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首页> 外文期刊>Physical review >Weak antilocalization in HgTe quantum wells and topological surface states: Massive versus massless Dirac fermions
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Weak antilocalization in HgTe quantum wells and topological surface states: Massive versus massless Dirac fermions

机译：HgTe量子阱和拓扑表面态中的弱反局部化：大量与无质量狄拉克费米子

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摘要

HgTe quantum wells and surfaces of three-dimensional topological insulators support Dirac fermions with a single-valley band dispersion. In the presence of disorder they experience weak antilocalization, which has been observed in recent transport experiments. In this work we conduct a comparative theoretical study of the weak antilocalization in HgTe quantum wells and topological surface states. The difference between these two single-valley systems comes from a finite band gap (effective Dirac mass) in HgTe quantum wells in contrast to gapless (massless) surface states in topological insulators. The finite effective Dirac mass implies a broken internal symmetry, leading to suppression of the weak antilocalization in HgTe quantum wells at times larger than certain τ_M, inversely proportional to the Dirac mass. This corresponds to the opening of a relaxation gap τ_M~(-1) in the Cooperon diffusion mode which we obtain from the Bethe-Salpeter equation including relevant spin degrees of freedom. We demonstrate that the relaxation gap exhibits an interesting nonmonotonic dependence on both carrier density and band gap, vanishing at a certain combination of these parameters. The weak-antilocalization conductivity reflects this nonmonotonic behavior which is unique to HgTe quantum wells and absent for topological surface states. On the other hand, the topological surface states exhibit specific weak-antilocalization magnetoconductivity in a parallel magnetic field due to their exponential decay in the bulk.
机译：HgTe量子阱和三维拓扑绝缘体的表面以单谷带分散支持Dirac费米子。在存在障碍的情况下，它们的抗定位能力较弱，这在最近的运输实验中已观察到。在这项工作中，我们对HgTe量子阱和拓扑表面态中的弱反局部化进行了比较理论研究。这两个单谷系统之间的差异来自于HgTe量子阱中的有限带隙（有效狄拉克质量），而拓扑绝缘子中的无间隙（无质量）表面状态则与此相反。有限的有效狄拉克质量意味着破裂的内部对称性，导致在大于某些τ_M的时间抑制HgTe量子阱中弱的反局部化，与狄拉克质量成反比。这对应于我们从包括相关自旋自由度的Bethe-Salpeter方程获得的Cooperon扩散模式下张弛间隙τ_M〜（-1）的打开。我们证明，弛豫间隙对载流子密度和带隙都表现出有趣的非单调依赖性，在这些参数的一定组合下消失。弱的抗局部电导率反映了这种非单调行为，这是HgTe量子阱所特有的，并且对于拓扑表面状态是不存在的。另一方面，由于其表面的指数衰减，拓扑表面态在平行磁场中显示出特定的弱反局部磁导率。

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