviations the density of states is modified: it is redistributed in favor of the subband, in which the Fermi level is located, and for U >Uc the Mott gap disappears.

Individual Magnetic Molecules on Ultrathin Insulating Surfaces

Science.gov (United States)

El Hallak, Fadi; Warner, Ben; Hirjibehedin, Cyrus

2012-02-01

Single molecule magnets have attracted ample interest because of their exciting magnetic and quantum properties. Recent studies have demonstrated that some of these molecules can be evaporated on surfaces without losing their magnetic properties [M. Mannini et al., Nature 468, 417, (2010)]. This remarkable progress enhances the chances of real world applications for these molecules. We present STM imaging and spectroscopy data on iron phthalocyanine molecules deposited on Cu(100) and on a Cu2N ultrathin insulating surface. These molecules have been shown to display a large magnetic anisotropy on another thin insulating surface, oxidized Cu(110) [N. Tsukahara et al., Phys. Rev. Lett. 102, 167203 (2009)]. By using a combination of elastic and inelastic electron tunnelling spectroscopy, we investigate the binding of the molecules to the surface and the impact that the surface has on their electronic and magnetic properties.

Hundness versus Mottness in a three-band Hund model with relevance for iron-pnictides

Energy Technology Data Exchange (ETDEWEB)

Stadler, Katharina M.; Delft, Jan von; Weichselbaum, Andreas [Ludwig Maximilians University, Munich (Germany); Yin, Zhiping; Kotliar, Gabriel [Rutgers University, New Jersey (United States)

2016-07-01

The recently discovered iron pnictide superconductors (as well as chalcogenides, ruthenates, and other 4d transition metal oxides) show puzzling anomalous properties, like a coherence-incoherence crossover, also in the normal state. While there is consensus about strong correlation effects playing a key role in these materials, their precise origin (Coulomb repulsion or Hund's rule coupling between electrons of different orbitals) has been under debate as one of the major open questions in the field many years. In a recent detailed study of the Hund metal problem the coherence-incoherence crossover was shown to be connected to spin-orbital separation and to be clearly driven by Hund's rule coupling. In order to better understand the differences between Mott insulators and Hund metals we explore the phase diagram for a three-band model with Coulomb repulsion and Hund's rule coupling on a Bethe lattice at 1/3 filling using the numerical renormalization group to obtain a numerically exact dynamical mean-field theory solution.

Hubbard physics in the PAW GW approximation

Energy Technology Data Exchange (ETDEWEB)

Booth, J. M., E-mail: jamie.booth@rmit.edu.au; Smith, J. S.; Russo, S. P. [Theoretical Chemical and Quantum Physics, School of Science, RMIT University, Melbourne, VIC (Australia); Drumm, D. W. [Theoretical Chemical and Quantum Physics, School of Science, RMIT University, Melbourne, VIC (Australia); Australian Research Council Centre of Excellence for Nanoscale BioPhotonics, School of Science, RMIT University, Melbourne, VIC (Australia); Casey, P. S. [CSIRO Manufacturing, Clayton, VIC (Australia)

2016-06-28

It is demonstrated that the signatures of the Hubbard Model in the strongly interacting regime can be simulated by modifying the screening in the limit of zero wavevector in Projector-Augmented Wave GW calculations for systems without significant nesting. This modification, when applied to the Mott insulator CuO, results in the opening of the Mott gap by the splitting of states at the Fermi level into upper and lower Hubbard bands, and exhibits a giant transfer of spectral weight upon electron doping. The method is also employed to clearly illustrate that the M{sub 1} and M{sub 2} forms of vanadium dioxide are fundamentally different types of insulator. Standard GW calculations are sufficient to open a gap in M{sub 1} VO{sub 2}, which arise from the Peierls pairing filling the valence band, creating homopolar bonds. The valence band wavefunctions are stabilized with respect to the conduction band, reducing polarizability and pushing the conduction band eigenvalues to higher energy. The M{sub 2} structure, however, opens a gap from strong on-site interactions; it is a Mott insulator.

Effects of the electron's anomaly in relativistic laser-assisted Mott scattering

International Nuclear Information System (INIS)

Ngoko Djiokap, J.M.; Tetchou Nganso, H.M.; Kwato Njock, M.G.

2006-02-01

We investigate the influence of the electron's anomalous magnetic moment on the process of relativistic Mott scattering in a powerful electromagnetic plane wave for which the ponderomotive energy is of the order of the magnitude of the electron's rest mass. For this purpose, we use the Coulomb-Dirac-Volkov and the Dirac-Volkov functions with the electron's anomaly to describe the initial and final states respectively. First-order Born differential cross sections of induced and inverse bremsstrahlung are obtained for linearly polarized laser light. Numerical calculations are carried out for various parameters values (i.e. scattering angle, the nucleus charge, photon energy, electrical field) and are compared with results obtained by Li et al. It is found that for parameters used in the present work, incorporating the anomaly of the electron in the initial and final states yields cross sections which are strongly modified whatever the scattering geometry, as compared to the outcome of the previous treatment. (author)

The Mott transition in the strong coupling perturbation theory

International Nuclear Information System (INIS)

Sherman, A.

2015-01-01

Using the strong coupling diagram technique a self-consistent equation for the electron Green's function is derived for the repulsive Hubbard model. Terms of two lowest orders of the ratio of the bandwidth Δ to the Hubbard repulsion U are taken into account in the irreducible part of the Larkin equation. The obtained equation is shown to retain causality and reduces to Green's function of uncorrelated electrons in the limit U→0. Calculations were performed for the semi-elliptical initial band. It is shown that the approximation describes the Mott transition, which occurs at U c =√(3)Δ/2. This value coincides with that obtained in the Hubbard-III approximation. At half-filling, for 0U c the Mott gap disappears

Resonant X-Ray Scattering and the jeff=1/2 Electronic Ground State in Iridate Perovskites

DEFF Research Database (Denmark)

Sala, M. Moretti; Boseggia, S.; McMorrow, Desmond Francis

2014-01-01

The resonant x-ray scattering (magnetic elastic, RXMS, and inelastic, RIXS) of Ir4+ at the L-2,L-3 edges relevant to spin-orbit Mott insulators A(n+1) Ir(n)O3(n+1) (A = Sr, Ba, etc.) are calculated using a single-ion model which treats the spin-orbit and tetragonal crystal-field terms on an equal...

Spin-Orbital Quantum Liquid on the Honeycomb Lattice

Directory of Open Access Journals (Sweden)

Philippe Corboz

2012-11-01

Full Text Available The main characteristic of Mott insulators, as compared to band insulators, is to host low-energy spin fluctuations. In addition, Mott insulators often possess orbital degrees of freedom when crystal-field levels are partially filled. While in the majority of Mott insulators, spins and orbitals develop long-range order, the possibility for the ground state to be a quantum liquid opens new perspectives. In this paper, we provide clear evidence that the spin-orbital SU(4 symmetric Kugel-Khomskii model of Mott insulators on the honeycomb lattice is a quantum spin-orbital liquid. The absence of any form of symmetry breaking—lattice or SU(N—is supported by a combination of semiclassical and numerical approaches: flavor-wave theory, tensor network algorithm, and exact diagonalizations. In addition, all properties revealed by these methods are very accurately accounted for by a projected variational wave function based on the π-flux state of fermions on the honeycomb lattice at 1/4 filling. In that state, correlations are algebraic because of the presence of a Dirac point at the Fermi level, suggesting that the symmetric Kugel-Khomskii model on the honeycomb lattice is an algebraic quantum spin-orbital liquid. This model provides an interesting starting point to understanding the recently discovered spin-orbital-liquid behavior of Ba_{3}CuSb_{2}O_{9}. The present results also suggest the choice of optical lattices with honeycomb geometry in the search for quantum liquids in ultracold four-color fermionic atoms.

Excitonic Order and Superconductivity in the Two-Orbital Hubbard Model: Variational Cluster Approach

Science.gov (United States)

Fujiuchi, Ryo; Sugimoto, Koudai; Ohta, Yukinori

2018-06-01

Using the variational cluster approach based on the self-energy functional theory, we study the possible occurrence of excitonic order and superconductivity in the two-orbital Hubbard model with intra- and inter-orbital Coulomb interactions. It is known that an antiferromagnetic Mott insulator state appears in the regime of strong intra-orbital interaction, a band insulator state appears in the regime of strong inter-orbital interaction, and an excitonic insulator state appears between them. In addition to these states, we find that the s±-wave superconducting state appears in the small-correlation regime, and the dx2 - y2-wave superconducting state appears on the boundary of the antiferromagnetic Mott insulator state. We calculate the single-particle spectral function of the model and compare the band gap formation due to the superconducting and excitonic orders.

Ellen N. La Motte: the making of a nurse, writer, and activist.

Science.gov (United States)

Williams, Lea M

2015-01-01

This article examines the early career of Ellen N. La Motte (1873-1961) to trace how her training at the Johns Hopkins Training School for Nurses and years spent as a tuberculosis nurse in Baltimore shaped her perception of tuberculosis prevention and women's suffrage. Although studies of tuberculosis have frequently alluded to her work, no sustained biocritical discussion of her development as a nurse and scholar exists. Between 1902, when she graduated from nursing school, and 1914, the start of the Great War, La Motte published a textbook and dozens of articles in journals devoted to nursing and social reform and delivered many speeches at local, regional, and national meetings. In addition, as her reputation as an expert in the field of tuberculosis nursing grew, her advocacy for the vote for women increased, and she used her writing and speaking skills on behalf of the suffrage cause. This article assesses how the skills La Motte acquired during these years helped mold her into a successful and respected nurse, writer, and activist.

Metal-Insulator Transition in Copper Oxides Induced by Apex Displacements

Directory of Open Access Journals (Sweden)

Swagata Acharya

2018-05-01

Full Text Available High temperature superconductivity has been found in many kinds of compounds built from planes of Cu and O, separated by spacer layers. Understanding why critical temperatures are so high has been the subject of numerous investigations and extensive controversy. To realize high temperature superconductivity, parent compounds are either hole doped, such as La_{2}CuO_{4} (LCO with Sr (LSCO, or electron doped, such as Nd_{2}CuO_{4} (NCO with Ce (NCCO. In the electron-doped cuprates, the antiferromagnetic phase is much more robust than the superconducting phase. However, it was recently found that the reduction of residual out-of-plane apical oxygen dramatically affects the phase diagram, driving those compounds to a superconducting phase. Here we use a recently developed first-principles method to explore how displacement of the apical oxygen (AO in LCO affects the optical gap, spin and charge susceptibilities, and superconducting order parameter. By combining quasiparticle self-consistent GW (QS GW and dynamical mean-field theory (DMFT, we show that LCO is a Mott insulator, but small displacements of the apical oxygen drive the compound to a metallic state through a localization-delocalization transition, with a concomitant maximum in d-wave order parameter at the transition. We address the question of whether NCO can be seen as the limit of LCO with large apical displacements, and we elucidate the deep physical reasons why the behavior of NCO is so different from the hole-doped materials. We shed new light on the recent correlation observed between T_{c} and the charge transfer gap, while also providing a guide towards the design of optimized high-T_{c} superconductors. Further, our results suggest that strong correlation, enough to induce a Mott gap, may not be a prerequisite for high-T_{c} superconductivity.

Coulomb effects in relativistic laser-assisted Mott scattering

International Nuclear Information System (INIS)

Ngoko Djiokap, J.M.; Kwato Njock, M.G.; Tetchou Nganso, H.M.

2004-09-01

We reconsider the influence of the Coulomb interaction on the process of relativistic Mott scattering in a powerful electromagnetic plane wave for which the ponderomotive energy is of the order of the magnitude of the electron's rest mass. Coulomb effects of the bare nucleus on the laser-dressed electron are treated more completely than in the previous work of Li et al. [J. Phys. B: At. Mol. Opt. Phys. 37 (2004) 653]. To this end we use Coulomb-Dirac-Volkov functions to describe the initial and the final states of the electron. First-order Born differential cross sections of induced and inverse bremsstrahlung are obtained for circularly and linearly polarized laser light. Numerical calculations are carried out from both polarizations, for various nucleus charge values, three angular configurations and an incident energy in the MeV range. It is found that for parameters used in the present work, incorporating Coulomb effects of the target nucleus either in the initial state or in the final state yields cross sections which are quite similar whatever the scattering geometry and polarization considered. When Coulomb distortions are included in both states, the cross sections are strongly modified with the increase of Z, as compared to the outcome of the prior form of the T-matrix treatment. (author)

Real-space visualization of remnant Mott gap and magnon excitations.

Science.gov (United States)

Wang, Y; Jia, C J; Moritz, B; Devereaux, T P

2014-04-18

We demonstrate the ability to visualize real-space dynamics of charge gap and magnon excitations in the Mott phase of the single-band Hubbard model and the remnants of these excitations with hole or electron doping. At short times, the character of magnetic and charge excitations is maintained even for large doping away from the Mott and antiferromagnetic phases. Doping influences both the real-space patterns and long timescales of these excitations with a clear carrier asymmetry attributable to particle-hole symmetry breaking in the underlying model. Further, a rapidly oscillating charge-density-wave-like pattern weakens, but persists as a visible demonstration of a subleading instability at half-filling which remains upon doping. The results offer an approach to analyzing the behavior of systems where momentum space is either inaccessible or poorly defined.

Electrical resistivity study of insulators

International Nuclear Information System (INIS)

Liesegang, J.; Senn, B.C.; Holcombe, S.R.; Pigram, P.J.

1998-01-01

Full text: Conventional methods of electrical resistivity measurement of dielectric materials involve the application of electrodes to a sample whereby a potential is applied and a current through the material is measured. Although great care and ingenuity has often been applied to this technique, the recorded values of electrical resistivity (p), especially for insulator materials, show great disparity. In earlier work by the authors, a method for determining surface charge decay [Q(t)], using a coaxial cylindrical capacitor arrangement interfaced to a personal computer, was adapted to allow the relatively straightforward measurement of electrical resistivity in the surface region of charged insulator materials. This method was used to develop an ionic charge transport theory, based on Mott-Gurney diffusion to allow a greater understanding into charge transport behaviour. This theory was extended using numerical analysis to produce a two dimensional (2-D) computational model to allow the direct comparison between experimental and theoretical charge decay data. The work also provided a means for the accurate determination of the diffusion coefficient (D) and the layer of thickness of surface charge (Δz) on the sample. The work outlined here involves an extension of the theoretical approach previously taken, using a computational model based more closely on the 3-D experimental set-up, to reinforce the level of confidence in the results achieved for the simpler 2-D treatment. Initially, a 3-D rectangular box arrangement similar to the experimental set-up was modelled and a theoretical and experimental comparison of voltage decay results made. This model was then transferred into cylindrical coordinates to allow it to be almost identical to the experiment and again a comparison made. In addition, theoretical analysis of the coupled non-linear partial differential equations governing the charge dissipation process has led to a simplification involving directly, the

Magnetic correlations in a classic Mott system

International Nuclear Information System (INIS)

Bao, W.; Broholm, C.; Aeppli, G.; Carter, S.A.; Dai, D.; Frost, C.D.

1997-07-01

The metal-insulator transition in V 2 O 3 causes a fundamental change in its magnetism. While the antiferromagnetic insulator (AFI) is a Heisenberg localized spin system, the antiferromagnetism in the strongly correlated metal is determined by a Fermi surface instability. Paramagnetic fluctuations in the metal and insulator represent similar spatial spin correlations, but are unrelated to the long range order in the AFI. The phase transition to the AFI induces an abrupt switching of magnetic correlations to a different magnetic wave vector. The AFI transition, therefore, is not a conventional spin order-disorder transition. Instead it is accounted for by an ordering in the occupation of the two degenerate d-orbitals at the Fermi level

Locking of iridium magnetic moments to the correlated rotation of oxygen octahedra in Sr2IrO4 revealed by x-ray resonant scattering

DEFF Research Database (Denmark)

Boseggia, S.; Walker, H. C.; Vale, J.

2013-01-01

Sr2IrO4 is a prototype of the class of Mott insulators in the strong spin–orbit interaction (SOI) limit described by a Jeff = 1/2 ground state. In Sr2IrO4, the strong SOI is predicted to manifest itself in the locking of the canting of the magnetic moments to the correlated rotation by 11.8(1)° o...

Disordered spinor Bose-Hubbard model

International Nuclear Information System (INIS)

LaPcki, Mateusz; Paganelli, Simone; Ahufinger, Veronica; Sanpera, Anna; Zakrzewski, Jakub

2011-01-01

We study the zero-temperature phase diagram of the disordered spin-1 Bose-Hubbard model in a two-dimensional square lattice. To this aim, we use a mean-field Gutzwiller ansatz and a probabilistic mean-field perturbation theory. The spin interaction induces two different regimes, corresponding to a ferromagnetic and antiferromagnetic order. In the ferromagnetic case, the introduction of disorder reproduces analogous features of the disordered scalar Bose-Hubbard model, consisting in the formation of a Bose glass phase between Mott insulator lobes. In the antiferromagnetic regime, the phase diagram differs more from the scalar case. Disorder in the chemical potential can lead to the disappearance of Mott insulator lobes with an odd-integer filling factor and, for sufficiently strong spin coupling, to Bose glass of singlets between even-filling Mott insulator lobes. Disorder in the spinor coupling parameter results in the appearance of a Bose glass phase only between the n and the n+1 lobes for n odd. Disorder in the scalar Hubbard interaction inhibits Mott insulator regions for occupation larger than a critical value.

On metal-insulator transition in cubic fullerides

Science.gov (United States)

Iwahara, Naoya; Chibotaru, Liviu

The interplay between degenerate orbital and electron correlation is a key to characterize the electronic phases in, for example, transition metal compounds and alkali-doped fullerides. Besides, the degenerate orbital couples to spin and lattice degrees of freedom ,giving rise to exotic phenomena. Here, we develop the self-consistent Gutzwiller approach for the simultaneous treatment of the Jahn-Teller effect and electron correlation, and apply the methodology to reveal the nature of the ground electronic state of fullerides. For small Coulomb repulsion on site U, the fulleride is quasi degenerate correlated metal. With increase of U, we found the quantum phase transition from the metallic phase to JT split phase. In the latter, the Mott transition (MT) mainly develops in the half-filled subband, whereas the empty and the completely filled subbands are almost uninvolved. Therefore, we can qualify the metal-insulator transition in fullerides as an orbital selective MT induced by JT effect.

Identifying Two-Dimensional Z 2 Antiferromagnetic Topological Insulators

Science.gov (United States)

Bègue, F.; Pujol, P.; Ramazashvili, R.

2018-01-01

We revisit the question of whether a two-dimensional topological insulator may arise in a commensurate Néel antiferromagnet, where staggered magnetization breaks the symmetry with respect to both elementary translation and time reversal, but retains their product as a symmetry. In contrast to the so-called Z 2 topological insulators, an exhaustive characterization of antiferromagnetic topological phases with the help of topological invariants has been missing. We analyze a simple model of an antiferromagnetic topological insulator and chart its phase diagram, using a recently proposed criterion for centrosymmetric systems [13]. We then adapt two methods, originally designed for paramagnetic systems, and make antiferromagnetic topological phases manifest. The proposed methods apply far beyond the particular examples treated in this work, and admit straightforward generalization. We illustrate this by two examples of non-centrosymmetric systems, where no simple criteria have been known to identify topological phases. We also present, for some cases, an explicit construction of edge states in an antiferromagnetic topological insulator.

The happy marriage between electron-phonon superconductivity and Mott physics in Cs3C60: A first-principle phase diagram

Science.gov (United States)

Capone, Massimo; Nomura, Yusuke; Sakai, Shiro; Giovannetti, Gianluca; Arita, Ryotaro

The phase diagram of doped fullerides like Cs3C60 as a function of the spacing between fullerene molecules is characterized by a first-order transition between a Mott insulator and an s-wave superconductor with a dome-shaped behavior of the critical temperature. By means of an ab-initio modeling of the bandstructure, the electron-phonon interaction and the interaction parameter and a Dynamical Mean-Field Theory solution, we reproduce the phase diagram and demonstrate that phonon superconductivity benefits from strong correlations confirming earlier model predictions. The role of correlations is manifest also in infrared measurements carried out by L. Baldassarre. The superconducting phase shares many similarities with ''exotic'' superconductors with electronic pairing, suggesting that the anomalies in the ''normal'' state, rather than the pairing glue, can be the real common element unifying a wide family of strongly correlated superconductors including cuprates and iron superconductors

Development and validation of cryogenic foam insulation for LH2 subsonic transports

Science.gov (United States)

Anthony, F. M.; Colt, J. Z.; Helenbrook, R. G.

1981-01-01

Fourteen foam insulation specimens were tested. Some were plain foam while others contained flame retardants, chopped fiberglass reinforcement and/or vapor barriers. The thermal performance of the insulation was determined by measuring the rate at which LH2 boiled from an aluminum tank insulated with the test material. The test specimens were approximately 50 mm (2 in.) thick. They were structurally scaled so that the test cycle would duplicate the maximum thermal stresses predicted for the thicker insulation of an aircraft liquid hydrogen fuel tank during a typical subsonic flight. The simulated flight cycle of approximately 10 minutes duration heated the other insulation surface to 316 K (110 F) and cooled it to 226 K (20 F) while the inner insulation surface remained at liquid hydrogen temperature of 20 K (-423 F). Two urethane foam insulations exceeded the initial life goal of 2400 simulated flight cycles and sustained 4400 cycles with only minor damage. The addition of fiberglass reinforcement of flame retardant materials to an insulation degraded thermal performance and/or the life of the foam material. Installation of vapor barriers enhanced the structural integrity of the material but did not improve thermal performance. All of the foams tested were available materials; none were developed specifically for LH2 service.

Soft deconfinement — critical phenomena at the Mott transition in a field theory for quarks and mesons

Science.gov (United States)

Hüfner, J.; Klevansky, S. P.; Rehberg, P.

1996-02-01

Critical phenomena associated with Mott transitions are investigated in the finite temperature SUf(3) Nambu-Jona-Lasinio model, that describes quarks u, d, s and bound mesons π, K. Critical exponents for the behavior close to the Mott temperature TM are determined for the static properties of a pion, such as mπ( T), gπqq( T), fπ( T), π, and the pion polarizabilities αC, N, as well as for the behavior of mK( T), gKqs( T) fK( T) in the strange sector. The effect of the Mott transitions on the q overlineq and ππ scattering lengths and for hadronization cross sections σ q overlineq→ππ (T) is discussed. Divergencies that occur in these quantities at TM indicate an intransparence with respect to hadronic and photonic probes, much like the phenomenon of critical opalescence. Physically, the Mott transition models the deconfinement transition expected of QCD since it corresponds to a delocalizayion of the bound states when the temperature is raised above TM.

A Review on Disorder-Driven Metal-Insulator Transition in Crystalline Vacancy-Rich GeSbTe Phase-Change Materials.

Science.gov (United States)

Wang, Jiang-Jing; Xu, Ya-Zhi; Mazzarello, Riccardo; Wuttig, Matthias; Zhang, Wei

2017-07-27

Metal-insulator transition (MIT) is one of the most essential topics in condensed matter physics and materials science. The accompanied drastic change in electrical resistance can be exploited in electronic devices, such as data storage and memory technology. It is generally accepted that the underlying mechanism of most MITs is an interplay of electron correlation effects (Mott type) and disorder effects (Anderson type), and to disentangle the two effects is difficult. Recent progress on the crystalline Ge₁Sb₂Te₄ (GST) compound provides compelling evidence for a disorder-driven MIT. In this work, we discuss the presence of strong disorder in GST, and elucidate its effects on electron localization and transport properties. We also show how the degree of disorder in GST can be reduced via thermal annealing, triggering a disorder-driven metal-insulator transition. The resistance switching by disorder tuning in crystalline GST may enable novel multilevel data storage devices.

Travel funds for Stanford University to Host Mott MURI Annual Review and Oxide Workshop, August 6-8, 2013

Science.gov (United States)

2016-02-25

Travel funds for Stanford University to host Mott MURI Annual Review and Oxide Workshop, August 6-8, 2013 In conjunction with a program review for...Number of Papers published in non peer-reviewed journals: Final Report: Travel funds for Stanford University to host Mott MURI Annual Review and Oxide

High-quality LaVO3 films as solar energy conversion material

International Nuclear Information System (INIS)

Zhang, Hai-Tian; Brahlek, Matthew; Ji, Xiaoyu; Lei, Shiming; Lapano, Jason

2017-01-01

Mott insulating oxides and their heterostructures have recently been identified as potential photovoltaic materials with favorable absorption properties and an intrinsic built-in electric field that can efficiently separate excited electron hole pairs. At the same time, they are predicted to overcome the Shockley-Queisser limit due to strong electron electron interaction present. Despite these premises a high concentration of defects commonly observed in Mott insulating films acting as recombination centers can derogate the photovoltaic conversion efficiency. With use of the self-regulated growth kinetics in hybrid molecular beam epitaxy, this obstacle can be overcome. High-quality, stoichiometric LaVO 3 films were grown with defect densities of in-gap states up to 2 orders of magnitude lower compared to the films in the literature, and a factor of 3 lower than LaVO 3 bulk single crystals. Photoconductivity measurements revealed a significant photoresponsivity increase as high as tenfold of stoichiometric LaVO 3 films compared to their nonstoichiometric counterparts. Furthermore, this work marks a critical step toward the realization of high-performance Mott insulator solar cells beyond conventional semiconductors.

Phase coexistence in the metal-insulator transition of a VO2 thin film

International Nuclear Information System (INIS)

Chang, Y.J.; Koo, C.H.; Yang, J.S.; Kim, Y.S.; Kim, D.H.; Lee, J.S.; Noh, T.W.; Kim, Hyun-Tak; Chae, B.G.

2005-01-01

Vanadium dioxide (VO 2 ) shows a metal-insulator transition (MIT) near room temperature, accompanied by an abrupt resistivity change. Since the MIT of VO 2 is known to be a first order phase transition, it is valuable to check metallic and insulating phase segregation during the MIT process. We deposited (100)-oriented epitaxial VO 2 thin films on R-cut sapphire substrates. From the scanning tunneling spectroscopy (STS) spectra, we could distinguish metallic and insulating regions by probing the band gap. Optical spectroscopic analysis also supported the view that the MIT in VO 2 occurs through metal and insulator phase coexistence

Reassessment of the electronic state, magnetism, and superconductivity in high-T{sub c} cuprates with the Nd{sub 2}CuO{sub 4} structure

Energy Technology Data Exchange (ETDEWEB)

Naito, Michio, E-mail: minaito@cc.tuat.ac.jp [Department of Applied Physics, Tokyo University of Agriculture and Technology, Naka-cho 2-24-16, Koganei, Tokyo 184-8588 (Japan); Krockenberger, Yoshiharu; Ikeda, Ai; Yamamoto, Hideki [NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198 (Japan)

2016-04-15

Highlights: • The 30-year history of “electron-doped” cuprates is reviewed, including basic physics and material issues. • Undoped cuprates with the Nd{sub 2}CuO{sub 4} (T’) structure are superconducting with T{sub c} over 30 K. • Electron doping by Ce in T’-RE{sub 2}CuO{sub 4} lowers T{sub c} and the highest T{sub c} is obtained at no doping. - Abstract: The electronic phase diagram of the cuprates remains enigmatic and is still a key ingredient to understand the mechanism of high-T{sub c} superconductivity. It has been believed for a long time that parent compounds of cuprates were universally antiferromagnetic Mott insulators (charge-transfer insulators) and that high-T{sub c} superconductivity would develop upon doping holes or electrons in a Mott–Hubbard insulator (“doped Mott-insulator scenario”). However, our recent discovery of superconductivity in the parent compounds of square-planar cuprates with the Nd{sub 2}CuO{sub 4} (T’) structure and the revised electronic phase diagram in T’ cuprates urged a serious reassessment to the above scenario. In this review, we present the main results derived from our synthesis and experiments on T’ cuprates in the undoped or heavily underdoped regime over 20 years, including material issues and basic physics. The key material issue is how to remove excess oxygen ions at the apical site without introducing oxygen vacancies in the CuO{sub 2} planes. In order to put this into practice, the basic knowledge of complex solid-state chemistry in T’ cuprates is required, which is also included in this review.

Charge disproportionation in RNiO3 at the metal-insulator transition

International Nuclear Information System (INIS)

Alonso, J.A.; Martinez-Lope, M.J.; Casais, M.T.; Garcia-Munoz, J.L.; Fernandez-Diaz, M.T.; Aranda, M.A.G.

1999-01-01

Complete text of publication follows. Neutron and synchrotron diffraction data provide the first observation of changes in the crystal symmetry at the metal-insulator (MI) transition in RNiO 3 perovskites [1]. At high temperatures, YNiO 3 is orthorhombic and metallic but below T MI = 582 K it changes to a monoclinic insulator. The monoclinic symmetry is due to a partial 2 Ni 3+ → Ni 3+δ + Ni 3-δ charge disproportionation associated to the MI transition. In the insulating state the presence of two NiO 6 octahedra is reported with, respectively, expanded (Ni1) and contracted (Ni2) Ni-O bonds, that alternated along the three directions of the crystal. Corroborating the charge disproportion, unequal moments are found at Ni1 and Ni2 octahedra in the low temperature monoclinic phase. (author) J.A. Alonso et al, Phys. Rev. Lett. in press

Surface electrical resistivity of insulators

International Nuclear Information System (INIS)

Senn, B. C.; Liesegang, J.

1996-01-01

A method is presented here for measuring surface charge decay, and theory has been developed so as to produce determinations of resistivity in the surface region of insulator films or wafers. This method incorporates the use of a coaxial cylindrical capacitor arrangement and an electrometer interfaced to a PC. The charge transport theory given here is based on Mott-Gurney diffusion, and allows easy interpretation of the experimental data, especially for the initial phase of surface charge decay. Resistivity measurements are presented for glass, mica, perspex and polyethylene, covering a range of 10 9 to 10 18 Ωm, as an illustration of the useful range of the instrument for static and antistatic materials, particularly in film or sheet form. Values for the surface charge diffusion constants of the materials are also presented. The charge transport theory has also been extended to allow the experimental and computational theoretical comparison of surface charge decay not only over the initial phase of charge decay, but also over longer times. The theoretical predictions show excellent agreement with experiment using the values for the diffusion constants referred to above

Metastability and avalanche dynamics in strongly correlated gases with long-range interactions

Science.gov (United States)

Hruby, Lorenz; Dogra, Nishant; Landini, Manuele; Donner, Tobias; Esslinger, Tilman

2018-03-01

We experimentally study the stability of a bosonic Mott insulator against the formation of a density wave induced by long-range interactions and characterize the intrinsic dynamics between these two states. The Mott insulator is created in a quantum degenerate gas of 87-Rubidium atoms, trapped in a 3D optical lattice. The gas is located inside and globally coupled to an optical cavity. This causes interactions of global range, mediated by photons dispersively scattered between a transverse lattice and the cavity. The scattering comes with an atomic density modulation, which is measured by the photon flux leaking from the cavity. We initialize the system in a Mott-insulating state and then rapidly increase the global coupling strength. We observe that the system falls into either of two distinct final states. One is characterized by a low photon flux, signaling a Mott insulator, and the other is characterized by a high photon flux, which we associate with a density wave. Ramping the global coupling slowly, we observe a hysteresis loop between the two states—a further signature of metastability. A comparison with a theoretical model confirms that the metastability originates in the competition between short- and global-range interactions. From the increasing photon flux monitored during the switching process, we find that several thousand atoms tunnel to a neighboring site on the timescale of the single-particle dynamics. We argue that a density modulation, initially forming in the compressible surface of the trapped gas, triggers an avalanche tunneling process in the Mott-insulating region.

Extension of the Mott-Gurney Law for a Bilayer Gap

Science.gov (United States)

Dubinov, A. E.; Kitayev, I. N.

2018-04-01

Steady drift states of an electron flow in a planar gap filled with a bilayer dielectric have been considered. Exact mathematical formulas have been derived that describe the distributions of the electrostatic potential and space charge limited electron flow current (extended Mott-Gurney law for a bilayer diode).

Ginsburg-Landau equation around the superconductor-insulator transition

International Nuclear Information System (INIS)

Ng, T.K.

1991-01-01

Based on the scaling theory of localization, we construct a Ginsburg-Landau (GL) equation for superconductors in an arbitrary strength of disordered potential. Using this GL equation, we reexamine the criteria for the superconductor-insulator transition and find that the transition to a localized superconductor can happen on both sides of the (normal) metal-insulator transition, in contrast to a previous prediction by Ma and Lee [Phys. Rev. B 32, 5658 (1985)] that the transition can only be on the insulator side. Furthermore, by comparing our theory with a recent scaling theory of dirty bosons by Fisher et al. [Phys. Rev. Lett. 64, 587 (1990)], we conclude that nontrivial crossover behavior in transport properties may occur in the vicinity of the superconductor-insulator transition

High-pressure versus isoelectronic doping effect on the honeycomb iridate Na2IrO3

Science.gov (United States)

Hermann, V.; Ebad-Allah, J.; Freund, F.; Pietsch, I. M.; Jesche, A.; Tsirlin, A. A.; Deisenhofer, J.; Hanfland, M.; Gegenwart, P.; Kuntscher, C. A.

2017-11-01

We study the effect of isoelectronic doping and external pressure in tuning the ground state of the honeycomb iridate Na2IrO3 by combining optical spectroscopy with synchrotron x-ray diffraction measurements on single crystals. The obtained optical conductivity of Na2IrO3 is discussed in terms of a Mott-insulating picture versus the formation of quasimolecular orbitals and in terms of Kitaev interactions. With increasing Li content x , (Na1 -xLix )2IrO3 moves deeper into the Mott-insulating regime, and there are indications that up to a doping level of 24% the compound comes closer to the Kitaev limit. The optical conductivity spectrum of single-crystalline α -Li2IrO3 does not follow the trends observed for the series up to x =0.24 . There are strong indications that α -Li2IrO3 is not as close to the Kitaev limit as Na2IrO3 and lies closer to the quasimolecular orbital picture instead. Except for the pressure-induced hardening of the phonon modes, the optical properties of Na2IrO3 seem to be robust against external pressure. Possible explanations of the unexpected evolution of the optical conductivity with isolectronic doping and the drastic change between x =0.24 and x =1 are given by comparing the pressure-induced changes of lattice parameters and the optical conductivity with the corresponding changes induced by doping.

Importance of space-time fluctuations and non-linearities for the transport inside insulating glasses

International Nuclear Information System (INIS)

Ladieu, F.

2003-07-01

This work deals with transport in insulating glasses. In such solids, the discrete translational symmetry is lost, which means that the plane wave analysis is not a priori the right 'starting point'. As a result, the transport is more difficult to handle, and a huge amount of works have been devoted to many aspects of transport in disordered systems, especially since the seventies. Here we focus on three specific questions: (i) the heat transport in glasses submitted to micro-beams and the associated irreversible vaporization; (ii) the electronic d.c. transport, below 1 Kelvin, in Mott-Anderson insulators, i.e. in 'electron glasses' where both disorder and electron-electron interactions are relevant; (iii) the low frequency dielectric constant in 'structural glasses' (i.e. 'ordinary glasses') which, below 1 Kelvin, is both universal (i.e. independent on the chemical composition) and very different of that of crystals. For each topic, we present both original experiments and the new theoretical concepts that we have elaborated so as to understand the main experimental features. Eventually, it appears that, in any case, transport in insulating glasses is strongly dominated by quite a small part of the 'glass-applied field' ensemble and that the nonlinear response is a relevant tool to get informations on this 'sub-part' which dominates the transport in the whole system. (author)

Emergent Chiral Spin State in the Mott Phase of a Bosonic Kane-Mele-Hubbard Model

Science.gov (United States)

Plekhanov, Kirill; Vasić, Ivana; Petrescu, Alexandru; Nirwan, Rajbir; Roux, Guillaume; Hofstetter, Walter; Le Hur, Karyn

2018-04-01

Recently, the frustrated X Y model for spins 1 /2 on the honeycomb lattice has attracted a lot of attention in relation with the possibility to realize a chiral spin liquid state. This model is relevant to the physics of some quantum magnets. Using the flexibility of ultracold atom setups, we propose an alternative way to realize this model through the Mott regime of the bosonic Kane-Mele-Hubbard model. The phase diagram of this model is derived using bosonic dynamical mean-field theory. Focusing on the Mott phase, we investigate its magnetic properties as a function of frustration. We do find an emergent chiral spin state in the intermediate frustration regime. Using exact diagonalization we study more closely the physics of the effective frustrated X Y model and the properties of the chiral spin state. This gapped phase displays a chiral order, breaking time-reversal and parity symmetry, but is not topologically ordered (the Chern number is zero).

Magnetic gating of a 2D topological insulator

Science.gov (United States)

Dang, Xiaoqian; Burton, J. D.; Tsymbal, Evgeny Y.

2016-09-01

Deterministic control of transport properties through manipulation of spin states is one of the paradigms of spintronics. Topological insulators offer a new playground for exploring interesting spin-dependent phenomena. Here, we consider a ferromagnetic ‘gate’ representing a magnetic adatom coupled to the topologically protected edge state of a two-dimensional (2D) topological insulator to modulate the electron transmission of the edge state. Due to the locked spin and wave vector of the transport electrons the transmission across the magnetic gate depends on the mutual orientation of the adatom magnetic moment and the current. If the Fermi energy matches an exchange-split bound state of the adatom, the electron transmission can be blocked due to the full back scattering of the incident wave. This antiresonance behavior is controlled by the adatom magnetic moment orientation so that the transmission of the edge state can be changed from 1 to 0. Expanding this consideration to a ferromagnetic gate representing a 1D chain of atoms shows a possibility to control the spin-dependent current of a strip of a 2D topological insulator by magnetization orientation of the ferromagnetic gate.

Extension of the radiative lifetime of Wannier-Mott excitons in semiconductor nanoclusters

International Nuclear Information System (INIS)

Kukushkin, V. A.

2015-01-01

The purpose of the study is to calculate the radiative lifetime of Wannier-Mott excitons in three-dimensional potential wells formed of direct-gap narrow-gap semiconductor nanoclusters in wide-gap semiconductors and assumed to be large compared to the exciton radius. Calculations are carried out for the InAs/GaAs heterosystem. It is shown that, as the nanocluster dimensions are reduced to values on the order of the exciton radius, the exciton radiative lifetime becomes several times longer compared to that in a homogeneous semiconductor. The increase in the radiative lifetime is more pronounced at low temperatures. Thus, it is established that the placement of Wannier-Mott excitons into direct-gap semiconductor nanoclusters, whose dimensions are of the order of the exciton radius, can be used for considerable extension of the exciton radiative lifetime

Phase diagram and topological phases in the triangular lattice Kitaev-Hubbard model

Science.gov (United States)

Li, Kai; Yu, Shun-Li; Gu, Zhao-Long; Li, Jian-Xin

2016-09-01

We study the half-filled Hubbard model on a triangular lattice with spin-dependent Kitaev-like hopping. Using the variational cluster approach, we identify five phases: a metallic phase, a non-coplanar chiral magnetic order, a 120° magnetic order, a nonmagnetic insulator (NMI), and an interacting Chern insulator (CI) with a nonzero Chern number. The transition from CI to NMI is characterized by the change of the charge gap from an indirect band gap to a direct Mott gap. Based on the slave-rotor mean-field theory, the NMI phase is further suggested to be a gapless Mott insulator with a spinon Fermi surface or a fractionalized CI with nontrivial spinon topology, depending on the strength of the Kitaev-like hopping. Our work highlights the rising field in which interesting phases emerge from the interplay between band topology and Mott physics.

On the interplay of Jahn-Teller physics and Mott physics in cuprates

International Nuclear Information System (INIS)

Kamimura, H; Ushio, H

2008-01-01

The extended two-story house model which is now called the Kamimura-Suwa (K-S) model has clarified how the interplay of Mott physics and Jahn-Teller physics plays an important role in determining the superconducting as well as metallic state of underdoped cuprates. In this paper it is first pointed out for underdoped cuprates that Mott physics leads to the existence of local antiferromagnetic order constructed from the localized spins while that the anti-Jahn-Teller effect as a central issue of Jahn-Teller physics leads to the existence of two kinds of orbitals parallel and perpendicular to a CuO 2 plane whose states have nearly the same energy. As a result of the interplay of both physics the K-S model has shown that the exchange interactions between the spins of a localized hole and of a carrier hole play an important role in producing the coexistence of superconductivity and antiferromagnetism in underdoped cuprates. The appearance of d-wave superconductivity even in the phonon-involved mechanism is also shown to be due to the interplay of Jahn-Teller physics and Mott Physics. Brief review of these facts as well as the K-S model is given in this paper. More outstanding result in this paper is that the origin of pseudogap in the deeply underdoped regime has been clarified. In this paper it is shown theoretically for the first time that the so-called T* pseudogap observed in ARPES, STM and tunneling experiments below T c in underdoped cuprates corresponds to the real transition of photo-excited electrons from the occupied states in the originally conduction band below the superconducting gap to a free-electron state above the vacuum level. Thus we conclude that the T* pseudogap in the underdoped cuprates which increases with decreasing the hole concentration is not 'pseudo', but a real gap which exists even below T c

Describing a Strongly Correlated Model System with Density Functional Theory.

Science.gov (United States)

Kong, Jing; Proynov, Emil; Yu, Jianguo; Pachter, Ruth

2017-07-06

The linear chain of hydrogen atoms, a basic prototype for the transition from a metal to Mott insulator, is studied with a recent density functional theory model functional for nondynamic and strong correlation. The computed cohesive energy curve for the transition agrees well with accurate literature results. The variation of the electronic structure in this transition is characterized with a density functional descriptor that yields the atomic population of effectively localized electrons. These new methods are also applied to the study of the Peierls dimerization of the stretched even-spaced Mott insulator to a chain of H 2 molecules, a different insulator. The transitions among the two insulating states and the metallic state of the hydrogen chain system are depicted in a semiquantitative phase diagram. Overall, we demonstrate the capability of studying strongly correlated materials with a mean-field model at the fundamental level, in contrast to the general pessimistic view on such a feasibility.

Climate protection with rapid payback. Energy and CO2 savings potential of industrial insulation in EU27

Energy Technology Data Exchange (ETDEWEB)

Neelis, M.; Blinde, P.; Overgaag, M.; Deng, Y. [Ecofys Netherlands, Utrecht (Netherlands)

2012-06-15

This study aims to answer the following four questions: (1) What is the energy savings and CO2 emissions mitigation potential resulting from insulating currently uninsulated parts and from better maintenance of insulation systems?; (2) What are the energy savings and CO2 mitigation potential from improving current insulation to cost-effective levels? Cost-effective insulation in this study is defined as the insulation that minimises the sum of the costs of heat loss and the costs of insulation; (3) What is the energy savings and CO2 mitigation potential from improving current insulation beyond cost-effective levels to even more energy-efficient levels? Energy-efficient insulation in this study is defined as the insulation at which the sum of the costs of heat loss and the annualised insulation investments are equal to the costs of typical current insulation while offering an additional energy savings and CO2 mitigation potential; and (4) How can these potentials best be realised? This study investigates savings potentials from improved insulation in EU industry and the power sector under realistic market conditions. Nuclear power plants and power production by renewable sources were left outside the scope of this study as well as insulations of cold applications. Case studies of insulation projects have been used to compare energy loss and investments related to different levels of insulation. The analysis was performed for three temperature levels: <100C; 100-300C and >300C. Results at the level of the case studies were extrapolated to European level using data on current energy use. Other assumptions have been made where needed on the basis of literature and expert input. All potentials are based on a 9% discount rate, an average insulation lifetime of 15 years and a 2-3% per year increase of the price of energy net of inflation.

Metal insulator semiconductor solar cell devices based on a Cu2O substrate utilizing h-BN as an insulating and passivating layer

International Nuclear Information System (INIS)

Ergen, Onur; Gibb, Ashley; Vazquez-Mena, Oscar; Zettl, Alex; Regan, William Raymond

2015-01-01

We demonstrate cuprous oxide (Cu 2 O) based metal insulator semiconductor Schottky (MIS-Schottky) solar cells with efficiency exceeding 3%. A unique direct growth technique is employed in the fabrication, and hexagonal boron nitride (h-BN) serves simultaneously as a passivation and insulation layer on the active Cu 2 O layer. The devices are the most efficient of any Cu 2 O based MIS-Schottky solar cells reported to date

2D-ACAR spectra of insulating and superconducting Y-123

International Nuclear Information System (INIS)

Smedskjaer, L.C.; Bansil, A.

1992-09-01

An overview of the two-dimensional angular correlation (2D-ACAR) positron annihilation results for the three fundamental phases of YBa 2 Cu 3 O x , namely, the normal metal, the superconductor, and the insulator, is presented. In addition to the c-axis projected momentum density, the recent results for the a-axis projection as well as the insulating Y123 are discussed. The experimental results are compared and contrasted with the corresponding band theory predictions as far as possible in order to gain insight into the electronic structure and Fermiology of this archetypal high-T c superconductor

De la motte au château d’artillerie, la fouille du château de Guingamp (Côtes-d’Armor

Directory of Open Access Journals (Sweden)

Laurent Beuchet

2010-02-01

Full Text Available L’opération d’archéologie préventive du château de Guingamp (Côtes-d’Armor a été réalisée dans le cadre d'un projet de création d'une salle culturelle sur le site du château. La fouille a été menée sur une superficie de 2000 m², sur une durée effective de cinq mois entre octobre 2004 et mars 2005, avec un effectif moyen de sept personnes.À l’issue de la fouille, trois phases principales d’occupation peuvent être identifiées :la motte des Comtes de Guingamp (XIe-XIIe s. ;une enceinte polygon...

Parity violation and superconductivity in doped Mott insulators

International Nuclear Information System (INIS)

Khveshchenko, D.V.; Kogan, Ya.I.

1989-12-01

We study parity violating states of strongly correlated two-dimensional electronic systems. On the basis of mean field theory for the SU(2N)-symmetric generalization of the system involved we give the arguments supporting the existence of these states at a filling number different from one-half. We derive an effective Lagrangian describing the long wavelength dynamics of magnetic excitations and their interaction with charged spinless holes. We establish that the ground state of a doped system is superconducting and discuss the phenomenological manifestations of the parity violation. (author). 48 refs, 3 figs

Parity violation and superconductivity in doped Mott insulators

International Nuclear Information System (INIS)

Khveshchenko, D.Y.; Kogan, Y.I.

1990-01-01

The authors study parity violating states of strongly correlated two-dimensional electronic systems. On the basis of mean field theory for the SU(2N)-symmetric generalization of the system involved the authors give the arguments supporting the existence of these states at a filling number different from one-half. The authors derive an effective Lagrangian describing the long wavelength dynamics of magnetic excitations and their interaction with charged spinless holes. This paper establishes the ground state of a doped system is superconducting and discuss the phenomenological manifestations of the parity violation

Metal insulator semiconductor solar cell devices based on a Cu{sub 2}O substrate utilizing h-BN as an insulating and passivating layer

Energy Technology Data Exchange (ETDEWEB)

Ergen, Onur; Gibb, Ashley; Vazquez-Mena, Oscar; Zettl, Alex, E-mail: azettl@berkeley.edu [Department of Physics, University of California at Berkeley, Berkeley, California 94720 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Kavli Energy Nanosciences Institute at the University of California, Berkeley, and the Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Regan, William Raymond [Department of Physics, University of California at Berkeley, Berkeley, California 94720 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2015-03-09

We demonstrate cuprous oxide (Cu{sub 2}O) based metal insulator semiconductor Schottky (MIS-Schottky) solar cells with efficiency exceeding 3%. A unique direct growth technique is employed in the fabrication, and hexagonal boron nitride (h-BN) serves simultaneously as a passivation and insulation layer on the active Cu{sub 2}O layer. The devices are the most efficient of any Cu{sub 2}O based MIS-Schottky solar cells reported to date.

Local Peltier-effect-induced reversible metal–insulator transition in VO2 nanowires

International Nuclear Information System (INIS)

Takami, Hidefumi; Kanki, Teruo; Tanaka, Hidekazu

2016-01-01

We report anomalous resistance leaps and drops in VO 2 nanowires with operating current density and direction, showing reversible and nonvolatile switching. This event is associated with the metal–insulator phase transition (MIT) of local nanodomains with coexistence states of metallic and insulating phases induced by thermoelectric cooling and heating effects. Because the interface of metal and insulator domains has much different Peltier coefficient, it is possible that a significant Peltier effect would be a source of the local MIT. This operation can be realized by one-dimensional domain configuration in VO 2 nanowires because one straight current path through the electronic domain-interface enables theoretical control of thermoelectric effects. This result will open a new method of reversible control of electronic states in correlated electron materials.

Two-magnon Raman scattering in a Mott-Hubbard antiferromagnet

International Nuclear Information System (INIS)

Basu, S.; Singh, A.

1996-01-01

A perturbation-theoretic diagrammatic scheme is developed for systematically studying the two-magnon Raman scattering in a Mott-Hubbard antiferromagnet. The fermionic structure of the magnon interaction vertex is obtained at order-1/N level in an inverse-degeneracy expansion, and the relevant two-magnon propagator is obtained by incorporating magnon interactions at a ladder-sum level. Evaluation of the magnon interaction vertex in the large-U limit yields a nearest-neighbor instantaneous interaction with interaction energy -J. Application of this approach to the intermediate-U regime, which is of relevance for cuprate antiferromagnets, is also discussed. Incorporating the zero-temperature magnon damping, which is estimated in terms of quantum spin fluctuations, the two-magnon Raman scattering intensity is evaluated and compared with experiments on La 2 CuO 4 . copyright 1996 The American Physical Society

Topological insulators in Bi2Se3, Bi2Te3 and Sb2Te3 with a single Dirac cone on the surface

Science.gov (United States)

Zhang, Haijun; Liu, Chao-Xing; Qi, Xiao-Liang; Dai, Xi; Fang, Zhong; Zhang, Shou-Cheng

2009-06-01

Topological insulators are new states of quantum matter in which surface states residing in the bulk insulating gap of such systems are protected by time-reversal symmetry. The study of such states was originally inspired by the robustness to scattering of conducting edge states in quantum Hall systems. Recently, such analogies have resulted in the discovery of topologically protected states in two-dimensional and three-dimensional band insulators with large spin-orbit coupling. So far, the only known three-dimensional topological insulator is BixSb1-x, which is an alloy with complex surface states. Here, we present the results of first-principles electronic structure calculations of the layered, stoichiometric crystals Sb2Te3, Sb2Se3, Bi2Te3 and Bi2Se3. Our calculations predict that Sb2Te3, Bi2Te3 and Bi2Se3 are topological insulators, whereas Sb2Se3 is not. These topological insulators have robust and simple surface states consisting of a single Dirac cone at the Γ point. In addition, we predict that Bi2Se3 has a topologically non-trivial energy gap of 0.3eV, which is larger than the energy scale of room temperature. We further present a simple and unified continuum model that captures the salient topological features of this class of materials.

E(y)2/Sus1 is required for blocking PRE silencing by the Wari insulator in Drosophila melanogaster.

Science.gov (United States)

Erokhin, Maksim; Parshikov, Alexander; Georgiev, Pavel; Chetverina, Darya

2010-06-01

Chromatin insulators affect interactions between promoters and enhancers/silencers and function as barriers to the spread of repressive chromatin. Recently, we have found an insulator, named Wari, located on the 3' side of the white gene. Here, we show that the previously identified 368-bp core of this insulator is sufficient for blocking Polycomb response element-mediated silencing. Although Wari does not contain binding sites for known insulator proteins, the E(y)2 and CP190 proteins bind to Wari as well as to the Su(Hw)-containing insulators in vivo. It may well be that these proteins are recruited to the insulator by as yet unidentified DNA-binding protein. Partial inactivation of E(y)2 in a weak e(y)2 ( u1 ) mutation impairs only the anti-silencing but not the enhancer-blocking activity of the Wari insulator. Thus, the E(y)2 protein in different Drosophila insulators serves to protect gene expression from silencing.

Fundamental models of electronic transport in amorphous semiconductors

International Nuclear Information System (INIS)

Emin, D.

1982-01-01

Significant fundamental questions lie at the heart of our understanding of the electronic and optical properties of semiconducting and insulating glasses. In this article the principal features of the Mott-CFO model and the small-polaron model are described. While the Mott-CFO model seems to apply to the high-mobility electron transport in glassy SiO 2 and Cd 2 As 3 it does not appear applicable to the most frequently studied chalocogenide glasses. Furthermore, the Mott-CFO model does not account for as basic a feature as the sign of the Hall effect. On the other hand, the small-polaron model accounts for the observed d.c. conductivity, Peltier heat and Hall mobility in a very simple and direct manner

Phase diagram of two-component bosons on an optical lattice

International Nuclear Information System (INIS)

Altman, Ehud; Hofstetter, Walter; Demler, Eugene; Lukin, Mikhail D

2003-01-01

We present a theoretical analysis of the phase diagram of two-component bosons on an optical lattice. A new formalism is developed which treats the effective spin interactions in the Mott and superfluid phases on the same footing. Using this new approach we chart the phase boundaries of the broken spin symmetry states up to the Mott to superfluid transition and beyond. Near the transition point, the magnitude of spin exchange can be very large, which facilitates the experimental realization of spin-ordered states. We find that spin and quantum fluctuations have a dramatic effect on the transition, making it first order in extended regions of the phase diagram. When each species is at integer filling, an additional phase transition may occur, from a spin-ordered insulator to a Mott insulator with no broken symmetries. We determine the phase boundaries in this regime and show that this is essentially a Mott transition in the spin sector

Converters and electric machines. Solid insulating materials. Electrical characteristics; Convertisseurs et machines electriques. Materiaux isolants solides. Caracteristiques electriques

Energy Technology Data Exchange (ETDEWEB)

Anton, A. [Institut National Superieur de Chimie Industrielle, 76 - Rouen (France)

2003-08-01

The aim of this article is to allow a preselection of a solid insulating material using the most common electrical characteristics: tangent of the loss angle, relative permittivity, dielectric rigidity, superficial resistivity, transverse resistivity, resistance to high voltage creeping spark currents, index of creeping resistance. The characteristics of the main solid insulating materials are presented in tables for: thermoplastics, thermosetting materials, natural insulating materials, mineral insulating materials, rubber and synthetic elastomers, stratified insulating materials, thermoplastic films, composite synthetic papers. A comparison is made between the different materials using the three properties: tangent of the loss angle, relative permittivity and resistance to HV spark creeping currents. (J.S.)

Analysis and design of insulation systems for LH2-fueled aircraft

Science.gov (United States)

Cunnington, G. R., Jr.

1979-01-01

An analytical program was conducted to evaluate the performance of 15 potential insulations for the fuel tanks of a subsonic LH2-fueled transport aircraft intended for airline service in the 1990-1995 time period. As a result, two candidate insulation systems are proposed for subsonic transport aircraft applications. Both candidates are judged to be the optimum available and should meet the design requirements. However, because of the long-life cyclic nature of the application and the cost sensitivity of airline operations, an experimental tank/insulation development or proof-of-concept program is recommended. This program should be carried out with a nearly full-scale system which would be subjected to the cyclic thermal and mechanical inputs anticipated in aircraft service.

Mott mechanism and the hadronic to quark matter phase transition

International Nuclear Information System (INIS)

Blaschke, D.; Reinholz, F.

1984-01-01

A unified description of both the hadronic and quark matter can be found using the technique of thermodynamic Green functions. The destruction of bound states (quark deconfinement) is related microscopically to the Mott mechanism which leads to a different behaviour of free particle energies and bound state energies if the particle density is increasing. A simple model calculation is performed to obtain a rough estimate for the critical temperature of the hadronic-quark matter phase transition

Quasistatic antiferromagnetism in the quantum wells of SmTiO3/SrTiO3 heterostructures

Science.gov (United States)

Need, Ryan F.; Marshall, Patrick B.; Kenney, Eric; Suter, Andreas; Prokscha, Thomas; Salman, Zaher; Kirby, Brian J.; Stemmer, Susanne; Graf, Michael J.; Wilson, Stephen D.

2018-03-01

High carrier density quantum wells embedded within a Mott insulating matrix present a rich arena for exploring unconventional electronic phase behavior ranging from non-Fermi-liquid transport and signatures of quantum criticality to pseudogap formation. Probing the proposed connection between unconventional magnetotransport and incipient electronic order within these quantum wells has however remained an enduring challenge due to the ultra-thin layer thicknesses required. Here we address this challenge by exploring the magnetic properties of high-density SrTiO3 quantum wells embedded within the antiferromagnetic Mott insulator SmTiO3 via muon spin relaxation and polarized neutron reflectometry measurements. The one electron per planar unit cell acquired by the nominal d0 band insulator SrTiO3 when embedded within a d1 Mott SmTiO3 matrix exhibits slow magnetic fluctuations that begin to freeze into a quasistatic spin state below a critical temperature T*. The appearance of this quasistatic well magnetism coincides with the previously reported opening of a pseudogap in the tunneling spectra of high carrier density wells inside this film architecture. Our data suggest a common origin of the pseudogap phase behavior in this quantum critical oxide heterostructure with those observed in bulk Mott materials close to an antiferromagnetic instability.

Pressure-driven insulator-metal transition in cubic phase UO2

Science.gov (United States)

Huang, Li; Wang, Yilin; Werner, Philipp

2017-09-01

Understanding the electronic properties of actinide oxides under pressure poses a great challenge for experimental and theoretical studies. Here, we investigate the electronic structure of cubic phase uranium dioxide at different volumes using a combination of density functional theory and dynamical mean-field theory. The ab initio calculations predict an orbital-selective insulator-metal transition at a moderate pressure of ∼45 GPa. At this pressure the uranium's 5f 5/2 state becomes metallic, while the 5f 7/2 state remains insulating up to about 60 GPa. In the metallic state, we observe a rapid decrease of the 5f occupation and total angular momentum with pressure. Simultaneously, the so-called “Zhang-Rice state”, which is of predominantly 5f 5/2 character, quickly disappears after the transition into the metallic phase.

Microscopic description of orbital-selective spin ordering in BaMn2As2

Science.gov (United States)

Craco, L.; Carara, S. S.

2018-05-01

Using generalized gradient approximation+dynamical mean-field theory, we provide a microscopic description of orbital-selective spin ordering in the tetragonal manganese pnictide BaMn2As2 . We demonstrate the coexistence of local moments and small band-gap electronic states in the parent compound. We also explore the role played by electron/hole doping, showing that the Mott insulating state is rather robust to small removal of electron charge carriers similar to cuprate oxide superconductors. Good qualitative accord between theory and angle-resolved photoemission as well as electrical transport provides support to our view of orbital-selective spin ordering in BaMn2As2 . Our proposal is expected to be an important step to understanding the emergent correlated electronic structure of materials with persisting ordered localized moments coexisting with Coulomb reconstructed nonmagnetic electronic states.

Transformation of the superconducting gap to an insulating pseudogap at a critical hole density in the cuprates

Science.gov (United States)

Liu, Ye-Hua; Wang, Wan-Sheng; Wang, Qiang-Hua; Zhang, Fu-Chun; Rice, T. M.

2017-07-01

We apply the recent wave-packet formalism developed by Ossadnik to describe the origin of the short-range ordered pseudogap state as the hole doping is lowered through a critical density in cuprates. We argue that the energy gain that drives this precursor state to Mott localization, follows from maximizing umklapp scattering near the Fermi energy. To this end, we show how energy gaps driven by umklapp scattering can open on an appropriately chosen surface, as proposed earlier by Yang, Rice, and Zhang. The key feature is that the pairing instability includes umklapp scattering, leading to an energy gap not only in the single-particle spectrum but also in the pair spectrum. As a result the superconducting gap at overdoping is turned into an insulating pseudogap in the antinodal parts of the Fermi surface.

Exploring the validity and limitations of the Mott-Gurney law for charge-carrier mobility determination of semiconducting thin-films.

Science.gov (United States)

Röhr, Jason A; Moia, Davide; Haque, Saif A; Kirchartz, Thomas; Nelson, Jenny

2018-03-14

Using drift-diffusion simulations, we investigate the voltage dependence of the dark current in single carrier devices typically used to determine charge-carrier mobilities. For both low and high voltages, the current increases linearly with the applied voltage. Whereas the linear current at low voltages is mainly due to space charge in the middle of the device, the linear current at high voltage is caused by charge-carrier saturation due to a high degree of injection. As a consequence, the current density at these voltages does not follow the classical square law derived by Mott and Gurney, and we show that for trap-free devices, only for intermediate voltages, a space-charge-limited drift current can be observed with a slope that approaches a value of two. We show that, depending on the thickness of the semiconductor layer and the size of the injection barriers, the two linear current-voltage regimes can dominate the whole voltage range, and the intermediate Mott-Gurney regime can shrink or disappear. In this case, which will especially occur for thicknesses and injection barriers typical of single-carrier devices used to probe organic semiconductors, a meaningful analysis using the Mott-Gurney law will become unachievable, because a square-law fit can no longer be achieved, resulting in the mobility being substantially underestimated. General criteria for when to expect deviations from the Mott-Gurney law when used for analysis of intrinsic semiconductors are discussed.

Exploring the validity and limitations of the Mott-Gurney law for charge-carrier mobility determination of semiconducting thin-films

Science.gov (United States)

Röhr, Jason A.; Moia, Davide; Haque, Saif A.; Kirchartz, Thomas; Nelson, Jenny

2018-03-01

Using drift-diffusion simulations, we investigate the voltage dependence of the dark current in single carrier devices typically used to determine charge-carrier mobilities. For both low and high voltages, the current increases linearly with the applied voltage. Whereas the linear current at low voltages is mainly due to space charge in the middle of the device, the linear current at high voltage is caused by charge-carrier saturation due to a high degree of injection. As a consequence, the current density at these voltages does not follow the classical square law derived by Mott and Gurney, and we show that for trap-free devices, only for intermediate voltages, a space-charge-limited drift current can be observed with a slope that approaches a value of two. We show that, depending on the thickness of the semiconductor layer and the size of the injection barriers, the two linear current-voltage regimes can dominate the whole voltage range, and the intermediate Mott-Gurney regime can shrink or disappear. In this case, which will especially occur for thicknesses and injection barriers typical of single-carrier devices used to probe organic semiconductors, a meaningful analysis using the Mott-Gurney law will become unachievable, because a square-law fit can no longer be achieved, resulting in the mobility being substantially underestimated. General criteria for when to expect deviations from the Mott-Gurney law when used for analysis of intrinsic semiconductors are discussed.

Enhanced PEC performance of nanoporous Si photoelectrodes by covering HfO2 and TiO2 passivation layers

Science.gov (United States)

Xing, Zhuo; Ren, Feng; Wu, Hengyi; Wu, Liang; Wang, Xuening; Wang, Jingli; Wan, Da; Zhang, Guozhen; Jiang, Changzhong

2017-03-01

Nanostructured Si as the high efficiency photoelectrode material is hard to keep stable in aqueous for water splitting. Capping a passivation layer on the surface of Si is an effective way of protecting from oxidation. However, it is still not clear in the different mechanisms and effects between insulating oxide materials and oxide semiconductor materials as passivation layers. Here, we compare the passivation effects, the photoelectrochemical (PEC) properties, and the corresponding mechanisms between the HfO2/nanoporous-Si and the TiO2/nanoporous-Si by I-V curves, Motte-schottky (MS) curves, and electrochemical impedance spectroscopy (EIS). Although the saturated photocurrent densities of the TiO2/nanoporous Si are lower than that of the HfO2/nanoporous Si, the former is more stable than the later.

Enhanced PEC performance of nanoporous Si photoelectrodes by covering HfO2 and TiO2 passivation layers.

Science.gov (United States)

Xing, Zhuo; Ren, Feng; Wu, Hengyi; Wu, Liang; Wang, Xuening; Wang, Jingli; Wan, Da; Zhang, Guozhen; Jiang, Changzhong

2017-03-02

Nanostructured Si as the high efficiency photoelectrode material is hard to keep stable in aqueous for water splitting. Capping a passivation layer on the surface of Si is an effective way of protecting from oxidation. However, it is still not clear in the different mechanisms and effects between insulating oxide materials and oxide semiconductor materials as passivation layers. Here, we compare the passivation effects, the photoelectrochemical (PEC) properties, and the corresponding mechanisms between the HfO 2 /nanoporous-Si and the TiO 2 /nanoporous-Si by I-V curves, Motte-schottky (MS) curves, and electrochemical impedance spectroscopy (EIS). Although the saturated photocurrent densities of the TiO 2 /nanoporous Si are lower than that of the HfO 2 /nanoporous Si, the former is more stable than the later.

Evolution of ferromagnetism in two-dimensional electron gas of LaTiO3/SrTiO3

Science.gov (United States)

Wen, Fangdi; Cao, Yanwei; Liu, Xiaoran; Pal, B.; Middey, S.; Kareev, M.; Chakhalian, J.

2018-03-01

Understanding, creating, and manipulating spin polarization of two-dimensional electron gases at complex oxide interfaces present an experimental challenge. For example, despite almost a decade long research effort, the microscopic origin of ferromagnetism in LaAlO3/SrTiO3 heterojunctions is still an open question. Here, by using a prototypical two-dimensional electron gas (2DEG) which emerges at the interface between band insulator SrTiO3 and antiferromagnetic Mott insulator LaTiO3, the experiment reveals the evidence for magnetic phase separation in a hole-doped Ti d1 t2g system, resulting in spin-polarized 2DEG. The details of electronic and magnetic properties of the 2DEG were investigated by temperature-dependent d.c. transport, angle-dependent X-ray photoemission spectroscopy, and temperature-dependent magnetoresistance. The observation of clear hysteresis in magnetotransport at low magnetic fields implies spin-polarization from magnetic islands in the hole rich LaTiO3 near the interface. These findings emphasize the role of magnetic instabilities in doped Mott insulators, thus providing another path for designing all-oxide structures relevant to spintronic applications.

Molecular beam epitaxial growth of Bi2Te3 and Sb2Te3 topological insulators on GaAs (111 substrates: a potential route to fabricate topological insulator p-n junction

Directory of Open Access Journals (Sweden)

Zhaoquan Zeng

2013-07-01

Full Text Available High quality Bi2Te3 and Sb2Te3 topological insulators films were epitaxially grown on GaAs (111 substrate using solid source molecular beam epitaxy. Their growth and behavior on both vicinal and non-vicinal GaAs (111 substrates were investigated by reflection high-energy electron diffraction, atomic force microscopy, X-ray diffraction, and high resolution transmission electron microscopy. It is found that non-vicinal GaAs (111 substrate is better than a vicinal substrate to provide high quality Bi2Te3 and Sb2Te3 films. Hall and magnetoresistance measurements indicate that p type Sb2Te3 and n type Bi2Te3 topological insulator films can be directly grown on a GaAs (111 substrate, which may pave a way to fabricate topological insulator p-n junction on the same substrate, compatible with the fabrication process of present semiconductor optoelectronic devices.

Pulsed laser deposition of {CeO_2} and {Ce_{1-x}M_xO_2} (M = La, Zr): Application to insulating barrier in cuprate heterostructures

Science.gov (United States)

Berger, S.; Contour, J.-P.; Drouet, M.; Durand, O.; Khodan, A.; Michel, D.; Régi, F.-X.

1998-03-01

SrTiO_3 had been often tentatively used as an insulating barrier for HT superconductor/insulator heterostructures. Unfortunately, the deposition of SrTiO_3 on the YBa_2Cu_3O_7 inverse interface results in a poor epitaxial regrowth producing a high roughness dislocated titanate layer. Taking into account the good matching with YBa_2Cu_3O_7 and LaAlO_3, CeO_2 and Ce_{1-x}M_xO_2 (M = La, Zr), epitaxial layers were grown by pulsed laser deposition on LaAlO_3 substrates and introduced into YBa_2Cu_3O_7 based heterostructures as insulating barrier. After adjusting the growth parameters from RHEED oscillations, epitaxial growth is achieved, the oxide crystal axes being rotated by 45^circ from those of the substrate. The surface roughness of 250 nm thick films is very low with a rms value lower than 0.5 nm over 1;μ m^2. The YBa_2Cu_3O_7 layers of a YBa_2Cu_3O_7/CeO_2 /YBa_2Cu_3O_7 heterostructures grown using these optimized parameters show an independent resistive transition, when the thickness is larger than 25 nm, respectively at T_c_1 = 89.6;K and T_c_2 = 91.4;{K}. SrTiO3 est souvent utilisé comme barrière isolante dans des hétérostructures SIS de cuprates supraconducteurs, cependant les défauts générés lors de la croissance de ce titanate sur l'interface inverse de YBa2Cu3O7 conduisent à un matériau dont la qualité cristalline et les propriétés physiques sont médiocres. L'oxyde de cérium CeO2 est également une barrière isolante potentielle intéressante pour ces structures SIS basées sur YBa2Cu3O7 car cet oxyde cubique (a = 0,5411 nm, asqrt{2}/2 = 0,3825 nm) qui est peu désaccordé par rapport au plan ab du cuprate (Δ a/a = - 0,18 %, Δ b/a = 1,6 %) présente de plus un coefficient de dilatation thermique (10,6 × 10^{-6 circ}C^{-1}) très voisin de celui de YBa2Cu3O7 (13 × 10^{-6 circ}C^{-1}). Nous avons donc étudié l'épitaxie de CeO2 et des oxydes de type Ce{1-x}MxO2 (M = La, Zr) en ablation laser pulsée afin de définir des conditions de

Insulators for fusion applications

International Nuclear Information System (INIS)

1987-04-01

Design studies for fusion devices and reactors have become more detailed in recent years and with this has come a better understanding of requirements and operating conditions for insulators in these machines. Ceramic and organic insulators are widely used for many components of fusion devices and reactors namely: radio frequency (RF) energy injection systems (BeO, Al 2 O 3 , Mg Al 2 O 4 , Si 3 N 4 ); electrical insulation for the torus structure (SiC, Al 2 O 3 , MgO, Mg Al 2 O 4 , Si 4 Al 2 O 2 N 6 , Si 3 N 4 , Y 2 O 3 ); lightly-shielded magnetic coils (MgO, MgAl 2 O 4 ); the toroidal field coil (epoxies, polyimides), neutron shield (B 4 C, TiH 2 ); high efficiency electrical generation; as well as the generation of very high temperatures for high efficiency hydrogen production processes (ZrO 2 and Al 2 O 3 - mat, graphite and carbon - felt). Timely development of insulators for fusion applications is clearly necessary. Those materials to be used in fusion machines should show high resistance to radiation damage and maintain their structural integrity. Now the need is urgent for a variety of radiation resistant materials, but much effort in these areas is required for insulators to be considered seriously by the design community. This document contains 14 papers from an IAEA meeting. It was the objective of this meeting to identify existing problems in analysing various situations of applications and requirements of electrical insulators and ceramics in fusion and to recommend strategies and different stages of implementation. This meeting was endorsed by the International Fusion Research Council

Magnetic heat transport in Sr{sub 2}IrO{sub 4}

Energy Technology Data Exchange (ETDEWEB)

Steckel, Frank [Leibniz Institute for Solid State and Materials Research, IFW Dresden (Germany); Takagi, Hidenori [Max-Planck-Institute for Solid State Research, Stuttgart (Germany); Buechner, Bernd; Hess, Christian [Leibniz Institute for Solid State and Materials Research, IFW Dresden (Germany); Center for Transport and Devices, TU Dresden (Germany)

2015-07-01

The layered perovskite Sr{sub 2}IrO{sub 4} is a 5d transition metal oxide with an enhanced spin-orbit coupling leading to a Mott insulating ground state with J{sub eff}=(1)/(2). It exhibits canted antiferromagnetism below T{sub N}=240 K with an antiferromagnetic coupling constant of about J=0.1 eV. Thermal conductivity measurements along the ab plane of a Sr{sub 2}IrO{sub 4} single crystal provide evidence for a contribution of magnons (below T{sub N}) to the thermal conductivity, similar to that of the isostructural 2D S=(1)/(2) Heisenberg antiferromagnet La{sub 2}CuO{sub 4}, where a significant magnonic contribution to the heat transport is known.

Wrapped Multilayer Insulation

Science.gov (United States)

Dye, Scott A.

2015-01-01

New NASA vehicles, such as Earth Departure Stage (EDS), Orion, landers, and orbiting fuel depots, need improved cryogenic propellant transfer and storage for long-duration missions. Current cryogen feed line multilayer insulation (MLI) performance is 10 times worse per area than tank MLI insulation. During each launch, cryogenic piping loses approximately 150,000 gallons (equivalent to $300,000) in boil-off during transfer, chill down, and ground hold. Quest Product Development Corp., teaming with Ball Aerospace, developed an innovative advanced insulation system, Wrapped MLI (wMLI), to provide improved thermal insulation for cryogenic feed lines. wMLI is high-performance multilayer insulation designed for cryogenic piping. It uses Quest's innovative discrete-spacer technology to control layer spacing/ density and reduce heat leak. The Phase I project successfully designed, built, and tested a wMLI prototype with a measured heat leak 3.6X lower than spiral-wrapped conventional MLI widely used for piping insulation. A wMLI prototype had a heat leak of 7.3 W/m2, or 27 percent of the heat leak of conventional MLI (26.7 W/m2). The Phase II project is further developing wMLI technology with custom, molded polymer spacers and advancing the product toward commercialization via a rigorous testing program, including developing advanced vacuuminsulated pipe for ground support equipment.

Effect of Nano Al2O3 Doping on Thermal Aging Properties of Oil-Paper Insulation

Directory of Open Access Journals (Sweden)

Ningchuan Liang

2018-05-01

Full Text Available The thermal aging property of oil-paper insulation is a key factor affecting the service life of transformers. In this study, nano-Al2O3 was added to insulating paper to improve its anti-thermal aging property and delay the aging rate of the insulating oil. The composite paper containing 2% nano-Al2O3 had the highest tensile strength and therefore was selected for the thermal aging test. The composite and normal papers were treated with an accelerated thermal aging experiment at the temperature of 130 °C for 56 days. The variations of the degree of polymerization (DP and tensile strength of the insulating papers with aging time were obtained. The characteristics of the insulating oil, including color, acid content, breakdown voltage, and dielectric loss were analyzed. The results revealed that compared with a plain paper, the composite paper maintained a higher DP, and its tensile strength decreased more slowly during the aging process. The oil-impregnated composite paper presented a lighter-colored oil, less viscosity changes, and a considerably lower quantity of thermal aging products. In addition, nano-Al2O3 can effectively adsorb copper compounds and keep part of the acid products and water away from the thermal aging process. This characteristic restrained the catalysis of copper compounds and H+ in the thermal aging reaction and reduced the thermal aging speed of both the insulating paper and the insulating oil.

Estimation of thermal insulation performance in multi-layer insulator for liquid helium pipe

International Nuclear Information System (INIS)

Shibanuma, Kiyoshi; Kuriyama, Masaaki; Shibata, Takemasa

1991-01-01

For a multi-layer insulator around the liquid helium pipes for cryopumps of JT-60 NBI, a multi-layer insulator composed of 10 layers, which can be wound around the pipe at the same time and in which the respective layers are in concentric circles by shifting them in arrangement, has been developed and tested. As the result, it was shown that the newly developed multi-layer insulator has better thermal insulation performance than the existing one, i.e. the heat load of the newly developed insulator composed of 10 layers was reduced to 1/3 the heat load of the existing insulator, and the heat leak at the joint of the insulator in longitudinal direction of the pipe was negligible. In order to clarify thermal characteristics of the multi-layer insulator, the heat transfer through the insulator has been analyzed considering the radiation heat transfer by the netting spacer between the reflectors, and the temperature dependence on the emissivities and the heat transmission coefficients of these two components of the insulator. The analytical results were in good agreements with the experimental ones, so that the analytical method was shown to be valid. Concerning the influence of the number of layers and the layer density on the insulation performance of the insulator, analytical results showed that the multi-layer insulator with the number of layer about N = 20 and the layer density below 2.0 layer/mm was the most effective for the liquid helium pipe of a JT-60 cryopump. (author)

Improving thermal insulation of TC4 using YSZ-based coating and SiO2 aerogel

Directory of Open Access Journals (Sweden)

Lei Jin

2015-04-01

Full Text Available In this paper, air plasmas spray (APS was used to prepare YSZ and Sc2O3–YSZ (ScYSZ coating in order to improve the thermal insulation ability of TC4 alloy. SiO2 aerogel was also synthesized and affixed on TC4 titanium alloy to inhabit thermal flow. The microstructures, phase compositions and thermal insulation performance of three coatings were analyzed in detail. The results of thermal diffusivity test by a laser flash method showed that the thermal diffusivities of YSZ, Sc2O3–YSZ and SiO2 aerogel are 0.553, 0.539 and 0.2097×10−6 m2/s, respectively. Then, the thermal insulation performances of three kinds of coating were investigated from 20 °C to 400 °C using high infrared radiation heat flux technology. The experimental results indicated that the corresponding temperature difference between the top TC4 alloy (400 °C and the bottom surface of YSZ is 41.5 °C for 0.6 mm thickness coating. For 1 mm thickness coating, the corresponding temperature difference between the top TC4 alloys (400 °C and the bottom surface of YSZ, ScYSZ, SiO2 aerogel three specimens is 54, 54.6 and 208 °C, respectively. The coating thickness and species were found to influence the heat insulation ability. In these materials, YSZ and ScYSZ exhibited a little difference for heat insulation behavior. However, SiO2 aerogel was the best one among them and it can be taken as protection material on TC4 alloys. In outer space, SiO2 aerogel can meet the need of thermal insulation of TC4 of high-speed aircraft.

Chern structure in the Bose-insulating phase of Sr2RuO4 nanofilms

Science.gov (United States)

Nobukane, Hiroyoshi; Matsuyama, Toyoki; Tanda, Satoshi

2017-01-01

The quantum anomaly that breaks the symmetry, for example the parity and the chirality, in the quantization leads to a physical quantity with a topological Chern invariant. We report the observation of a Chern structure in the Bose-insulating phase of Sr2RuO4 nanofilms by employing electric transport. We observed the superconductor-to-insulator transition by reducing the thickness of Sr2RuO4 single crystals. The appearance of a gap structure in the insulating phase implies local superconductivity. Fractional quantized conductance was observed without an external magnetic field. We found an anomalous induced voltage with temperature and thickness dependence, and the induced voltage exhibited switching behavior when we applied a magnetic field. We suggest that there was fractional magnetic-field-induced electric polarization in the interlayer. These anomalous results are related to topological invariance. The fractional axion angle Θ = π/6 was determined by observing the topological magneto-electric effect in the Bose-insulating phase of Sr2RuO4 nanofilms.

Room temperature giant and linear magnetoresistance in topological insulator Bi2Te3 nanosheets.

Science.gov (United States)

Wang, Xiaolin; Du, Yi; Dou, Shixue; Zhang, Chao

2012-06-29

Topological insulators, a new class of condensed matter having bulk insulating states and gapless metallic surface states, have demonstrated fascinating quantum effects. However, the potential practical applications of the topological insulators are still under exploration worldwide. We demonstrate that nanosheets of a Bi(2)Te(3) topological insulator several quintuple layers thick display giant and linear magnetoresistance. The giant and linear magnetoresistance achieved is as high as over 600% at room temperature, with a trend towards further increase at higher temperatures, as well as being weakly temperature-dependent and linear with the field, without any sign of saturation at measured fields up to 13 T. Furthermore, we observed a magnetic field induced gap below 10 K. The observation of giant and linear magnetoresistance paves the way for 3D topological insulators to be useful for practical applications in magnetoelectronic sensors such as disk reading heads, mechatronics, and other multifunctional electromagnetic applications.

Quasi-one-dimensional Hall physics in the Harper–Hofstadter–Mott model

Science.gov (United States)

Kozarski, Filip; Hügel, Dario; Pollet, Lode

2018-04-01

We study the ground-state phase diagram of the strongly interacting Harper–Hofstadter–Mott model at quarter flux on a quasi-one-dimensional lattice consisting of a single magnetic flux quantum in y-direction. In addition to superfluid phases with various density patterns, the ground-state phase diagram features quasi-one-dimensional analogs of fractional quantum Hall phases at fillings ν = 1/2 and 3/2, where the latter is only found thanks to the hopping anisotropy and the quasi-one-dimensional geometry. At integer fillings—where in the full two-dimensional system the ground-state is expected to be gapless—we observe gapped non-degenerate ground-states: at ν = 1 it shows an odd ‘fermionic’ Hall conductance, while the Hall response at ν = 2 consists of the transverse transport of a single particle–hole pair, resulting in a net zero Hall conductance. The results are obtained by exact diagonalization and in the reciprocal mean-field approximation.

Local Peltier-effect-induced reversible metal–insulator transition in VO{sub 2} nanowires

Energy Technology Data Exchange (ETDEWEB)

Takami, Hidefumi; Kanki, Teruo, E-mail: kanki@sanken.osaka-u.ac.jp, E-mail: h-tanaka@sanken.osaka-u.ac.jp; Tanaka, Hidekazu, E-mail: kanki@sanken.osaka-u.ac.jp, E-mail: h-tanaka@sanken.osaka-u.ac.jp [Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)

2016-06-15

We report anomalous resistance leaps and drops in VO{sub 2} nanowires with operating current density and direction, showing reversible and nonvolatile switching. This event is associated with the metal–insulator phase transition (MIT) of local nanodomains with coexistence states of metallic and insulating phases induced by thermoelectric cooling and heating effects. Because the interface of metal and insulator domains has much different Peltier coefficient, it is possible that a significant Peltier effect would be a source of the local MIT. This operation can be realized by one-dimensional domain configuration in VO{sub 2} nanowires because one straight current path through the electronic domain-interface enables theoretical control of thermoelectric effects. This result will open a new method of reversible control of electronic states in correlated electron materials.

NSF-DMR Highlight from NHMFL-PFF 2017

Energy Technology Data Exchange (ETDEWEB)

Mielke, Charles H. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2017-07-12

The alkali-doped fullerides provide the first example of a transition from a three-dimensional Mott insulator to a superconductor, enabling the effects of both dimensionality and electron correlations on superconductivity to be explored. Chemically, the alkali species tunes the superconductivity in the vicinity of the Mott transition by varying the unit cell volume.

Ferromagnetism in the two-dimensional periodic Anderson model

International Nuclear Information System (INIS)

Batista, C. D.; Bonca, J.; Gubernatis, J. E.

2001-01-01

Using the constrained-path Monte Carlo method, we studied the magnetic properties of the two-dimensional periodic Anderson model for electron fillings between 1/4 and 1/2. We also derived two effective low-energy theories to assist in interpreting the numerical results. For 1/4 filling, we found that the system can be a Mott or a charge-transfer insulator, depending on the relative values of the Coulomb interaction and the charge-transfer gap between the two noninteracting bands. The insulator may be a paramagnet or antiferromagnet. We concentrated on the effect of electron doping on these insulating phases. Upon doping we obtained a partially saturated ferromagnetic phase for low concentrations of conduction electrons. If the system were a charge-transfer insulator, we would find that the ferromagnetism is induced by the well-known Ruderman-Kittel-Kasuya-Yosida interaction. However, we found a novel correlated hopping mechanism inducing the ferromagnetism in the region where the nondoped system is a Mott insulator. Our regions of ferromagnetism spanned a much smaller doping range than suggested by recent slave boson and dynamical mean-field theory calculations, but they were consistent with that obtained by density-matrix renormalization group calculations of the one-dimensional periodic Anderson model

Hydrogen storage in insulated pressure vessels

Energy Technology Data Exchange (ETDEWEB)

Aceves, S.M.; Garcia-Villazana, O. [Lawrence Livermore National Lab., CA (United States)

1998-08-01

Insulated pressure vessels are cryogenic-capable pressure vessels that can be fueled with liquid hydrogen (LH{sub 2}) or ambient-temperature compressed hydrogen (CH{sub 2}). Insulated pressure vessels offer the advantages of liquid hydrogen tanks (low weight and volume), with reduced disadvantages (lower energy requirement for hydrogen liquefaction and reduced evaporative losses). This paper shows an evaluation of the applicability of the insulated pressure vessels for light-duty vehicles. The paper shows an evaluation of evaporative losses and insulation requirements and a description of the current analysis and experimental plans for testing insulated pressure vessels. The results show significant advantages to the use of insulated pressure vessels for light-duty vehicles.

Flashover of a vacuum-insulator interface: A statistical model

Directory of Open Access Journals (Sweden)

W. A. Stygar

2004-07-01

Full Text Available We have developed a statistical model for the flashover of a 45° vacuum-insulator interface (such as would be found in an accelerator subject to a pulsed electric field. The model assumes that the initiation of a flashover plasma is a stochastic process, that the characteristic statistical component of the flashover delay time is much greater than the plasma formative time, and that the average rate at which flashovers occur is a power-law function of the instantaneous value of the electric field. Under these conditions, we find that the flashover probability is given by 1-exp(-E_{p}^{β}t_{eff}C/k^{β}, where E_{p} is the peak value in time of the spatially averaged electric field E(t, t_{eff}≡∫[E(t/E_{p}]^{β}dt is the effective pulse width, C is the insulator circumference, k∝exp(λ/d, and β and λ are constants. We define E(t as V(t/d, where V(t is the voltage across the insulator and d is the insulator thickness. Since the model assumes that flashovers occur at random azimuthal locations along the insulator, it does not apply to systems that have a significant defect, i.e., a location contaminated with debris or compromised by an imperfection at which flashovers repeatedly take place, and which prevents a random spatial distribution. The model is consistent with flashover measurements to within 7% for pulse widths between 0.5 ns and 10   μs, and to within a factor of 2 between 0.5 ns and 90 s (a span of over 11 orders of magnitude. For these measurements, E_{p} ranges from 64 to 651  kV/cm, d from 0.50 to 4.32 cm, and C from 4.96 to 95.74 cm. The model is significantly more accurate, and is valid over a wider range of parameters, than the J. C. Martin flashover relation that has been in use since 1971 [J. C. Martin on Pulsed Power, edited by T. H. Martin, A. H. Guenther, and M. Kristiansen (Plenum, New York, 1996]. We have generalized the statistical model to estimate the total-flashover probability of an

Analysis list: Ets2 [Chip-atlas[Archive

Lifescience Database Archive (English)

Full Text Available Ets2 Blood + mm9 http://dbarchive.biosciencedbc.jp/kyushu-u/mm9/target/Ets2.1.tsv h...ttp://dbarchive.biosciencedbc.jp/kyushu-u/mm9/target/Ets2.5.tsv http://dbarchive.biosciencedbc.jp/kyushu-u/mm9/target/Et...s2.10.tsv http://dbarchive.biosciencedbc.jp/kyushu-u/mm9/colo/Ets2.Blood.tsv http://dbarchive.biosciencedbc.jp/kyushu-u/mm9/colo/Blood.gml ...

Existence of Mott-Schwinger interaction proved by means of p-/sup 12/C elastic scattering. [450 to 600 keV

Energy Technology Data Exchange (ETDEWEB)

Krause, H H; Arnold, W; Berg, H; Ulbricht, J; Clausnitzer, G [Giessen Univ. (Germany, F.R.). Inst. fuer Kernphysik

1979-01-01

The aim of this work was the unambiguous proof of the existence of the Mott-Schwinger interaction. The analyzing power of the p-/sup 12/C elastic scattering was measured in the energy range from 450 to 600 keV for scattering angles theta/sub Lab/ = 90/sup 0/ and 120/sup 0/ with an overall accuracy up to ..delta..A = 1 x /sup -4/. The data can be described very well with the R-matrix formalism including Mott-Schwinger interaction. Omitting this interaction results in large discrepancies.

Molecular and functional characterization of the promoter of ETS2, the human c-ets-2 gene

International Nuclear Information System (INIS)

Mavrothalassitis, G.J.; Watson, D.K.; Papas, T.S.

1990-01-01

The 5' end of the human c-ets-2 gene, ETS2, was cloned and characterized. The major transcription initiation start sites were identified, and the pertinent sequences surrounding the ETS2 promoter were determined. The promoter region of ETS2 does not possess typical TATA and CAAT elements. However, this promoter contains several repeat regions, as well as two consensus AP2 binding sites and three putative Sp1 sites. There is also a palindromic region similar to the serum response element of the c-fos gene, located 1,400 base pairs (bp) upstream from the first major transcription initiation site. A G+C-rich sequence (GC element) with dyad symmetry can be seen in the ETS2 promoter, immediately following an unusually long polypurine-polypyrimidine tract. A series of deletion fragments from the putative promoter region were ligated in front of the bacterial chloramphenicol acetyltransferase gene and tested for activity following transfection into HeLa cells. The 5' boundary of the region needed for maximum promoter activity was found to be 159 bp upstream of the major initiation site. The promoter of ETS2 (within the polypyrimidine tract) serves to illustrate an alternative structure that may be present in genes with TATA-less promoters

Thermal test of the insulation structure for LH 2 tank by using the large experimental apparatus

Science.gov (United States)

Kamiya, S.; Onishi, K.; Konshima, N.; Nishigaki, K.

Conceptual designs of large mass LH 2 (liquid hydrogen) storage systems, whose capacity is 50,000 m3, have been studied in the Japanese hydrogen project, World Energy Network (WE-NET) [K. Fukuda, in: WE-NET Hydrogen Energy Symposium, 1999, P1-P41]. This study has concluded that their thermal insulation structures for the huge LH 2 tanks should be developed. Their actual insulation structures comprise not only the insulation material but also reinforced members and joints. To evaluate their thermal performance correctly, a large test specimen including reinforced members and joints will be necessary. After verifying the thermal performance of a developed large experimental apparatus [S. Kamiya, Cryogenics 40 (1) (2000) 35] for measuring the thermal conductance of various insulation structures, we tested two specimens, a vacuum multilayer insulation (MLI) with a glass fiber reinforced plastic (GFRP) support and a vacuum solid insulation (microtherm ®) with joints. The thermal background test for verifying the thermal design of the experimental apparatus showed that the background heat leak is 0.1 W, small enough to satisfy apparatus performance requirement. The thermal conductance measurements of specimens also showed that thermal heat fluxes of MLI with a GFRP support and microtherm ® are 8 and 5.4 W/m2, respectively.

Phonon density of states and anharmonicity of UO2

Science.gov (United States)

Pang, Judy W. L.; Chernatynskiy, Aleksandr; Larson, Bennett C.; Buyers, William J. L.; Abernathy, Douglas L.; McClellan, Kenneth J.; Phillpot, Simon R.

2014-03-01

Phonon density of states (PDOS) measurements have been performed on polycrystalline UO2 at 295 and 1200 K using time-of-flight inelastic neutron scattering to investigate the impact of anharmonicity on the vibrational spectra and to benchmark ab initio PDOS simulations performed on this strongly correlated Mott insulator. Time-of-flight PDOS measurements include anharmonic linewidth broadening, inherently, and the factor of ˜7 enhancement of the oxygen spectrum relative to the uranium component by the increased neutron sensitivity to the oxygen-dominated optical phonon modes. The first-principles simulations of quasiharmonic PDOS spectra were neutron weighted and anharmonicity was introduced in an approximate way by convolution with wave-vector-weighted averages over our previously measured phonon linewidths for UO2, which are provided in numerical form. Comparisons between the PDOS measurements and the simulations show reasonable agreement overall, but they also reveal important areas of disagreement for both high and low temperatures. The discrepancies stem largely from a ˜10 meV compression in the overall bandwidth (energy range) of the oxygen-dominated optical phonons in the simulations. A similar linewidth-convoluted comparison performed with the PDOS spectrum of Dolling et al. obtained by shell-model fitting to their historical phonon dispersion measurements shows excellent agreement with the time-of-flight PDOS measurements reported here. In contrast, we show by comparisons of spectra in linewidth-convoluted form that recent first-principles simulations for UO2 fail to account for the PDOS spectrum determined from the measurements of Dolling et al. These results demonstrate PDOS measurements to be stringent tests for ab inito simulations of phonon physics in UO2 and they indicate further the need for advances in theory to address the lattice dynamics of UO2.

Momentum Dependence of Charge Excitations in YBa2Cu3O7-δ and Nd2-xCexCuO4

Science.gov (United States)

Ishii, Kenji

2006-03-01

Resonant inelastic x-ray scattering (RIXS) studies at Cu K-edge on high-Tc superconducting cuprates, YBa2Cu3O7-δ and Nd2-xCexCuO4 are presented. The superconductivity occurs in the vicinity of the Mott insulating state and it is important to clarify the nature of the Mott gap and its doping dependence. Because RIXS has an advantage that we can measure charge excitation in a wide energy-momentum space, it gives a unique opportunity to study the electronic structure of materials. We apply this technique to high-Tc superconducting cuprates. In particular the electronic structure of strongly correlated metals is in the focus of our RIXS study. The experiments were performed at BL11XU of SPring-8, Japan, where a specially designed spectrometer for inelastic x-ray scattering is installed. In optimally doped YBa2Cu3O7-δ, anisotropic spectra are observed in the ab plane of a twin-free crystal. The Mott gap excitation from the one-dimensional CuO chain is enhanced at 2 eV near the zone boundary of the chain direction, while the excitation from the CuO2 plane is broad at 1.5-4 eV and almost independent of momentum. Theoretical calculation based on the one-dimensional and two-dimensional Hubbard model reproduces the observed features in the RIXS spectra when smaller values of the on-site Coulomb energy of the chain than that of the plane are assumed. This means that the charge transfer gap of the chain is smaller than that of the plane. On the other hand, both interband excitation across the Mott gap and intraband excitation in the upper Hubbard band are observed in the electron-doped Nd2-xCexCuO4. The intensity of the interband excitation is concentrated at ˜ 2 eV near the zone boundary while a dispersion relation with a momentum-dependent width emerges in the intraband excitation. The author would like to acknowledge to his collaborators, K. Tsutsui, Y. Endoh, T. Tohyama, K. Kuzushita, T. Inami, K. Ohwada, M. Hoesch, M. Tsubota, Y. Murakami, J. Mizuki, S. Maekawa, T

Electrical insulators for the theta-pinch fusion reactor

International Nuclear Information System (INIS)

Clinard, F.W. Jr.

1976-01-01

The five major applications for electrical insulators in the Reference Theta Pinch Reactor are as follows: (1) first-wall insulator, (2) blanket intersegment insulator, (3) graphite encapsulating insulator, (4) implosion coil insulator, and (5) compression coil insulator. Insulator design proposals and some preliminary test results are given for each application

Strain effects in topological insulators: Topological order and the emergence of switchable topological interface states in Sb2Te3/Bi2Te3 heterojunctions

Science.gov (United States)

Aramberri, H.; Muñoz, M. C.

2017-05-01

We investigate the effects of strain on the topological order of the Bi2Se3 family of topological insulators by ab initio first-principles methods. Strain can induce a topological phase transition and we present the phase diagram for the 3D topological insulators, Bi2Te3 , Sb2Te3 , Bi2Se3 , and Sb2Se3 , under combined uniaxial and biaxial strain. Their phase diagram is universal and shows metallic and insulating phases, both topologically trivial and nontrivial. In particular, uniaxial tension can drive the four compounds into a topologically trivial insulating phase. We propose a Sb2Te3/Bi2Te3 heterojunction in which a strain-induced topological interface state arises in the common gap of this normal insulator-topological insulator heterojunction. Unexpectedly, the interface state is confined in the topologically trivial subsystem and is physically protected from ambient impurities. It can be switched on or off by means of uniaxial strain and therefore Sb2Te3 /Bi2Te3 heterojunctions provide a topological system which hosts tunable robust helical interface states with promising spintronic applications.

Quantum phases of AB2 fermionic chains

International Nuclear Information System (INIS)

Murcia-Correa, L S; Franco, R; Silva-Valencia, J

2016-01-01

A fermionic chain is a one-dimensional system with fermions that interact locally and can jump between sites in the lattice, in particular an AB n chain type, where A and B are sites that exhibit a difference in energy level of Δ and site B is repeated n-times, such that the unit cell has n +1 sites. A limit case of this model, called the ionic Hubbard model (n = 1), has been widely studied due to its interesting physics and applications. In this paper, we study the ground state of an AB 2 chain, which describes the material R 4 [Pt 2 (P 2 O 5 H 2 ) 4 X] · nH 2 O. Specifically, we consider a filling with two electrons per unit cell, and using the density matrix renormalization group method we found that the system exhibits the band insulator and Mott correlated insulator phases, as well as an intermediate phase between them. For couplings of Δ = 2,10 and 20, we estimate the critical points that separate these phases through the structure factor and the energy gap in the sector of charge and spin, finding that the position of the critical point rises as a function of Δ. (paper)

Liquid hydrogen and deuterium targets; Cibles a hydrogene et deuterium liquides

Energy Technology Data Exchange (ETDEWEB)

Bougon, M; Marquet, M; Prugne, P [Commissariat a l' Energie Atomique, Saclay (France).Centre d' Etudes Nucleaires

1961-07-01

A description is given of 1) Atmospheric pressure target: liquid hydrogen, 400 mm thickness; thermal insulation: styrofoam; the hydrogen vapors are used to improve the target cooling; Mylar windows. 2) Vacuum target: 12 liter content: hydrogen or deuterium; liquid thickness 400 mm; thermal insulation is afforded by a vacuum vessel and a liquid nitrogen shield. Recovery and liquefaction of deuterium vapors are managed in the vacuum vessel which holds the target. The target emptying system is designed for operating in a few minutes. (author) [French] Description de: 1) Cible a pression atmospherique; hydrogene liquide, 400 mm d'epaisseur; l'isolement thermique: styrofoam; on utilise les vapeurs d'hydrogene pour ameliorer le refroidissement de la cible; hublots en Mylar. 2) Cible sous vide; contenance 12 litres; hydrogene ou deuterium; epaisseur du liquide 400 mm; l'isolement thermique est assure par une cuve a vide et un ecran d'azote liquide. Recuperation et liquefaction des vapeurs de deuterium sont effectuees dans la cuve a vide contenant la cible. Le systeme de vidange pour la cible est concu pour fonctionner en quelques minutes. (auteur)

Magnon spin Hall magnetoresistance of a gapped quantum paramagnet

NARCIS (Netherlands)

Ulloa, Camilo; Duine, R.A.

2018-01-01

Motivated by recent experimental work, we consider spin transport between a normal metal and a gapped quantum paramagnet. We model the latter as the magnonic Mott-insulating phase of an easy-plane ferromagnetic insulator. We evaluate the spin current mediated by the interface exchange coupling

Development of advanced materials composites for use as insulations for LH2 tanks

Science.gov (United States)

Lemons, C. R.; Salmassy, O. K.

1973-01-01

A study of thread-reinforced polyurethane foam and glass fabric liner, serving as internally bonded insulation for space shuttle LH2 tanks, is reported. Emphasis was placed on an insulation system capable of reentry and multiple reuse in the shuttle environment. The optimized manufacturing parameters associated with each element of the composite are established and the results, showing successful completion of subscale system evaluation tests using the shuttle flight environmental requirements, are given.

Infrared and Raman spectroscopic study of BDA-TTP [2,5-bis(1,3-dithian-2-ylidene) 1,3,4,6-tetrathiapentalene] and its charge-transfer salts

Science.gov (United States)

Uruichi, Mikio; Nakano, Chikako; Tanaka, Masayuki; Yakushi, Kyuya; Kaihatsu, Takayuki; Yamada, Jun-ichi

2008-09-01

Infrared and Raman spectra in the frequency range of 1200-1600 cm -1 were observed using BDA-TTP and (BDA-TTP)CuCl 2 crystals. The C =C stretching and CH 2 bending modes in this frequency region were assigned based on quantum chemical calculation of the normal modes by the density functional theory (DFT) method. The three C =C stretching modes of BDA-TTP showed a significant low-frequency shift upon oxidation. One of the Raman-active C =C stretching modes is strongly coupled with the charge-transfer excited state. Vibrational analysis was applied to β-(BDA-TTP) 2I 3. The infrared-active C =C stretching mode strongly suggests that the insulating state of β-(BDA-TTP) 2I 3 is characterized as a dimer-Mott state below 150 K.

A New Generation of Building Insulation by Foaming Polymer Blend Materials with CO₂

Energy Technology Data Exchange (ETDEWEB)

Yang, Arthur [Industrial Science & Technology Network, Inc., Lancaster, PA (United States); Domszy, Roman [Industrial Science & Technology Network, Inc., Lancaster, PA (United States); Yang, Jeff [Industrial Science & Technology Network, Inc., Lancaster, PA (United States)

2016-03-30

Advanced thermal insulation is among the most effective technologies in transforming our nation’s energy system and contributing to DOE’s stated goal of 50% less building energy consumption by 2030. The installation of an advanced thermal insulation would prevent energy waste without the need for any maintenance, and ISTN conservatively estimates that the commercialization of such a new technology would contribute to annual U.S. energy savings of 0.361 Quads and $8 billion in annual economic savings. The key challenge to improving building insulation is to maintain and surpass the industry standard of R-5 per inch insulation value in a cost-competitive manner. Improvements in R-value without cost-efficiency are not likely to impact the market given the cost-sensitive nature of the construction industry (insulation is already the lowest-cost component of the building envelope). However, significantly higher insulating value at competitive costs is extremely appealing to the market given the greater potential to save on energy consumption and costs over the long-term. Thus, our goal is to develop a super-thermal insulation with 50% greater insulation value (R-9 to R-10 per inch) and manufacturing costs that are equal on a per-R-value basis (< $0.70/ft²).

Phase diagram of the disordered Bose-Hubbard model

International Nuclear Information System (INIS)

Gurarie, V.; Pollet, L.; Prokof'ev, N. V.; Svistunov, B. V.; Troyer, M.

2009-01-01

We establish the phase diagram of the disordered three-dimensional Bose-Hubbard model at unity filling which has been controversial for many years. The theorem of inclusions, proven by Pollet et al. [Phys. Rev. Lett. 103, 140402 (2009)] states that the Bose-glass phase always intervenes between the Mott insulating and superfluid phases. Here, we note that assumptions on which the theorem is based exclude phase transitions between gapped (Mott insulator) and gapless phases (Bose glass). The apparent paradox is resolved through a unique mechanism: such transitions have to be of the Griffiths type when the vanishing of the gap at the critical point is due to a zero concentration of rare regions where extreme fluctuations of disorder mimic a regular gapless system. An exactly solvable random transverse field Ising model in one dimension is used to illustrate the point. A highly nontrivial overall shape of the phase diagram is revealed with the worm algorithm. The phase diagram features a long superfluid finger at strong disorder and on-site interaction. Moreover, bosonic superfluidity is extremely robust against disorder in a broad range of interaction parameters; it persists in random potentials nearly 50 (!) times larger than the particle half-bandwidth. Finally, we comment on the feasibility of obtaining this phase diagram in cold-atom experiments, which work with trapped systems at finite temperature.

THE EFFICACY OF THE CABLES OF 6–110 KW WITH XLPE INSULATION. Part 2

Directory of Open Access Journals (Sweden)

M. A. Korotkevich

2017-01-01

Full Text Available The assessment of the suitability of cables of 6–110 kW with XLPE insulation in comparison with cables of the same voltage but possessing paper-oil insulation has been fulfilled on the basis of the method of multi-objective optimization that makes it possible to account not only the quantitative characteristics (of reduced costs, but also qualitative ones. As an indicator of the reliability of the cable line the maximum mean time to failure (the value inversely proportional to the parameter of succession of failures, which is an order more for cable lines with XLPE insulation than for cable lines with paper insulation, is adopted. A comprehensive assessment of the convenience of installation of cable lines revealed that the installation of cable with XLPE insulation features a 1.2–1.6 times easier installation as compared to three-wire (voltage 10 kW and 1.4 times easier installation as compared to single-core oil-filled cables (voltage of 110 kW. The efficacy of the cables 6–110 kW with XLPE insulation is proved on the basis on the method of multi-objective optimization, that took into account as the costs for the construction and operation of cable lines and the reliability of its operation, ease of its installation and other quality indicators. If the goals taken into account are considered as equally important, the polyethylene-insulated cables for a voltage of 10–110 kW is more efficient as compared to three-wire (voltage 10 kW and solid (110 kW cables with paper insulation. Herewith, the cost of the cable with XLPE insulation may exceed the cost of cable with paper insulation up to two times. If the most important aim is to provide the minimum reduced costs for the construction and operation of the cable line, the use of cables with XLPE insulation for voltage of 10 kW is most advisable in individual cases.

Field evaluation of reflective insulation in south east Asia

Science.gov (United States)

Teh, Khar San; Yarbrough, David W.; Lim, Chin Haw; Salleh, Elias

2017-12-01

The objective of this research was to obtain thermal performance data for reflective insulations in a South East Asia environment. Thermal resistance data (RSI, m2 ṡ K/W) for reflective insulations are well established from 1-D steady-state tests, but thermal data for reflective insulation in structures like those found in South East Asia are scarce. Data for reflective insulations in South East Asia will add to the worldwide database for this type of energy-conserving material. RSI were obtained from heat flux and temperature data of three identical structures in the same location. One unit did not have insulation above the ceiling, while the second and third units were insulated with reflective insulation with emittance less than 0.05. RSI for the uninsulated test unit varied from 0.37 to 0.40 m2 ṡ K/W. RSI for a single-sheet reflective insulation (woven foil) varied from 2.15 to 2.26 m2 ṡ K/W, while bubble-foil insulation varied from 2.69 to 3.09 m2 ṡ K/W. The range of RSI values resulted from differences in the spacing between the reflective insulation and the roof. In addition, the reflective insulation below the roof lowered attic temperatures by as much as 9.7° C. Reductions in ceiling heat flux of 80 to 90% relative to the uninsulated structure, due to the reflective insulation, were observed.

INSUL, Calculation of Thermal Insulation of Various Materials Immersed in He

International Nuclear Information System (INIS)

Kinkead, A.N.; Pitchford, B.E.

1977-01-01

1 - Nature of the physical problem solved: Performance of thermal insulation immersed in helium. 2 - Method of solution: Mineral fibre, metal fibre and metallic multi-layer foils are studied. An approximate analysis for performance evaluation of multi-layer insulation in vertical gas spaces including the regime between fully suppressed natural convection and that for which an accepted power relationship applies is included

Step tunneling enhanced asymmetry in metal-insulator-insulator-metal (MIIM) diodes for rectenna applications

Science.gov (United States)

Alimardani, N.; Conley, J. F.

2013-09-01

We combine nanolaminate bilayer insulator tunnel barriers (Al2O3/HfO2, HfO2/Al2O3, Al2O3/ZrO2) deposited via atomic layer deposition (ALD) with asymmetric work function metal electrodes to produce MIIM diodes with enhanced I-V asymmetry and non-linearity. We show that the improvements in MIIM devices are due to step tunneling rather than resonant tunneling. We also investigate conduction processes as a function of temperature in MIM devices with Nb2O5 and Ta2O5 high electron affinity insulators. For both Nb2O5 and Ta2O5 insulators, the dominant conduction process is established as Schottky emission at small biases and Frenkel-Poole emission at large biases. The energy depth of the traps that dominate Frenkel-Poole emission in each material are estimated.

Planar Nernst effect and Mott relation in (In,Fe)Sb ferromagnetic semiconductor

Science.gov (United States)

Bui, Cong Tinh; Garcia, Christina A. C.; Tu, Nguyen Thanh; Tanaka, Masaaki; Hai, Pham Nam

2018-05-01

Transverse magneto-thermoelectric effects were studied in an (In,Fe)Sb ferromagnetic semiconductor thin film under an in-plane magnetic field. We find that the thermal voltage is governed by the planar Nernst effect. We show that the magnetic field intensity dependence, magnetic field direction dependence, and temperature dependence of the transverse Seebeck coefficient can be explained by assuming a Mott relation between the in-plane magneto-transport and magneto-thermoelectric phenomena in (In,Fe)Sb.

Duality-mediated critical amplitude ratios for the (2 + 1)-dimensional S = 1XY model

Science.gov (United States)

Nishiyama, Yoshihiro

2017-09-01

The phase transition for the (2 + 1)-dimensional spin-S = 1XY model was investigated numerically. Because of the boson-vortex duality, the spin stiffness ρs in the ordered phase and the vortex-condensate stiffness ρv in the disordered phase should have a close relationship. We employed the exact diagonalization method, which yields the excitation gap directly. As a result, we estimate the amplitude ratios ρs,v/Δ (Δ: Mott insulator gap) by means of the scaling analyses for the finite-size cluster with N ≤ 22 spins. The ratio ρs/ρv admits a quantitative measure of deviation from selfduality.

Molecular beam epitaxial growth of Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} topological insulators on GaAs (111) substrates: a potential route to fabricate topological insulator p-n junction

Energy Technology Data Exchange (ETDEWEB)

Zeng, Zhaoquan; Morgan, Timothy A.; Li, Chen; Hirono, Yusuke; Hu, Xian; Hawkridge, Michael E.; Benamara, Mourad; Salamo, Gregory J. [Arkansas Institute for Nanoscale Material Sciences and Engineering, University of Arkansas, Fayetteville, AR 72701 (United States); Fan, Dongsheng; Yu, Shuiqing [Arkansas Institute for Nanoscale Material Sciences and Engineering, University of Arkansas, Fayetteville, AR 72701 (United States); Department of Electrical Engineering, University of Arkansas, Fayetteville, AR 72701 (United States); Zhao, Yanfei [International Center for Quantum Materials, School of Physics, Peking University, Beijing, 100871 (China); Lee, Joon Sue [The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, PA 16802 (United States); Wang, Jian [International Center for Quantum Materials, School of Physics, Peking University, Beijing, 100871 (China); The Center for Nanoscale Science and Department of Physics, The Pennsylvania State University, University Park, PA 16802 (United States); Wang, Zhiming M. [Arkansas Institute for Nanoscale Material Sciences and Engineering, University of Arkansas, Fayetteville, AR 72701 (United States); State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054 (China); Engineering Research Center for Semiconductor Integrated Technology, Institute of Semiconductors, Chinese Academy of Science, Beijing 100083 (China)

2013-07-15

High quality Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} topological insulators films were epitaxially grown on GaAs (111) substrate using solid source molecular beam epitaxy. Their growth and behavior on both vicinal and non-vicinal GaAs (111) substrates were investigated by reflection high-energy electron diffraction, atomic force microscopy, X-ray diffraction, and high resolution transmission electron microscopy. It is found that non-vicinal GaAs (111) substrate is better than a vicinal substrate to provide high quality Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} films. Hall and magnetoresistance measurements indicate that p type Sb{sub 2}Te{sub 3} and n type Bi{sub 2}Te{sub 3} topological insulator films can be directly grown on a GaAs (111) substrate, which may pave a way to fabricate topological insulator p-n junction on the same substrate, compatible with the fabrication process of present semiconductor optoelectronic devices.

A New Numerical Method for Z2 Topological Insulators with Strong Disorder

Science.gov (United States)

Akagi, Yutaka; Katsura, Hosho; Koma, Tohru

2017-12-01

We propose a new method to numerically compute the Z2 indices for disordered topological insulators in Kitaev's periodic table. All of the Z2 indices are derived from the index formulae which are expressed in terms of a pair of projections introduced by Avron, Seiler, and Simon. For a given pair of projections, the corresponding index is determined by the spectrum of the difference between the two projections. This difference exhibits remarkable and useful properties, as it is compact and has a supersymmetric structure in the spectrum. These properties enable highly efficient numerical calculation of the indices of disordered topological insulators. The method, which we propose, is demonstrated for the Bernevig-Hughes-Zhang and Wilson-Dirac models whose topological phases are characterized by a Z2 index in two and three dimensions, respectively.

Insulator-semiconductor interface fixed charges in AlGaN/GaN metal-insulator-semiconductor devices with Al2O3 or AlTiO gate dielectrics

Science.gov (United States)

Le, Son Phuong; Nguyen, Duong Dai; Suzuki, Toshi-kazu

2018-01-01

We have investigated insulator-semiconductor interface fixed charges in AlGaN/GaN metal-insulator-semiconductor (MIS) devices with Al2O3 or AlTiO (an alloy of Al2O3 and TiO2) gate dielectrics obtained by atomic layer deposition on AlGaN. Analyzing insulator-thickness dependences of threshold voltages for the MIS devices, we evaluated positive interface fixed charges, whose density at the AlTiO/AlGaN interface is significantly lower than that at the Al2O3/AlGaN interface. This and a higher dielectric constant of AlTiO lead to rather shallower threshold voltages for the AlTiO gate dielectric than for Al2O3. The lower interface fixed charge density also leads to the fact that the two-dimensional electron concentration is a decreasing function of the insulator thickness for AlTiO, whereas being an increasing function for Al2O3. Moreover, we discuss the relationship between the interface fixed charges and interface states. From the conductance method, it is shown that the interface state densities are very similar at the Al2O3/AlGaN and AlTiO/AlGaN interfaces. Therefore, we consider that the lower AlTiO/AlGaN interface fixed charge density is not owing to electrons trapped at deep interface states compensating the positive fixed charges and can be attributed to a lower density of oxygen-related interface donors.

The inaccuracy of heat transfer characteristics for non-insulated and insulated spherical containers neglecting the influence of heat radiation

International Nuclear Information System (INIS)

Wong, King-Leung; Salazar, Jose Luis Leon; Prasad, Leo; Chen, Wen-Lih

2011-01-01

In this investigation, the differences of heat transfer characteristics for insulated and non-insulated spherical containers between considering and neglecting the influence of heat radiation are studied by the simulations in some practical situations. It is found that the heat radiation effect cannot be ignored in conditions of low ambient convection heat coefficients (such ambient air) and high surface emissivities, especially for the non-insulated and thin insulated cases. In most practical situations when ambient temperature is different from surroundings temperature and the emissivity of insulation surface is different from that of metal wall surface, neglecting heat radiation will result in inaccurate insulation effect and heat transfer errors even with very thick insulation. However, the insulation effect considering heat radiation will only increase a very small amount after some dimensionless insulated thickness (such insulation thickness/radius ≥0.2 in this study), thus such dimensionless insulated thickness can be used as the optimum thickness in practical applications. Meanwhile, wrapping a material with low surface emissivity (such as aluminum foil) around the oxidized metal wall or insulation layer (always with high surface emissivity) can achieve very good insulated effect for the non-insulated or thin insulated containers.

Temperature and polarization dependent Raman measurements of Ca{sub 2}RuO{sub 4}

Energy Technology Data Exchange (ETDEWEB)

German, Raphael [II. Physikalisches Institut, Univ. Koeln (Germany)

2016-07-01

Ca{sub 2}RuO{sub 4} is a Mott-like insulator, which undergoes a metal-insulator transition at 357 K and antiferromagnetic ordering at T{sub N} = 110 K. Here, we report a temperature and polarization dependent Raman scattering study. Earlier studies claimed a Raman active two-magnon excitation around 100 cm{sup -1}. This, however, is incompatible with the results from recent inelastic neutron scattering measurements, which suggest that this mode might be of single magnon nature. Instead, it is more likely that the feature which appears at ∝ 650 cm{sup -1}, previously claimed to be due to a charge gap, has a two-magnon origin. Another open question in the interpretation of the Raman spectra is the origin of the high-energy peak at ∝1360 cm{sup -1}. We will discuss the origin of the Raman peaks in terms of one- and two-magnon processes; magnon-phonon coupling, and possible crystal field excitations.

Improving thermal insulation of TC4 using YSZ-based coating and SiO2 aerogel

OpenAIRE

Jin, Lei; Li, Peizhong; Zhou, Haibin; Zhang, Wei; Zhou, Guodong; Wang, Chun

2015-01-01

In this paper, air plasmas spray (APS) was used to prepare YSZ and Sc2O3–YSZ (ScYSZ) coating in order to improve the thermal insulation ability of TC4 alloy. SiO2 aerogel was also synthesized and affixed on TC4 titanium alloy to inhabit thermal flow. The microstructures, phase compositions and thermal insulation performance of three coatings were analyzed in detail. The results of thermal diffusivity test by a laser flash method showed that the thermal diffusivities of YSZ, Sc2O3–YSZ and SiO2...

Intrinsic optical conductivity of a {{\\rm{C}}}_{2v} symmetric topological insulator

Science.gov (United States)

Sengupta, Parijat; Matsubara, Masahiko; Bellotti, Enrico; Shi, Junxia

2017-07-01

In this work we analytically investigate the longitudinal optical conductivity of the {{{C}}}2v symmetric topological insulator. The conductivity expressions at T = 0 are derived using the Kubo formula and expressed as a function of the ratio of the Dresselhaus and Rashba parameters that characterize the low-energy Hamiltonian. We find that the longitudinal inter-band conductivity vanishes when Dresselhaus and Rashba parameters are equal in strength, also called the persistent spin helix state. The calculations are extended to obtain the frequency-dependent real and imaginary components of the optical conductivity for the topological Kondo insulator SmB6 which exhibits {{{C}}}2v symmetric and anisotropic Dirac cones hosting topological states at \\overline{X} point on the surface Brillouin zone.

Surface quantum oscillations and weak antilocalization effect in topological insulator (Bi0.3Sb0.7)2Te3

Science.gov (United States)

Urkude, Rajashri; Rawat, Rajeev; Palikundwar, Umesh

2018-04-01

In 3D topological insulators, achieving a genuine bulk-insulating state is an important topic of research. The material system (Bi,Sb)2(Te,Se)3 has been proposed as a topological insulator with high resistivity and low carrier concentration. Topological insulators are predicted to present interesting surface transport phenomena but their experimental studies have been hindered by metallic bulk conduction that overwhelms the surface transport. Here we present a study of the bulk-insulating properties of (Bi0.3Sb0.7)2Te3. We show that a high resistivity exceeding 1 Ωm as a result of variable-range hopping behavior of state and Shubnikov-de Haas oscillations as coming from the topological surface state. We have been able to clarify both the bulk and surface transport channels, establishing a comprehensive understanding of the transport properties in this material. Our results demonstrate that (Bi0.3Sb0.7)2Te3 is a good material for studying the surface quantum transport in a topological insulator.

Etude hyperfrequence et ultrasonore des supraconducteurs organiques kappa-(ET)(2)X (X = copper(thiocyanogen), copper[N(CN)(2)]bromine)

Science.gov (United States)

Frikach, Kamal

2001-09-01

Dans ce travail je presente une etude de l'impedance de surface, ainsi que de l'attenuation et la variation de la vitesse ultrasonores dans les etats normal et supraconducteur sur les composes organiques k-(ET)2X (X = Cu(SCN) 2, Cu[N(CN)2]Br). A partir des mesures d'impedance de surface, les deux composantes sigma 1 et sigma2 de la conductivite complexe sont extraites en utilisant le modele de Drude. Ces mesures montrent que la symetrie du parametre d'ordre dans ces composes est differente de celle du cas BCS. Afin de comprendre le profil de sigma1 (T) nous avons etudie les fluctuations supraconductrices a partir de la paraconductivite sigma'( T). Cette etude est rendue possible grace a la structure quasi-2D des composes k-(ET)2X dans lesquelles les fluctuations supraconductrices sont fortes. Ces dernieres sont observees sur deux decades de temperatures dans le Cu(SCN)2. L'application du modele de Aslamazov-Larkin 2D et 3D montre la possibilite du passage du regime 2D a haute temperature au regime 3D au voisinage de Tc. En se basant sur ce resultat, nous avons calcule la paraconductivite en utilisant une approche a l'ordre d'une boucle a partir du modele de Lawrence-Doniach. En tenant compte de la correction par la self energie dans la limite dynamique (17 GHz), l'ajustement de la paraconductivite calculee est en bon accord avec les donnees experimentales. Le couplage interplan obtenu est compatible avec le caractere quasi-2D des composes organiques. Le temps de relaxation des quasi-particules dans l'etat supraconducteur est ensuite extrait pour la premiere fois dans ces composes dont le comportement en fonction de la temperature est compatible avec la presence des noeuds dans le gap. Dans l'etat normal, la variation de la vitesse ultrasonore presente un comportement anormal caracterise par un fort ramollissement a T = 38 K et 50 K dans k-(ET) 2Cu(SCN)2 et k-(ET)2Cu[N(CN) 2]Br respectivement dont l'amplitude est independante du champ magnetique jusqu'a H = Hc 2

Oke et al 2 (12).cdr

African Journals Online (AJOL)

Timothy Ademakinwa

The study revealed that PES contained calcium, aluminum, and iron as part of its major components. 2+. 2+ ... carbon (Chan et al., 1994) , chitosan (Schmub et al., .... (1.735 g of nickel chloride) in 200 ml of distilled. ÷. ÷. ר. צ. ח. ח. ט. ז. -. = 1. 2. 1. 100. (%). W. W. W. Mc. ÷. ÷. ר. צ. ח. ח. ט. ז. -. = 2. 3. 2. 100. (%). W. W. W. VS. ÷. ÷.

Electric Field and Current Density Performance Analysis of Sf6, C4f8 and CO2 Gases As An Insulation

Science.gov (United States)

Mazli, Ahmad Danial Ahmad; Jamail, Nor Akmal Mohd; Azlin Othman, Nordiana

2017-08-01

SF6 gases are not only widely used as an insulating component in electric power industry but also as an arc extinguishing performance in high voltage (HV) gas-insulated circuit breaker (GCB). SF6 gases is generally used in the production of semiconductor materials and devices. Though these gasses is widely used in many application, the presences of temperature hotspot in the insulations may affect the insulation characteristics particularly electric field and current density. Therefore, it is important to determine the relationship between electric field and current density of gasses used in the insulator in the presence of hotspot. In this paper, three types of gases in particular Sulphur Hexafluoride (SF6), Octafluorocylobutane (C4F8), and Carbon Dioxide (CO2) was used in the insulator for gas insulation with the presence of two hotspots. These two hotspost were detected by referring the rising temperature in the insulator which are 1000 and 2000 Kelvin temperature for hotspot 1 and hotspot 2, respectively. From the simulation results, it can be concluded that Sulphur Hexafluoride (SF6) is the best choice for gas insulation since it had the lowest current density and electric field compared to Octafluorocylobutane (C4F8), and Carbon Dioxide (CO2). It is observed that the maximum current density and electric field for SF6 during normal condition are 358.94 × 103 V/m and 0.643 × 109 A/m2, respectively. Meanwhile, during temperature rising at hotspot 1 and hotspot 2, SF6 also had lowest current density and electric field compared to the other gasses where the results for Emax and Jmax at hotspot 1 are 322.34 × 103 V/m and 1.934 × 109 A/m2, respectively; While, Emax and Jmax at hotspot 2 are 259.77× 103 V/m and 2.824 × 109 A/m2. The results of this analysis can be used to find the best choices of gas that can be used in the insulator.

Acoustic study of YBa2Cu3Ox thin films

International Nuclear Information System (INIS)

Lee, S.; Chi, C.; Koren, G.; Gupta, A.

1991-01-01

The attenuation of surface acoustic waves by epitaxial YBa 2 Cu 3 O x films has been studied for x congruent 6 to 7. For fully oxygenated samples, the acoustic attenuation as a function of temperature shows two broad peaks at about 135 and 240 K, and decreases monotonically below the lower peak temperature. The cause of attenuation peaks is attributed to scattering by optical phonons. Our data do not show any gap structure at T c due to relatively weak electron-phonon interactions at the acoustic frequencies. As the oxygen deficiency increases, the temperature dependence of the dc resistance changes from metallic to semiconducting and finally to insulating behavior. Acoustic attenuation data correspondingly show a drastic change due to different attenuation mechanisms: from the phonon scattering loss in the metallic regime to the electric-field coupling loss in the semiconducting and insulating regimes. In the latter regimes, the temperature dependence of low-frequency resistance calculated from the attenuation data can be fitted to a three-dimensional Mott variable-range-hopping model

NMR Studies of the Vanadium Spin Dynamics and Spin Structure in LiV₂O₄, CaV₂O₄, and (Li_xV_1-x)₃BO₅ (x ≈ 0.33, 0.40)

Energy Technology Data Exchange (ETDEWEB)

Zong, Xiaopeng [Iowa State Univ., Ames, IA (United States)

2007-01-01

Strong electron correlation is believed to be an essential and unifying factor in diverse properties of condensed matter systems. Ground states that can arise due to electron correlation effects include Mott insulators, heavy fermion, ferromagnetism and antiferromagnetism, spin glasses, and high-temperature superconductivity. The electronic systems in transition metal oxide compounds are often highly correlated. In this thesis, the author presents experimental studies on three strongly correlated vanadium oxide compounds: LiV₂O₄, (Li_xV_1-x)₃BO₅, and CaV₂O₄, which have completely different ground states.

Phase diagram of a bosonic ladder with two coupled chains

International Nuclear Information System (INIS)

Luthra, Meetu Sethi; Mishra, Tapan; Pai, Ramesh V.; Das, B. P.

2008-01-01

We study a bosonic ladder with two coupled chains using the finite-size density-matrix renormalization group method. We show that in a commensurate bosonic ladder the critical on-site interaction (U C ) for the superfluid to Mott insulator transition gets larger as the interchain hopping (t perpendicular ) increases. We analyze this quantum phase transition and obtain the phase diagram in the t perpendicular -U plane. We also consider the asymmetric case where the on-site interactions are different in the two chains and have shown that the system as a whole will not be in the Mott insulator phase unless both the chains have on-site interactions greater than the critical value

Cellulose Insulation

Science.gov (United States)

1980-01-01

Fire retardant cellulose insulation is produced by shredding old newspapers and treating them with a combination of chemicals. Insulating material is blown into walls and attics to form a fiber layer which blocks the flow of air. All-Weather Insulation's founders asked NASA/UK-TAP to help. They wanted to know what chemicals added to newspaper would produce an insulating material capable of meeting federal specifications. TAP researched the query and furnished extensive information. The information contributed to successful development of the product and helped launch a small business enterprise which is now growing rapidly.

Disorder and pseudogap in strongly correlated systems: Phase diagram in the DMFT + Σ approach

International Nuclear Information System (INIS)

Kuleeva, N. A.; Kuchinskii, E. Z.

2013-01-01

The influence of disorder and pseudogap fluctuations on the Mott insulator-metal transition in strongly correlated systems has been studied in the framework of the generalized dynamic mean field theory (DMFT + Σ approach). Using the results of investigations of the density of states (DOS) and optical conductivity, a phase diagram (disorder-Hubbard interaction-temperature) is constructed for the paramagnetic Anderson-Hubbard model, which allows both the effects of strong electron correlations and the influence of strong disorder to be considered. Strong correlations are described using the DMFT, while a strong disorder is described using a generalized self-consistent theory of localization. The DOS and optical conductivity of the paramagnetic Hubbard model have been studied in a pseudogap state caused by antiferromagnetic spin (or charge) short-range order fluctuations with a finite correlation length, which have been modeled by a static Gaussian random field. The effect of a pseudogap on the Mott insulator-metal transition has been studied. It is established that, in both cases, the static Gaussian random field (related to the disorder or pseudogap fluctuations) leads to suppression of the Mott transition, broadening of the coexistence region of the insulator and metal phases, and an increase in the critical temperature at which the coexistence region disappears

High-frequency effects in antiferromagnetic Sr3Ir2O7

Science.gov (United States)

Williamson, Morgan; Seinige, Heidi; Shen, Shida; Wang, Cheng; Cao, Gang; Zhou, Jianshi; Goodenough, John; Tsoi, Maxim

Antiferromagnetic (AFM) spintronics is one of many promising routes for `beyond the CMOS' technologies where unique properties of AFM materials are exploited to achieve new and improved functionalities. AFMs are especially interesting for high-speed memory applications thanks to their high natural frequencies. Here we report the effects of high-frequency (microwave) currents on transport properties of antiferromagnetic Mott insulator Sr3Ir2O7. The microwaves at 3-7 GHz were found to affect the material's current-voltage characteristic and produce resonance-like features that we tentatively associate with the dissipationless magnonics recently predicted to occur in antiferromagnetic insulators subject to ac electric fields. Our observations support the potential of antiferromagnetic materials for high-speed/high-frequency spintronic applications. This work was supported in part by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA, by NSF Grants DMR-1207577, DMR-1265162, DMR-1600057, and DMR-1122603, and by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under Award No. OSR-2015-CRG4-2626.

Phase-field model of insulator-to-metal transition in VO2 under an electric field

Science.gov (United States)

Shi, Yin; Chen, Long-Qing

2018-05-01

The roles of an electric field and electronic doping in insulator-to-metal transitions are still not well understood. Here we formulated a phase-field model of insulator-to-metal transitions by taking into account both structural and electronic instabilities as well as free electrons and holes in VO2, a strongly correlated transition-metal oxide. Our phase-field simulations demonstrate that in a VO2 slab under a uniform electric field, an abrupt universal resistive transition occurs inside the supercooling region, in sharp contrast to the conventional Landau-Zener smooth electric breakdown. We also show that hole doping may decouple the structural and electronic phase transitions in VO2, leading to a metastable metallic monoclinic phase which could be stabilized through a geometrical confinement and the size effect. This work provides a general mesoscale thermodynamic framework for understanding the influences of electric field, electronic doping, and stress and strain on insulator-to-metal transitions and the corresponding mesoscale domain structure evolution in VO2 and related strongly correlated systems.

Effect Of Low External Flow On Flame Spreading Over ETFE Insulated Wire Under Microgravity

Science.gov (United States)

Nishizawa, Katsuhiro; Fujita, Osamu; Ito, Kenichi; Kikuchi, Masao; Olson, Sandra L.; Kashiwagi, Takashi

2003-01-01

Fire safety is one of the most important issues for manned space missions. A likely cause of fires in spacecraft is wire insulation combustion in electrical system. Regarding the wire insulation combustion it important to know the effect of low external flow on the combustion because of the presence of ventilation flow in spacecraft. Although, there are many researches on flame spreading over solid material at low external flows under microgravity, research dealing with wire insulation is very limited. An example of wire insulation combustion in microgravity is the Space Shuttle experiments carried out by Greenberg et al. However, the number of experiments was very limited. Therefore, the effect of low flow velocity is still not clear. The authors have reported results on flame spreading over ETFE (ethylene - tetrafluoroetylene) insulated wire in a quiescent atmosphere in microgravity by 10 seconds drop tower. The authors also performed experiments of polyethylene insulated nichrom wire combustion in low flow velocity under microgravity. The results suggested that flame spread rate had maximum value in low flow velocity condition. Another interesting issue is the effect of dilution gas, especially CO2, which is used for fire extinguisher in ISS. There are some researches working on dilution gas effect on flame spreading over solid material in quiescent atmosphere in microgravity. However the research with low external flow is limited and, of course, the research discussing a relation of the appearance of maximum wire flammability in low flow velocity region with different dilution gas cannot be found yet. The present paper, therefore, investigates the effect of opposed flow with different dilution gas on flame spreading over ETFE insulated wire and change in the presence of the maximum flammability depending on the dilution gas type is discussed within the limit of microgravity time given by ground-based facility.

Review and calculation of Mott scattering cross section by unscreened point nuclei

International Nuclear Information System (INIS)

Idoeta, R.; Legarda, F.

1992-01-01

A new tabulation of the ratio of the ''exact'' Mott cross section for unscreened point nuclei to the classical Rutherford cross section for electrons and positions has been made. Because of the infinite slowly converging series appearing in this ratio we have made two series transformations. With this evaluation the ratio reached convergence within six significant figures after less than a hundred terms and very low computing time. So the ratios evaluated have less relative error than those in the literature and covers a greater range of energy and atomic number. (orig.)

Development of flame retardant, radiation resistant insulating materials

Energy Technology Data Exchange (ETDEWEB)

Hagiwara, M.

1984-01-01

On the cables used for nuclear power stations, in particular those ranked as IE class, flame retardation test, simulated LOCA environment test, radiation resistance test and so on are imposed. The results of the evaluation of performance by these tests largely depend on the insulating materials mainly made of polymers. Ethylene propylene copolymer rubber has been widely used as cable insulator because of its electrical characteristics, workability, economy and relatively good radiation resistance, but it is combustible, therefore, in the practical use, it is necessary to make it fire resistant. The author et al. have advanced the research on the molecular design of new fire retarding materials, and successfully developed acenaphthylene bromide condensate, which is not only fire resistant but also effective for improving radiation resistance. The condition of flame retardant, radiation resistant auxiliary agents is explained, and there are additive type and reaction type in fire retarding materials. The synthesis of acenaphthylene bromide condensate and its effect of giving flame retardant and radiation resistant properties are reported. The characteristics of the cables insulated with the flame retardant ethylene propylene rubber containing acenaphthylene bromide condensate were tested, and the results are shown. (Kako, I.).

Topological insulators/superconductors: Potential future electronic materials

International Nuclear Information System (INIS)

Hor, Y. S.

2014-01-01

A new material called topological insulator has been discovered and becomes one of the fastest growing field in condensed matter physics. Topological insulator is a new quantum phase of matter which has Dirac-like conductivity on its surface, but bulk insulator through its interior. It is considered a challenging problem for the surface transport measurements because of dominant internal conductance due to imperfections of the existing crystals of topological insulators. By a proper method, the internal bulk conduction can be suppressed in a topological insulator, and permit the detection of the surface currents which is necessary for future fault-tolerant quantum computing applications. Doped topological insulators have depicted a large variety of bulk physical properties ranging from magnetic to superconducting behaviors. By chemical doping, a TI can change into a bulk superconductor. Nb x Bi 2 Se 3 is shown to be a superconductor with T c ∼ 3.2 K, which could be a potential candidate for a topological superconductor

Phase transitions and spin excitations of spin-1 bosons in optical lattice

Science.gov (United States)

Zhu, Min-Jie; Zhao, Bo

2018-03-01

For spin-1 bosonic system trapped in optical lattice, we investigate two main problems, including MI-SF phase transition and magnetic phase separations in MI phase, with extended standard basis operator (SBO) method. For both ferromagnetic (U2 0) systems, we analytically figure out the symmetry properties in Mott-insulator and superfluid phases, which would provide a deeper insight into the MI-SF phase transition process. Then by applying self-consistent approach to the method, we include the effect of quantum and thermal fluctuations and derive the MI-SF transition phase diagram, which is in quantitative agreement with recent Monte-Carlo simulation at zero temperature, and at finite temperature, we find the underestimation of finite-temperature-effect in the mean-field approximation method. If we further consider the spin excitations in the insulating states of spin-1 system in external field, distinct spin phases are expected. Therefore, in the Mott lobes with n = 1 and n = 2 atoms per site, we give analytical and numerical boundaries of the singlet, nematic, partially magnetic and ferromagnetic phases in the magnetic phase diagrams.

Topological Field Theory of Time-Reversal Invariant Insulators

Energy Technology Data Exchange (ETDEWEB)

Qi, Xiao-Liang; Hughes, Taylor; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

2010-03-19

We show that the fundamental time reversal invariant (TRI) insulator exists in 4 + 1 dimensions, where the effective field theory is described by the 4 + 1 dimensional Chern-Simons theory and the topological properties of the electronic structure is classified by the second Chern number. These topological properties are the natural generalizations of the time reversal breaking (TRB) quantum Hall insulator in 2 + 1 dimensions. The TRI quantum spin Hall insulator in 2 + 1 dimensions and the topological insulator in 3 + 1 dimension can be obtained as descendants from the fundamental TRI insulator in 4 + 1 dimensions through a dimensional reduction procedure. The effective topological field theory, and the Z{sub 2} topological classification for the TRI insulators in 2+1 and 3+1 dimensions are naturally obtained from this procedure. All physically measurable topological response functions of the TRI insulators are completely described by the effective topological field theory. Our effective topological field theory predicts a number of novel and measurable phenomena, the most striking of which is the topological magneto-electric effect, where an electric field generates a magnetic field in the same direction, with an universal constant of proportionality quantized in odd multiples of the fine structure constant {alpha} = e{sup 2}/hc. Finally, we present a general classification of all topological insulators in various dimensions, and describe them in terms of a unified topological Chern-Simons field theory in phase space.

Ambipolar field effect in the ternary topological insulator (BixSb1–x)2Te3 by composition tuning

KAUST Repository

Kong, Desheng

2011-10-02

Topological insulators exhibit a bulk energy gap and spin-polarized surface states that lead to unique electronic properties 1-9, with potential applications in spintronics and quantum information processing. However, transport measurements have typically been dominated by residual bulk charge carriers originating from crystal defects or environmental doping 10-12, and these mask the contribution of surface carriers to charge transport in these materials. Controlling bulk carriers in current topological insulator materials, such as the binary sesquichalcogenides Bi 2Te 3, Sb 2Te 3 and Bi 2Se 3, has been explored extensively by means of material doping 8,9,11 and electrical gating 13-16, but limited progress has been made to achieve nanostructures with low bulk conductivity for electronic device applications. Here we demonstrate that the ternary sesquichalcogenide (Bi xSb 1-x) 2Te 3 is a tunable topological insulator system. By tuning the ratio of bismuth to antimony, we are able to reduce the bulk carrier density by over two orders of magnitude, while maintaining the topological insulator properties. As a result, we observe a clear ambipolar gating effect in (Bi xSb 1-x) 2Te 3 nanoplate field-effect transistor devices, similar to that observed in graphene field-effect transistor devices 17. The manipulation of carrier type and density in topological insulator nanostructures demonstrated here paves the way for the implementation of topological insulators in nanoelectronics and spintronics. © 2011 Macmillan Publishers Limited. All rights reserved.

Critical behavior near the Mott transition in the half-filled asymmetric Hubbard model

Energy Technology Data Exchange (ETDEWEB)

Hoang, Anh-Tuan, E-mail: hatuan@iop.vast.ac.vn [Institute of Physics, Vietnam Academy of Science and Technology, Hanoi (Viet Nam); Le, Duc-Anh [Faculty of Physics, Hanoi National University of Education, Xuan Thuy 136, Cau Giay, Hanoi 10000 (Viet Nam)

2016-03-15

We study the half-filled asymmetric Hubbard model within the two-site dynamical mean field theory. At zero temperature, explicit expressions of the critical interaction U{sub c} for the Mott transition and the local self-energy are analytically derived. Critical behavior of the quasiparticle weights and the double occupancy are obtained analytically as functions of the on-site interaction U and the hopping asymmetry r. Our results are in good agreement with the ones obtained by much more sophisticated theory.

Dynamical mean-field theory and path integral renormalisation group calculations of strongly correlated electronic states

Energy Technology Data Exchange (ETDEWEB)

Heilmann, D.B.

2007-02-15

The two-plane HUBBARD model, which is a model for some electronic properties of undoped YBCO superconductors as well as displays a MOTT metal-to-insulator transition and a metal-to-band insulator transition, is studied within Dynamical Mean-Field Theory using HIRSCH-FYE Monte Carlo. In order to find the different transitions and distinguish the types of insulator, we calculate the single-particle spectral densities, the self-energies and the optical conductivities. We conclude that there is a continuous transition from MOTT to band insulator. In the second part, ground state properties of a diagonally disordered HUBBARD model is studied using a generalisation of Path Integral Renormalisation Group, a variational method which can also determine low-lying excitations. In particular, the distribution of antiferromagnetic properties is investigated. We conclude that antiferromagnetism breaks down in a percolation-type transition at a critical disorder, which is not changed appreciably by the inclusion of correlation effects, when compared to earlier studies. Electronic and excitation properties at the system sizes considered turn out to primarily depend on the geometry. (orig.)

Dynamical mean-field theory and path integral renormalisation group calculations of strongly correlated electronic states

International Nuclear Information System (INIS)

Heilmann, D.B.

2007-02-01

The two-plane HUBBARD model, which is a model for some electronic properties of undoped YBCO superconductors as well as displays a MOTT metal-to-insulator transition and a metal-to-band insulator transition, is studied within Dynamical Mean-Field Theory using HIRSCH-FYE Monte Carlo. In order to find the different transitions and distinguish the types of insulator, we calculate the single-particle spectral densities, the self-energies and the optical conductivities. We conclude that there is a continuous transition from MOTT to band insulator. In the second part, ground state properties of a diagonally disordered HUBBARD model is studied using a generalisation of Path Integral Renormalisation Group, a variational method which can also determine low-lying excitations. In particular, the distribution of antiferromagnetic properties is investigated. We conclude that antiferromagnetism breaks down in a percolation-type transition at a critical disorder, which is not changed appreciably by the inclusion of correlation effects, when compared to earlier studies. Electronic and excitation properties at the system sizes considered turn out to primarily depend on the geometry. (orig.)

Artificial heart system thermal insulation component development

International Nuclear Information System (INIS)

Svedberg, R.C.; Buckman, R.W. Jr.

1975-01-01

A concentric cup vacuum multifoil insulation system has been selected by virtue of its size, weight, and thermal performance to insulate the hot radioisotope portion of the thermal converter of an artificial implantable heart system. A factor of 2 improvement in thermal performance, based on the heat loss per number of foil layers (minimum system weight and volume) has been realized over conventional spiral wrapped multifoil vacuum insulation. This improvement is the result of the concentric cup construction to maintain a uniform interfoil spacing and the elimination of corner heat losses. Based on external insulation system dimensions (surface area in contact with host body), heat losses of 0.019 W/ cm 2 at 1140 0 K (1600 0 F) and 0.006 W/cm 2 at 920 0 K (1200 0 F) have been achieved. Factors which influence thermal performance of the nickel foil concentric cup insulation system include the number of cups, configuration and method of application of zirconia (ZrO 2 ) spacer material, system pressure, emittance of the cups, and operating temperature

Magnetic Excitations across the Metal-Insulator Transition in the Pyrochlore Iridate Eu2Ir2O7

Science.gov (United States)

Chun, Sae Hwan; Yuan, Bo; Casa, Diego; Kim, Jungho; Kim, Chang-Yong; Tian, Zhaoming; Qiu, Yang; Nakatsuji, Satoru; Kim, Young-June

2018-04-01

We report a resonant inelastic x-ray scattering study of the magnetic excitation spectrum in a highly insulating Eu2 Ir2 O7 single crystal that exhibits a metal-insulator transition at TMI=111 (7 ) K . A propagating magnon mode with a 20 meV bandwidth and a 28 meV magnon gap is found in the excitation spectrum at 7 K, which is expected in the all-in-all-out magnetically ordered state. This magnetic excitation exhibits substantial softening as the temperature is raised towards TMI and turns into a highly damped excitation in the paramagnetic phase. Remarkably, the softening occurs throughout the whole Brillouin zone including the zone boundary. This observation is inconsistent with the magnon renormalization expected in a local moment system and indicates that the strength of the electron correlation in Eu2 Ir2 O7 is only moderate, so that electron itinerancy should be taken into account in describing its magnetism.

Thermal insulation

International Nuclear Information System (INIS)

Aspden, G.J.; Howard, R.S.

1988-01-01

The patent concerns high temperature thermal insulation of large vessels, such as the primary vessel of a liquid metal cooled nuclear reactor. The thermal insulation consists of multilayered thermal insulation modules, and each module comprises a number of metal sheet layers sandwiched between a back and front plate. The layers are linked together by straps and clips to control the thickness of the module. (U.K.)

Exotic topological insulator states and topological phase transitions in Sb2Se3-Bi2Se3 heterostructures

KAUST Repository

Zhang, Qianfan; Zhang, Zhiyong; Zhu, Zhiyong; Schwingenschlö gl, Udo; Cui, Yi

2012-01-01

in controlling the electronic properties of semiconductor devices, are interesting for topological insulators. Here, we studied the spatial distribution of the topological state in Sb 2Se 3-Bi 2Se 3 heterostructures by first-principle simulation and discovered

Tetradymites as thermoelectrics and topological insulators

Science.gov (United States)

Heremans, Joseph P.; Cava, Robert J.; Samarth, Nitin

2017-10-01

Tetradymites are M2X3 compounds — in which M is a group V metal, usually Bi or Sb, and X is a group VI anion, Te, Se or S — that crystallize in a rhombohedral structure. Bi2Se3, Bi2Te3 and Sb2Te3 are archetypical tetradymites. Other mixtures of M and X elements produce common variants, such as Bi2Te2Se. Because tetradymites are based on heavy p-block elements, strong spin-orbit coupling greatly influences their electronic properties, both on the surface and in the bulk. Their surface electronic states are a cornerstone of frontier work on topological insulators. The bulk energy bands are characterized by small energy gaps, high group velocities, small effective masses and band inversion near the centre of the Brillouin zone. These properties are favourable for high-efficiency thermoelectric materials but make it difficult to obtain an electrically insulating bulk, which is a requirement of topological insulators. This Review outlines recent progress made in bulk and thin-film tetradymite materials for the optimization of their properties both as thermoelectrics and as topological insulators.

Spin-orbit torque-driven magnetization switching in 2D-topological insulator heterostructure

Science.gov (United States)

Soleimani, Maryam; Jalili, Seifollah; Mahfouzi, Farzad; Kioussis, Nicholas

2017-02-01

Charge pumping and spin-orbit torque (SOT) are two reciprocal phenomena widely studied in ferromagnet (FM)/topological insulator (TI) heterostructures. However, the SOT and its corresponding switching phase diagram for a FM island in proximity to a two-dimensional topological insulator (2DTI) has not been explored yet. We have addressed these features, using the recently developed adiabatic expansion of time-dependent nonequilibrium Green's function (NEGF) in the presence of both precessing magnetization and bias voltage. We have calculated the angular and spatial dependence of different components of the SOT on the FM island. We determined the switching phase diagram of the FM for different orientations of the easy axis. The results can be used as a guideline for the future experiments on such systems.

Doped Sc2C(OH)2 MXene: new type s-pd band inversion topological insulator.

Science.gov (United States)

Balcı, Erdem; Akkuş, Ünal Özden; Berber, Savas

2018-04-18

The electronic structures of Si and Ge substitutionally doped Sc 2 C(OH) 2 MXene monolayers are investigated in density functional theory. The doped systems exhibit band inversion, and are found to be topological invariants in Z 2 theory. The inclusion of spin orbit coupling results in band gap openings. Our results point out that the Si and Ge doped Sc 2 C(OH) 2 MXene monolayers are topological insulators. The band inversion is observed to have a new mechanism that involves s and pd states.

Doped Sc2C(OH)2 MXene: new type s-pd band inversion topological insulator

Science.gov (United States)

Balcı, Erdem; Özden Akkuş, Ünal; Berber, Savas

2018-04-01

The electronic structures of Si and Ge substitutionally doped Sc2C(OH)2 MXene monolayers are investigated in density functional theory. The doped systems exhibit band inversion, and are found to be topological invariants in Z 2 theory. The inclusion of spin orbit coupling results in band gap openings. Our results point out that the Si and Ge doped Sc2C(OH)2 MXene monolayers are topological insulators. The band inversion is observed to have a new mechanism that involves s and pd states.

Infrared circular photogalvanic effect in topological insulators

Science.gov (United States)

Luo, Siyuan

2018-04-01

Topological insulators have attracted a lot of attention in recent years due to its unique phenomena. Circular photogalvanic effect (CPGE) is one of the important phenomena in topological insulators. Bi2Se3, as one of the 3D topological insulators, consist of a single Dirac cone at the Γ point in k-space [1], corresponding to the surface states. Controlled by the Berry curvature of the surface band, the dominant photo response due to the interband transition is helicity dependent [2]. In addition, due to the spin-momentum locking in topological insulators' surface, the sign of spin-angular-momentum of obliquely incident light and photo currents are locked together. On the other hand, Bi2Se3 consists of quintuple layers which make it possible to be exfoliated and transferred based on graphene fabrication. In this paper, Bi2Se3 devices were fabricated and Ohm contact was achieved. We experimentally demonstrated the CPGE in Bi2Se3 using 1550nm incident laser.

Disentangled Cooperative Orderings in Artificial Rare-Earth Nickelates

Science.gov (United States)

Middey, S.; Meyers, D.; Kareev, M.; Cao, Yanwei; Liu, X.; Shafer, P.; Freeland, J. W.; Kim, J.-W.; Ryan, P. J.; Chakhalian, J.

2018-04-01

Coupled transitions between distinct ordered phases are important aspects behind the rich phase complexity of correlated oxides that hinder our understanding of the underlying phenomena. For this reason, fundamental control over complex transitions has become a leading motivation of the designer approach to materials. We have devised a series of new superlattices by combining a Mott insulator and a correlated metal to form ultrashort period superlattices, which allow one to disentangle the simultaneous orderings in RENiO3 . Tailoring an incommensurate heterostructure period relative to the bulk charge ordering pattern suppresses the charge order transition while preserving metal-insulator and antiferromagnetic transitions. Such selective decoupling of the entangled phases resolves the long-standing puzzle about the driving force behind the metal-insulator transition and points to the site-selective Mott transition as the operative mechanism. This designer approach emphasizes the potential of heterointerfaces for selective control of simultaneous transitions in complex materials with entwined broken symmetries.

Signatures of charge inhomogeneities in the infrared spectra of topological insulators Bi2Se3, Bi2Te3 and Sb2Te3

International Nuclear Information System (INIS)

Dordevic, S V; Wolf, M S; Stojilovic, N; Lei Hechang; Petrovic, C

2013-01-01

We present the results of an infrared spectroscopy study of topological insulators Bi 2 Se 3 , Bi 2 Te 3 and Sb 2 Te 3 . Reflectance spectra of all three materials look similar, with a well defined plasma edge. However, there are some important differences. Most notably, as temperature decreases the plasma edge shifts to lower frequencies in Bi 2 Se 3 , whereas in Bi 2 Te 3 and Sb 2 Te 3 it shifts to higher frequencies. In the loss function spectra we identify asymmetric broadening of the plasmon, and assign it to the presence of charge inhomogeneities. It remains to be seen if charge inhomogeneities are characteristic of all topological insulators, and whether they are of intrinsic or extrinsic nature.

Plasma Deposited SiO2 for Planar Self-Aligned Gate Metal-Insulator-Semiconductor Field Effect Transistors on Semi-Insulating InP

Science.gov (United States)

Tabory, Charles N.; Young, Paul G.; Smith, Edwyn D.; Alterovitz, Samuel A.

1994-01-01

Metal-insulator-semiconductor (MIS) field effect transistors were fabricated on InP substrates using a planar self-aligned gate process. A 700-1000 A gate insulator of Si02 doped with phosphorus was deposited by a direct plasma enhanced chemical vapor deposition at 400 mTorr, 275 C, 5 W, and power density of 8.5 MW/sq cm. High frequency capacitance-voltage measurements were taken on MIS capacitors which have been subjected to a 700 C anneal and an interface state density of lxl0(exp 11)/eV/cq cm was found. Current-voltage measurements of the capacitors show a breakdown voltage of 107 V/cm and a insulator resistivity of 10(exp 14) omega cm. Transistors were fabricated on semi-insulating InP using a standard planar self-aligned gate process in which the gate insulator was subjected to an ion implantation activation anneal of 700 C. MIS field effect transistors gave a maximum extrinsic transconductance of 23 mS/mm for a gate length of 3 microns. The drain current drift saturated at 87.5% of the initial current, while reaching to within 1% of the saturated value after only 1x10(exp 3). This is the first reported viable planar InP self-aligned gate transistor process reported to date.

Mott transition in the Hubbard model

International Nuclear Information System (INIS)

Shastry, B.S.

1992-01-01

In this article, the author discuss W. Kohn's criterion for a metal insulator transition, within the framework of a one-band Hubbard model. This and related ideas are applied to 1-dimensional Hubbard systems, and some interesting miscellaneous results discussed. The Jordan-Wigner transformation converting the two species of fermions to two species of hardcore bosons is performed in detail, and the extra phases arising from odd-even effects are explicitly derived. Bosons are shown to prefer zero flux (i.e., diamagnetism) and the corresponding happy fluxes: for the fermions identified. A curios result following from the interplay between orbital diamagnetism and spin polarization is highlighted. A spin-statistics like theorem, showing that the anticommutation relations between fermions of opposite spin are crucial to obtain the SU(2) invariance is pointed out

Corrosion of mineral insulated (MI) cables at MAPS-2

International Nuclear Information System (INIS)

Bora, J.S.; Babar, A.K.

1989-01-01

It has been experimentally verified that the cause of undesirable behaviour of mineral insulated (MI) cables at Madras Atomic Power Station Unit 2 (MAPS-2) is due to corrosion of termination. It is always possible to restore them to their normal condition by heating if degradation is due to absorption of moisture and by cutting and removing the affected portion in case of short or open failures. During extended shutdown, it is advisable to check other MI terminations and take appropriate corrective action in order to prevent failures in future. During installation MI Cables are to be heated before sealing and should never be heated after sealing. (author)

Acoustic study of YBa sub 2 Cu sub 3 O sub x thin films

Energy Technology Data Exchange (ETDEWEB)

Lee, S.; Chi, C.; Koren, G.; Gupta, A. (IBM Research Division, Thomas J. Watson Research Center, P. O. Box 218, Yorktown Heights, New York 10598 (US))

1991-03-01

The attenuation of surface acoustic waves by epitaxial YBa{sub 2}Cu{sub 3}O{sub {ital x}} films has been studied for {ital x}{congruent}6 to 7. For fully oxygenated samples, the acoustic attenuation as a function of temperature shows two broad peaks at about 135 and 240 K, and decreases monotonically below the lower peak temperature. The cause of attenuation peaks is attributed to scattering by optical phonons. Our data do not show any gap structure at {ital T}{sub {ital c}} due to relatively weak electron-phonon interactions at the acoustic frequencies. As the oxygen deficiency increases, the temperature dependence of the dc resistance changes from metallic to semiconducting and finally to insulating behavior. Acoustic attenuation data correspondingly show a drastic change due to different attenuation mechanisms: from the phonon scattering loss in the metallic regime to the electric-field coupling loss in the semiconducting and insulating regimes. In the latter regimes, the temperature dependence of low-frequency resistance calculated from the attenuation data can be fitted to a three-dimensional Mott variable-range-hopping model.

Thermal insulating panel

Energy Technology Data Exchange (ETDEWEB)

Hughes, J.T.

1985-09-11

A panel of thermal insulation material has at least one main portion which comprises a dry particulate insulation material compressed within a porous envelope so that it is rigid or substantially rigid and at least one auxiliary portion which is secured to and extends along at least one of the edges of the main portions. The auxiliary portions comprise a substantially uncompressed dry particulate insulation material contained within an envelope. The insulation material of the auxiliary portion may be the same as or may be different from the insulation material of the main portion. The envelope of the auxiliary portion may be made of a porous or a non-porous material. (author).

Impact of Moistened Bio-insulation on Whole Building Energy Use

Directory of Open Access Journals (Sweden)

Latif Eshrar

2017-01-01

Full Text Available One of the key properties of hemp insulation is its moisture adsorption capacity. Adsorption of moisture can increase both thermal conductivity and heat capacity of the insulation. The current study focuses on the effect of moisture induced thermal mass of installed hemp insulation on the whole building energy use. Hygrothermal and thermal simulations were performed using the CIBSE TRY weather data of Edinburgh and Birmingham with the aid of following simulation tools: WUFI and IES. Following simplified building types were considered: building-1 with dry hemp wall and loft insulations, building-2 with moistened hemp wall and loft insulation and building-3 with stone wool insulation. It was observed that the overall conditioning load of building-1 was 1.2 to 2.3% higher than building-2 and 3. However, during the summer season, the cooling load of building-2 was 3-7.5% lower than the other buildings. It implies that, moistened insulation can potentially mitigate the effect of increasing cooling degree days induced by global warming.

Positron Annihilation in Insulating Materials

International Nuclear Information System (INIS)

Asoka-Kumar, P; Sterne, PA

2002-01-01

We describe positron results from a wide range of insulating materials. We have completed positron experiments on a range of zeolite-y samples, KDP crystals, alkali halides and laser damaged SiO 2 . Present theoretical understanding of positron behavior in insulators is incomplete and our combined theoretical and experimental approach is aimed at developing a predictive understanding of positrons and positronium annihilation characteristics in insulators. Results from alkali halides and alkaline-earth halides show that positrons annihilate with only the halide ions, with no apparent contribution from the alkali or alkaline-earth cations. This contradicts the results of our existing theory for metals, which predicts roughly equal annihilation contributions from cation and anion. We also present result obtained using Munich positron microprobe on laser damaged SiO 2 samples

Ultrafast Doublon Dynamics in Photoexcited 1 T -TaS2

Science.gov (United States)

Ligges, M.; Avigo, I.; Golež, D.; Strand, H. U. R.; Beyazit, Y.; Hanff, K.; Diekmann, F.; Stojchevska, L.; Kalläne, M.; Zhou, P.; Rossnagel, K.; Eckstein, M.; Werner, P.; Bovensiepen, U.

2018-04-01

Strongly correlated materials exhibit intriguing properties caused by intertwined microscopic interactions that are hard to disentangle in equilibrium. Employing nonequilibrium time-resolved photoemission spectroscopy on the quasi-two-dimensional transition-metal dichalcogenide 1 T -Ta S2 , we identify a spectroscopic signature of doubly occupied sites (doublons) that reflects fundamental Mott physics. Doublon-hole recombination is estimated to occur on timescales of electronic hopping ℏ/J ≈14 fs . Despite strong electron-phonon coupling, the dynamics can be explained by purely electronic effects captured by the single-band Hubbard model under the assumption of weak hole doping, in agreement with our static sample characterization. This sensitive interplay of static doping and vicinity to the metal-insulator transition suggests a way to modify doublon relaxation on the few-femtosecond timescale.

Wall insulation system

Energy Technology Data Exchange (ETDEWEB)

Kostek, P.T.

1987-08-11

In a channel specially designed to fasten semi-rigid mineral fibre insulation to masonry walls, it is known to be constructed from 20 gauge galvanized steel or other suitable material. The channel is designed to have pre-punched holes along its length for fastening of the channel to the drywall screw. The unique feature of the channel is the teeth running along its length which are pressed into the surface of the butted together sections of the insulation providing a strong grip between the two adjacent pieces of insulation. Of prime importance to the success of this system is the recent technological advancements of the mineral fibre itself which allow the teeth of the channel to engage the insulation fully and hold without mechanical support, rather than be repelled or pushed back by the inherent nature of the insulation material. After the insulation is secured to the masonry wall by concrete nail fastening systems, the drywall is screwed to the channel.

Mapping the electron correlation onto a model Hamiltonian for Cs/GaAs(110): a Mott-Hubbard insulator at quarter filling

CERN Document Server

Chen Chang Feng

1998-01-01

We have constructed an effective model Hamiltonian in the Hubbard formalism for the Cs/GaAs(110) surface at quarter-monolayer coverage with all of the parameters extracted from constrained local-density-approximation (LDA) pseudopotential calculations. The single-particle excitation spectrum of the model has been calculated using an exact-diagonalization technique to help determine the relevant interaction terms. It is shown that the intersite interaction between the nearest-neighbour Ga sites plays the key role in determining the insulating nature of the system and must be included in the model, in contrast to suggestions of some previous work. Our results show that a reliable mapping of LDA results onto an effective model Hamiltonian can be achieved by combining constrained LDA calculations for the Hamiltonian parameters and many-body calculations of the single-particle excitation spectrum for identifying relevant interaction terms. (author)

Improvement of Surface Flashover Performance of Al2O3 Ceramics in Vacuum by Adopting A-B-A Insulation System

International Nuclear Information System (INIS)

Li Shengtao; Zhang Tuo; Huang Qifeng; Li Weiwei; Ni Fengyan; Li Jianying

2011-01-01

A new insulation system with inorganic A-B-A insulators was proposed to improve the surface flashover performance in vacuum. Inorganic A-B-A insulator samples of Mo/Al 2 O 3 cermet-Al 2 O 3 ceramic-Mo/Al 2 O 3 cermet were prepared, in which the conductivity and permittivity of the Mo/Al 2 O 3 cermets were controlled through different amount of metallic molybdenum powder added. The effects of both conductivity and permittivity of Mo/Al 2 O 3 cermets on the DC and impulse surface flashover voltage in vacuum were experimentally investigated. The result showed that the DC and impulse surface flashover voltage were improved by 52% and 95%, respectively. For the distribution of electric field, two triple junctions, i.e., vacuum-layer A-cathode (TJ1) and vacuum-layer A-layer B (TJ2) were prepared with the introduction of layer A into the A-B-A insulation system. Based on the electric field distribution obtained via electrostatic field simulation and Maxwell-Wagner three-layer model, the electric field of TJ1 decreases while that of TJ2 increases with the increase in conductivity and permittivity of layer A under applied DC and impulse voltage, respectively. Therefore, the improvement of surface flashover performance of A-B-A insulators has been reasonably explained. (fusion engineering)

HgTe based topological insulators

International Nuclear Information System (INIS)

Bruene, Christoph

2014-01-01

This PhD thesis summarizes the discovery of topological insulators and highlights the developments on their experimental observations. The work focuses on HgTe. The thesis is structured as follows: - The first chapter of this thesis will give a brief overview on discoveries in the field of topological insulators. It focuses on works relevant to experimental results presented in the following chapters. This includes a short outline of the early predictions and a summary of important results concerning 2-dimensional topological insulators while the final section discusses observations concerning 3-dimensional topological insulators. - The discovery of the quantum spin Hall effect in HgTe marked the first experimental observation of a topological insulator. Chapter 2 focuses on HgTe quantum wells and the quantum spin Hall effect. The growth of high quality HgTe quantum wells was one of the major goals for this work. In a final set of experiments the spin polarization of the edge channels was investigated. Here, we could make use of the advantage that HgTe quantum well structures exhibit a large Rashba spin orbit splitting. - HgTe as a 3-dimensional topological insulator is presented in chapter 3. - Chapters 4-6 serve as in depth overviews of selected works: Chapter 4 presents a detailed overview on the all electrical detection of the spin Hall effect in HgTe quantum wells. The detection of the spin polarization of the quantum spin Hall effect is shown in chapter 5 and chapter 6 gives a detailed overview on the quantum Hall effect originating from the topological surface state in strained bulk HgTe.

Effect of oxygen vacancies on magnetic and transport properties of Sr2IrO4

Science.gov (United States)

Dwivedi, Vinod Kumar; Mukhopadhyay, Soumik

2018-05-01

Iridates have recently attracted growing interest because of their potential for realizing various interesting phases like interaction driven Mott-type insulator and magnetically driven Slater-type. In this paper, we present the magnetic and electrical transport properties of polycrystalline Sr2IrO4 synthesized by solid state reaction route. We find a ferromagnetic transition at 240 K. The Curie-Weiss law behavior hold good above the magnetic transition temperature TMag = 240 K with a small effective paramagnetic magnetic moment μeff = 0.25 µB/f.u. and a Curie-Weiss temperature, θCW = +100 K. Zero field cooled (ZFC) magnetization shows a gradual dcrease below 150 K, while same for field cooled (FC) below 50 K. Interestingly, below temperatures, ⁓ 10 K, a sharp increase in ZFC and FC magnetization can be seen. A temperature dependent resistivity reveals insulating behavior followed by power law mechanism. The sintering of sample in air leads to the very low value of resistivity is likely related to Sr or oxygen vacancies.

Oxygen stoichiometry of LaTiO{sub 3} thin films studied by in-situ photoemission

Energy Technology Data Exchange (ETDEWEB)

Scheiderer, Philipp; Goessmann, Alex; Sing, Michael; Claessen, Ralph [Universitaet Wuerzburg, Physikalisches Institut and Roentgen Center for Complex Material Systems (RCCM), 97074 Wuerzburg (Germany)

2015-07-01

As in the famous oxide heterostructure LaAlO{sub 3}/SrTiO{sub 3} (LAO/STO) a two dimensional electron system is found at the interface between the strongly correlated Mott insulator LaTi{sup 3+}O{sub 3} and the band insulator STO. The stabilization of LaTi{sup 3+}O{sub 3} requires strong reducing growth conditions since the thermodynamically stable bulk phase is the oxygen rich La{sub 2}Ti{sup 4+}{sub 2}O{sub 7}. Therefore, we have systematically studied the impact of the oxygen background atmosphere on LaTi{sup 3+}O{sub 3} thin film growth by PLD. Reflection high-energy diffraction intensity oscillations of the specular spot indicate a layer by layer growth mode for thin films, which merges into the formation of islands for thicker films. In-situ photoemission measurements enables us to determine the oxidation state of Ti indicating excess or lack of oxygen present in the prepared samples. Our experiments show that even for films grown in vacuum, strong oxygen excess is present probably due to oxygen out-diffusion from the STO substrate. We find that an LAO buffer layer serves as an effective barrier for this process. The spectral weight of the lower Hubbard band, being a characteristic feature for the Mott insulating phase, is found to scale inversely with the amount of excess oxygen.

Physics Colloquium: Theory of the spin wave Seebeck effect in magnetic insulators

CERN Multimedia

Université de Genève

2011-01-01

Geneva University Physics Department 24, quai Ernest-Ansermet CH-1211 Geneva 4 Lundi 28 février 2011 17h00 - École de Physique, Auditoire Stückelberg Theory of the spin wave Seebeck effect in magnetic insulators Prof. Gerrit Bauer Delft University of Technology The subfield of spin caloritronics addresses the coupling of heat, charge and spin currents in nanostructures. In the center of interest is here the spin Seebeck effect, which was discovered in an iron-nickel alloy. Uchida et al. recently observed the effect also in an electrically insulating Yttrium Iron Garnett (YIG) thin magnetic film. To our knowledge this is the first observation of a Seebeck effect generated by an insulator, implying that the physics is fundamentally different from the conventional Seebeck effect in metals. We explain the experiments by the pumping of a spin current into the detecting contacts by the thermally excited magnetization dynamics. In this talk I will give a brief overview over the state o...

Effects of reductive annealing on insulating polycrystalline thin films of Nb-doped anatase TiO2: recovery of high conductivity

International Nuclear Information System (INIS)

Nakao, Shoichiro; Hirose, Yasushi; Hasegawa, Tetsuya

2016-01-01

We studied the effects of reductive annealing on insulating polycrystalline thin films of anatase Nb-doped TiO 2 (TNO). The insulating TNO films were intentionally fabricated by annealing conductive TNO films in oxygen ambient at 400 °C. Reduced free carrier absorption in the insulating TNO films indicated carrier compensation due to excess oxygen. With H 2 -annealing, both carrier density and Hall mobility recovered to the level of conducting TNO, demonstrating that the excess oxygen can be efficiently removed by the annealing process without introducing additional scattering centers. (paper)

Reduction of heat insulation upon soaking of the insulation layer

Science.gov (United States)

Achtliger, J.

1983-09-01

Improved thermal protection of hollow masonry by introduction of a core insulation between the inner and outer shell is discussed. The thermal conductivity of insulation materials was determined in dry state and after soaking by water with different volume-related moisture contents. The interpolated thermal conductivity values from three measured values at 10 C average temperature are presented as a function of the pertinent moisture content. Fills of expanded polystyrene, perlite and granulated mineral fibers, insulating boards made of mineral fibers and in situ cellular plastics produced from urea-formaldehyde resin were investigated. Test results show a confirmation of thermal conductivity values for insulating materials in hollow masonry.

Probing correlated quantum many-body systems at the single-particle level

Energy Technology Data Exchange (ETDEWEB)

Endres, Manuel

2013-02-27

The detection of correlation and response functions plays a crucial role in the experimental characterization of quantum many-body systems. In this thesis, we present novel techniques for the measurement of such functions at the single-particle level. Specifically, we show the single-atom- and single-site-resolved detection of an ultracold quantum gas in an optical lattice. The quantum gas is described by the Bose-Hubbard model, which features a zero temperature phase transition from a superfluid to a Mott-insulating state, a paradigm example of a quantum phase transition. We used the aforementioned detection techniques to study correlation and response properties across the superfluid-Mott-insulator transition. The single-atom sensitivity of our method is achieved by fluorescence detection of individual atoms with a high signal-to-noise ratio. A high-resolution objective collects the fluorescence light and yields in situ 'snapshots' of the quantum gas that allow for a single-site-resolved reconstruction of the atomic distribution. This allowed us to measure two-site and non-local correlation-functions across the superfluid-Mott-insulator transition. Non-local correlation functions are based on the information of an extended region of the system and play an important role for the characterization of low-dimensional quantum phases. While non-local correlation functions were so far only theoretical tools, our results show that they are actually experimentally accessible. Furthermore, we used a new thermometry scheme, based on the counting of individual thermal excitations, to measure the response of the system to lattice modulation. Using this method, we studied the excitation spectrum of the system across the two-dimensional superfluid-Mott-insulator transition. In particular, we detected a 'Higgs' amplitude mode in the strongly-interacting superfluid close to the transition point where the system is described by an effectively Lorentz

Probing correlated quantum many-body systems at the single-particle level

International Nuclear Information System (INIS)

Endres, Manuel

2013-01-01

The detection of correlation and response functions plays a crucial role in the experimental characterization of quantum many-body systems. In this thesis, we present novel techniques for the measurement of such functions at the single-particle level. Specifically, we show the single-atom- and single-site-resolved detection of an ultracold quantum gas in an optical lattice. The quantum gas is described by the Bose-Hubbard model, which features a zero temperature phase transition from a superfluid to a Mott-insulating state, a paradigm example of a quantum phase transition. We used the aforementioned detection techniques to study correlation and response properties across the superfluid-Mott-insulator transition. The single-atom sensitivity of our method is achieved by fluorescence detection of individual atoms with a high signal-to-noise ratio. A high-resolution objective collects the fluorescence light and yields in situ 'snapshots' of the quantum gas that allow for a single-site-resolved reconstruction of the atomic distribution. This allowed us to measure two-site and non-local correlation-functions across the superfluid-Mott-insulator transition. Non-local correlation functions are based on the information of an extended region of the system and play an important role for the characterization of low-dimensional quantum phases. While non-local correlation functions were so far only theoretical tools, our results show that they are actually experimentally accessible. Furthermore, we used a new thermometry scheme, based on the counting of individual thermal excitations, to measure the response of the system to lattice modulation. Using this method, we studied the excitation spectrum of the system across the two-dimensional superfluid-Mott-insulator transition. In particular, we detected a 'Higgs' amplitude mode in the strongly-interacting superfluid close to the transition point where the system is described by an effectively Lorentz-invariant low-energy theory

Many-body Anderson localization of strongly interacting bosons in random lattices

International Nuclear Information System (INIS)

Katzer, Roman

2015-05-01

In the present work, we investigate the problem of many-body localization of strongly interacting bosons in random lattices within the disordered Bose-Hubbard model. This involves treating both the local Mott-Hubbard physics as well as the non-local quantum interference processes, which give rise to the phenomenon of Anderson localization, within the same theory. In order to determine the interaction induced transition to the Mott insulator phase, it is necessary to treat the local particle interaction exactly. Therefore, here we use a mean-field approach that approximates only the kinetic term of the Hamiltonian. This way, the full problem of interacting bosons on a random lattice is reduced to a local problem of a single site coupled to a particle bath, which has to be solved self-consistently. In accordance to previous works, we find that a finite disorder width leads to a reduced size of the Mott insulating regions. The transition from the superfluid phase to the Bose glass phase is driven by the non-local effect of Anderson localization. In order to describe this transition, one needs to work within a theory that is non-local as well. Therefore, here we introduce a new approach to the problem. Based on the results for the local excitation spectrum obtained within the mean-field theory, we reduce the full, interacting model to an effective, non-interacting model by applying a truncation scheme to the Hilbert space. Evaluating the long-ranged current density within this approximation, we identify the transition from the Bose glass to the superfluid phase with the Anderson transition of the effective model. Resolving this transition using the self-consistent theory of localization, we obtain the full phase diagram of the disordered Bose-Hubbard model in the regime of strong interaction and larger disorder. In accordance to the theorem of inclusions, we find that the Mott insulator and the superfluid phase are always separated by the compressible, but insulating

Insulation systems for superconducting transmission cables

DEFF Research Database (Denmark)

Tønnesen, Ole

1996-01-01

the electrical insulation is placed outside both the superconducting tube and the cryostat. The superconducting tube is cooled by liquid nitrogen which is pumped through the hollow part of the tube.2) The cryogenic dielectric design, where the electrical insulation is placed inside the cryostat and thus is kept...

Ultrathin Topological Insulator Bi 2 Se 3 Nanoribbons Exfoliated by Atomic Force Microscopy

KAUST Repository

Hong, Seung Sae; Kundhikanjana, Worasom; Cha, Judy J.; Lai, Keji; Kong, Desheng; Meister, Stefan; Kelly, Michael A.; Shen, Zhi-Xun; Cui, Yi

2010-01-01

Ultrathin topological insulator nanostructures, in which coupling between top and bottom surface states takes place, are of great intellectual and practical importance. Due to the weak van der Waals interaction between adjacent quintuple layers (QLs), the layered bismuth selenide (Bi2Se 3), a single Dirac-cone topological insulator with a large bulk gap, can be exfoliated down to a few QLs. In this paper, we report the first controlled mechanical exfoliation of Bi2Se3 nanoribbons (>50 QLs) by an atomic force microscope (AFM) tip down to a single QL. Microwave impedance microscopy is employed to map out the local conductivity of such ultrathin nanoribbons, showing drastic difference in sheet resistance between 1-2 QLs and 4-5 QLs. Transport measurement carried out on an exfoliated (>5 QLs) Bi2Se3 device shows nonmetallic temperature dependence of resistance, in sharp contrast to the metallic behavior seen in thick (>50 QLs) ribbons. These AFM-exfoliated thin nanoribbons afford interesting candidates for studying the transition from quantum spin Hall surface to edge states. © 2010 American Chemical Society.

Ultrathin Topological Insulator Bi 2 Se 3 Nanoribbons Exfoliated by Atomic Force Microscopy

KAUST Repository

Hong, Seung Sae

2010-08-11

Ultrathin topological insulator nanostructures, in which coupling between top and bottom surface states takes place, are of great intellectual and practical importance. Due to the weak van der Waals interaction between adjacent quintuple layers (QLs), the layered bismuth selenide (Bi2Se 3), a single Dirac-cone topological insulator with a large bulk gap, can be exfoliated down to a few QLs. In this paper, we report the first controlled mechanical exfoliation of Bi2Se3 nanoribbons (>50 QLs) by an atomic force microscope (AFM) tip down to a single QL. Microwave impedance microscopy is employed to map out the local conductivity of such ultrathin nanoribbons, showing drastic difference in sheet resistance between 1-2 QLs and 4-5 QLs. Transport measurement carried out on an exfoliated (>5 QLs) Bi2Se3 device shows nonmetallic temperature dependence of resistance, in sharp contrast to the metallic behavior seen in thick (>50 QLs) ribbons. These AFM-exfoliated thin nanoribbons afford interesting candidates for studying the transition from quantum spin Hall surface to edge states. © 2010 American Chemical Society.

Raman Scattering from Higgs Mode Oscillations in the Two-Dimensional Antiferromagnet Ca_{2}RuO_{4}.

Science.gov (United States)

Souliou, Sofia-Michaela; Chaloupka, Jiří; Khaliullin, Giniyat; Ryu, Gihun; Jain, Anil; Kim, B J; Le Tacon, Matthieu; Keimer, Bernhard

2017-08-11

We present and analyze Raman spectra of the Mott insulator Ca_{2}RuO_{4}, whose quasi-two-dimensional antiferromagnetic order has been described as a condensate of low-lying spin-orbit excitons with angular momentum J_{eff}=1. In the A_{g} polarization geometry, the amplitude (Higgs) mode of the spin-orbit condensate is directly probed in the scalar channel, thus avoiding infrared-singular magnon contributions. In the B_{1g} geometry, we observe a single-magnon peak as well as two-magnon and two-Higgs excitations. Model calculations using exact diagonalization quantitatively agree with the observations. Together with recent neutron scattering data, our study provides strong evidence for excitonic magnetism in Ca_{2}RuO_{4} and points out new perspectives for research on the Higgs mode in two dimensions.

Recent Progress in Electrical Insulation Techniques for HTS Power Apparatus

Science.gov (United States)

Hayakawa, Naoki; Kojima, Hiroki; Hanai, Masahiro; Okubo, Hitoshi

This paper describes the electrical insulation techniques at cryogenic temperatures, i.e. Cryodielectrics, for HTS power apparatus, e.g. HTS power transmission cables, transformers, fault current limiters and SMES. Breakdown and partial discharge characteristics are discussed for different electrical insulation configurations of LN2, sub-cooled LN2, solid, vacuum and their composite insulation systems. Dynamic and static insulation performances with and without taking account of quench in HTS materials are also introduced.

Exotic topological insulator states and topological phase transitions in Sb2Se3-Bi2Se3 heterostructures

KAUST Repository

Zhang, Qianfan

2012-03-27

Topological insulator is a new state of matter attracting tremendous interest due to its gapless linear dispersion and spin momentum locking topological states located near the surface. Heterostructures, which have traditionally been powerful in controlling the electronic properties of semiconductor devices, are interesting for topological insulators. Here, we studied the spatial distribution of the topological state in Sb 2Se 3-Bi 2Se 3 heterostructures by first-principle simulation and discovered that an exotic topological state exists. Surprisingly, the state migrates from the nontrivial Bi 2Se 3 into the trivial Sb 2Se 3 region and spreads across the entire Sb 2Se 3 slab, extending beyond the concept of "surface" state while preserving all of the topological surface state characteristics. This unusual topological state arises from the coupling between different materials and the modification of electronic structure near Fermi energy. Our study demonstrates that heterostructures can open up opportunities for controlling the real-space distribution of the topological state and inducing quantum phase transitions between topologically trivial and nontrivial states. © 2012 American Chemical Society.

Ground-state and spectral properties of an asymmetric Hubbard ladder

Science.gov (United States)

Abdelwahab, Anas; Jeckelmann, Eric; Hohenadler, Martin

2015-04-01

We investigate a ladder system with two inequivalent legs, namely, a Hubbard chain and a one-dimensional electron gas. Analytical approximations, the density-matrix renormalization group method, and continuous-time quantum Monte Carlo simulations are used to determine ground-state properties, gaps, and spectral functions of this system at half-filling. Evidence for the existence of four different phases as a function of the Hubbard interaction and the rung hopping is presented. First, a Luttinger liquid exists at very weak interchain hopping. Second, a Kondo-Mott insulator with spin and charge gaps induced by an effective rung exchange coupling is found at moderate interchain hopping or strong Hubbard interaction. Third, a spin-gapped paramagnetic Mott insulator with incommensurate excitations and pairing of doped charges is observed at intermediate values of the rung hopping and the interaction. Fourth, the usual correlated band insulator is recovered for large rung hopping. We show that the wave numbers of the lowest single-particle excitations are different in each insulating phase. In particular, the three gapped phases exhibit markedly different spectral functions. We discuss the relevance of asymmetric two-leg ladder systems as models for atomic wires deposited on a substrate.

Propagation Characteristics of Multilayer Hybrid Insulator-Metal-Insulator and Metal-Insulator-Metal Plasmonic Waveguides

Directory of Open Access Journals (Sweden)

M. Talafi Noghani

2014-02-01

Full Text Available Propagation characteristics of symmetrical and asymmetrical multilayer hybrid insulator-metal-insulator (HIMI and metal-insulator-metal (HMIM plasmonic slab waveguides are investigated using the transfer matrix method. Propagation length (Lp and spatial length (Ls are used as two figures of merit to qualitate the plasmonic waveguides. Symmetrical structures are shown to be more performant (having higher Lp and lower Ls, nevertheless it is shown that usage of asymmetrical geometry could compensate for the performance degradation in practically realized HIMI waveguides with different substrate materials. It is found that HMIM slab waveguide could support almost long-range subdiffraction plasmonic modes at dimensions lower than the spatial length of the HIMI slab waveguide.

External Tank (ET) Foam Thermal/Structural Analysis Project

Science.gov (United States)

Moore, David F.; Ungar, Eugene K.; Chang, Li C.; Malroy, Eric T.; Stephan, Ryan A.

2008-01-01

An independent study was performed to assess the pre-launch thermally induced stresses in the Space Shuttle External Tank Bipod closeout and Ice/Frost ramps (IFRs). Finite element models with various levels of detail were built that included the three types of foam (BX-265, NCFI 24-124, and PDL 1034) and the underlying structure and bracketry. Temperature profiles generated by the thermal analyses were input to the structural models to calculate the stress levels. An area of high stress in the Bipod closeout was found along the aluminum tank wall near the phenolic insulator and along the phenolic insulator itself. This area of high stress might be prone to cracking and possible delamination. There is a small region of slightly increased stress in the NCFI 24-124 foam near its joint with the Bipod closeout BX-265 foam. The calculated stresses in the NCFI 24-124 acreage foam are highest at the NCFI 24-124/PDL 1034/tank wall interface under the LO2 and LH2 IFRs. The highest calculated stresses in the LH2 NCFI 24-124 foam are higher than in similar locations in the LO2 IFR. This finding is consistent with the dissection results of IFRs on ET-120.

Efficient production of long-lived ultracold Sr2 molecules

Science.gov (United States)

Ciamei, Alessio; Bayerle, Alex; Chen, Chun-Chia; Pasquiou, Benjamin; Schreck, Florian

2017-07-01

We associate Sr atom pairs on sites of a Mott insulator optically and coherently into weakly bound ground-state molecules, achieving an efficiency above 80%. This efficiency is 2.5 times higher than in our previous work [S. Stellmer, B. Pasquiou, R. Grimm, and F. Schreck, Phys. Rev. Lett. 109, 115302 (2012), 10.1103/PhysRevLett.109.115302] and obtained through two improvements. First, the lifetime of the molecules is increased beyond one minute by using an optical lattice wavelength that is further detuned from molecular transitions. Second, we compensate undesired dynamic light shifts that occur during the stimulated Raman adiabatic passage (STIRAP) used for molecule association. We also characterize and model STIRAP, providing insights into its limitations. Our work shows that significant molecule association efficiencies can be achieved even for atomic species or mixtures that lack Feshbach resonances suitable for magnetoassociation.

Direct evidence of spin frustration in the fcc antiferromagnet NiS sub 2

CERN Document Server

Matsuura, M; Endoh, Y; Hirota, K; Yamada, K

2002-01-01

NiS sub 2 is a well-known Mott insulator with anomalous antiferromagnetic long-range order of coexistent type I (Q sub M =(1,0,0), T sub N sub 1 =40 K) and type II (Q sub M =(1/2,1/2,1/2), T sub N sub 2 =30 K). Extensive neutron-scattering measurements reveal that magnetism in NiS sub 2 is governed by geometrical spin frustration, resulting in magnetic diffuse scattering extending along the fcc zone boundary. Although the diffuse scattering exists at temperatures as high as 250 K (6T sub N sub 1), it disappears rapidly below T sub N sub 2 , associated with minor crystal distortion. We observed a clear energy gap in addition to the low-energy spin-wave excitation at significantly below 30 K, and obtain evidence that degeneracy due to the coexistence of the two types of antiferromagnetism is relieved in the ground state via the reduction in symmetry due to distortion. (orig.)

Quantum Hall effect on top and bottom surface states of topological insulator (Bi1-xSbx)2Te3 films.

Science.gov (United States)

Yoshimi, R; Tsukazaki, A; Kozuka, Y; Falson, J; Takahashi, K S; Checkelsky, J G; Nagaosa, N; Kawasaki, M; Tokura, Y

2015-04-14

The three-dimensional topological insulator is a novel state of matter characterized by two-dimensional metallic Dirac states on its surface. To verify the topological nature of the surface states, Bi-based chalcogenides such as Bi2Se3, Bi2Te3, Sb2Te3 and their combined/mixed compounds have been intensively studied. Here, we report the realization of the quantum Hall effect on the surface Dirac states in (Bi1-xSbx)2Te3 films. With electrostatic gate-tuning of the Fermi level in the bulk band gap under magnetic fields, the quantum Hall states with filling factor ±1 are resolved. Furthermore, the appearance of a quantum Hall plateau at filling factor zero reflects a pseudo-spin Hall insulator state when the Fermi level is tuned in between the energy levels of the non-degenerate top and bottom surface Dirac points. The observation of the quantum Hall effect in three-dimensional topological insulator films may pave a way toward topological insulator-based electronics.

Passive Collecting of Solar Radiation Energy using Transparent Thermal Insulators, Energetic Efficiency of Transparent Thermal Insulators

Directory of Open Access Journals (Sweden)

Smajo Sulejmanovic

2014-11-01

Full Text Available This paper explains passive collection of solar radiation energy using transparent thermal insulators. Transparent thermal insulators are transparent for sunlight, at the same time those are very good thermal insulators. Transparent thermal insulators can be placed instead of standard conventional thermal insulators and additionally transparent insulators can capture solar radiation, transform it into heat and save heat just as standard insulators. Using transparent insulators would lead to reduce in usage of fossil fuels and would help protection of an environment and reduce effects of global warming, etc.

Self-Healing Wire Insulation

Science.gov (United States)

Parrish, Clyde F. (Inventor)

2012-01-01

A self-healing system for an insulation material initiates a self-repair process by rupturing a plurality of microcapsules disposed on the insulation material. When the plurality of microcapsules are ruptured, reactants within the plurality of microcapsules react to form a replacement polymer in a break of the insulation material. This self-healing system has the ability to repair multiple breaks in a length of insulation material without exhausting the repair properties of the material.

Ets2 in tumor fibroblasts promotes angiogenesis in breast cancer.

Directory of Open Access Journals (Sweden)

Julie A Wallace

Full Text Available Tumor fibroblasts are active partners in tumor progression, but the genes and pathways that mediate this collaboration are ill-defined. Previous work demonstrates that Ets2 function in stromal cells significantly contributes to breast tumor progression. Conditional mouse models were used to study the function of Ets2 in both mammary stromal fibroblasts and epithelial cells. Conditional inactivation of Ets2 in stromal fibroblasts in PyMT and ErbB2 driven tumors significantly reduced tumor growth, however deletion of Ets2 in epithelial cells in the PyMT model had no significant effect. Analysis of gene expression in fibroblasts revealed a tumor- and Ets2-dependent gene signature that was enriched in genes important for ECM remodeling, cell migration, and angiogenesis in both PyMT and ErbB2 driven-tumors. Consistent with these results, PyMT and ErbB2 tumors lacking Ets2 in fibroblasts had fewer functional blood vessels, and Ets2 in fibroblasts elicited changes in gene expression in tumor endothelial cells consistent with this phenotype. An in vivo angiogenesis assay revealed the ability of Ets2 in fibroblasts to promote blood vessel formation in the absence of tumor cells. Importantly, the Ets2-dependent gene expression signatures from both mouse models were able to distinguish human breast tumor stroma from normal stroma, and correlated with patient outcomes in two whole tumor breast cancer data sets. The data reveals a key function for Ets2 in tumor fibroblasts in signaling to endothelial cells to promote tumor angiogenesis. The results highlight the collaborative networks that orchestrate communication between stromal cells and tumor cells, and suggest that targeting tumor fibroblasts may be an effective strategy for developing novel anti-angiogenic therapies.

Improved design of a high-voltage vacuum-insulator interface

Directory of Open Access Journals (Sweden)

W. A. Stygar

2005-05-01

Full Text Available We have conducted a series of experiments designed to measure the flashover strength of various azimuthally symmetric 45° vacuum-insulator configurations. The principal objective of the experiments was to identify a configuration with a flashover strength greater than that of the standard design, which consists of a 45° polymethyl-methacrylate (PMMA insulator between flat electrodes. The thickness d and circumference C of the insulators tested were held constant at 4.318 and 95.74 cm, respectively. The peak voltage applied to the insulators ranged from 0.8 to 2.2 MV. The rise time of the voltage pulse was 40–60 ns; the effective pulse width [as defined in Phys. Rev. ST Accel. Beams 7, 070401 (2004PRABFM1098-440210.1103/PhysRevSTAB.7.070401] was on the order of 10 ns. Experiments conducted with flat aluminum electrodes demonstrate that the flashover strength of a crosslinked polystyrene (Rexolite insulator is (18±7% higher than that of PMMA. Experiments conducted with a Rexolite insulator and an anode plug, i.e., an extension of the anode into the insulator, demonstrate that a plug can increase the flashover strength by an additional (44±11%. The results are consistent with the Anderson model of anode-initiated flashover, and confirm previous measurements. It appears that a Rexolite insulator with an anode plug can, in principle, increase the peak electromagnetic power that can be transmitted across a vacuum interface by a factor of [(1.18(1.44]^{2}=2.9 over that which can be achieved with the standard design.

Ferromagnetic-insulators-modulated transport properties on the surface of a topological insulator

International Nuclear Information System (INIS)

Guo Jun-Ji; Liao Wen-Hu

2014-01-01

Transport properties on the surface of a topological insulator (TI) under the modulation of a two-dimensional (2D) ferromagnet/ferromagnet junction are investigated by the method of wave function matching. The single ferromagnetic barrier modulated transmission probability is expected to be a periodic function of the polarization angle and the planar rotation angle, that decreases with the strength of the magnetic proximity exchange increasing. However, the transmission probability for the double ferromagnetic insulators modulated n—n junction and n—p junction is not a periodic function of polarization angle nor planar rotation angle, owing to the combined effects of the double ferromagnetic insulators and the barrier potential. Since the energy gap between the conduction band and the valence band is narrowed and widened respectively in ranges of 0 ≤ θ < π/2 and π/2 < θ ≤ π, the transmission probability of the n—n junction first increases rapidly and then decreases slowly with the increase of the magnetic proximity exchange strength. While the transmission probability for the n—p junction demonstrates an opposite trend on the strength of the magnetic proximity exchange because the band gaps contrarily vary. The obtained results may lead to the possible realization of a magnetic/electric switch based on TIs and be useful in further understanding the surface states of TIs

Superconductivity and ferromagnetism in topological insulators

Science.gov (United States)

Zhang, Duming

Topological insulators, a new state of matter discovered recently, have attracted great interest due to their novel properties. They are insulating inside the bulk, but conducting at the surface or edges. This peculiar behavior is characterized by an insulating bulk energy gap and gapless surface or edge states, which originate from strong spin-orbit coupling and time-reversal symmetry. The spin and momentum locked surface states not only provide a model system to study fundamental physics, but can also lead to applications in spintronics and dissipationless electronics. While topological insulators are interesting by themselves, more exotic behaviors are predicted when an energy gap is induced at the surface. This dissertation explores two types of surface state gap in topological insulators, a superconducting gap induced by proximity effect and a magnetic gap induced by chemical doping. The first three chapters provide introductory theory and experimental details of my research. Chapter 1 provides a brief introduction to the theoretical background of topological insulators. Chapter 2 is dedicated to material synthesis principles and techniques. I will focus on two major synthesis methods: molecular beam epitaxy for the growth of Bi2Se3 thin films and chemical vapor deposition for the growth of Bi2Se3 nanoribbons and nanowires. Material characterization is discussed in Chapter 3. I will describe structural, morphological, magnetic, electrical, and electronic characterization techniques used to study topological insulators. Chapter 4 discusses the experiments on proximity-induced superconductivity in topological insulator (Bi2Se3) nanoribbons. This work is motivated by the search for the elusive Majorana fermions, which act as their own antiparticles. They were proposed by Ettore Majorara in 1937, but have remained undiscovered. Recently, Majorana's concept has been revived in condensed matter physics: a condensed matter analog of Majorana fermions is predicted to

Intrinsic Rashba-like splitting in asymmetric Bi{sub 2}Te{sub 3}/Sb{sub 2}Te{sub 3} heterogeneous topological insulator films

Energy Technology Data Exchange (ETDEWEB)

Liu, Xiaofei; Guo, Wanlin, E-mail: wlguo@nuaa.edu.cn [State Key Laboratory of Mechanics and Control for Mechanical Structures and Key Laboratory for Intelligent Nano Materials and Devices (MOE), Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China)

2014-08-25

We show by density functional theory calculations that asymmetric hetero-stacking of Bi{sub 2}Te{sub 3}/Sb{sub 2}Te{sub 3} films can modulate the topological surface states. Due to the structure inversion asymmetry, an intrinsic Rashba-like splitting of the conical surface bands is aroused. While such splitting in homogeneous Bi{sub 2}Te{sub 3}-class topological insulators can be realized in films with more than three quintuple layers under external electric fields, the hetero-stacking breaks the limit of thickness for preserving the topological nature into the thinnest two quintuple layers. These results indicate that the hetero-stacking can serve as an efficient strategy for spin-resolved band engineering of topological insulators.

Insulators form gene loops by interacting with promoters in Drosophila.

Science.gov (United States)

Erokhin, Maksim; Davydova, Anna; Kyrchanova, Olga; Parshikov, Alexander; Georgiev, Pavel; Chetverina, Darya

2011-09-01

Chromatin insulators are regulatory elements involved in the modulation of enhancer-promoter communication. The 1A2 and Wari insulators are located immediately downstream of the Drosophila yellow and white genes, respectively. Using an assay based on the yeast GAL4 activator, we have found that both insulators are able to interact with their target promoters in transgenic lines, forming gene loops. The existence of an insulator-promoter loop is confirmed by the fact that insulator proteins could be detected on the promoter only in the presence of an insulator in the transgene. The upstream promoter regions, which are required for long-distance stimulation by enhancers, are not essential for promoter-insulator interactions. Both insulators support basal activity of the yellow and white promoters in eyes. Thus, the ability of insulators to interact with promoters might play an important role in the regulation of basal gene transcription.

Monte Carlo study of one hole in a quantum antiferromagnet

International Nuclear Information System (INIS)

Sorella, S.

1992-01-01

Using the standard Quantum Monte Carlo technique for the Hubbard model, I present here a numerical investigation of the hole propagation in a Quantum Antiferromagnet. The calculation is very well stabilized, using selected sized systems and special use of the trial wavefunction that satisfy the close shell condition in presence of an arbitrarily weak Zeeman magnetic field, vanishing in the thermodynamic limit. In this paper the author investigates the question of vanishing or nonvanishing quasiparticle weight, in order to clarify whether the Mott insulator should behave just as conventional insulator with an upper and lower Hubbard band. By comparing the present finite size scaling with several techniques predicting a finite quasiparticle weight the data seem more consistent with a vanishing quasiparticle weight, i.e., as recently suggested by P.W. Anderson the Hubbard-Mott insulator should be characterized by non-trivial excitations which cannot be interpreted in a simple quasi-particle picture. However it cannot be excluded, based only on numerical grounds, that a very small but non vanishing quasiparticle weight should survive in the thermodynamic limit

Particle contamination in gas-insulated systems: new control methods and optimum SF6/N2 mixtures

International Nuclear Information System (INIS)

Pace, M.O.; Adcock, J.L.; Christophorou, L.G.

1984-01-01

The feasibilities of two new separate techniques to control particle contamination in practical gas-insulated sytems were tested in a small-scale concentric cylinder geometry. In one technique an insulating coating was first formed on the particles in a contaminated system by low-pressure discharges in appropriate gases such as 1-C 3 F 6 and c-C 4 F 8 . When SF 6 was subsequently introduced into the same system at practical pressure as the operating insulation, the considerable harm ordinarily caused by particles was found to be eliminated. The nature of the coating formed also on the electrodes in this process was studied, with the conclusion that the observed benefits were primarily due to coating on particles, not on electrodes. In the second technique the particles, moved randomly by electrical stress, struck and adhered to the surface of a tacky insulating solid material; they were subsequently encapsulated in a melt-resolidify cycle without electrical stress. This trapping technique was also found to eliminate the harmful effects of particles in SF 6 at practical pressure. A technique for producing a trapping material with temperature characteristics appropriate for practical apparatus was devised. The effect of particle contamination on the dielectric strength of SF 6 /N 2 mixtures was studied as a function of total pressure and percentage of each gas. Optimum total pressure (approx. 6 atm) and optimum percentages (60% SF 6 /40% N 2 ) were observed in breakdown tests in particle-contaminated concentric cylinder geometry

Heat insulation support device

International Nuclear Information System (INIS)

Takahashi, Hiroyuki; Koda, Tomokazu; Motojima, Osamu; Yamamoto, Junya.

1994-01-01

The device of the present invention comprises a plurality of heat insulation legs disposed in a circumferential direction. Each of the heat insulative support legs has a hollow shape, and comprises an outer column and an inner column as support structures having a heat insulative property (heat insulative structure), and a thermal anchor which absorbs compulsory displacement by a thin flat plate (displacement absorber). The outer column, the thermal anchor and the inner column are connected by a support so as to offset the positional change of objects to be supported due to shrinkage when they are shrunk. In addition, the portion between the superconductive coils as the objects to be supported and the inner column is connected by the support. The superconductive thermonuclear device is entirely contained in a heat insulative vacuum vessel, and the heat insulative support legs are disposed on a lower lid of the heat insulative vacuum vessel. With such a constitution, they are strengthened against lateral load and buckling, thereby enabling to reduce the amount of heat intrusion while keeping the compulsory displacement easy to be absorbed. (I.N.)

Complete biallelic insulation at the H19/Igf2 imprinting control region position results in fetal growth retardation and perinatal lethality.

Directory of Open Access Journals (Sweden)

Dong-Hoon Lee

2010-09-01

Full Text Available The H19/Igf2 imprinting control region (ICR functions as an insulator exclusively in the unmethylated maternal allele, where enhancer-blocking by CTCF protein prevents the interaction between the Igf2 promoter and the distant enhancers. DNA methylation inhibits CTCF binding in the paternal ICR allele. Two copies of the chicken β-globin insulator (ChβGI(2 are capable of substituting for the enhancer blocking function of the ICR. Insulation, however, now also occurs upon paternal inheritance, because unlike the H19 ICR, the (ChβGI(2 does not become methylated in fetal male germ cells. The (ChβGI(2 is a composite insulator, exhibiting enhancer blocking by CTCF and chromatin barrier functions by USF1 and VEZF1. We asked the question whether these barrier proteins protected the (ChβGI(2 sequences from methylation in the male germ line.We genetically dissected the ChβGI in the mouse by deleting the binding sites USF1 and VEZF1. The methylation of the mutant versus normal (ChβGI(2 significantly increased from 11% to 32% in perinatal male germ cells, suggesting that the barrier proteins did have a role in protecting the (ChβGI(2 from methylation in the male germ line. Contrary to the H19 ICR, however, the mutant (mChβGI(2 lacked the potential to attain full de novo methylation in the germ line and to maintain methylation in the paternal allele in the soma, where it consequently functioned as a biallelic insulator. Unexpectedly, a stricter enhancer blocking was achieved by CTCF alone than by a combination of the CTCF, USF1 and VEZF1 sites, illustrated by undetectable Igf2 expression upon paternal transmission.In this in vivo model, hypomethylation at the ICR position together with fetal growth retardation mimicked the human Silver-Russell syndrome. Importantly, late fetal/perinatal death occurred arguing that strict biallelic insulation at the H19/Igf2 ICR position is not tolerated in development.

Economically optimal thermal insulation

Energy Technology Data Exchange (ETDEWEB)

Berber, J.

1978-10-01

Exemplary calculations to show that exact adherence to the demands of the thermal insulation ordinance does not lead to an optimal solution with regard to economics. This is independent of the mode of financing. Optimal thermal insulation exceeds the values given in the thermal insulation ordinance.

Panels of microporous insulation

Energy Technology Data Exchange (ETDEWEB)

McWilliams, J.A.; Morgan, D.E.; Jackson, J.D.J.

1990-08-07

Microporous thermal insulation materials have a lattice structure in which the average interstitial dimension is less than the mean free path of the molecules of air or other gas in which the material is arranged. This results in a heat flow which is less than that attributable to the molecular heat diffusion of the gas. According to this invention, a method is provided for manufacturing panels of microporous thermal insulation, in particular such panels in which the insulation material is bonded to a substrate. The method comprises the steps of applying a film of polyvinyl acetate emulsion to a non-porous substrate, and compacting powdery microporous thermal insulation material against the film so as to cause the consolidated insulation material to bond to the substrate and form a panel. The polyvinyl acetate may be applied by brushing or spraying, and is preferably allowed to dry prior to compacting the insulation material. 1 fig.

Strong magnetization and Chern insulators in compressed graphene/CrI 3 van der Waals heterostructures

Science.gov (United States)

Zhang, Jiayong; Zhao, Bao; Zhou, Tong; Xue, Yang; Ma, Chunlan; Yang, Zhongqin

2018-02-01

Graphene-based heterostructures are a promising material system for designing the topologically nontrivial Chern insulating devices. Recently, a two-dimensional monolayer ferromagnetic insulator CrI3 was successfully synthesized in experiments [B. Huang et al., Nature (London) 546, 270 (2017), 10.1038/nature22391]. Here, these two interesting materials are proposed to build a heterostructure (Gr /CrI3). Our first-principles calculations show that the system forms a van der Waals (vdW) heterostructure, which is relatively facilely fabricated in experiments. A Chern insulating state is acquired in the Gr /CrI3 heterostructure if the vdW gap is compressed to a distance between about 3.3 and 2.4 Å, corresponding to a required external pressure between about 1.4 and 18.3 GPa. Amazingly, very strong magnetization (about 150 meV) is found in graphene, induced by the substrate CrI3, despite the vdW interactions between them. A low-energy effective model is employed to understand the mechanism. The work functions, contact types, and band alignments of the Gr /CrI3 heterostructure system are also studied. Our work demonstrates that the Gr /CrI3 heterostructure is a promising system to observe the quantum anomalous Hall effect at high temperatures (up to 45 K) in experiments.

Total dose hardening of buried insulator in implanted silicon-on-insulator structures

International Nuclear Information System (INIS)

Mao, B.Y.; Chen, C.E.; Pollack, G.; Hughes, H.L.; Davis, G.E.

1987-01-01

Total dose characteristics of the buried insulator in implanted silicon-on-insulator (SOI) substrates have been studied using MOS transistors. The threshold voltage shift of the parasitic back channel transistor, which is controlled by charge trapping in the buried insulator, is reduced by lowering the oxygen dose as well as by an additional nitrogen implant, without degrading the front channel transistor characteristics. The improvements in the radiation characteristics of the buried insulator are attributed to the decrease in the buried oxide thickness or to the presence of the interfacial oxynitride layer formed by the oxygen and nitrogen implants

Survey of thermal insulation systems

International Nuclear Information System (INIS)

Kinoshita, Izumi

1983-01-01

Better thermal insulations have been developed to meet the growing demands of industry, and studies on thermal insulation at both high temperature and low temperature have been widely performed. The purpose of this survey is to summarize data on the performances and characteristics of thermal insulation materials and thermal insulation structures (for instance, gas cooled reactors, space vehicles and LNG storage tanks), and to discuss ravious problems regarding the design of thermal insulation structures of pool-type LMFBRs. (author)

Electrical Detection of Spin-to-Charge Conversion in a Topological Insulator Bi2Te3

Science.gov (United States)

Li, Connie H.; van't Erve, Olaf M. J.; Li, Yaoyi; Li, Lian; Jonker, Berry T.

Spin-momentum locking in topological insulators (TIs) dictates that an unpolarized charge current creates a net spin polarization. We recently demonstrated the first electrical detection of this spontaneous polarization in a transport geometry, using a ferromagnetic (FM) / tunnel barrier contact, where the projection of the TI surface state spin on the magnetization of detector is measured as a voltage [1]. Alternatively, if spins are injected into the TI surface state system, it is distinctively associated with a unique carrier momentum, and hence should generated a charge accumulation, similar to that of inverse spin Hall effect. Here we experimentally demonstrate both effects in the same device fabricated in Bi2Te3: the electrical detection of the spin accumulation generated by an unpolarized current flowing through the surface states, and that of the charge accumulation generated by spins injected into the surface states system. This reverse measurement is an independent confirmation of spin-momentum locking in the TI surface states, and offers additional avenue for spin manipulation. It further demonstrates the robustness and versatility of electrical access to the TI surface state spin system, an important step towards its utilization in TI-based spintronics devices. C.H. Li et al., Nat. Nanotech. 9, 218 (2014). Supported by NRL core funds and Nanoscience Institute.

Detection of UV Pulse from Insulators and Application in Estimating the Conditions of Insulators

Science.gov (United States)

Wang, Jingang; Chong, Junlong; Yang, Jie

2014-10-01

Solar radiation in the band of 240-280 nm is absorbed by the ozone layer in the atmosphere, and corona discharges from high-voltage apparatus emit in air mainly in the 230-405 nm range of ultraviolet (UV), so the band of 240-280 nm is called UV Solar Blind Band. When the insulators in a string deteriorate or are contaminated, the voltage distribution along the string will change, which causes the electric fields in the vicinity of insulators change and corona discharge intensifies. An UV pulse detection method to check the conditions of insulators is presented based on detecting the UV pulse among the corona discharge, then it can be confirmed that whether there exist faulty insulators and whether the surface contamination of insulators is severe for the safe operation of power systems. An UV-I Insulator Detector has been developed, and both laboratory tests and field tests have been carried out which demonstrates the practical viability of UV-I Insulator Detector for online monitoring.

Super-insulation

International Nuclear Information System (INIS)

Gerold, J.

1985-01-01

The invention concerns super-insulation, which also acts as spacing between two pressurized surfaces, where the crossing bars in at least two layers are provided, with interposed foil. The super-insulation is designed so that it can take compression forces and limits thermal radiation and thermal conduction sufficiently, where the total density of heat flow is usually limited to a few watts per m 2 . The solution to the problem is characterized by the fact that the bars per layer are parallel and from layer to layer they are at an angle to each other and the crossover positions of the bars of different layers are at fixed places and so form contact columns. The basic idea is that bars crossing over each other to support compression forces are used so that contact columns are formed, which are compressed to a certain extent by the load. (orig./PW) [de

Thermal insulation

International Nuclear Information System (INIS)

Pinsky, G.P.

1977-01-01

Thermal insulation for vessels and piping within the reactor containment area of nuclear power plants is disclosed. The thermal insulation of this invention can be readily removed and replaced from the vessels and piping for inservice inspection, can withstand repeated wettings and dryings, and can resist high temperatures for long periods of time. 4 claims, 3 figures

Uncertainty relations and topological-band insulator transitions in 2D gapped Dirac materials

International Nuclear Information System (INIS)

Romera, E; Calixto, M

2015-01-01

Uncertainty relations are studied for a characterization of topological-band insulator transitions in 2D gapped Dirac materials isostructural with graphene. We show that the relative or Kullback–Leibler entropy in position and momentum spaces, and the standard variance-based uncertainty relation give sharp signatures of topological phase transitions in these systems. (paper)

Superconductor-insulator transitions in 2D: the experimental situation

International Nuclear Information System (INIS)

Markovic, N.; Christiansen, C.; Mack, A.; Goldman, A.M.

2000-01-01

Superconductor-insulator (SI) transitions in ultrathin films have attracted significant attention over the last decade because of the possibility that they are quantum phase transitions. Magnetic field, film thickness, or carrier concentration can be used as control parameters. The bosonic pictures of these transitions proposed some years ago are only in qualitative agreement with experiment. In particular, the critical resistance appears not to be universal, and there are variations in the values of critical exponents. It has been concluded that in real films fermionic degrees of freedom must be taken into account. There are also indications that the phase diagram may include a significant metallic phase separating the superconducting and insulating phases, and that the transition may have a significant percolative aspect. The experimental situation will be broadly reviewed with attention paid to issues relating to materials and measurements. (orig.)

Soft Coulomb gap and asymmetric scaling towards metal-insulator quantum criticality in multilayer MoS2.

Science.gov (United States)

Moon, Byoung Hee; Bae, Jung Jun; Joo, Min-Kyu; Choi, Homin; Han, Gang Hee; Lim, Hanjo; Lee, Young Hee

2018-05-24

Quantum localization-delocalization of carriers are well described by either carrier-carrier interaction or disorder. When both effects come into play, however, a comprehensive understanding is not well established mainly due to complexity and sparse experimental data. Recently developed two-dimensional layered materials are ideal in describing such mesoscopic critical phenomena as they have both strong interactions and disorder. The transport in the insulating phase is well described by the soft Coulomb gap picture, which demonstrates the contribution of both interactions and disorder. Using this picture, we demonstrate the critical power law behavior of the localization length, supporting quantum criticality. We observe asymmetric critical exponents around the metal-insulator transition through temperature scaling analysis, which originates from poor screening in insulating regime and conversely strong screening in metallic regime due to free carriers. The effect of asymmetric scaling behavior is weakened in monolayer MoS 2 due to a dominating disorder.

The elastic constants of V2O3 in the insulating phase

International Nuclear Information System (INIS)

Yelon, W.B.; Keem, J.E.

1979-01-01

The initial slopes of the acoustic phonon dispersion curves in (Vsub(0.98)Crsub(0.02)) 2 O 3 have been measured at room temperature in several of the high symmetry directions by inelastic neutron scattering. From these data several sound velocities and four independent elastic constants have been determined. Although the Cr doped specimen is in the insulating phase and pure V 2 O 3 is metallic, these results are in good agreement with recent data obtained by ultrasonic measurements on pure V 2 O 3 . (author)

Electronic properties of high Tc superconductors

International Nuclear Information System (INIS)

Rojo, A.G.

1989-01-01

Using analytical and numerical methods, the electronic properties of the copper-oxygen plane in the normal phase of high Tc superconductors are described. Using the slave-boson technique in the saddle point, a theory of the metal insulator transition which generalizes the notions of a Mott insulator to the case of more than a single band for those planes is presented. A phase-diagram is obtained in the parameter space and effective masses, optical gaps and metallization are calculated as a function of the number of carriers. Based on the experimental evidence, the theory permits classification of superconducting compounds as charge transfer insulators in the stoichiometric case. The insulator state is characterized by a non-zero optical gap and a divergent effective mass which corresponds to the breakage of a Fermi-liquid scheme. The results obtained are applicable to metal-transition-oxides whose behaviour has been traditionally controversial and it is concluded that it is necessary to broaden the meaning of a Mott insulator to the case of more than a single band to better understand them. Based on the ideas of group renormalization in a real space, a lattice approximation is presented, which allows: a) To complement the treatment of slave-bosons in phase diagrams and optical gaps; b) Identification of an attraction mechanism between carriers originating from purely repulsive interactions. Numerical calculations in small clusters show the existence of a pairing mechanism showing a superconducting instability from a charge transfer insulator. (Author) [es

Electronic properties of high Tc superconductors. Propiedades electronicas de los superconductores de alta temperatura critica

Energy Technology Data Exchange (ETDEWEB)

Rojo, A G

1989-01-01

Using analytical and numerical methods, the electronic properties of the copper-oxygen plane in the normal phase of high Tc superconductors are described. Using the slave-boson technique in the saddle point, a theory of the metal insulator transition which generalizes the notions of a Mott insulator to the case of more than a single band for those planes is presented. A phase-diagram is obtained in the parameter space and effective masses, optical gaps and metallization are calculated as a function of the number of carriers. Based on the experimental evidence, the theory permits classification of superconducting compounds as charge transfer insulators in the stoichiometric case. The insulator state is characterized by a non-zero optical gap and a divergent effective mass which corresponds to the breakage of a Fermi-liquid scheme. The results obtained are applicable to metal-transition-oxides whose behaviour has been traditionally controversial and it is concluded that it is necessary to broaden the meaning of a Mott insulator to the case of more than a single band to better understand them. Based on the ideas of group renormalization in a real space, a lattice approximation is presented, which allows: a) To complement the treatment of slave-bosons in phase diagrams and optical gaps; b) Identification of an attraction mechanism between carriers originating from purely repulsive interactions. Numerical calculations in small clusters show the existence of a pairing mechanism showing a superconducting instability from a charge transfer insulator. (Author).

Electrical insulator requirements for mirror fusion reactors

International Nuclear Information System (INIS)

Condit, R.H.; Van Konynenburg, R.A.

1977-01-01

The requirements for mirror fusion electrical insulators are discussed. Insulators will be required at the neutral beam injectors, injector power supplies, direct converters, and superconducting magnets. Insulators placed at the neutral beam injectors will receive the greatest radiation exposure, 10 14 to 10 16 neutrons/m 2 .s and 0.3 to 3 Gy/s (10 5 to 10 6 R/h) of gamma rays, with shielding. Direct converter insulators may receive the highest temperature (up to 1300 0 K), but low voltage holding requirements. Insulators made from organic materials (e.g., plastics) for the magnet coils may be satisfactory. Immediate conductivity increases of all insulators result from gamma irradiation. With an upper limit to gamma flux exposures of 300 Gy/s in a minimally shielded region, the conductivity could reach 10 -6 S/m. Damage from neutron irradiation may not be serious during several years' exposure. Surface changes in ceramics at the neutral beam injector may be serious. The interior of the injector will contain atomic hydrogen, and sputtering may transfer material away from or onto the ceramic insulators. Unknown and potentially damaging interactions between irradiation, electric fields, temperature gradients, cycling of temperature, surface and joint reactions, sputtering, polarization, and electrotransport in the dielectrics are of concern. Materials research to deal with these problems is needed

Magnetically self-insulated transformers

International Nuclear Information System (INIS)

Novac, B.M.; Smith, I.R.; Brown, J.

2002-01-01

Magnetic insulation is the only practicable form of insulation for much equipment used in ultrahigh pulsed-power work, including transmission lines and plasma opening switches. It has not however so far been successfully exploited in the transformers that are necessarily involved, and the first proposed design that appeared more than 30 years ago raised apparently insuperable problems. The two novel arrangements for a magnetically insulated transformer described in this paper overcome the problems faced by the earlier designs and also offer considerable scope for development in a number of important areas. Theoretical justification is given for their insulating properties, and this is confirmed by proof-of-principle results obtained from a small-scale experimental prototype in which magnetic insulation was demonstrated at up to 100 kV. (author)

Spray-on foam insulations for launch vehicle cryogenic tanks

Science.gov (United States)

Fesmire, J. E.; Coffman, B. E.; Meneghelli, B. J.; Heckle, K. W.

2012-04-01

Spray-on foam insulation (SOFI) has been developed for use on the cryogenic tanks of space launch vehicles beginning in the 1960s with the Apollo program. The use of SOFI was further developed for the Space Shuttle program. The External Tank (ET) of the Space Shuttle, consisting of a forward liquid oxygen tank in line with an aft liquid hydrogen tank, requires thermal insulation over its outer surface to prevent ice formation and avoid in-flight damage to the ceramic tile thermal protection system on the adjacent Orbiter. The insulation also provides system control and stability throughout the lengthy process of cooldown, loading, and replenishing the tank. There are two main types of SOFI used on the ET: acreage (with the rind) and closeout (machined surface). The thermal performance of the seemingly simple SOFI system is a complex array of many variables starting with the large temperature difference of 200-260 K through the typical 25-mm thickness. Environmental factors include air temperature and humidity, wind speed, solar exposure, and aging or weathering history. Additional factors include manufacturing details, launch processing operations, and number of cryogenic thermal cycles. The study of the cryogenic thermal performance of SOFI under large temperature differentials is the subject of this article. The amount of moisture taken into the foam during the cold soak phase, termed Cryogenic Moisture Uptake, must also be considered. The heat leakage rates through these foams were measured under representative conditions using laboratory standard liquid nitrogen boiloff apparatus. Test articles included baseline, aged, and weathered specimens. Testing was performed over the entire pressure range from high vacuum to ambient pressure. Values for apparent thermal conductivity and heat flux were calculated and compared with prior data. As the prior data of record was obtained for small temperature differentials on non-weathered foams, analysis of the different

Spray-On Foam Insulations for Launch Vehicle Cryogenic Tanks

Science.gov (United States)

Fesmire, J. E.; Cofman, B. E.; Menghelli, B. J.; Heckle, K. W.

2011-01-01

Spray-on foam insulation (SOFI) has been developed for use on the cryogenic tanks of space launch vehicles beginning in the 1960s with the Apollo program. The use of SOFI was further developed for the Space Shuttle program. The External Tank (ET) of the Space Shuttle, consisting of a forward liquid oxygen tank in line with an aft liquid hydrogen tank, requires thermal insulation over its outer surface to prevent ice formation and avoid in-flight damage to the ceramic tile thermal protection system on the adjacent Orbiter. The insulation also provides system control and stability with throughout the lengthy process of cooldown, loading, and replenishing the tank. There are two main types of SOFI used on the ET: acreage (with the rind) and closeout (machined surface). The thermal performance of the seemingly simple SOFI system is a complex of many variables starting with the large temperature difference of from 200 to 260 K through the typical 25-mm thickness. Environmental factors include air temperature and humidity, wind speed, solar exposure, and aging or weathering history. Additional factors include manufacturing details, launch processing operations, and number of cryogenic thermal cycles. The study of the cryogenic thermal performance of SOFI under large temperature differentials is the subject of this article. The amount of moisture taken into the foam during the cold soak phase, termed Cryogenic Moisture Uptake, must also be considered. The heat leakage rates through these foams were measured under representative conditions using laboratory standard liquid nitrogen boiloff apparatus. Test articles included baseline, aged, and weathered specimens. Testing was performed over the entire pressure range from high vacuum to ambient pressure. Values for apparent thermal conductivity and heat flux were calculated and compared with prior data. As the prior data of record was obtained for small temperature differentials on non-weathered foams, analysis of the

Post-Insulation of Existing Buildings Constructed Between 1850 and 1920

DEFF Research Database (Denmark)

Rasmussen, Torben Valdbjørn

2010-01-01

as a result of post-insulation measures. Besides lower heating costs and reduced CO2 emissions, improvement of the insulation standard could contribute to the elimination of other aspects of discomfort, such as draught originating from cold surfaces inside. This paper considers post-insulation of a simulated...

Topological insulators and superconductors: tenfold way and dimensional hierarchy

International Nuclear Information System (INIS)

Ryu, Shinsei; Schnyder, Andreas P; Furusaki, Akira; Ludwig, Andreas W W

2010-01-01

It has recently been shown that in every spatial dimension there exist precisely five distinct classes of topological insulators or superconductors. Within a given class, the different topological sectors can be distinguished, depending on the case, by a Z or a Z 2 topological invariant. This is an exhaustive classification. Here we construct representatives of topological insulators and superconductors for all five classes and in arbitrary spatial dimension d, in terms of Dirac Hamiltonians. Using these representatives we demonstrate how topological insulators (superconductors) in different dimensions and different classes can be related via 'dimensional reduction' by compactifying one or more spatial dimensions (in 'Kaluza-Klein'-like fashion). For Z-topological insulators (superconductors) this proceeds by descending by one dimension at a time into a different class. The Z 2 -topological insulators (superconductors), on the other hand, are shown to be lower-dimensional descendants of parent Z-topological insulators in the same class, from which they inherit their topological properties. The eightfold periodicity in dimension d that exists for topological insulators (superconductors) with Hamiltonians satisfying at least one reality condition (arising from time-reversal or charge-conjugation/particle-hole symmetries) is a reflection of the eightfold periodicity of the spinor representations of the orthogonal groups SO(N) (a form of Bott periodicity). Furthermore, we derive for general spatial dimensions a relation between the topological invariant that characterizes topological insulators and superconductors with chiral symmetry (i.e., the winding number) and the Chern-Simons invariant. For lower-dimensional cases, this formula relates the winding number to the electric polarization (d=1 spatial dimensions) or to the magnetoelectric polarizability (d=3 spatial dimensions). Finally, we also discuss topological field theories describing the spacetime theory of

Metal-insulator transition in Pt-C nanowires grown by focused-ion-beam-induced deposition

International Nuclear Information System (INIS)

Fernandez-Pacheco, A.; Ibarra, M. R.; De Teresa, J. M.; Cordoba, R.

2009-01-01

We present a study of the transport properties of Pt-C nanowires created by focused-ion-beam (FIB)-induced deposition. By means of the measurement of the resistance while the deposit is being performed, we observe a progressive decrease in the nanowire resistivity with thickness, changing from 10 8 μΩ cm for thickness ∼20 nm to a lowest saturated value of 700 μΩ cm for thickness >150 nm. Spectroscopy analysis indicates that this dependence on thickness is caused by a gradient in the metal-carbon ratio as the deposit is grown. We have fabricated nanowires in different ranges of resistivity and studied their conduction mechanism as a function of temperature. A metal-insulator transition as a function of the nanowire thickness is observed. The results will be discussed in terms of the Mott-Anderson theory for noncrystalline materials. An exponential decrease in the conductance with the electric field is found for the most resistive samples, a phenomenon understood by the theory of hopping in lightly doped semiconductors under strong electric fields. This work explains the important discrepancies found in the literature for Pt-C nanostructures grown by FIB and opens the possibility to tune the transport properties of this material by an appropriate selection of the growth parameters.

Design and analysis of the PBFA-Z vacuum insulator stack

International Nuclear Information System (INIS)

Shoup, R.W.; Long, F.; Martin, T.H.; Stygar, W.A.; Spielman, R.B.; Struve, K.W.; Mostrom, M.; Corcoran, P.; Smith, I.

1996-01-01

Sandia is developing PBFA-Z, a 20-MA driver for z-pinch experiments by replacing the water lines, insulator stack, and MITLs on PBFA II with new hardware. The design of the vacuum insulator stack was dictated by the drive voltage, the electric field stress and grading requirements, the water line and MITL interface requirements, and the machine operations and maintenance requirements. The insulator stack will consist of four separate modules, each of a different design because of different voltage drive and hardware interface requirements. The shape of the components in each module, i.e., grading rings, insulator rings, flux excluders, anode and cathode conductors, and the design of the water line and MITL interfaces, were optimized by using the electrostatic analysis codes, ELECTRO and JASON. The time-dependent performance of the insulator stack was evaluated using IVORY, a 2-D PIC code. The insulator stack design and present the results of the ELECTRO and IVORY analyses are described. (author). 2 tabs., 9 figs., 3 refs

Design and analysis of the PBFA-Z vacuum insulator stack

Energy Technology Data Exchange (ETDEWEB)

Shoup, R W [Field Command Defense Nuclear Agency, Kirtland AFB, NM (United States); Long, F; Martin, T H; Stygar, W A; Spielman, R B [Sandia National Laboratories, Albuquerque, NM (United States). Dept 9573; Ives, H [EG and G, Albuquerque, NM (United States); Struve, K W; Mostrom, M [Mission Research Corp., Albuquerque, NM (United States); Corcoran, P; Smith, I [Pulse Sciences, Inc., San Leandro, CA (United States)

1997-12-31

Sandia is developing PBFA-Z, a 20-MA driver for z-pinch experiments by replacing the water lines, insulator stack, and MITLs on PBFA II with new hardware. The design of the vacuum insulator stack was dictated by the drive voltage, the electric field stress and grading requirements, the water line and MITL interface requirements, and the machine operations and maintenance requirements. The insulator stack will consist of four separate modules, each of a different design because of different voltage drive and hardware interface requirements. The shape of the components in each module, i.e., grading rings, insulator rings, flux excluders, anode and cathode conductors, and the design of the water line and MITL interfaces, were optimized by using the electrostatic analysis codes, ELECTRO and JASON. The time-dependent performance of the insulator stack was evaluated using IVORY, a 2-D PIC code. The insulator stack design and present the results of the ELECTRO and IVORY analyses are described. (author). 2 tabs., 9 figs., 3 refs.

Acoustic excitation of containment insulation cover plate

International Nuclear Information System (INIS)

Fenech, H.; Rao, A.K.

1978-01-01

An experimental and theoretical program has been implemented by NRC-BNL since 1975 at the University of California, Santa Barbara to assess the reliability of the PCRV thermal insulation cover plate and the possible safety problem caused by the failure of this plate. A typical large HTGR PCRV unit [1160 MW(e)] and thermal insulation class A were selected. The upper core cavity is estimated to be the most critical volume where the noise pressure levels are expected to reach 110 to 130 dB (rel. to 2 x 10 -4 dynes/cm 2 ). The noise spectrum in that cavity is a composite of circulator noise, vortex shedding boundary layer turbulence, and flow impingement. Some anticipated safety related problems associated with the thermal insulation failure are examined

Unconventional quantum Hall effect in Floquet topological insulators

KAUST Repository

Tahir, M.

2016-07-27

We study an unconventional quantum Hall effect for the surface states of ultrathin Floquet topological insulators in a perpendicular magnetic field. The resulting band structure is modified by photon dressing and the topological property is governed by the low-energy dynamics of a single surface. An exchange of symmetric and antisymmetric surface states occurs by reversing the lights polarization. We find a novel quantum Hall state in which the zeroth Landau level undergoes a phase transition from a trivial insulator state, with Hall conductivity αyx = 0 at zero Fermi energy, to a Hall insulator state with αyx = e2/2h. These findings open new possibilities for experimentally realizing nontrivial quantum states and unusual quantum Hall plateaus at (±1/2,±3/2,±5/2, ...)e2/h. © 2016 IOP Publishing Ltd Printed in the UK.

Unconventional quantum Hall effect in Floquet topological insulators

KAUST Repository

Tahir, M.; Vasilopoulos, P.; Schwingenschlö gl, Udo

2016-01-01

We study an unconventional quantum Hall effect for the surface states of ultrathin Floquet topological insulators in a perpendicular magnetic field. The resulting band structure is modified by photon dressing and the topological property is governed by the low-energy dynamics of a single surface. An exchange of symmetric and antisymmetric surface states occurs by reversing the lights polarization. We find a novel quantum Hall state in which the zeroth Landau level undergoes a phase transition from a trivial insulator state, with Hall conductivity αyx = 0 at zero Fermi energy, to a Hall insulator state with αyx = e2/2h. These findings open new possibilities for experimentally realizing nontrivial quantum states and unusual quantum Hall plateaus at (±1/2,±3/2,±5/2, ...)e2/h. © 2016 IOP Publishing Ltd Printed in the UK.

Effect of Ti doping on magnetic properties and magnetoresistance in LaSr2Mn2O7

International Nuclear Information System (INIS)

Feng, J.; Che, P.; Wang, J.P.; Lu, M.F.; Liu, J.F.; Cao, X.Q.; Meng, J.

2005-01-01

The effect of Ti substitution for Mn on magnetic and transport properties has been investigated for layered manganese oxides LaSr 2 Mn 2-x Ti x O 7 . Titanium doping hampered the canted antiferromagnetic (AFM) exchange at low temperature and their Neel temperature (T N ) decreased from 138 K (x = 0) to 106 K (x = 0.1). Meanwhile, spin glass, charge ordering and metal-insulator transition are suppressed by Ti addition. This can be attributed to Mn-site disorder caused by random substitution of Ti 4+ . The suppression of charge ordering leads to magntetoresistance (MR) ratio increase and MR reaches maximum at x = 0.3. The resistivity increases obviously with x increasing because of double exchange interaction channel broken by Ti 4+ addition. The resistivity of all samples in low temperature range fits to the Mott's variable range hopping (VRH) model, while it fits to nearest neighbor hopping of small polarons model in high temperature range. We also found that both disorder and distortion in A-site and B-site will induce the similar effect to electrical and magnetic properties

Research on vacuum insulation for cryocables

International Nuclear Information System (INIS)

Graneau, P.

1974-01-01

Vacuum insulation, as compared with solid insulation, simplifies the construction of both resistive or superconducting cryogenic cables. The common vacuum space in the cable can furnish thermal insulation between the environment and the cryogenic coolant, provide electrical insulation between conductors, and establish thermal isolation between go- and return-coolant streams. The differences between solid and vacuum high voltage insulation are discussed, and research on the design, materials selection, and testing of vacuum insulated cryogenic cables is described

Tunable Quantum Spin Liquidity in Mo3O13 Cluster Mott Insulators

Science.gov (United States)

Akbari-Sharbaf, Arash; Ziat, Djamel; Verrier, Aime; Quilliam, Jeffrey A.; Sinclair, Ryan; Zhou, Haidong D.; Sun, Xuefeng F.

A study of a tunable quantum spin liquid (QSL) phase in the compound Li2In1- x ScxMo3O8 (x = 0.2, 0.4, 0.6, 0.8, 1) will be presented. Crystal structure of these compounds can be viewed as Mo ions arranged on an asymmetric Kagome lattice (KL), with two different Mo-Mo bond lengths, separated by nonmagnetic layers composed of Li, In, and Sc ions. Using X-ray diffraction spectroscopy, muon spin relaxation spectroscopy, bulk magnetic susceptibility and specific heat measurements we show that by changing the composition of the nonmagnetic layers we can drive the system from an ordered antiferromagnetic state to a quantum spin liquid state. The mechanism responsible for the tunability of the magnetic phase in this class of materials may be associated with the degree of asymmetry of the KL controlled by the composition of the nonmagnetic layers. For high degree of asymmetry the constraint on the electronic distribution leads to a configuration of Mo3O8 clusters with net spin-1/2 per cluster arrange on a triangular lattice and long range antiferromagnetic order. For low degree of asymmetry the electronic distribution leads to a magnetic phase with QSL character. We acknowledge support from NSERC and CFREF.

Antiferromagnetic and superconducting gaps and their interrelation in high-T sub c cuprates

CERN Document Server

Arrigoni, E; Eckl, T; Hanke, W

2003-01-01

We propose a phenomenological model, comprising a microscopic SO(5) model plus the on-site Hubbard interaction U (projected SO(5) model) to understand the interrelation between the d-wave-gap modulation observed by recent angle-resolved photoemission experiments in the insulating antiferromagnet Ca sub 2 CuO sub 2 Cl sub 2 and the d-wave gap of high-T sub c superconducting materials. The on-site interaction U is important in order to produce a Mott gap of the correct order of magnitude, which would be absent in an exact SO(5) theory. The projected SO(5)-model explains the gap characteristics, namely both the symmetry and the different order of magnitude of the gap modulations between the AF and the SCc phases. Furthermore, it is shown that the projected SO(5) theory can provide an explanation for a recent observation [E. Pavarini et al., Phys. Rev. Lett. 87, 47003 (2001)], i. e. that the maximum T sub c observed in a large variety of high-T sub c cuprates scales with the next-nearest-neighbor hopping matrix e...

Antiferromagnetic and superconducting gaps and their interrelation in high-Tc cuprates

International Nuclear Information System (INIS)

Arrigoni, E.; Zacher, M.G.; Eckl, T.; Hanke, W.

2003-01-01

We propose a phenomenological model, comprising a microscopic SO(5) model plus the on-site Hubbard interaction U (projected SO(5) model) to understand the interrelation between the d-wave-gap modulation observed by recent angle-resolved photoemission experiments in the insulating antiferromagnet Ca 2 CuO 2 Cl 2 and the d-wave gap of high-T c superconducting materials. The on-site interaction U is important in order to produce a Mott gap of the correct order of magnitude, which would be absent in an exact SO(5) theory. The projected SO(5)-model explains the gap characteristics, namely both the symmetry and the different order of magnitude of the gap modulations between the AF and the SCc phases. Furthermore, it is shown that the projected SO(5) theory can provide an explanation for a recent observation [E. Pavarini et al., Phys. Rev. Lett. 87, 47003 (2001)], i. e. that the maximum T c observed in a large variety of high-T c cuprates scales with the next-nearest-neighbor hopping matrix element t'. (Abstract Copyright [2003], Wiley Periodicals, Inc.)

Thermal insulation. Non-utilized energy need not be generated. Four rules for a successful thermal insulation by means of building insulation; Waermedaemmung. Energie, die nicht gebraucht wird, muss man nicht erzeugen. Vier Regeln fuer erfolgreichen Waermeschutz durch Gebaeudedaemmung

Energy Technology Data Exchange (ETDEWEB)

Patschke, Markus [3E-Consult, Nordkirchen (Germany); Drewer, Arnold [IpeG-Institut, Paderborn (Germany)

2011-07-15

The heat supply of buildings causes nearly one third of the energy consumption of an industrialized country. In 2006, the climate-adjusted heat consumption of private households in Germany amounted nearly 600 billion kWh. This consumption caused more than 167 million tons of CO{sub 2}. Heat insulation measures in buildings are required for all heat-transferring enveloping surface. Under this aspect, the contribution under consideration reports on four fundamental rules for a cost-efficient building insulation: (a) Only heated rooms should be insulated thermally; (b) Location and thermal insulation of cavities; (c) Selection of a suitable insulating material; (d) Consideration of an economic sustainability.

Sound Insulation between Dwellings

DEFF Research Database (Denmark)

Rasmussen, Birgit

2011-01-01

Regulatory sound insulation requirements for dwellings exist in more than 30 countries in Europe. In some countries, requirements have existed since the 1950s. Findings from comparative studies show that sound insulation descriptors and requirements represent a high degree of diversity...... and initiate – where needed – improvement of sound insulation of new and existing dwellings in Europe to the benefit of the inhabitants and the society. A European COST Action TU0901 "Integrating and Harmonizing Sound Insulation Aspects in Sustainable Urban Housing Constructions", has been established and runs...... 2009-2013. The main objectives of TU0901 are to prepare proposals for harmonized sound insulation descriptors and for a European sound classification scheme with a number of quality classes for dwellings. Findings from the studies provide input for the discussions in COST TU0901. Data collected from 24...

Localization and interaction effects during superconductor-insulator transition of Bi2Sr2Ca1-xGdxCu2O8+d

International Nuclear Information System (INIS)

Jayaram, B.; Lanchester, P.C.; Weller, M.T.

1991-01-01

An extensive study has been made of the resistivity of superconducting and semiconducting samples of the Bi 2 Sr 2 Ca 1-x Gd x Cu 2 O 8+d system. The effect of changing the Gd concentration and the annealing conditions is found to be a gradual change in the normal-state resistivity measured at 280 K (ρ n ). With the increase in ρ n , T c is depressed. The form of the T c depression is found to be consistent with a theory of localization and interaction effects on the superconductivity. In the insulator regime, however, the resistivity is due to variable-range hopping (VRH), the dimensionality of which changes from two to three as the ρ n increases away from the superconductor-insulator boundary. The observation of the two-dimensional VRH behavior in juxtaposition with the superconductivity is in qualitative agreement with a theoretical model that considers the competition between superconductivity and localization in a disordered system. When ρ n >1 Ω cm, the resistivity variation is found to be dominated by multiphonon-assisted hopping

Stability of low-carrier-density topological-insulator Bi2Se3 thin films and effect of capping layers

International Nuclear Information System (INIS)

Salehi, Maryam; Brahlek, Matthew; Koirala, Nikesh; Moon, Jisoo; Oh, Seongshik; Wu, Liang; Armitage, N. P.

2015-01-01

Although over the past number of years there have been many advances in the materials aspects of topological insulators (TIs), one of the ongoing challenges with these materials is the protection of them against aging. In particular, the recent development of low-carrier-density bulk-insulating Bi 2 Se 3 thin films and their sensitivity to air demands reliable capping layers to stabilize their electronic properties. Here, we study the stability of the low-carrier-density Bi 2 Se 3 thin films in air with and without various capping layers using DC and THz probes. Without any capping layers, the carrier density increases by ∼150% over a week and by ∼280% over 9 months. In situ-deposited Se and ex situ-deposited poly(methyl methacrylate) suppress the aging effect to ∼27% and ∼88%, respectively, over 9 months. The combination of effective capping layers and low-carrier-density TI films will open up new opportunities in topological insulators

Thermal insulation product for insulation, especially in nuclear power engineering, and method of its production

International Nuclear Information System (INIS)

Veselovsky, P.; Zink, S.; Balacek, P.; Mares, I.

1989-01-01

The insulation consists of a sewn fabric cover made of inorganic fibers, in which the fiber filling is reinforced mechanically by dense point interweaving. The inorganic fibers, 1 to 5 μm in diameter, consist of min. 97 wt.% mixture of aluminium and silicon oxides in the vitreous state. The fibers making up the cover consist of min. 95% silicon, aluminium, calcium, magnesium and boron oxides in the vitreous state; the rest can consist of alloy steel fibres. The bulk density of the insulation is 70 to 150 kg/m 3 . The product is highly resistant to temperature and to the action of chemicals, water, and acid and alkaline deactivation solutions. Its manufacture is fast and undemanding. It is designed for thermal insulation of pipes, tanks and valves in nuclear power plants. (M.D.). 2 figs

Insulator-metal transition in substrate-independent VO2 thin film for phase-change devices.

Science.gov (United States)

Taha, Mohammad; Walia, Sumeet; Ahmed, Taimur; Headland, Daniel; Withayachumnankul, Withawat; Sriram, Sharath; Bhaskaran, Madhu

2017-12-20

Vanadium has 11 oxide phases, with the binary VO 2 presenting stimuli-dependent phase transitions that manifest as switchable electronic and optical features. An elevated temperature induces an insulator-to-metal transition (IMT) as the crystal reorients from a monoclinic state (insulator) to a tetragonal arrangement (metallic). This transition is accompanied by a simultaneous change in optical properties making VO 2 a versatile optoelectronic material. However, its deployment in scalable devices suffers because of the requirement of specialised substrates to retain the functionality of the material. Sensitivity to oxygen concentration and larger-scale VO 2 synthesis have also been standing issues in VO 2 fabrication. Here, we address these major challenges in harnessing the functionality in VO 2 by demonstrating an approach that enables crystalline, switchable VO 2 on any substrate. Glass, silicon, and quartz are used as model platforms to show the effectiveness of the process. Temperature-dependent electrical and optical characterisation is used demonstrating three to four orders of magnitude in resistive switching, >60% chromic discrimination at infrared wavelengths, and terahertz property extraction. This capability will significantly broaden the horizon of applications that have been envisioned but remained unrealised due to the lack of ability to realise VO 2 on any substrate, thereby exploiting its untapped potential.

Electrical insulating liquid: A review

Directory of Open Access Journals (Sweden)

Deba Kumar Mahanta

2017-08-01

Full Text Available Insulating liquid plays an important role for the life span of the transformer. Petroleum-based mineral oil has become dominant insulating liquid of transformer for more than a century for its excellent dielectric and cooling properties. However, the usage of petroleum-based mineral oil, derived from a nonrenewable energy source, has affected the environment for its nonbiodegradability property. Therefore, researchers direct their attention to renewable and biodegradable alternatives. Palm fatty acid ester, coconut oil, sunflower oil, etc. are considered as alternatives to replace mineral oil as transformer insulation liquid. This paper gives an extensive review of different liquid insulating materials used in a transformer. Characterization of different liquids as an insulating material has been discussed. An attempt has been made to classify different insulating liquids-based on different properties.

Fabrication of Al2O3 Nano-Structure Functional Film on a Cellulose Insulation Polymer Surface and Its Space Charge Suppression Effect

Directory of Open Access Journals (Sweden)

Jian Hao

2017-10-01

Full Text Available Cellulose insulation polymer (paper/pressboard has been widely used in high voltage direct current (HVDC transformers. One of the most challenging issues in the insulation material used for HVDC equipment is the space charge accumulation. Effective ways to suppress the space charge injection/accumulation in insulation material is currently a popular research topic. In this study, an aluminium oxide functional film was deposited on a cellulose insulation pressboard surface using reactive radio frequency (RF magnetron sputtering. The sputtered thin film was characterized by the scanning electron microscopy/energy dispersive spectrometer (SEM/EDS, X-ray photoelectron spectroscopy (XPS, and X-ray diffraction (XRD. The influence of the deposited functional film on the dielectric properties and the space charge injection/accumulation behaviour was investigated. A preliminary exploration of the space charge suppression effect is discussed. SEM/EDS, XPS, and XRD results show that the nano-structured Al2O3 film with amorphous phase was successfully fabricated onto the fibre surface. The cellulose insulation pressboard surface sputtered by Al2O3 film has lower permittivity, conductivity, and dissipation factor values in the lower frequency (<103 Hz region. The oil-impregnated sputtered pressboard presents an apparent space-charge suppression effect. Compared with the pressboard sputtered with Al2O3 film for 90 min, the pressboard sputtered with Al2O3 film for 60 min had a better space charge suppression effect. Ultra-small Al2O3 particles (<10 nm grew on the surface of the larger nanoparticles. The nano-structured Al2O3 film sputtered on the fibre surface could act as a functional barrier layer for suppression of the charge injection and accumulation. This study offers a new perspective in favour of the application of insulation pressboard with a nano-structured function surface against space charge injection/accumulation in HVDC equipment.

Biodegradation performance of environmentally-friendly insulating oil

Science.gov (United States)

Yang, Jun; He, Yan; Cai, Shengwei; Chen, Cheng; Wen, Gang; Wang, Feipeng; Fan, Fan; Wan, Chunxiang; Wu, Liya; Liu, Ruitong

2018-02-01

In this paper, biodegradation performance of rapeseed insulating oil (RDB) and FR3 insulating oil (FR3) was studied by means of ready biodegradation method which was performed with Organization for Economic Co-operation and Development (OECD) 301B. For comparison, the biodegradation behaviour of 25# mineral insulating oil was also characterized with the same method. The testing results shown that the biodegradation degree of rapeseed insulating oil, FR3 insulating oil and 25# mineral insulating oil was 95.8%, 98.9% and 38.4% respectively. Following the “new chemical risk assessment guidelines” (HJ/T 154 - 2004), which illustrates the methods used to identify and assess the process safety hazards inherent. The guidelines can draw that the two vegetable insulating oils, i.e. rapeseed insulating oil and FR3 insulating oil are easily biodegradable. Therefore, the both can be classified as environmentally-friendly insulating oil. As expected, 25# mineral insulating oil is hardly biodegradable. The main reason is that 25# mineral insulating oil consists of isoalkanes, cyclanes and a few arenes, which has few unsaturated bonds. Biodegradation of rapeseed insulating oil and FR3 insulating oil also remain some difference. Biodegradation mechanism of vegetable insulating oil was revealed from the perspective of hydrolysis kinetics.

Voltage-driven magnetization control in topological insulator/magnetic insulator heterostructures

Directory of Open Access Journals (Sweden)

Michael E. Flatté

2017-05-01

Full Text Available A major barrier to the development of spin-based electronics is the transition from current-driven spin torque, or magnetic-field-driven magnetization reversal, to a more scalable voltage-driven magnetization reversal. To achieve this, multiferroic materials appear attractive, however the effects in current materials occur at very large voltages or at low temperatures. Here the potential of a new class of hybrid multiferroic materials is described, consisting of a topological insulator adjacent to a magnetic insulator, for which an applied electric field reorients the magnetization. As these materials lack conducting states at the chemical potential in their bulk, no dissipative charge currents flow in the bulk. Surface states at the interface, if present, produce effects similar to surface recombination currents in bipolar devices, but can be passivated using magnetic doping. Even without conducting states at the chemical potential, for a topological insulator there is a finite spin Hall conductivity provided by filled bands below the chemical potential. Spin accumulation at the interface with the magnetic insulator provides a torque on the magnetization. Properly timed voltage pulses can thus reorient the magnetic moment with only the flow of charge current required in the leads to establish the voltage. If the topological insulator is sufficiently thick the resulting low capacitance requires little charge current.

Gas insulated substations

CERN Document Server

2014-01-01

This book provides an overview on the particular development steps of gas insulated high-voltage switchgear, and is based on the information given with the editor's tutorial. The theory is kept low only as much as it is needed to understand gas insulated technology, with the main focus of the book being on delivering practical application knowledge. It discusses some introductory and advanced aspects in the meaning of applications. The start of the book presents the theory of Gas Insulated Technology, and outlines reliability, design, safety, grounding and bonding, and factors for choosing GIS. The third chapter presents the technology, covering the following in detail: manufacturing, specification, instrument transformers, Gas Insulated Bus, and the assembly process. Next, the book goes into control and monitoring, which covers local control cabinet, bay controller, control schemes, and digital communication. Testing is explained in the middle of the book before installation and energization. Importantly, ...

Localization of holes near charged defects in orbitally degenerate, doped Mott insulators

Science.gov (United States)

Avella, Adolfo; Oleś, Andrzej M.; Horsch, Peter

2018-05-01

We study the role of charged defects, disorder and electron-electron (e-e) interactions in a multiband model for t2g electrons in vanadium perovskites R1-xCaxVO3 (R = La,…,Y). By means of unrestricted Hartree-Fock calculations, we find that the atomic multiplet structure persists up to 50% Ca doping. Using the inverse participation number, we explore the degree of localization and its doping dependence for all electronic states. The observation of strongly localized wave functions is consistent with our conjecture that doped holes form spin-orbital polarons that are strongly bound to the charged Ca2+ defects. Interestingly, the long-range e-e interactions lead to a discontinuity in the wave function size across the chemical potential, where the electron removal states are more localized than the addition states.

Aharonov–Bohm interference in topological insulator nanoribbons

KAUST Repository

Peng, Hailin

2009-12-13

Topological insulators represent unusual phases of quantum matter with an insulating bulk gap and gapless edges or surface states. The two-dimensional topological insulator phase was predicted in HgTe quantum wells and confirmed by transport measurements. Recently, Bi2 Se3 and related materials have been proposed as three-dimensional topological insulators with a single Dirac cone on the surface, protected by time-reversal symmetry. The topological surface states have been observed by angle-resolved photoemission spectroscopy experiments. However, few transport measurements in this context have been reported, presumably owing to the predominance of bulk carriers from crystal defects or thermal excitations. Here we show unambiguous transport evidence of topological surface states through periodic quantum interference effects in layered single-crystalline Bi2 Se3 nanoribbons, which have larger surface-to-volume ratios than bulk materials and can therefore manifest surface effects. Pronounced Aharonov-Bohm oscillations in the magnetoresistance clearly demonstrate the coherent propagation of two-dimensional electrons around the perimeter of the nanoribbon surface, as expected from the topological nature of the surface states. The dominance of the primary h/e oscillation, where h is Plancks constant and e is the electron charge, and its temperature dependence demonstrate the robustness of these states. Our results suggest that topological insulator nanoribbons afford promising materials for future spintronic devices at room temperature.

Recovery Act. Advanced Building Insulation by the CO₂ Foaming Process

Energy Technology Data Exchange (ETDEWEB)

Yang, Arthur [Industrial Science and Technology Network, Inc., Lancaster, PA (United States)

2013-12-30

In this project, ISTN proposed to develop a new "3rd" generation of insulation technology. The focus was a cost-effective foaming process that could be used to manufacture XPS and other extruded polymer foams using environmentally clean blowing agents, and ultimately achieve higher R-values than existing products while maintaining the same level of cost-efficiency. In the U.S., state-of-the-art products are primarily manufactured by two companies: Dow and Owens Corning. These products (i.e., STYROFOAM and FOAMULAR) have a starting thermal resistance of R-5.0/inch, which declines over the life of the product as the HFC blowing agents essential to high R-value exchange with air in the environment. In the existing technologies, the substitution of CO2 for HFCs as the primary foaming agent results in a much lower starting R-value, as evidenced in CO2-foamed varieties of XPS in Europe with R-4.2/inch insulation value. The major overarching achievement from this project was ISTN's development of a new process that uses CO2 as a clean blowing agent to achieve up to R-5.2/inch at the manufacturing scale, with a production cost on a per unit basis that is less than the cost of Dow and Owens Corning XPS products.

Operation of a Five-Stage 40,000-CM2-Area Insulator Stack at 158 KV/CM

International Nuclear Information System (INIS)

Anderson RA; Clark, Robert E; Corcoran, PA; Douglas, John W; Gilliland, TL; Horry, ML; Hughes, Thomas P; Ives, HC; Long, FW; Martin, TH; McDaniel, DH; Milton, Osborne; Mostrom, Michael A; Seamen, JF; Shoup, RW; Smith, ID; Smith, JW; Spielman, RB; Struve, KW; Stygar, WA; Vogtlin, George E; Wagoner, TC; Yamamoto, Osamu

1999-01-01

We have demonstrated successful operation of a 3.35- m-diameter insulator stack at 158 kV/cm on five consecutive Z-accelerator shots. The stack consisted of five +45 deg;-profile 5.715-cm-thick cross-linked-polystyrene (Rexolite- 1422) insulator rings, and four anodized- aluminum grading rings shaped to reduce the field at cathode triple junctions. The width of the voltage pulse at 89% of peak was 32 ns. We compare this result to a new empirical flashover relation developed from previous small-insulator experiments conducted with flat unanodized electrodes. The relation predicts a 50% flashover probability for a Rexolite insulator during an applied voltage pulse when E max e -0.27/d (t eff C) 1/10 = 224, where E max is the peak mean electric field (kV/cm), d is the insulator thickness (cm), t eff is the effective pulse width (ps), and C is the insulator circumference (cm). We find the Z stack can be operated at a stress at least 19% higher than predicted. This result, and previous experiments conducted by Vogtlin, suggest anodized electrodes with geometries that reduce the field at both anode and cathode triple junctions would improve the flashover strength of +45 deg; insulators

Bankole et al (2)

African Journals Online (AJOL)

DELL

Relationships of Clay-filled Channels on the Delta Flanks (Modified after Doust and Omatsola, 1990 and Lawrence et al., 2002). ... and in the Indo-Malaysian area (Germeraad et al.,. 1968). The genus ..... Upper Cretaceous of British Guiana.

Analysis of Pathogenesis of Autoimmune Insulitis in NOD Mice: Adoptive Transfer Experiments of Insulitis in ILI and NOD Nude Mice

OpenAIRE

Nakamura, Moritaka; Nishimura, Masahiko; Koide, Yukio; Takato, O.Yoshida

2003-01-01

In an effort to study the pathophysiological events in the development of insulitis in NOD mice, we have developed ILI- and NOD-nu/nu mice. ILI mice are a nondiabetic inbred strain but are derived from the same Jcl:ICR mouse as NOD mice and share the same H-2 allotype with NOD mice. Splenocytes and CD4+ cells from diabetic NOD mice appeared to transfer insulitis to ILI-nu/nu mice, suggesting that ILI mice already express autoantigen(s) responsible for insulitis. But reciprocal thymic grafts f...

Intersite Coulomb interaction and Heisenberg exchange

NARCIS (Netherlands)

Eder, R; van den Brink, J.; Sawatzky, G.A

1996-01-01

Based on exact diagonalization results for small clusters we discuss the effect of intersite Coulomb repulsion in Mott-Hubbard or charge transfers insulators. Whereas the exchange constant J for direct exchange is enhanced by intersite Coulomb interaction, that for superexchange is suppressed. The

Ojo et al (2)

African Journals Online (AJOL)

DELL

network geometry hence control how the samples' ... generate different permeability curves from wire- ... occupy in the reservoir pore system (McPhee et. ..... Fig.3. Poroperm cross-plot for a homogenous reservoir. Ojo et al.: Rock Type Based ...

Insulation structure of thermonuclear device

International Nuclear Information System (INIS)

Suzuki, Takayuki; Usami, Saburo; Tsukamoto, Hideo; Kikuchi, Mitsuru

1998-01-01

The present invention provides an insulating structure of a thermonuclear device, in which insulation materials between toroidal coils are not broken even if superconductive toroidal coils are used. Namely, a tokamak type thermonuclear device of an insulating structure type comprises superconductive toroidal coils for confining plasmas arranged in a circular shape directing the center each at a predetermined angle, and the toroidal coils are insulated from each other. The insulation materials are formed by using a biaxially oriented fiber reinforced plastics. The contact surface of the toroidal coils and the insulating materials are arranged so that they are contact at a woven surface of the fiber reinforced plastics. Either or both of the contact surfaces of the fiber reinforced plastics and the toroidal coils are coated with a high molecular compound having a low friction coefficient. With such a constitution, since the interlayer shearing strength of the biaxially oriented fiber reinforced plastics is about 1/10 of the compression strength, the shearing stress exerted on the insulation material is reduced. Since a static friction coefficient on the contact surface is reduced to provide a structure causing slipping, shearing stress does not exceeds a predetermined limit. As a result, breakage of the insulation materials between the toroidal coils can be prevented. (I.S.)

Thermal insulation

International Nuclear Information System (INIS)

Durston, J.G.; Birch, W.; Facer, R.I.; Stuart, R.A.

1977-01-01

Reference is made to liquid metal cooled nuclear reactors. In the arrangement described the reactor vessel is clad with thermal insulation comprising a layer of insulating blocks spaced from the wall and from each other; each block is rigidly secured to the wall, and the interspaces are substantially closed against convectional flow of liquid by resilient closure members. A membrane covering is provided for the layer of blocks, with venting means to allow liquid from the reactor vessel to penetrate between the covering and the layer of blocks. The membrane covering may comprise a stainless steel sheet ribbed in orthogonal pattern to give flexibility for the accommodation of thermal strain. The insulating blocks may be comprised of stainless steel or cellular or porous material and may be hollow shells containing ceramic material or gas fillings. (U.K.)

Insulation Reformulation Development

Science.gov (United States)

Chapman, Cynthia; Bray, Mark

2015-01-01

The current Space Launch System (SLS) internal solid rocket motor insulation, polybenzimidazole acrylonitrile butadiene rubber (PBI-NBR), is a new insulation that replaced asbestos-based insulations found in Space Shuttle heritage solid rocket boosters. PBI-NBR has some outstanding characteristics such as an excellent thermal erosion resistance, low thermal conductivity, and low density. PBI-NBR also has some significant challenges associated with its use: Air entrainment/entrapment during manufacture and lay-up/cure and low mechanical properties such as tensile strength, modulus, and fracture toughness. This technology development attempted to overcome these challenges by testing various reformulated versions of booster insulation. The results suggest the SLS program should continue to investigate material alternatives for potential block upgrades or use an entirely new, more advanced booster. The experimental design was composed of a logic path that performs iterative formulation and testing in order to maximize the effort. A lab mixing baseline was developed and documented for the Rubber Laboratory in Bldg. 4602/Room 1178.

Impact of insulation and consumer behavior on natural gas consumption

Energy Technology Data Exchange (ETDEWEB)

van Mastrigt, P.

1983-09-01

The influence of insulation measures and certain changes in behavioral patterns on gas consumption for home heating has been examined, both on an annual basis and on the maximum day and at the maximum hour. By means of good insulation (cavity wall insulation and double glazing on the ground floor) annual gas consumption can be brought down by 28-35%, depending on the type of dwelling, as compared with moderate insulation. Maximum day consumption will go down by 26-33% and maximum hour consumption by no more than 20-28%. Further insulation, to current Danish standards, would enable savings of up to 72% of annual consumption, 64-66% of maximum day consumption and 52-55% of maximum hour consumption. By further night reduction from 14.5 degrees C to 12 degrees C 2% of the annual consumption can be saved in moderately insulated dwellings. It also leads, however, to an increase in maximum hour consumption by some 11%. In heavily insulated dwellings further night reduction does not yield any additional savings on the annual consumption. By lowering the thermostat setting by 2 degrees C in the daytime annual consumption in a moderately insulated dwelling can be cut by 9%. With increasing insulation level the savings will get higher, up to 11% in heavily insulated dwellings. Drawing the curtains during the evening and night may yield savings of 4-6% depending on the ratio of glass surface to total outer wall surface. These savings will be lower as the insulation level increases. The results of the study have been converted to the overall domestic natural gas consumption in the Netherlands. In 1985 the annual consumption will be 7% lower than in 1978 as a result of insulation measures and changes in consumer behavior, even at a rise in the total number of connections. Maximum day consumption will be 5% lower and maximum hour consumption will be virtually the same. This trend became already manifest during the 1978-1982 period.

Designing in-plane heterostructures of quantum spin Hall insulators from first principles: 1T'-MoS2 with adsorbates

DEFF Research Database (Denmark)

Olsen, Thomas

2016-01-01

opportunity to change the local topology by adsorption of atoms or molecules and thus comprise an ideal platform for designing topological heterostructures. Here we apply first-principles calculations to show that the quantum spin Hall insulator 1T'-MoS2 exhibits a phase transition to a trivial insulator upon....... This is in sharp contrast to topological edge states, which typically exhibit strong dispersion that are sensitive to a particular edge termination. The heterostructure is also suggestive of a simple design of one-dimensional metallic networks in sheets of 1T'-MoS2....

Experimental evidence for a Mott-Wigner glass phase of magnetite above the Verwey temperature

International Nuclear Information System (INIS)

Boekema, C.; Lichti, R.L.; Chan, K.C.B.; Brabers, V.A.M.; Denison, A.B.; Cooke, D.W.; Heffner, R.H.; Hutson, R.L.; Schillaci, M.E.

1986-01-01

New muon-spin-relaxation (μSR) results on magnetite are reported and discussed in light of earlier Moessbauer, neutron, and μSR results. Modification of the μSR anomaly (observed at 247 K in zero field), when an external magnetic field is applied, provides evidence that the anomaly results from cross relaxation between the muon Larmor precession and the electron-correlation process in the B sublattice. The combined results strongly indicate that phonon-assisted electron hopping is the principal conduction mechanism above the Verwey transition temperature (T/sub V/). Together with theoretical evidence, these data support Mott's suggestion that above T/sub V/ magnetite is in the Wigner-glass state

Insulation Strength and Decomposition Characteristics of a C6F12O and N2 Gas Mixture

Directory of Open Access Journals (Sweden)

Xiaoxing Zhang

2017-08-01

Full Text Available This paper explores the decomposition characteristics of a new type of environmentally friendly insulating gas C6F12O and N2 mixed gas under AC voltage. The breakdown behavior of 3% C6F12O and N2 mixed gas in quasi-uniform field was investigated through a breakdown experiment. The self-recovery of the mixed gas was analyzed by 100 breakdown experiments. The decomposition products of C6F12O and N2 under breakdown voltage were determined by gas chromatography–mass spectrometer (GC-MS. Finally, the decomposition process of the products was calculated by density functional theory, and the ionization energy, affinity, and molecular orbital gap of the decomposition products were also calculated. The properties of the decomposition products were analyzed from the aspects of insulation and environmental protection. The experimental results show that the 3% C6F12O and N2 mixed gas did not show a downward trend over 100 breakdown tests under a 0.10 MPa breakdown voltage. The decomposition products after breakdown were CF4, C2F6, C3F6, C3F8, C4F10, and C5F12. The ionization energies of several decomposition products are more than 10 eV. The Global Warming Potential (GWP values of the main products are lower than SF6. C2F6, C3F8, and C4F10 have better insulation properties.

Magnetic and transport properties of Ni2MnGa-BaTiO3 metal-insulator particulate composite with percolation threshold

International Nuclear Information System (INIS)

Won, C.J.; Kambale, R.C.; Hur, N.

2011-01-01

Highlights: → The Ni 2 MnGa-BaTiO 3 type composites were first time prepared by solid state reaction. → Temperature dependent magnetic properties reveal two kinds of transitions in these composite. → The present materials show negative magnetoresistance effect. → The present studies on magnetic and electrical transport of metal/insulator (NMG/BTO) composites shows the resistivity change associated to filamentary conducting path at percolation threshold. - Abstract: Here we report the magnetic and transport properties of the metal/insulator (f NMG )Ni 2 MnGa/(1 - f NMG )BaTiO 3 composites. The X-ray diffraction study confirms the formation of both the phases in composite. The microstructure reveals that the conducting Ni 2 MnGa particles are well dispersed in an insulating BaTiO 3 matrix. Temperature dependent magnetization shows two transitions one above 300 K and other below 150 K. The temperature dependence resistivity near the percolation threshold f NMG = 0.4 had drastic changes which is higher than the f NMG = 0.5. Also the negative magnetoresistance effect was observed for the studied materials. We suggest that magnetic and transport properties at the percolation threshold can be adjusted by the strain from the surrounding insulator particle.

Reflective Insulation for Energy Conservation in South East Asia

Science.gov (United States)

San Teh, Khar; Yarbrough, David W.; Haw Lim, Chin; Salleh, Elias

2017-05-01

Thermal resistances have been measured for attic spaces insulated with reflective insulations. Three test units located in Malaysia were instrumented to provide heat flux and temperatures for the calculation of time-average RSI-values (RSI is representing R-value in SI units). The RSI for attics with enclosed reflective air spaces were in the range 2-3 m2·K/W while the uninsulated attics averaged about 0.4 m2·K/W. The RSI-values determined in this project were for heat-flow down, the predominant heat-flow direction for attic spaces in Equatorial regions. The observed thermal resistances due to the installation of the reflective insulation results in an 80-90% annual decrease in the heat transfer across the ceiling. This reduces utility usage for air conditioned units and improved comfort for occupants. The research demonstrates the use of transient data for the determination of thermal insulation performance and usefulness of enclosed reflective air spaces for thermal resistance.

Charge transport through superconductor/Anderson-insulator interfaces

International Nuclear Information System (INIS)

Frydman, A.; Ovadyahu, Z.

1997-01-01

We report on a study of charge transport through superconductor-insulator-superconductor and normal metal endash insulator endash superconductor structures (SIS and NIS junctions, respectively) where the insulator is of the Anderson type. Devices which are characterized by a junction resistance larger than 10 kΩ show behavior which is typical of Giaever tunnel junctions. In structures having smaller resistance, several peculiar features are observed. In the SIS junctions, Josephson coupling is detected over distances much larger then the typical insulator localization length. In addition, a series of resistance peaks appears at voltages of 2Δ/n, where Δ is the superconducting gap. The NIS Junctions exhibit a large resistance dip at subgap bias. We discuss possible interpretations of these findings and suggest that they may result from the presence of high transmission channels through the barrier region. copyright 1997 The American Physical Society

Microscopic effects of Dy doping in the topological insulator Bi2Te3

Science.gov (United States)

Duffy, L. B.; Steinke, N.-J.; Krieger, J. A.; Figueroa, A. I.; Kummer, K.; Lancaster, T.; Giblin, S. R.; Pratt, F. L.; Blundell, S. J.; Prokscha, T.; Suter, A.; Langridge, S.; Strocov, V. N.; Salman, Z.; van der Laan, G.; Hesjedal, T.

2018-05-01

Magnetic doping with transition metal ions is the most widely used approach to break time-reversal symmetry in a topological insulator (TI)—a prerequisite for unlocking the TI's exotic potential. Recently, we reported the doping of Bi2Te3 thin films with rare-earth ions, which, owing to their large magnetic moments, promise commensurately large magnetic gap openings in the topological surface states. However, only when doping with Dy has a sizable gap been observed in angle-resolved photoemission spectroscopy, which persists up to room temperature. Although disorder alone could be ruled out as a cause of the topological phase transition, a fundamental understanding of the magnetic and electronic properties of Dy-doped Bi2Te3 remained elusive. Here, we present an x-ray magnetic circular dichroism, polarized neutron reflectometry, muon-spin rotation, and resonant photoemission study of the microscopic magnetic and electronic properties. We find that the films are not simply paramagnetic but that instead the observed behavior can be well explained by the assumption of slowly fluctuating, inhomogeneous, magnetic patches with increasing volume fraction as the temperature decreases. At liquid helium temperatures, a large effective magnetization can be easily introduced by the application of moderate magnetic fields, implying that this material is very suitable for proximity coupling to an underlying ferromagnetic insulator or in a heterostructure with transition-metal-doped layers. However, the introduction of some charge carriers by the Dy dopants cannot be excluded at least in these highly doped samples. Nevertheless, we find that the magnetic order is not mediated via the conduction channel in these samples and therefore magnetic order and carrier concentration are expected to be independently controllable. This is not generally the case for transition-metal-doped topological insulators, and Dy doping should thus allow for improved TI quantum devices.

Effects of insulating vanadium oxide composite in concomitant mixed phases via interface barrier modulations on the performance improvements in metal-insulator-metal diodes

Directory of Open Access Journals (Sweden)

Kaleem Abbas

2018-03-01

Full Text Available The performance of metal-insulator-metal diodes is investigated for insulating vanadium oxide (VOx composite composed of concomitant mixed phases using the Pt metal as the top and the bottom electrodes. Insulating VOx composite in the Pt/VOx/Pt diode exhibits a high asymmetry of 10 and a very high sensitivity of 2,135V−1 at 0.6 V. The VOx composite provides Schottky-like barriers at the interface, which controls the current flow and the trap-assisted conduction mechanism. Such dramatic enhancement in asymmetry and rectification performance at low applied bias may be ascribed to the dynamic control of the insulating and metallic phases in VOx composites. We find that the nanostructure details of the insulating VOx layer can be critical in enhancing the performance of MIM diodes.

New Light on the Metal-Insulator Transition in VO₂: A Terahertz Perspective

DEFF Research Database (Denmark)

Jepsen, Peter Uhd; Fischer, Bernd M.; Thoman, Andreas

2005-01-01

We investigate the metal-insulator (MI) transition in vanadium dioxide (VO2), thin films with Terahertz Time-Domains Spectroscopy (THz-TDS). The capability of detecting both amplitude and phase of the transmission characteristics as the phase of the transmitted THz signal switches at a markedly...

Influence of the valence states of atoms on conducting properties of PrBa2Cu3O6+x

International Nuclear Information System (INIS)

Romanenko, A.I.; Zakharchuk, N.F.; Naumov, N.G.; Fedorov, V.E.; Paek, U.H.

1997-01-01

Pr 3+ valent state only was discovered in PrBa 2 Cu 3 O 6+x within the oxygen content range 0.4 ≤ x ≤ 0.6. Out of this range, Pr 4+ state appears also. All the samples obtained showed insulating behavior of resistivity r(T). In PrBa 2 Cu 3 O 6+x (0.4 ≤ x ≤ 0.6), the resistivity is Mott variable-range hopping conduction type and is connected with oxygen disorder only. Out of this range, the localization is much stronger; this increase is due to Pr 4+ /Pr 3+ position disorder. Also, the localization decreases after annealing at room temperature is the result of ordering. Thus, the absence of metallic (and therefore superconducting) state in PrBa 2 Cu 3 O 6+x is due to the presence of both Pr 4+ and Pr 4+ /Pr 3+ disorder

Insulation coordination workstation for AC and DC substations

International Nuclear Information System (INIS)

Booth, R.R.; Hileman, A.R.

1990-01-01

The Insulation Coordination Workstation was designed to aid the substation design engineer in the insulation coordination process. The workstation utilizes state of the art computer technology to present a set of tools necessary for substation insulation coordination, and to support the decision making process for all aspects of insulation coordination. The workstation is currently being developed for personal computers supporting OS/2 Presentation Manager. Modern Computer-Aided Software Engineering (CASE) technology was utilized to create an easily expandable framework which currently consists of four modules, each accessing a central application database. The heart of the workstation is a library of user-friendly application programs for the calculation of important voltage stresses used for the evaluation of insulation coordination. The Oneline Diagram is a graphic interface for data entry into the EPRI distributed EMTP program, which allows the creation of complex systems on the CRT screen using simple mouse clicks and keyboard entries. Station shielding is graphically represented in the Geographic Viewport using a three-dimensional substation model, and the interactive plotting package allows plotting of EPRI EMTP output results on the CRT screen, printer, or pen plotter. The Insulation Coordination Workstation was designed by Advanced Systems Technology (AST), a division of ABB Power Systems, Inc., and sponsored by the Electric Power Research Institute under RP 2323-5, AC/DC Insulation Coordination Workstation

A Mott polarimeter for the search of time reversal violation in the decay of free neutrons

International Nuclear Information System (INIS)

Ban, G.; Beck, M.; Bialek, A.; Bodek, K.; Gorel, P.; Kirch, K.; Kistryn, St.; Kozela, A.; Kuzniak, M.; Lindroth, A.; Naviliat-Cuncic, O.; Pulut, J.; Severijns, N.; Stephan, E.; Zejma, J.

2006-01-01

A new polarimeter for low-energy electrons has been built and tested. The device was developed for the measurement of the transverse polarization of beta particles emitted in the decay of polarized cold neutrons. The decay electrons are identified by multi-wire proportional chambers made of low-Z materials and are detected with plastic scintillator hodoscopes. The transverse polarization is analyzed by means of large angle Mott scattering on a thin Pb foil. We describe here the elements of the apparatus and present the results of test measurements which illustrate its performance

A Mott polarimeter for the search of time reversal violation in the decay of free neutrons

Energy Technology Data Exchange (ETDEWEB)

Ban, G. [Laboratoire de Physique Corpusculaire, Caen (France); Beck, M. [Catholic University, Leuven (Belgium); Bialek, A. [Institute of Physics, Polish Academy of Sciences, Cracow (Poland); Bodek, K. [Institute of Physics, Jagiellonian University, Cracow (Poland)]. E-mail: ufbodek@if.uj.edu.pl; Gorel, P. [Laboratoire de Physique Corpusculaire, Caen (France); Paul Scherrer Institute, Villigen (Switzerland); Kirch, K. [Paul Scherrer Institute, Villigen (Switzerland); Kistryn, St. [Institute of Physics, Jagiellonian University, Cracow (Poland); Kozela, A. [Institute of Physics, Polish Academy of Sciences, Cracow (Poland); Kuzniak, M. [Institute of Physics, Jagiellonian University, Cracow (Poland); Lindroth, A. [Catholic University, Leuven (Belgium); Naviliat-Cuncic, O. [Laboratoire de Physique Corpusculaire, Caen (France); Pulut, J. [Institute of Physics, Jagiellonian University, Cracow (Poland); Paul Scherrer Institute, Villigen (Switzerland); Catholic University, Leuven (Belgium); Severijns, N. [Catholic University, Leuven (Belgium); Stephan, E. [Institute of Physics, University of Silesia, Katowice (Poland); Zejma, J. [Institute of Physics, Jagiellonian University, Cracow (Poland)

2006-09-15

A new polarimeter for low-energy electrons has been built and tested. The device was developed for the measurement of the transverse polarization of beta particles emitted in the decay of polarized cold neutrons. The decay electrons are identified by multi-wire proportional chambers made of low-Z materials and are detected with plastic scintillator hodoscopes. The transverse polarization is analyzed by means of large angle Mott scattering on a thin Pb foil. We describe here the elements of the apparatus and present the results of test measurements which illustrate its performance.

Cooper Pairs in Insulators?

International Nuclear Information System (INIS)

Valles, James

2008-01-01

Nearly 50 years elapsed between the discovery of superconductivity and the emergence of the microscopic theory describing this zero resistance state. The explanation required a novel phase of matter in which conduction electrons joined in weakly bound pairs and condensed with other pairs into a single quantum state. Surprisingly, this Cooper pair formation has also been invoked to account for recently uncovered high-resistance or insulating phases of matter. To address this possibility, we have used nanotechnology to create an insulating system that we can probe directly for Cooper pairs. I will present the evidence that Cooper pairs exist and dominate the electrical transport in these insulators and I will discuss how these findings provide new insight into superconductor to insulator quantum phase transitions.

Structural, electronic and magnetic properties of the series of double perovskites (Ca,Sr){sub 2−x}La{sub x}FeIrO{sub 6}

Energy Technology Data Exchange (ETDEWEB)

Bufaiçal, L., E-mail: lbufaical@ufg.br [Instituto de Física, Universidade Federal de Goiás, 74001-970 Goiânia, GO (Brazil); Adriano, C. [Instituto de Física “Gleb Wataghin”, UNICAMP, 13083-859 Campinas, SP (Brazil); Lora-Serrano, R. [Instituto de Física, Universidade Federal de Uberlândia, 38400-902 Uberlândia, MG (Brazil); Duque, J.G.S. [Núcleo de Física, Universidade Federal de Sergipe, Campus Itabaiana, 49500-000 Itabaiana, SE (Brazil); Mendonça-Ferreira, L. [Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, 09210-170 Santo André, SP (Brazil); Rojas-Ayala, C.; Baggio-Saitovitch, E.; Bittar, E.M. [Centro Brasileiro de Pesquisas Físicas, 22290-180 Rio de Janeiro, RJ (Brazil); Pagliuso, P.G. [Instituto de Física “Gleb Wataghin”, UNICAMP, 13083-859 Campinas, SP (Brazil)

2014-04-01

Polycrystalline samples of the series of double perovskites Sr{sub 2−x}La{sub x}FeIrO{sub 6} were synthesized. Their structural, electronic and magnetic properties were investigated by X-ray powder diffraction, Mössbauer spectroscopy, magnetic susceptibility, heat capacity and electrical resistivity experiments. The compounds crystallize in a monoclinic structure and were fitted in space group P2{sub 1}/n, with a significant degree of Fe/Ir cationic disorder. As in Ca{sub 2−x}La{sub x}FeIrO{sub 6} the Sr-based system seems to evolve from an antiferromagnetic ground state for the end members (x=0.0 and x=2.0) to a ferrimagnetic order in the intermediate regions (x∼1). Since Mössbauer spectra indicate that Fe valence remains 3+ with doping, this tendency of change in the nature of the microscopic interaction could be attributed to Ir valence changes, induced by La{sup 3+} electrical doping. Upon comparing both Ca and Sr series, Sr{sub 2−x}La{sub x}FeIrO{sub 6} is more structurally homogenous and presents higher magnetization and transition temperatures. Magnetic susceptibility measurements at high temperatures on Sr{sub 1.2}La{sub 0.8}FeIrO{sub 6} indicate a very high ferrimagnetic Curie temperature T{sub C}∼700K. For the Sr{sub 2}FeIrO{sub 6} compound, electrical resistivity experiments under applied pressure suggest that this material might be a Mott insulator. - Graphical abstract: The Weiss constant as a function of La doping for the (Ca,Sr){sub 2−x}La{sub x}FeIrO{sub 6} series, indicating changes in Fe–Ir magnetic coupling on both families. - Highlights: • The double perovskite series (Ca,Sr){sub 2−x}La{sub x}FeIrO{sub 6} were synthesized. • Changes in the Fe-Ir magnetic coupling due to La doping on both series. • Evidence of high T{sub C} on Sr{sub 1.2}La{sub 0.8}FeIrO{sub 6}. • Indication of Mott insulator behavior on Sr{sub 2}FeIrO{sub 6}.

2D layered insulator hexagonal boron nitride enabled surface passivation in dye sensitized solar cells.

Science.gov (United States)

Shanmugam, Mariyappan; Jacobs-Gedrim, Robin; Durcan, Chris; Yu, Bin

2013-11-21

A two-dimensional layered insulator, hexagonal boron nitride (h-BN), is demonstrated as a new class of surface passivation materials in dye-sensitized solar cells (DSSCs) to reduce interfacial carrier recombination. We observe ~57% enhancement in the photo-conversion efficiency of the DSSC utilizing h-BN coated semiconductor TiO2 as compared with the device without surface passivation. The h-BN coated TiO2 is characterized by Raman spectroscopy to confirm the presence of highly crystalline, mixed monolayer/few-layer h-BN nanoflakes on the surface of TiO2. The passivation helps to minimize electron-hole recombination at the TiO2/dye/electrolyte interfaces. The DSSC with h-BN passivation exhibits significantly lower dark saturation current in the low forward bias region and higher saturation in the high forward bias region, respectively, suggesting that the interface quality is largely improved without impeding carrier transport at the material interface. The experimental results reveal that the emerging 2D layered insulator could be used for effective surface passivation in solar cell applications attributed to desirable material features such as high crystallinity and self-terminated/dangling-bond-free atomic planes as compared with high-k thin-film dielectrics.

Correlated effective field theory in transition metal compounds

International Nuclear Information System (INIS)

Mukhopadhyay, Subhasis; Chatterjee, Ibha

2004-01-01

Mean field theory is good enough to study the physical properties at higher temperatures and in higher dimensions. It explains the critical phenomena in a restricted sense. Near the critical temperatures, when fluctuations become important, it may not give the correct results. Similarly in low dimensions, the correlations become important and the mean field theory seems to be inadequate to explain the physical phenomena. At low-temperatures too, the quantum correlations become important and these effects are to be treated in an appropriate way. In 1974, Prof. M.E. Lines of Bell Laboratories, developed a theory which goes beyond the mean field theory and is known as the correlated effective field (CEF) theory. It takes into account the fluctuations in a semiempirical way. Lines and his collaborators used this theory to explain the short-range correlations and their anisotropy in the paramagnetic phase. Later Suzuki et al., Chatterjee and Desai, Mukhopadhyay and Chatterjee applied this theory to the magnetically ordered phase and a tremendous success of the theory has been found in real systems. The success of the CEF theory is discussed in this review. In order to highlight the success of this theory, earlier effective field theories and their improvements over mean field theories e.g., Bethe-Peierls-Weiss method, reaction field approximation, etc., are also discussed in this review for completeness. The beauty of the CEF theory is that it is mean field-like, but captures the essential physics of real systems to a great extent. However, this is a weak correlated theory and as a result is inappropriate for the metallic phase when strong correlations become important. In recent times, transition metal oxides become important due to the discovery of the high-temperature superconductivity and the colossal magnetoresistance phenomena. These oxides seem to be Mott insulators and undergo an insulator to metal transition by applying magnetic field, pressure and by changing

Metal–insulator transition in Ni-doped Na0.75CoO2: Insights from ...

Indian Academy of Sciences (India)

resistivity on lowering the temperature, with the metal-to-insulator transition temperature. (TMIT) increasing with the Ni ... The Ni-doped sample is seen to change over from a metallic to insulating behaviour at ~175 K. The ..... neutron diffraction to look for structural changes, viz., changes in bond lengths and site occupancies ...

Environmental safety providing during heat insulation works and using thermal insulation materials

Directory of Open Access Journals (Sweden)

Velichko Evgeny

2017-01-01

Full Text Available This article considers the negative effect of thermal insulating materials and products on human health and environment pollution, particularly in terms of the composition of environmentally hazardous construction products. The authors have analyzed the complex measures for providing ecological safety, sanitary and epidemiological requirements, rules and regulations both during thermal insulation works and throughout the following operation of buildings and premises. The article suggests the protective and preventive measures to reduce and eliminate the negative impact of the proceeding of thermal insulation works on the natural environment and on human health.

16 CFR 460.18 - Insulation ads.

Science.gov (United States)

2010-01-01

... Commercial Practices FEDERAL TRADE COMMISSION TRADE REGULATION RULES LABELING AND ADVERTISING OF HOME INSULATION § 460.18 Insulation ads. (a) If your ad gives an R-value, you must give the type of insulation and... your ad gives a price, you must give the type of insulation, the R-value at a specific thickness, the...

Growth of VO2 Nano wires from Supercooled Liquid Nano droplets and E-beam Irradiation for Ultra-sensitive sensor

International Nuclear Information System (INIS)

Byun, Ji Won; Baik, Jeong Min; Lee, Sang Hyun; Lee, Byung Cheol

2011-01-01

Vanadium dioxide is an interesting material on account of its easily accessible and sharp Mott metal-insulator transition at ∼ 68 .deg. C in the bulk, which is of great interest in sensing and catalytic applications. In this Paper, we describe the synthesis and properties of VO 2 nano wires as novel catalytic and gas sensor materials based on electron beam irradiation. High yields of single crystalline VO 2 nano wires are synthesized by atmospheric-pressure, physical vapor deposition using V 2 O 5 layer. Pd-decorated VO 2 nano wire sensors show extraordinary sensitivity towards hydrogen, an almost 3 order-of-magnitude increase in the current through the nano wire. By the Eb irradiation, the conductance of the nano wires significantly increased up to 5 times, reducing the response time by half and the operating temperature. The metal nanoparticles-VO 2 nano wire system will be very promising for high-sensitivity and high-selectivity under low temperature less than 100. deg. C

Bandgap modulation in photoexcited topological insulator Bi{sub 2}Te{sub 3} via atomic displacements

Energy Technology Data Exchange (ETDEWEB)

Hada, Masaki, E-mail: hadamasaki@okayama-u.ac.jp [Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530 (Japan); Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); PRESTO, Japan Science and Technology Agency, Kawaguchi 332-0012 (Japan); Norimatsu, Katsura; Tsuruta, Tetsuya; Igarashi, Kyushiro; Kayanuma, Yosuke; Sasagawa, Takao; Nakamura, Kazutaka G. [Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); Tanaka, Sei' ichi; Ishikawa, Tadahiko; Koshihara, Shin-ya [Department of Chemistry and Materials Science, Tokyo Institute of Technology, Tokyo 152-8551 (Japan); Keskin, Sercan [The Max Planck Institute for the Structure and Dynamics of Matter, The Hamburg Centre for Ultrafast Imaging, University of Hamburg, Hamburg 22761 (Germany); Miller, R. J. Dwayne [The Max Planck Institute for the Structure and Dynamics of Matter, The Hamburg Centre for Ultrafast Imaging, University of Hamburg, Hamburg 22761 (Germany); Departments of Chemistry and Physics, University of Toronto, Toronto M5S 3H6 (Canada); Onda, Ken [PRESTO, Japan Science and Technology Agency, Kawaguchi 332-0012 (Japan); Graduate School of Science and Engineering, Tokyo Institute of Technology, Yokohama 226-8502 (Japan)

2016-07-14

The atomic and electronic dynamics in the topological insulator (TI) Bi{sub 2}Te{sub 3} under strong photoexcitation were characterized with time-resolved electron diffraction and time-resolved mid-infrared spectroscopy. Three-dimensional TIs characterized as bulk insulators with an electronic conduction surface band have shown a variety of exotic responses in terms of electronic transport when observed under conditions of applied pressure, magnetic field, or circularly polarized light. However, the atomic motions and their correlation between electronic systems in TIs under strong photoexcitation have not been explored. The artificial and transient modification of the electronic structures in TIs via photoinduced atomic motions represents a novel mechanism for providing a comparable level of bandgap control. The results of time-domain crystallography indicate that photoexcitation induces two-step atomic motions: first bismuth and then tellurium center-symmetric displacements. These atomic motions in Bi{sub 2}Te{sub 3} trigger 10% bulk bandgap narrowing, which is consistent with the time-resolved mid-infrared spectroscopy results.

Thermal conductivity: recent developments on insulating and new materials; La conductivite thermique: developpements recents sur les isolants et les materiaux nouveaux

Energy Technology Data Exchange (ETDEWEB)

NONE

1996-12-31

This workshop organized by the thermo-kinetics section of the French society of thermal engineers deals with recent developments concerning insulating, dielectric and composite materials. The seven papers presented during this workshop concern the methods and results of thermal conductivity measurements performed in these materials and the possible applications of these materials in aerospace industry (carbon foams, ceramic-based composite materials), civil engineering (glazing materials, aerogels), power electronics (dielectric thin films, ceramics), and in other industries (heat resistant and thermal insulating materials). (J.S.)

Trap-size scaling in confined-particle systems at quantum transitions

International Nuclear Information System (INIS)

Campostrini, Massimo; Vicari, Ettore

2010-01-01

We develop a trap-size scaling theory for trapped particle systems at quantum transitions. As a theoretical laboratory, we consider a quantum XY chain in an external transverse field acting as a trap for the spinless fermions of its quadratic Hamiltonian representation. We discuss trap-size scaling at the Mott insulator to superfluid transition in the Bose-Hubbard model. We present exact and accurate numerical results for the XY chain and for the low-density Mott transition in the hard-core limit of the one-dimensional Bose-Hubbard model. Our results are relevant for systems of cold atomic gases in optical lattices.

Topological Insulator Nanowires and Nanoribbons

KAUST Repository

Kong, Desheng; Randel, Jason C.; Peng, Hailin; Cha, Judy J.; Meister, Stefan; Lai, Keji; Chen, Yulin; Shen, Zhi-Xun; Manoharan, Hari C.; Cui, Yi

2010-01-01

Recent theoretical calculations and photoemission spectroscopy measurements on the bulk Bi2Se3 material show that it is a three-dimensional topological insulator possessing conductive surface states with nondegenerate spins, attractive

Increased intragenic IGF2 methylation is associated with repression of insulator activity and elevated expression in serous ovarian carcinoma

Directory of Open Access Journals (Sweden)

Zhiqing eHuang

2013-05-01

Full Text Available Overexpression of insulin-like growth factor-II (IGF2 is a prominent characteristic of many epithelial ovarian malignancies. IGF2 imprinting and transcription are regulated in part through DNA methylation, which in turn regulates binding of the insulator protein, CTCF, within the IGF2/H19 imprint center. We have shown that IGF2 overexpression in ovarian cancer is associated with hypermethylation of CTCF binding sites within the IGF2/H19 imprint center. The aim of this study was to investigate the methylation and binding capacity of a novel putative CTCF binding motif located intragenic to IGF2 and determine how this relates to IGF2 expression. In 35 primary serous epithelial ovarian cancer specimens, methylation of two CpGs, including one within the core binding motif and another adjacent to this motif, was higher in the 18 cancers with elevated IGF2 expression versus 10 with low expression (avg. 68.2% vs. 38.5%; p<0.0001. We also found that the CpG site within the CTCF binding motif is hypermethylated in male gametes (>92%; avg. 93.2%; N=16. We confirmed binding of CTCF to this region in ovarian cancer cells, as well as the paralog of CTCF, BORIS, which is frequently overexpressed in cancers. The unmethylated CTCF binding motif has insulator activity in cells that express CTCF or BORIS, but not in cells that express both CTCF and BORIS. These intragenic CpG dinucleotides comprise a novel paternal germline imprint mark and are located in a binding motif for the insulator protein CTCF. Methylation of the CpG dinucleotides is positively correlated with IGF2 transcription, supporting that increased methylation represses insulator function. These combined results suggest that methylation and CTCF binding at this region play important roles in regulating the level of IGF2 transcription. Our data have revealed a novel epigenetic regulatory element within the IGF2/H19 imprinted domain that is highly relevant to aberrant IGF2 expression in ovarian

High-Resolution Faraday Rotation and Electron-Phonon Coupling in Surface States of the Bulk-Insulating Topological Insulator Cu_{0.02}Bi_{2}Se_{3}.

Science.gov (United States)

Wu, Liang; Tse, Wang-Kong; Brahlek, M; Morris, C M; Aguilar, R Valdés; Koirala, N; Oh, S; Armitage, N P

2015-11-20

We have utilized time-domain magnetoterahertz spectroscopy to investigate the low-frequency optical response of the topological insulator Cu_{0.02}Bi_{2}Se_{3} and Bi_{2}Se_{3} films. With both field and frequency dependence, such experiments give sufficient information to measure the mobility and carrier density of multiple conduction channels simultaneously. We observe sharp cyclotron resonances (CRs) in both materials. The small amount of Cu incorporated into the Cu_{0.02}Bi_{2}Se_{3} induces a true bulk insulator with only a single type of conduction with a total sheet carrier density of ~4.9×10^{12}/cm^{2} and mobility as high as 4000 cm^{2}/V·s. This is consistent with conduction from two virtually identical topological surface states (TSSs) on the top and bottom of the film with a chemical potential ~145 meV above the Dirac point and in the bulk gap. The CR broadens at high fields, an effect that we attribute to an electron-phonon interaction. This assignment is supported by an extended Drude model analysis of the zero-field Drude conductance. In contrast, in normal Bi_{2}Se_{3} films, two conduction channels were observed, and we developed a self-consistent analysis method to distinguish the dominant TSSs and coexisting trivial bulk or two-dimensional electron gas states. Our high-resolution Faraday rotation spectroscopy on Cu_{0.02}Bi_{2}Se_{3} paves the way for the observation of quantized Faraday rotation under experimentally achievable conditions to push the chemical potential in the lowest Landau level.

Constructions complying with tightened Danish sound insulation requirements for new housing

DEFF Research Database (Denmark)

Rasmussen, Birgit; Hoffmeyer, Dan

New sound insulation requirements in Denmark in 2008 New Danish Building Regulations with tightened sound insulation requirements were introduced in 2008 (and in 2010 with unchanged acoustic requirements). Compared to the Building Regulations from 1995, the airborne sound insulation requirements...... were 2 –3 dB stricter and the impact sound insulation requirements 5 dB stricter. The limit values are given using the descriptors R’w and L’n,w as before. For the first time, acoustic requirements for dwellings are not found as figures in the Building Regulations. Instead, it is stated......), Denmark. [2] "Lydisolering mellem boliger – Nybyggeri" (Sound insulation between dwellings – Newbuild)". Publication expected in April 2011. The guideline is a part of a series of seven new SBi acoustic guidelines. Project leader Birgit Rasmussen. The series shall replace the existing guidelines 1984...

External Insulation of Masonry Walls and Wood Framed Walls

Energy Technology Data Exchange (ETDEWEB)

Baker, P.

2013-01-01

The use of exterior insulation on a building is an accepted and effective means to increase the overall thermal resistance of the assembly that also has other advantages of improved water management and often increased air tightness of building assemblies. For thin layers of insulation (1" to 1 1/2"), the cladding can typically be attached directly through the insulation back to the structure. For thicker insulation layers, furring strips have been added as a cladding attachment location. This approach has been used in the past on numerous Building America test homes and communities (both new and retrofit applications), and has been proven to be an effective and durable means to provide cladding attachment. However, the lack of engineering data has been a problem for many designers, contractors, and code officials. This research project developed baseline engineering analysis to support the installation of thick layers of exterior insulation on existing masonry and frame walls. Furthermore, water management details necessary to integrate windows, doors, decks, balconies and roofs were created to provide guidance on the integration of exterior insulation strategies with other enclosure elements.

Metal-insulator-semiconductor photodetectors.

Science.gov (United States)

Lin, Chu-Hsuan; Liu, Chee Wee

2010-01-01

The major radiation of the sun can be roughly divided into three regions: ultraviolet, visible, and infrared light. Detection in these three regions is important to human beings. The metal-insulator-semiconductor photodetector, with a simpler process than the pn-junction photodetector and a lower dark current than the MSM photodetector, has been developed for light detection in these three regions. Ideal UV photodetectors with high UV-to-visible rejection ratio could be demonstrated with III-V metal-insulator-semiconductor UV photodetectors. The visible-light detection and near-infrared optical communications have been implemented with Si and Ge metal-insulator-semiconductor photodetectors. For mid- and long-wavelength infrared detection, metal-insulator-semiconductor SiGe/Si quantum dot infrared photodetectors have been developed, and the detection spectrum covers atmospheric transmission windows.

Metal-Insulator-Semiconductor Photodetectors

Directory of Open Access Journals (Sweden)

Chu-Hsuan Lin

2010-09-01

Full Text Available The major radiation of the Sun can be roughly divided into three regions: ultraviolet, visible, and infrared light. Detection in these three regions is important to human beings. The metal-insulator-semiconductor photodetector, with a simpler process than the pn-junction photodetector and a lower dark current than the MSM photodetector, has been developed for light detection in these three regions. Ideal UV photodetectors with high UV-to-visible rejection ratio could be demonstrated with III-V metal-insulator-semiconductor UV photodetectors. The visible-light detection and near-infrared optical communications have been implemented with Si and Ge metal-insulator-semiconductor photodetectors. For mid- and long-wavelength infrared detection, metal-insulator-semiconductor SiGe/Si quantum dot infrared photodetectors have been developed, and the detection spectrum covers atmospheric transmission windows.

Thermal stability study of the insulator layer in NiFe/CoFe/Al2O3/Co spin-dependent tunnel junction

International Nuclear Information System (INIS)

Liao, C.C.; Ho, C.H.; Huang, R.-T.; Chen, F.-R.; Kai, J.J.; Chen, L.-C.; Lin, M.-T.; Yao, Y.D.

2002-01-01

Spin-dependent tunnel junction, NiFe/CoFe/Al 2 O 3 /Co//Si, was fabricated to investigate the thermal stability induced diffusion behaviors. The interfacial diffusion causes the degradation of the ratio of the TMR, the enhancement of the switching field of the two magnetic electrodes, the thickness decrease of the insulator layer, and the increase of the interfacial roughness. The outward diffusion of oxygen from the insulator layer is faster than that of aluminum for samples annealed below 400 deg. C. The degradation of the ratio of TMR is attributed to the disturbance of the spin polarization in the magnetic layers, and the increase of the pinholes and spin-flip effect in the insulator layer. The relative roughness between the two interfaces of the insulator induces the surface magnetic dipoles, and hence, increases the switching field of the ferromagnetic electrodes

Highly Insulating Windows Volume Purchase Program Final Report

Energy Technology Data Exchange (ETDEWEB)

None

2013-04-01

This report documents the development, execution outcomes and lessons learned of the Highly Insulating Windows Volume Purchase (WVP) Program carried out over a three-year period from 2009 through 2012. The primary goals of the program were met: 1) reduce the incremental cost of highly insulating windows compared to ENERGY STAR windows; and 2) raise the public and potential buyers’ awareness of highly insulating windows and their benefits. A key outcome of the program is that the 2013 ENERGY STAR Most Efficient criteria for primary residential windows were adopted from the technical specifications set forth in the WVP program.

Energy conservation through thermally insulated structures

International Nuclear Information System (INIS)

Abu-Dayyeh, Ayoub

2006-01-01

The propose of this paper is to explicate its title through investigating the different available thermal insulating materials and the various techniques of application, as practiced in Jordan, in particular, and as practiced in many parts of the world in general, which will satisfy Jordanian standards in terms of heat transmittance and thermal comfort. A brief comparison with international standards will shed some light on the stringent measures enforced in the developed world and on our striving aspirations to keep pace. The paper consists of four main parts, pseudoally divided. The first part will deal with the mechanism of heat loss and heat gain in structures during summer and winter. It will also explain the Time-lag phenomenon which is vital for providing thermal comfort inside the dwellings. The second part will evaluate the damages induced by the temperature gradients on the different elements of the structure, particularly next to exterior opening. The paper will also demonstrate the damages induced by water condensation and fungus growth on the internal surfaces of the structure and within its skeleton. A correlation between condensation and thermal insulation will be established. The third part of the paper will evaluate the different available thermal insulating materials and the application techniques which will satisfy the needs for thermal insulating and thermal comfort at the least cost possible. The criteria of an economical design shall be established. As a conclusion, the paper infers answers to the following different criteria discussed throughout the different parts of the paper. The main theme of questions can be summarized as follows: 1)How energy conservation is possible due to thermal insulation? 2)The feasibility of investing in thermal insulation? 3)Is thermal comfort and a healthy atmosphere possible inside the dwellings during all season! What are the conditions necessary to sustain them? 4)What environmental impacts can exist due to

Shaking the entropy out of a lattice

DEFF Research Database (Denmark)

C. Tichy, Malte; Mølmer, Klaus; F. Sherson, Jacob

2012-01-01

, for which we implement a protocol that circumvents the constraints of unitarity. The preparation of large regions with precisely one atom per lattice site is discussed for both bosons and fermions. The resulting low-entropy Mott-insulating states may serve as high-fidelity register states for quantum...

Responses of Mixed-Phase Cloud Condensates and Cloud Radiative Effects to Ice Nucleating Particle Concentrations in NCAR CAM5 and DOE ACME Climate Models

Science.gov (United States)

Liu, X.; Shi, Y.; Wu, M.; Zhang, K.

2017-12-01

Mixed-phase clouds frequently observed in the Arctic and mid-latitude storm tracks have the substantial impacts on the surface energy budget, precipitation and climate. In this study, we first implement the two empirical parameterizations (Niemand et al. 2012 and DeMott et al. 2015) of heterogeneous ice nucleation for mixed-phase clouds in the NCAR Community Atmosphere Model Version 5 (CAM5) and DOE Accelerated Climate Model for Energy Version 1 (ACME1). Model simulated ice nucleating particle (INP) concentrations based on Niemand et al. and DeMott et al. are compared with those from the default ice nucleation parameterization based on the classical nucleation theory (CNT) in CAM5 and ACME, and with in situ observations. Significantly higher INP concentrations (by up to a factor of 5) are simulated from Niemand et al. than DeMott et al. and CNT especially over the dust source regions in both CAM5 and ACME. Interestingly the ACME model simulates higher INP concentrations than CAM5, especially in the Polar regions. This is also the case when we nudge the two models' winds and temperature towards the same reanalysis, indicating more efficient transport of aerosols (dust) to the Polar regions in ACME. Next, we examine the responses of model simulated cloud liquid water and ice water contents to different INP concentrations from three ice nucleation parameterizations (Niemand et al., DeMott et al., and CNT) in CAM5 and ACME. Changes in liquid water path (LWP) reach as much as 20% in the Arctic regions in ACME between the three parameterizations while the LWP changes are smaller and limited in the Northern Hemispheric mid-latitudes in CAM5. Finally, the impacts on cloud radiative forcing and dust indirect effects on mixed-phase clouds are quantified with the three ice nucleation parameterizations in CAM5 and ACME.