We study heat transport in a gas of one-dimensional fermions in the presence of a small temperature gradient. At temperatures well below the Fermi energy there are two types of relaxation processes in this system, with dramatically different relaxation rates. As a result, in addition to the usual thermal conductivity, one can introduce the thermal conductivity of the gas of elementary excitations, which quantifies the dissipation in the system in the broad range of frequencies between the two relaxation rates. We develop a microscopic theory of these transport coefficients in the limit of weak interactions between the fermions.
It is generally believed that conductivity platform can only exist in insulator with topological nontrivial bulk occupied states. Such rule exhibits in two dimensional quantum (anomalous) Hall effect, quantum spin Hall effect, and three dimensional topological insulator. In this letter, we propose a spin Hall conductivity (SHC) platform in a kind of three dimensional metallic materials with triply degenerate points around the Fermi level. With the help of a four bands \textbf{k}${\cdot}$\textbf{p} model, we prove that SHC platform can form between $|\frac{3}{2},\pm\frac{3}{2}\rangle$ and $|\fr…
Magnetoconductivity oscillations and absolute negative conductivity induced by nonequilibrium populations of excited subbands in a degenerate multisubband two-dimensional electron system are studied theoretically. The displacement from equilibrium, which can be caused by resonant microwave excitation or by any other reason, is assumed to be such that electron distributions can no longer be described by a single Fermi level. In this case, in addition to the well-known conductivity peaks occurring at the Shubnikov-de Haas conditions and small peaks of normal intersubband scattering, sign-changin…
Longitudinal conductivity of massless fermions with tilted Dirac cone in magnetic field
研究了在磁场中具有倾斜狄拉克锥的二维相对论电子气的纵向电导率。结果表明，电导率在平行于和垂直于圆锥倾斜方向上表现不同。在高磁场的电导率在非零朗道水平在垂直于倾斜的方向修改非平凡的，在平行的情况下。本文用数值方法研究了零温下狄拉克点处电导率从高到低磁场的交叉。研究发现，倾斜产生的各向异性的电导率随磁场，这是不同的各向异性来自费米速度。我们还讨论了在有限温度和有限磁场下的电导率，这些电导率可以直接与$α$ -（BEDT-TTF）$_2$ I $_3$有机导体的实验进行比较。我们发现，倾斜并没有影响这么多的磁场依赖性的电导率除了前因子。我们讨论了最近的实验数据的解释，并提出了一些建议，以检测在未来的实验倾斜的效果。
We investigate the density and optical responses of a linear triple component fermionic system in both non-interacting and interacting regimes by computing its dynamical polarization function, RPA dielectric function, plasmon mode and long wavelength optical conductivity and compare the results with those of Weyl fermions and three-dimensional free electron gas. Linear triple component fermions are pseudospin-1 generalization of Weyl fermions, consisting of two linearly dispersive bands and a flat band. The presence of flat band brings about notable modifications in the response properties wit…
Magneto-optical studies of Weyl semimetals have been proposed as a versatile tool for observing low-energy Weyl fermions in candidate materials including the chiral Landau level. However, previous theoretical results have been restricted to the linearized regime around the Weyl node and are at odds with experimental findings. Here, we derive a closed form expression for the magneto-optical conductivity of generic Weyl semimetals in the presence of an external magnetic field aligned with the tilt of the spectrum. The systems are taken to have linear dispersion in two directions, while the tilti…
The importance of the quantum metric in flat-band systems has been noticed recently in many contexts such as the superfluid stiffness, the dc electrical conductivity, and ideal Chern insulators. Both the quantum metric of degenerate and nondegenerate bands can be naturally described via the geometry of different Grassmannian manifolds, specific to the band degeneracies. Contrary to the (Abelian) Berry curvature, the quantum metric of a degenerate band resulting from the collapse of a collection of bands is not simply the sum of the individual quantum metrics. We provide a physical interpretati…
Exceptional points, which are topological non-Hermitian degeneracies, show up in the collective mode spectrum of Fermi Liquids with high angular momentum interactions. In this paper, we look for signatures of these non-trivial singularities by computing the AC conductivity of Fermi liquids with dipolar and quadrupolar interactions in a narrow slab. We show that the finite size of the slab imprints clear signatures of the structures of the collective mode spectrum in the conductivity as well as in the dephasing between the electric field and the current density in a wide range of coupling const…
Inter-Band Effects of Magnetic Field on Hall Conductivity in Multi Layered Massless Dirac Fermion System $α$-(BEDT-TTF)$_2$I$_3$
我们在有机导体$α$ -（BEDT-TTF）$_2$ I $_3$中发现了在高静水压下具有层状结构的二维零能隙材料。与石墨烯相反，除了在狄拉克点附近之外，电子-空穴对称性不好。因此，温度依赖性的化学势，$μ$，在该系统中的运输中起着重要的作用。给出了$μ$的实验配方。当$μ$通过狄拉克点时，我们成功地检测到了磁场对霍尔电导率的带间影响。
