Thermo-electric response in two-dimensional Dirac systems: the role of particle-hole pairs

石墨烯中狄拉克费米子的热电功率

Thermo-Electric Power of Dirac Fermions in Graphene

基于Dirac费米子在带电杂质散射下的自洽Born近似，利用热流-电流关联函数，建立了计算石墨烯中热电功率的理论.本方法的优点是它能够有效地处理低掺杂的情况下，涉及在上和下带的载流子的相干过程变得重要。我们表明，作为载流子浓度和温度的函数的热电功率的低温行为的实验观察到的可以成功地解释我们的计算。

Hydrodynamics of charged two-dimensional Dirac systems I: thermo-electric transport

In this paper we study thermo-electric transport in interacting two-dimensional Dirac-type systems using a phenomenological Boltzmann approach. We consider a setup that can accommodate electrons, holes, and collective modes. In the first part of the paper we consider the electron-hole hydrodynamics, a model that is popular in the context of graphene, and its transport properties. In a second part, we propose a novel type of hydrodynamics. In that setup, the `fluid' consists of electrons, holes, and plasmons. We study its transport properties, especially the thermo-electric behavior. The result…

电场作用下硅烯中Dirac锥的消失

Disappearance of the Dirac cone in silicene due to the presence of an electric field

采用二维离子哈伯德模型作为描述硅烯在衬底诱导的电场作用下的电子结构的简单基础，采用相干势近似计算了半填充时的零温相图和相应的光谱函数.我们发现，任何程度的破缺诱导的电场导致的硅烯结构失去其狄拉克费米子特性，从而提供了一个简单的机制狄拉克锥的消失。

从三维拓扑绝缘体的电磁对偶性看二维狄拉克费米子的粒子涡旋对偶性

Particle-vortex duality of 2d Dirac fermion from electric-magnetic duality of 3d topological insulators

粒子-涡旋对偶性是研究玻色子系统的有力理论工具。在这里，我们提出了一个类似的对偶狄拉克费米子在2 + 1维。本文提出用对偶理论QED 3来描述单狄拉克锥的物理，即对偶狄拉克费米子与规范场耦合的QED 3。这种对偶性是通过考虑三维拓扑绝缘体（TI）表面的两种替代描述而建立的。第一种描述是通常的狄拉克锥面态。第二种描述是通过一个电磁耦合到一个规范场，它映射到一个规范的拓扑超导体的大块TI的对偶性访问。这种交替的描述最终导致了一个新的表面理论-对偶QED 3。对偶理论提供了一个明确的推导T-Pfidian状态，建议的表面拓扑秩序的TI，这是简单的配对超流态的对偶费米子。时间逆转和粒子-空穴对称性的角色通过二元性交换，这将我们的一些结果与Son最近关于粒子-空穴对称量子霍尔态的猜想联系起来。

Magnetic-field enhanced high-thermoelectric performance in topological Dirac semimetal Cd$_3$As$_2$ crystal

Thermoelectric materials can be used to convert heat to electric power through the Seebeck effect. We study magneto-thermoelectric figure of merit (ZT) in three-dimensional Dirac semimetal Cd$_3$As$_2$ crystal. It is found that enhancement of power factor and reduction of thermal conductivity can be realized at the same time through magnetic field although magnetoresistivity is greatly increased. ZT can be highly enhanced from 0.17 to 1.1 by more than six times around 350 K under a perpendicular magnetic field of 7 Tesla. The huge enhancement of ZT by magnetic field arises from the linear Dira…

Weyl和Dirac半金属的热电性质

Thermoelectric properties of Weyl and Dirac semimetals

我们用半经典玻尔兹曼方法研究了电子对Weyl和Dirac半金属热导率和热电势的贡献。我们研究了各种弛豫过程，包括无序和相互作用对热电性能的影响，也考虑了远离外尔或狄拉克点的掺杂。我们发现，热导率和热电势有一个有趣的依赖于化学势的线性电子色散的特性，和电子-电子相互作用修改的洛伦兹数。对于相互作用系统，我们也使用Kubo形式来获得输运系数。我们发现在高温下的Kubo和玻尔兹曼方法之间的确切协议。我们还考虑了电场和磁场对导热系数的影响，在各种方向上的温度梯度。值得注意的是，当温度梯度和磁场是平行的，我们发现一个很大的贡献是二次的磁场强度的纵向热导率，类似的磁场依赖性的纵向电导率由于手性异常的存在下，当没有热梯度存在。

石墨烯中Dirac费米子的电输运理论

Electric Transport Theory of Dirac Fermions in Graphene

利用自洽玻恩近似，我们证明了有限程杂质散射下狄拉克费米子的电流-电流关联函数是由四个耦合积分方程决定的.这与具有短程电势的杂质的情况非常不同。作为本方法的一个测试，我们计算的导电性在石墨烯的带电杂质与屏蔽库仑电位。得到的零温电导率与载流子浓度呈线性关系，零掺杂时的最小电导率大于现有的理论预测，但仍小于实验测量值。由本计算得到的室温下的电导率的总体行为类似于在零温度下的电导率，除了最小电导率稍大。

Direct measurement of a beta function and an indirect check of the Schwinger effect near the boundary in Dirac-Weyl semimetals

The electric field inside typical conductors drops down exponentially with the screening length determined by an intrinsic length scale of the system such as the density of mobile carriers. We show that in a classically conformal system with boundaries, where the intrinsic length scale is absent, the screening of an external electric field is governed by the quantum conformal anomaly associated with the renormalization of the electric charge. The electric field decays algebraically with a fractional power determined by the beta function of the system. We argue that this `anomalous conformal sc…

拓扑狄拉克半金属 BaAl$_{4}$ 中的热电量子振荡与塞曼劈裂

Thermoelectric quantum oscillations and Zeeman splitting in topological Dirac semimetal BaAl$_{4}$

本文系统研究了拓扑狄拉克节线半金属 BaAl$_{4}$ 单晶的热电功率量子振荡，利用热电功率探测多个振荡频率并证实其中两个来自三维狄拉克能带，同时通过贝里相位和塞曼劈裂提取朗德 $g$ 因子，揭示了该材料家族的非平庸拓扑性质。

Electric field assisted amplification of magnetic fields in tilted Dirac cone systems

We show that the continuum limit of the tilted Dirac cone in materials such as $8Pmmn$-borophene and layered organic conductor $α$-(BEDT-TTF)$_2$I$_3$ deformation of the Minkowski spacetime of Dirac materials. From its Killing vectors we construct an emergent tilted-Lorentz (t-Lorentz) symmetry group for such systems. With t-Lorentz transformations we are able to obtain the exact solution of the Landau bands for a crossed configuration of electric and magnetic fields. For any given tilt parameter $0\leζ<1$ if the ratio $χ=v_FB_z/cE_y$ of the crossed magnetic and electric fields that satisfies …

A Nernst current from the conformal anomaly in Dirac and Weyl semimetals

We show that a conformal anomaly in Weyl/Dirac semimetals generates a bulk electric current perpendicular to a temperature gradient and the direction of a background magnetic field. The associated conductivity of this novel contribution to the Nernst effect is fixed by a beta function associated with the electric charge renormalization in the material.

Electric and Magnetic Responses of Two-dimensional Dirac Electrons in Organic Conductor $α$-(BETS)$_2$I$_3$

Effect of spin-orbit coupling (SOC) on Dirac electrons in the organic conductor $α$-(BETS)$_2$I$_3$ [BETS = bis(ethylenedithio)tetraselenafulvalene] has been examined by calculating electric conductivity and spin magnetic susceptibility. A tight-binding (TB) model with real and imaginary transfer energies is derived using first-principles density-functional theory method. The conductivity without the SOC depends on both anisotropies of the velocity of the Dirac cone and the tiling of the cone. Such conductivity is suppressed by the SOC, which gives rise to the imaginary part of the transfer en…

Holographic RG flow of thermo-electric transports with momentum dissipation

We construct the holographic renormalization group (RG) flow of thermo-electric conductivities when the translational symmetry is broken. The RG flow is probed by the intrinsic observers hovering on the sliding radial membranes. We obtain the RG flow by solving a matrix-form Riccati equation. The RG flow provides a high-efficient numerical method to calculate the thermo-electric conductivities of strongly coupled systems with momentum dissipation. As an illustration, we recover the AC thermo-electric conductivities in the Einstein-Maxwell-axion model. Moreover, in several homogeneous and isotr…