Simon Hartinger | Searcharxiv

arXiv2019

Dynamical separation of bulk and edge transport in HgTe-based 2D topological insulators

Topological effects in edge states are clearly visible on short lengths only, thus largely impeding their studies. On larger distances, one may be able to dynamically enhance topological signatures by exploiting the high mobility of edge states with respect to bulk carriers. Our work on microwave spectroscopy highlights the responses of the edges which host very mobile carriers, while bulk carriers are drastically slowed down in the gap. Though the edges are denser than expected, we establish that charge relaxation occurs on short timescales, and suggests that edge states can be addressed selectively on timescales over which bulk carriers are frozen.

cond-mat.mes-hall↗

arXiv2015

$4\pi$-periodic Josephson supercurrent in HgTe-based topological Josephson junctions

The Josephson effect describes the generic appearance of a supercurrent in a weak link between two superconductors. Its exact physical nature however deeply influences the properties of the supercurrent. Detailed studies of Josephson junctions can reveal microscopic properties of the superconducting pairing (spin-triplet correlations, $d$-wave symmetry) or of the electronic transport (quantum dot, ballistic channels). In recent years, considerable efforts have focused on the coupling of superconductors to topological insulators, in which transport is mediated by topologically protected Dirac surface states with helical spin polarization (while the bulk remains insulating). Here, the proximity of a superconductor is predicted to give rise to unconventional induced $p$-wave superconductivity, with a doublet of topologically protected gapless Andreev bound states, whose energies varies $4\pi$-periodically with the superconducting phase difference across the junction. In this article, we report the observation of an anomalous response to rf irradiation in a Josephson junction with a weak link of the 3D topological insulator HgTe. The response is understood as due to a $4\pi$-periodic contribution to the supercurrent, and its amplitude is compatible with the expected contribution of a gapless Andreev doublet.

cond-mat.mes-hall↗