Spatially Resolved Study of Backscattering in the Quantum Spin Hall State

Abstract

The discovery of the quantum spin Hall (QSH) state, and topological insulators in general, has sparked strong experimental efforts. Transport studies of the quantum spin Hall state have confirmed the presence of edge states, showed ballistic edge transport in micron-sized samples, and demonstrated the spin polarization of the helical edge states. While these experiments have confirmed the broad theoretical model, the properties of the QSH edge states have not yet been investigated on a local scale. Using scanning gate microscopy to perturb the QSH edge states on a submicron scale, we identify well-localized scattering sites which likely limit the expected nondissipative transport in the helical edge channels. In the micron-sized regions between the scattering sites, the edge states appear to propagate unperturbed, as expected for an ideal QSH system, and are found to be robust against weak induced potential fluctuations.

Topological Insulator Materials

“…70) The CdTe/HgTe/CdTe quantum well can be made very clean with the carrier mobility of up to $10 5 cm 2 V À1 s À1 , which makes it possible to study quantum transport properties. On the other hand, the drawback of this system is that the bulk band gap that opens due to the epitaxial strain is very small (up to $10 meV, depending on the thickness 71) ), which makes the detection of the TI phase to be possible only at very low temperature. Also, since the synthesis of CdTe/HgTe/CdTe quantum wells requires dedicated MBE machines, the sources of samples for basic physics experiments are currently very limited, which has made the progress of experimental studies of 2D TIs (QSH insulators) relatively slow.…”

Coulomb drag

“…Some theoretical predictions have already being made (Zyuzin and Fiete, 2010) and recent experimental advances (Altimiras et al, 2010;Du et al, 2015;König et al, 2013;Roth et al, 2009) bring these exciting perspectives within reach.…”

Shot noise in the edge states of 2D topological insulators

“…Nevertheless, there is a general opinion that the most probable reason of the observed breaking of topological protection of the edge states is the presence of structural defects and inelastic-scattering centers. This opinion is supported by the experiment [14] that revealed well-localized scattering centers.…”

“…The average current in it is given by Eq. (14). The spin-dependent chemical potentials of electrons in the puddle may be obtained either by solving Eqs.…”

“…In this paper, we calculate the resistance of the edge states and the nonequilibrium noise in them that result from the tunnel coupling between the edge states and charge puddles in the bulk of the insulators, which is suggested by recent experimental results [3,5,14]. These puddles are believed to form because of inhomogeneous distribution of doping impurities in the adjacent layers of material [11].…”