Weak antilocalization in HgTe quantum wells and topological surface states: Massive versus massless Dirac fermions

Details Weak antilocalization in HgTe quantum wells and topological surface states: Massive versus massless Dirac fermions Weak antilocalization in HgTe quantum wells and topological surface states: Massive versus massless Dirac fermions

2011-02-22

arxiv.org/abs/1102.4512v4

Phys. Rev. B 84, 035444 (2011)

Physics

Condensed Matter

Mesoscale and Nanoscale Physics

14 pages, 10 figures, version as published

Scientific paper

10.1103/PhysRevB.84.035444

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 t_M, inversely proportional to the Dirac mass. This corresponds to the opening of a relaxation gap 1/t_M 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 QWs 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.

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