Optimized ZT of Bi2Te3-GeTe compounds from first principles guided by homogeneous data

We predict the thermoelectric properties of layered [GeTe](m)[Bi2Te3](n) (GBT) compounds ( 1 <= m <= 8, 1 <= n <= 3), using first-principles-Boltzmann transport calculations of the homogeneous (Bi2Te3 and GeTe) data. The lattice strain and the quantum-confinement effects of compounds evolve the band-gap structures, resulting in asymmetric and large Seebeck coefficient, at high GeTe content. Using semiempirical calculations of electron scattering rate 1/tau(e), dominated by electron-acoustic phonon scattering, we reproduce reported TE properties of GBT compounds. We predict that, due to small Seebeck coefficient, the GBT compounds with high n- and p-type doping (similar to 10(20) cm(-3)), do not have high ZT near room temperature. However, we predict that the moderately doped (similar to 10(19) cm(-3)), p-type GBT compounds have enhanced ZT approximate to 1.4 near room temperature.1132Ysciescopu

Temperature-evolution of spectral function and optical conductivity in heavy fermion compound Ce2_{2}IrIn8_{8} under crystalline electric field

We investigate the role of the crystalline electric field (CEF) in the temperature ($T$)-evolution of the Kondo resonance states and its effect on optical conductivity. We perform the combined first principles calculation of the density functional theory and dynamical mean field theory on Ce$_{2}$IrIn$_{8}$. The calculated spectral function reproduces the experimental observed CEF states at low $T$, while it shows a drastic change of the Fermi surface upon increasing $T$. The effect of the CEF states on the Fermi surface as a function of $T$ is elucidated through the first principles calculations as well as the analysis on the Anderson impurity model. Consequently, we suggest the importance of the CEF-driven orbital anisotropy in the low-energy states of optical experiments.Comment: 6 pages, 4 figure

Enhanced immune response with foot and mouth disease virus VP1 and interleukin-1 fusion genes

The capsid of the foot and mouth disease (FMD) virus carries the epitopes that are critical for inducing the immune response. In an attempt to enhance the specific immune response, plasmid DNA was constructed to express VP1/interleukin-1α (IL-1α) and precursor capsid (P1) in combination with 2A (P1-2A)/IL-1α under the control of the human cytomegalovirus (HCMV) immediateearly promoter and intron. After DNA transfection into MA104 (monkey kidney) cells, Western blotting and an immunofluorescence assay were used to confirm the expression of VP1 or P1-2A and IL-1α. Mice were inoculated with the encoding plasmids via the intradermal route, and the IgG1 and IgG2a levels were used to determine the immune responses. These results show that although the immunized groups did not carry a high level of neutralizing antibodies, the plasmids encoding the VP1/IL-1α, and P1-2A/IL-1α fused genes were effective in inducing an enhanced immune response

Chemical and Hydrostatic Pressure Effect on Charge Density Waves of SmNiC2

Using a first-principles density functional theory method, we have investigated the chemical and the hydrostatic pressure effects on the charge density wave (CDW) properties of the quasi-one-dimensional (1D) compound SmNiC2. With increasing pressure, the relative 1D anisotropy of the electronic structure along a direction is enhanced because of its Ni chain structures. From the analysis of the Fermi surface and the generalized susceptibility, we also find that the Fermi surface nesting is enhanced along the modulation vector q(1) = (0.5, 0.52, 0) but is suppressed along q(R) = (0.5, 0.5, 0.5) under pressure. The enhancement of 1D anisotropy of SmNiC2 under pressure is responsible for increasing CDW strength along q(1). We suggest that this quantitative analysis could be used for analysis of the pressure effect on CDW materials.open1176sciescopu

Scaling of the Anderson Lattice Model Studied by DMFT with CTQMC Impurity Solver

The Kondo lattice model is known to be the minimal model for the heavy fermi liquid state of the heavy fermion systems. In spite of its fermi-liquid-like behaviour - T2 resistivity, T-linear specific heat, and T-independent spin susceptibility - its nature including the scaling relation of various physical quantities has not fully unveiled yet [1]. It is due to the fact that an analytic methodology based on the mean-field theory is limited to describe finitetemperature properties such as very incoherent spectrum near the Fermi level, and there is no concrete methodology for describing the strong coupling nature of the heavy fermion systems. On the other hand, DMFT is one of the most promising candidate for describing the strongly correlated system in a non-perturbative manner [2]. Using DMFT with numerically exact CTQMC impurity solver, we may perform a very well-controlled experiment on ideal model systems. In this work, we studied the Kondo lattice model by the dynamical mean-field theory (DMFT) with continuous time quantum Monte-Carlo (CTQMC) impurity solver [3]. As a result, we observed the scaling of various physical quantities such as the local spin susceptibility and scattering rate of the Kondo lattice model with different hybridisation strength and temperature. Compared with the Kondo impurity model, Kondo lattice shows different scaling energy scale due to the feedback effect of the DMFT. Additionally, temperature evolutions of the spectral properties such as the Fermi surface and band structure at the characteristic energy scale will be given. Discussion on how the feedback effect may change the RG beta function will be also given.1

In Situ Temperature-Dependent Transmission Electron Microscopy Studies of Psedobinary mGeTe center dot Bi2Te3 (m=3-8) Nanowires and First-Principles Calculations

Phase-change nanowires (NWs) have emerged as critical materials for fast-switching nonvolatile memory devices. In this study, we synthesized a series of mGeTe.Bi2Te3 (GBT) pseudobinary alloy NWsGe(3)Bi(2)Te(6) (m = 3), Ge4Bi2Te7 (m = 4), Ge5Bi2Te8 (m = 5), Ge6Bi2Te9 (m = 6), and Ge8Bi2Te11 (m = 8)and investigated their composition-dependent thermal stabilities and electrical properties. As m decreases, the phase of the NWs evolves from the cubic (C) to the hexagonal (H) phase, which produces unique superlattice structures that consist of periodic 2.2-3.8 nm slabs for m = 3-8. In situ temperature-dependent transmission electron microscopy reveals the higher thermal stability of the compositions with lower m values, and a phase transition from the H phase into the single-crystalline C phase at high temperatures (400 degrees C). First-principles calculations, performed for the superlattice structures (m = 1-8) of GBT and mGeTe.Sb2Te3 (GST), show an increasing stability of the H phase (versus the C phase) with decreasing m; the difference in stability being more marked for GBT than for GST. The calculations explain remarkably the phase evolution of the GBT and GST NWs as well as the composition-dependent thermal stabilities. Measurement of the current-voltage curves for individual GBT NWs shows that the resistivity is in the range 3-25 mO.cm, and the resistivity of the H phase is lower than that of the C phase, which has been supported by the calculations.X1167sciescopu

In Situ Temperature-Dependent Transmission Electron Microscopy Studies of Pseudobinary m GeTe·Bi2Te3 (m = 3-8) Nanowires and First-Principles Calculations

Phase-change nanowires (NWs) have emerged as critical materials for fast-switching nonvolatile memory devices. In this study, we synthesized a series of mGeTe·Bi2Te3 (GBT) pseudobinary alloy NWs - Ge3Bi2Te6 (m = 3), Ge4Bi2Te7 (m = 4), Ge5Bi2Te8 (m = 5), Ge6Bi2Te9 (m = 6), and Ge8Bi2Te11 (m = 8) - and investigated their composition-dependent thermal stabilities and electrical properties. As m decreases, the phase of the NWs evolves from the cubic (C) to the hexagonal (H) phase, which produces unique superlattice structures that consist of periodic 2.2-3.8 nm slabs for m = 3-8. In situ temperature-dependent transmission electron microscopy reveals the higher thermal stability of the compositions with lower m values, and a phase transition from the H phase into the single-crystalline C phase at high temperatures (400°C). First-principles calculations, performed for the superlattice structures (m = 1-8) of GBT and mGeTe·Sb2Te3 (GST), show an increasing stability of the H phase (versus the C phase) with decreasing m; the difference in stability being more marked for GBT than for GST. The calculations explain remarkably the phase evolution of the GBT and GST NWs as well as the composition-dependent thermal stabilities. Measurement of the current-voltage curves for individual GBT NWs shows that the resistivity is in the range 3-25 mΩ·cm, and the resistivity of the H phase is lower than that of the C phase, which has been supported by the calculations

Orbital anisotropy of heavy fermion Ce2IrIn8 under crystalline electric field and its energy scale

© 2022 American Physical Society.We investigate the temperature (T) evolution of orbital anisotropy and its effect on spectral function and optical conductivity in Ce2IrIn8 using a first-principles dynamical mean-field theory combined with density functional theory. The orbital anisotropy develops by lowering T and it is intensified below a temperature corresponding to the crystalline-electric field (CEF) splitting size. Interestingly, the depopulation of CEF excited states leaves a spectroscopic signature, "shoulder,"in the T-dependent spectral function at the Fermi level. From the two-orbital Anderson impurity model, we demonstrate that CEF splitting size is the key ingredient influencing the emergence and the position of the "shoulder."Besides the two conventional temperature scales TK and T∗, we introduce an additional temperature scale to deal with the orbital anisotropy in heavy fermion systems.11Nsciescopu

Comparison of the electronic and thermoelectric properties of three layered phases Bi2Te3, PbBi2Te4 and PbBi4Te7: LEGO thermoelectrics

The electronic and thermoelectric properties of Bi2Te3, PbBi2Te4 and PbBi4Te7 were examined on the basis of density functional theory (DFT) calculations and thermoelectric transport property measurements. The layered phase PbBi4Te7 is composed of the slabs forming the layered phases Bi2Te3 and PbBi2Te4. The electronic structure of PbBi4Te7 around the valence band maximum and conduction band minimum exhibits those of Bi2Te3 and PbBi2Te4. The band gap of PbBi4Te7 lies in between those of Bi2Te3 and PbBi2Te4, and the density of states of PbBi4Te7 is well approximated by the sum of those of Bi2Te3 and PbBi2Te4. In terms of the carrier concentration, the carrier mobility, the carrier lifetime, the electrical conductivity normalized to the carrier lifetime, and the effective mass, the layered phases Bi2Te3, PbBi4Te7 and PbBi2Te4 form a group of thermoelectrics, which have the structures composed of several different slabs and whose thermoelectric properties are approximated by the average of those of the constituent slabs. We propose to use the term “LEGO thermoelectrics” to describe such a family of thermoelectric materials that operate in a desired temperature range and possess predictable thermoelectric properties