Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany.
Phys Rev Lett. 2019 Aug 9;123(6):066804. doi: 10.1103/PhysRevLett.123.066804.
Surface-state contributions to the dc conductivity of most homogeneous metals exposed to uniform electric fields are usually as small as the system size is large compared to the lattice constant. In this Letter, we show that surface states of topological metals can contribute with the same order of magnitude as the bulk, even in large systems. This effect is intimately related to the intrinsic anomalous Hall effect, in which an applied voltage induces chiral surface-state currents proportional to the system size. Unlike the anomalous Hall effect, the large contribution of surface states to the dc conductivity is also present in time-reversal invariant Weyl semimetals, where the surface states come in counterpropagating time-reversed pairs. While the Hall voltage vanishes in the presence of time-reversal symmetry, the twinned chiral surface currents develop similarly as in the time-reversal-broken case. For this effect to occur, the relaxation length associated with scattering between time-reversed partner states needs to be larger than the separation of contributing surfaces, which results in a characteristic size dependence of the resistivity and a highly inhomogeneous current-density profile across the sample.
暴露于均匀电场中的大多数均匀金属的直流电导率的表面态贡献通常与晶格常数相比，系统尺寸较大时很小。在这封信中，我们表明拓扑金属的表面态即使在较大的系统中也可以与体相贡献相同数量级。这种效应与本征反常霍尔效应密切相关，其中施加的电压会感应出与系统尺寸成正比的手性表面态电流。与反常霍尔效应不同，表面态对直流电导率的大贡献也存在于时间反演不变的外尔半金属中，其中表面态来自相反传播的时间反转对。尽管在存在时间反演对称性的情况下霍尔电压为零，但孪生手性表面电流的发展与时间反演破坏的情况类似。为了发生这种效应，与时间反转伙伴态之间的散射相关的弛豫长度需要大于贡献表面的分离，这导致电阻率的特征尺寸依赖性以及穿过样品的高度不均匀的电流密度分布。
