Insulating State and Giant Nonlocal Response in anInAs/GaSbQuantum Well in the Quantum Hall Regime

Abstract

We present transport measurements performed in InAs/GaSb double quantum wells. At the electron-hole crossover tuned by a gate voltage, a strong increase in the longitudinal resistivity is observed with increasing perpendicular magnetic field. Concomitantly with a local resistance exceeding the resistance quantum by an order of magnitude, we find a pronounced non-local resistance signal of almost similar magnitude. The co-existence of these two effects is reconciled in a model of counter-propagating and dissipative quantum Hall edge channels providing backscattering, shorted by a residual bulk conductivity.An InAs/GaSb double quantum well (QW) sandwiched between two AlSb barriers shows a peculiar band alignment [1]. A QW for electrons in InAs and a QW for holes in GaSb coexist next to each other. If the QWs thicknesses are small enough, a hybridization gap is expected to open at the charge neutrality point (CNP) [2,3]. Depending on the QWs' thicknesses and on the perpendicular electric field, a rich phase diagram is predicted [4]. It should be possible to electrically tune the sample from standard conducting phases to insulating, semimetallic or topological insulator phases. Recent work on InAs/GaSb QWs showed signatures of topological phases in micron-sized Hall bars at zero magnetic field [5][6][7], as expected for the quantum spin Hall insulator regime [8]. Beyond the topological insulator properties, that manifest themselves, the fate of topological edge states at finite magnetic field has not been investigated so far. Similarly to other semi-metals like graphene [9,10] or CdHgTe/HgTe quantum wells [11,12], electron and hole Landau levels (LLs) can coexist close to the CNP [13,14]. A detailed understanding of the expected hybridization of LLs [15] and its manifestation in a transport experiment is still missing.Here we present magnetotransport measurements performed on gated InAs/GaSb double QWs. At high magnetic fields, in the electron and hole regimes, we observe the formation of standard LLs. Close to the CNP a peculiar state forms in which electrical transport is governed by counter-propagating edge channels of highly dissipative nature. We investigate the transport properties in this regime using different measurement configurations, and as a function of magnetic field and temperature.The experiments were performed on two devices (named device A and device B) obtained from the same wafer as described in Ref. 16. In Ref. 17 a nominally identical structure was used, and a hybridization gap of 3.6 meV was reported. Hall bar structures were fabricated by photolithography and argon plasma etching. Device A consisted of a single Hall bar with a width of 25 µm and a separation between lateral arms of 50 µm.Device B consisted of two Hall bars in series, oriented perpendicularly to each other. Their width is 25 µm and the lateral voltage probes have various separations, the shortest being 50 µm . Device A was covered by a 200 nm thick Si 3 N 4 insulating layer, device B by a 40 nm thick HfO 2 layer. On both sampl...

Images of Edge Current inInAs/GaSbQuantum Wells

“…InAs/GaSb suggests inversion of the lowest Landau levels, which is consistent with the inverted band structure necessary for the QSHE [31]. The growth of the Si-doped wafer is described in Ref.…”

Helical edge states and fractional quantum Hall effect in a graphene electron–hole bilayer

“…Such electron-hole quantum Hall states are observed in semi-metals but suffer from low hole-mobilities (9,10). In this respect, graphene is an attractive system because it has high carrier mobilities and is electron-hole symmetric.…”

Edge transport in InAs and InAs/GaSb quantum wells

“…With these insights about InAs in mind we now turn to the discussion of InAs/GaSb double quantum well structures, which contain a hybridized electron-hole system [27][28][29][30][31][32]. Despite multiple affirmations of edge conduction in the inverted regime of InAs/GaSb [8][9][10][11][12][13][14], a careful analysis of the various possible contributions to edge conduction is missing.…”