We study dispersions of Fermi arcs in the Weyl semimetal phase by constructing a simple effective model. We calculate how the surface Fermi-arc dispersions for the top- and bottom surfaces merge into the bulk Dirac cones in the Weyl semimetal at both ends of the arcs, and show that they have opposite velocities. This result is also confirmed by a calculation using a tight-binding model. Furthermore, by changing a parameter in the system while preserving time-reversal symmetry, we show that two Fermi arcs evolve into a surface Dirac cone when the system transits from the Weyl semimetal to the topological insulator phase. We also demonstrate that choices of surface terminations affect the pairing of Weyl nodes, from which the Fermi arcs are formed.
We calculate the extremal cross sectional areas and cyclotron masses for the Fermi-surface pockets in Dirac and Weyl topological semimetals. The calculation is carried out for the most general form of the electron energy bands in the vicinity of the Weyl and Dirac points. Using the obtained formulas, one can find parameters characterizing the Dirac and Weyl electrons in the topological semimetals from appropriate experimental data. As an example, we consider the W1 electrons in TaAs.
A minimal, "hydrogen atom" version of an inversion-breaking Weyl semimetal
外尔半金属的研究兴趣最近爆炸导致了许多外尔半金属候选人和一些外尔半金属在实际材料中的实验观察。通过这些经验，我们已经认识到，典型的外尔半金属拥有许多外尔点。例如，在实验中观察到的第一种外尔半金属TaAs拥有24个外尔点。类似地，Mo $_x$ W $_{1-x}$ Te $_2$系列，最近作为第一种II型外尔半金属被研究，具有八个外尔点。然而，众所周知，对于没有反转对称但具有时间反演对称的外尔半金属，外尔点的最小数量是四个。实现这样一个最小的外尔半金属是非常重要的，因为它将提供一个最简单的“氢原子“的反型破坏外尔半金属的例子。同时，在具有尽可能少的外尔点的系统中，输运实验和设备应用可能更简单。最近，TaIrTe $_4$已被预测为最小的，反转打破外尔半金属。然而，至关重要的是，外尔点和费米弧完全位于费米能级之上，这使得它们无法被传统的角度分辨光电子能谱（ARPES）所利用。在这里，我们使用泵浦-探测ARPES直接访问TaIrTe $_4$费米能级以上的能带结构。我们直接观察到Weyl点和拓扑费米弧，表明TaIrTe $_4$是Weyl半金属。我们发现，总的来说，TaIrTe $_4$有四个外尔点，提供了一个最小的反转破坏外尔半金属的第一个例子。我们的研究结果持有承诺访问外来传输现象中产生的外尔半金属在一个真正的材料。
Kramers Weyl semimetals are Weyl semimetals that have Weyl points pinned at the time reversal invariant momenta. Recently it has been discovered that all chiral crystals host Weyl points at time reversal invariant momenta, so metals with chiral lattice symmetry all belong to the category of Kramers Weyl semimetals. In this work, we show that due to the chiral lattice symmetry, Kramers Weyl semimetals have the unique longitudinal magnetoelectric effect in which the charge current induced spin and orbital magnetization is parallel to the direction of the current. This feature allows Kramers Weyl…
Magnetotransport and magneto-optics experiments offer a very powerful probe for studying the physical properties of materials. Here, we investigate the second-order nonlinear magnetoconductivity of tilted type-I Weyl and multi-Weyl semimetal. In contrast to the presence of chiral anomaly in the linear response regime, we show that Weyl semimetal do not host chiral charge pumping in the nonlinear transport regime. We predict that an inversion symmetry broken and tilted Weyl semimetal can support finite longitudinal nonlinear magnetoconductivity, which is otherwise absent in untilted Weyl semime…
We present a new switching mechanism that utilizes the proximity coupling between the surface spin texture of a Weyl semimetal and a superconductor, in a Weyl semimetal/superconductor/Weyl semimetal trilayer heterostructure. We show that the superconductivity in the middle layer can be fully suppressed by the surface spin texture of the Weyl semimetals in the presence of an external magnetic field, but it can be recovered again by only changing the field direction. The restoration of the middle-layer superconductivity indicates a sharp transition to a low-resistance state. This sharp switching…
Floquet engineering, the concept of tailoring a system by a periodic drive, is increasingly exploited to design and manipulate topological phases of matter. In this work, we study periodically driven higher-order topological Dirac semimetals associated with a $k$-dependent quantized quadrupole moment by applying circularly polarized light. The undriven Dirac semimetals feature gapless higher-order hinge Fermi arc states which are the consequence of the higher-order topology of the Dirac nodes. Floquet Weyl semimetal phases with hybrid-order topology, characterized by both a $k$-dependent quant…
The Fermi arcs of topological surface states in the three-dimensional multi-Weyl semimetals on surfaces by a continuum model are investigated systematically. We calculated analytically the energy spectra and wave function for bulk quadratic- and cubic-Weyl semimetal with a single Weyl point. The Fermi arcs of topological surface states in Weyl semimetals with single- and double-pair Weyl points are investigated systematically. The evolution of the Fermi arcs of surface states variating with the boundary parameter is investigated and the topological Lifshitz phase transition of the Fermi arc co…
We investigate the tunneling of the quasiparticles arising in multi-Weyl semimetals through a barrier consisting of both electrostatic and vector potentials, existing uniformly in a finite region along the transmission axis. The dispersion of a multi-Weyl semimetal is linear in one direction (say, $k_z$), and proportional to $k_\perp^J$ in the plane perpendicular to it (where $k_\perp =\sqrt{k_x^2+k_y^2}$). Hence, we study the cases when the barrier is perpendicular to $k_z$ and $k_x$, respectively. For comparison, we also state the corresponding results for the Weyl semimetal.
Topological magnetotorsional effect in Weyl semimetals
在这项工作中，我们介绍了热磁扭效应（TME）作为一种新的拓扑响应在磁性Weyl半金属。我们预测，垂直于外尔节点分离的磁化梯度引起的温度梯度仅取决于外尔节点的局部位置。TME是磁化诱导的有效扭转时空几何和有限温度Nieh-Yan异常的结果。与反常霍尔效应和手征反常类似，TME具有普遍的与材料无关的形式。我们预测在磁性Weyl半金属EuCd $_2$ As $_2$中可以观察到TME。
We study the current-induced torques in asymmetric magnetic tunnel junctions containing a conventional ferromagnet and a magnetic Weyl semimetal contact. The Weyl semimetal hosts chiral bulk states and topologically protected Fermi arc surface states which were found to govern the voltage behavior and efficiency of current-induced torques. We report how bulk chirality dictates the sign of the non-equilibrium torques acting on the ferromagnet and discuss the existence of large field-like torques acting on the magnetic Weyl semimetal which exceeds the theoretical maximum of conventional magnetic…
