Emergent quantum Hall effects below 50 mT in a two-dimensional topological insulator

Abstract

The realization of the quantum spin Hall effect in HgTe quantum wells has led to the development of topological materials, which, in combination with magnetism and superconductivity, are predicted to host chiral Majorana fermions. However, the large magnetization in conventional quantum anomalous Hall systems makes it challenging to induce superconductivity. Here, we report two different emergent quantum Hall effects in (Hg,Mn)Te quantum wells. First, a previously unidentified quantum Hall state emerges from the quantum spin Hall state at an exceptionally low magnetic field of ~50 mT. Second, tuning toward the bulk p-regime, we resolve quantum Hall plateaus at fields as low as 20 to 30 mT, where transport is dominated by a van Hove singularity in the valence band. These emergent quantum Hall phenomena rely critically on the topological band structure of HgTe, and their occurrence at very low fields makes them an ideal candidate for realizing chiral Majorana fermions.

Engineering topological phases in triple HgTe/CdTe quantum wells

“…It is also important to stress that the valence subbands obtained here also show the “ camel back ” profile 59 , 60 , thus also presenting an indirect gap defined by (see Fig. 1 b–e).…”

Flavoured quantum Hall phase in graphene/CrOCl heterostructures

“…This robust SIC-QHE phase in the graphene/CrOCl heterostructure prevails in much higher temperatures as compared to the QAHE systems so far reported, while the latter often requires temperatures of sub 2 K or even dilution fridge temperatures [35][36][37]. It also requires very relaxed experimental conditions as compared to such as doped (Hg,Mn)Te topological insulators quantum well, which is recently reported to show QH state below 50 mT at 20 mK [38]. It thus allows future applications in quantum metrology in the Système International d'unités [13,39].…”

Electron-hole scattering limited transport of Dirac fermions in a topological insulator

“…This feature results from the inverted band ordering of the Γ 6 and Γ − 8 bands and hybridization with the Γ + 8 band which is located between them. 9,12,16 Such hybridization-induced van Hove singularities commonly occur in topological materials (see e. g. 17 ).…”

“…We first calculate both electron, n e (T ), and hole, n h (T ), concentrations for the total charge densities n tot found in the experiment and electron temperatures T in the range of 0.4 K to 30 K. The intrinsic mobility for electrons µ e is calculated from the experimental low-temperature resistivity at zero heating current, where for simplicity we assume the holes to be localized. 16 The temperature-dependent resistivity can then be calculated as…”