Search

Efficient and precise calculations of thermal transport properties and figure of merit, alongside a deep comprehension of thermal transport mechanisms, are essential for the practical utilization of advanced thermoelectric materials. In this study, we explore the microscopic processes governing thermal transport in the distinguished crystalline material Tl$_9$SbTe$_6$ by integrating a unified thermal transport theory with machine learning-assisted self-consistent phonon calculations. Leveraging machine learning potentials, we expedite the analysis of phonon energy shifts, higher-order scattering mechanisms, and thermal conductivity arising from various contributing factors like population and coherence channels. Our finding unveils an exceptionally low thermal conductivity of 0.31 W m$^{-1}$ K$^{-1}$ at room temperature, a result that closely correlates with experimental observations. Notably, we observe that the off-diagonal terms of heat flux operators play a significant role in shaping the overall lattice thermal conductivity of Tl$_9$SbTe$_6$, where the ultralow thermal conductivity resembles that of glass due to limited group velocities. Furthermore, we achieve a maximum $ZT$ value of 3.17 in the $c$-axis orientation for \textit{p}-type Tl$_9$SbTe$_6$ at 600 K, and an optimal $ZT$ value of 2.26 in the $a$-axis and $b$-axis direction for \textit{n}-type Tl$_9$SbTe$_6$ at 500 K. The crystalline Tl$_9$SbTe$_6$ not only showcases remarkable thermal insulation but also demonstrates impressive electrical properties owing to the dual-degeneracy phenomenon within its valence band. These results not only elucidate the underlying reasons for the exceptional thermoelectric performance of Tl$_9$SbTe$_6$ but also suggest potential avenues for further experimental exploration.

The energy of the transition from Galactic to extra-galactic origin of cosmic rays is one of the major unresolved issues of cosmic-ray physics. However, strong constraints can be obtained from studying the anisotropy in the arrival directions of cosmic rays. The sensitivity to cosmic-ray anisotropy is, in particular, a matter of statistics. Recently, the cosmic ray anisotropy measurements in the TeV to PeV energy range were updated from IceCube using 11 years of data. The IceCube-Gen2 surface array will cover an area about 8 times larger than the existing IceTop surface array with a corresponding increase in statistics and capability to investigate cosmic-ray anisotropy with higher sensitivity. In this contribution, we present details on the performed simulation studies and sensitivity to the cosmic-ray anisotropy signal for the IceCube-Gen2 surface array., Comment: Presented at the 38th International Cosmic Ray Conference (ICRC2023). See arXiv:2307.13048 for all IceCube-Gen2 contributions

Weyl semimetals exhibitinging the topologically nontrivial touching points in electronic band dispersion of solids pave the wave way to novel electronic devices and functionalities. Here, we demonstrate the signature of topologically nontrivial Weyl points (WPs) in phonon dispersion of solids through a first-principles investigations. ofT noncentrosymmetric wurtzite CuI (cuprous iodide at high temperature). These type-II phononic WP in phonon dispersion of wurtzite CuI is manifested in noncentrosymmetric wurtzite CuI by six pairs of the nontrivial touching points in the k_z=0.0 plane. The ideal WPs in phonon dispersion are completely isolated from bulk phonon continuum, are different distinct from many type-II WPs in electronic band dispersion of solids associated with the overlapping band states. The opposite chirality of Weyl phonon nodes with quantized Berry curvature are utilized forproduces Weyl phonon Hall effect, in analogous analogy towith valley Hall effect of electrons. Such ideal type-II Weyl phonons are phase is readily observable in experiment, and could provideing a unique platform to study novel thermal transport properties different distinct from that in type-I Weyl phonons phase.

By nonperturbatively solving the nonequilibrium Anderson two-impurity model with the hierarchical equations of motion approach, we report a robust ferromagnetic (FM) phase in series-coupled double quantum dots, which can suppress the antiferromagnetic (AFM) phase and dominate the phase diagram at finite bias and detuning energy in the strongly correlated limit. The FM exchange interaction origins from the passive parallel spin arrangement caused by the Pauli exclusion principle during the electrons transport. At very low temperature, the Kondo screening of the magnetic moment in the FM phase induces some nonequilibrium Kondo effects in magnetic susceptibility, spectral functions and current. In the weakly correlated limit, the AFM phase is found still stable, therefore, a magnetic-field-free internal control of spin states can be expected through the continuous FM--AFM phase transition., Comment: 5 pages, 3 figures

Quantum tunneling dominates coherent transport at low temperatures in many systems of great interest. In this work we report a many--body tunneling (MBT), by nonperturbatively solving the Anderson multi-impurity model, and identify it a fundamental tunneling process on top of the well--acknowledged sequential tunneling and cotunneling. We show that the MBT involves the dynamics of doublons in strongly correlated systems. Proportional to the numbers of dynamical doublons, the MBT can dominate the off--resonant transport in the strongly correlated regime. A $T^{3/2}$--dependence of the MBT current on temperature is uncovered and can be identified as a fingerprint of the MBT in experiments. We also prove that the MBT can support the coherent long--range tunneling of doublons, which is well consistent with recent experiments on ultracold atoms. As a fundamental physical process, the MBT is expected to play important roles in general quantum systems., Comment: 5 pages, 4 figures

Pauli spin blockade (PSB) is a significant physical effect in double quantum dot (DQD) systems. In this paper, we start from the fundamental quantum model of the DQD with the electron-electron interaction being considered, and then systematically study the PSB effect in DQD by using a recently developed non-perturbative method, the hierarchical equations of motion (HEOM) approach. The physical picture of the PSB is elucidated explicitly and the gate voltage manipulation is described minutely, which are both qualitatively consistent with the experimental measurements. When dotdot exchange interaction is involved, the PSB effect may be lifted by the strong antiferromagnetic exchange coupling., Comment: 10 pages, 8 figures

We investigate the time-dependent transport properties of single and double quantum-impurity systems based on the hierarchical equations of motion (HEOM) approach. In the Kondo regime, the dynamical current in both cases is found oscillating due to the temporal coherence of electrons tunneling through the device, which shares the same mechanism as the single-level resonance without e-e interactions but shows some different characteristics. For single quantum-impurity systems, the temperature T plays an inhibitory action to the oscillations of dynamic current through its suppression to the Kondo effects. The amplitude of the current oscillations is attenuated by the e-e interaction $U$ in the Kondo regime. The frequency of the current oscillation is found almost independent of T and U. For parallel-coupling double quantum-impurity systems, the oscillation of the current shows similar behaviors to the single one, but with two-to-three times larger amplitudes. At the limit of small inter-impurity coupling the oscillation of the current exhibits enhanced characters while it is weakened at the other limit., Comment: 7 pages, 8 figures