Imaging currents in HgTe quantum wells in the quantum spin Hall regime

Abstract

The quantum spin Hall (QSH) state is a state of matter characterized by a non-trivial topology of its band structure, and associated conducting edge channels. The QSH state was predicted and experimentally demonstrated to be realized in HgTe quantum wells. The existence of the edge channels has been inferred from local and non-local transport measurements in sufficiently small devices. Here we directly confirm the existence of the edge channels by imaging the magnetic fields produced by current flowing in large Hall bars made from HgTe quantum wells. These images distinguish between current that passes through each edge and the bulk. On tuning the bulk conductivity by gating or raising the temperature, we observe a regime in which the edge channels clearly coexist with the conducting bulk, providing input to the question of how ballistic transport may be limited in the edge channels. Our results represent a versatile method for characterization of new QSH materials systems.

Proposal for an on-demand source of polarized electrons into the edges of a topological insulator

“…Recent experiments have shown that the edge states are characterizing by a width on the order of 5 µm. 10,11 In order to avoid overlap between the edge states, we estimate that the radius of the SpPS QD should be greater than the experimental measured width of the edge states. Within this assumption the screening of the Coulomb interaction induced by the top gate enables us to treat the system as non-interacting.…”

“…7,8 The edge nature of the particle transport in this material has been further addressed by specific experiments investigating the current distribution along the transversal direction of the sample. 10,11 Nowadays, a race for finding new 2D TI is running, one of the most promising candidates are InAs/GaSb quantum wells. 12,13 In this type of heterostructure quantum wells the edge state quantization is more accurate.…”

Magnetic Resonance Detection of Individual Proton Spins Using Quantum Reporters

“…Nuclear magnetic resonance and magnetic resonance imaging are essential tools for both the physical and life sciences [1,2], but have been limited to the detection of large ensembles of spins due to their low sensitivity [3,4], or the macroscopic nature of sensors [5,6]. Over the past decades, significant efforts [7][8][9][10][11] have been directed toward pushing this sensitivity to its ultimate physical limit, the detection of individual nuclear spin signals localized in a small volume.…”

Electrically Tunable Multiterminal SQUID-on-Tip

“…In contrast to conventional two-terminal/two-junction SQUIDs that display optimal sensitivity when flux biased to about a quarter of the flux quantum, the additional terminals and junctions allow optimal sensitivity at arbitrary applied flux, thus eliminating the magnetic field "blind spots". We demonstrate spin sensitivity of 5 to 8 µ B /Hz 1/2 over a continuous field range of 0 to 0.5 T, with promising applications for nanoscale scanning magnetic imaging.KEYWORDS: superconducting quantum interference device, SQUID on tip, nanoscale magnetic imaging, current-phase relations 2 In recent years, there has been a growing effort to develop and apply nanoscale magnetic imaging tools in order to address the rapidly evolving fields of nanomagnetism and spintronics.These include magnetic force microscopy (MFM) 1,2 , magnetic resonance force microscopy (MRFM) [3][4][5] , nitrogen vacancy (NV) centers sensors [6][7][8][9] , scanning Hall probe microscopy (SHPM) 10-12 , x-ray magnetic microscopy (XRM) 13 , and micro-or nano-superconducting quantum interference device (SQUID) [14][15][16][17][18][19][20] based scanning microscopy (SSM) [21][22][23][24][25][26][27][28][29][30][31][32] . Scanning micro-and nanoscale SQUIDs are of particular interest for magnetic imaging due to their high sensitivity and large bandwidth 15,19 .…”