Phase slips and parity jumps in quantum oscillations of inverted InAs/GaSb quantum wells

Abstract

We present magnetotransport measurements of a strongly hybridized inverted InAs/GaSb double quantum well. We find that the spin-orbit interaction leads to an appreciable spin-splitting of hole-like states, which form distinct Landau levels in a perpendicular magnetic field. The resulting quantum Hall state is governed by a periodic even and odd total filling arising due to the simultaneous occupation of electron-like and hole-like Landau levels of differing degeneracy. Furthermore, oscillatory charge transfer between all involved subbands leads to discrete phase slips in the usual sequential filling of Landau levels, and coincidentally the phase slips are close to π. These results shed new insights on the Landau level structure in composite systems and have consequences for interpreting intercepts obtained from index plots, which are routinely employed to investigate the presence of Berry's phase.InAs/GaSb double quantum wells (QWs) are a composite semiconductor system that hosts spatially separated electrons and holes and exhibits significant spinorbit interaction (SOI). The thicknesses of the constituent InAs and GaSb QWs determine the band alignment, which may be either inverted or noninverted. Application of electric and magnetic fields offers additional tunability, allowing for continuous control of this band alignment [1][2][3]. In the inverted phase, electrons and holes hybridize, opening an energy gap [4][5][6], which facilitates the formation of the quantum spin Hall insulator (QSHI) state under the right conditions [7][8][9][10][11][12].The inverted band structure and tunability of InAs/GaSb double QWs enable many interesting experiments not directly related to the QSHI state, such as the manipulation of the SOI in single-and two-carrier regimes [13], the observation of a giant spin-orbit splitting close to the charge neutrality point (CNP) [14] and tunable mixing of quantum Hall (QH) edge states [15].Here, we report our findings on the Landau level (LL) structure in a strongly inverted InAs/GaSb double QW featuring enhanced hybridization. Using transport measurements we uncover a periodic even and odd filling of Landau levels leading to a checkerboard pattern in the longitudinal resistivity ρ xx . Additionally, an anomalous shift violates the usual 1/B ⊥ -periodic sequence of LL filling. By analyzing Shubnikov-de Haas (SdH) oscillations and performing two and three-band transport modeling, we unravel the electron and hole-like charge carrier distribution in the system, thereby deducing the presence of an initially concealed SOI split hole-like subband. We then explain how the combination of SOI induced splitting and Landau quantization can lead to an unconventional filling sequence of LLs in this coupled electron-hole bilayer.Measurements were performed on a gated Hall bar of 10 µm width and 20 µm length oriented along the [011] crystallographic direction on a heterostructure consisting of an 8 nm GaSb QW and a 13.5 nm InAs QW [ Fig. 1(a)]. The Hall bar was defined by wet etching and covered by a SiN l...

Quantum Hall effect and Landau levels in the three-dimensional topological insulator HgTe

“…. This checkerboard pattern is very similar to the one observed in InAs/GaSb based electron-hole systems [7]. The checkerboard pattern is connected to an anomaly in the 𝜎 𝑥𝑦 traces taken for magnetic fields between 0.4 to 5 T, shown in Fig.…”

“…A more complicated situation arises when two-dimensional electron and hole systems coexist like in heterojunctions with broken gap (type III heterojunction), e.g., in InAs/GaSb quantum wells [5]. This gives rise to hybridization [6] and a complicated interplay between LLs [7]. With the advent of three-dimen-sional (3D) topological insulators (TI) [8][9][10][11] a new class of two-dimensional electron systems appeared on the scene where the two-dimensional charge carrier system consisting of Dirac fermions forms a closed surface "wrapped" around the insulating bulk.…”

Pseudospin Berry phase as a signature of nontrivial band topology in a two-dimensional system

“…4) demonstrate that it originates from the winding of a pseudospin and not a real spin. We add that field-induced interlayer charge transfer, which may cause a phase slip in the SdH oscillations away from the CNP [28], is not relevant near the CNP.…”