16 research outputs found
A non-invasive method for nanoscale electrostatic gating of pristine materials
Electrostatic gating is essential for defining and control of semiconducting
devices. However, nano-fabrication processes required for depositing gates
inevitably degrade the pristine quality of the material of interest. Examples
of materials that suffer from such degradation include ultra-high mobility
GaAs/AlGaAs two-dimensional electron gases (2DEGs), graphene, topological
insulators, and nanowires. To preserve the pristine material properties, we
have developed a flip-chip setup where gates are separated from the material by
a vacuum, which allows nanoscale electrostatic gating of the material without
exposing it to invasive nano-processing. An additional benefit is the vacuum
between gates and material, which, unlike gate dielectrics, is free from charge
traps. We demonstrate the operation and feasibility of the flip-chip setup by
achieving quantum interference at integer quantum Hall states in a
Fabry-P\'erot interferometer based on a GaAs/AlGaAs 2DEG. Our results pave the
way for the study of exotic phenomena including fragile fractional quantum Hall
states by preserving the high quality of the material.Comment: 25 pages including Supporting Informatio
Electric and Magnetic Tuning Between the Trivial and Topological Phases in InAs/GaSb Double Quantum Wells
Among the theoretically predicted two-dimensional topological insulators,
InAs/GaSb double quantum wells (DQWs) have a unique double-layered structure
with electron and hole gases separated in two layers, which enables tuning of
the band alignment via electric and magnetic fields. However, the rich
trivial-topological phase diagram has yet to be experimentally explored. We
present an in situ and continuous tuning between the trivial and topological
insulating phases in InAs/GaSb DQWs through electrical dual-gating.
Furthermore, we show that an in-plane magnetic field shifts the electron and
hole bands relatively to each other in momentum space, functioning as a
powerful tool to discriminate between the topologically distinct states
Giant spin-orbit splitting in inverted InAs/GaSb double quantum wells
Transport measurements in inverted InAs/GaSb quantum wells reveal a giant
spin-orbit splitting of the energy bands close to the hybridization gap. The
splitting results from the interplay of electron-hole mixing and spin-orbit
coupling, and can exceed the hybridization gap. We experimentally investigate
the band splitting as a function of top gate voltage for both electron-like and
hole-like states. Unlike conventional, noninverted two-dimensional electron
gases, the Fermi energy in InAs/GaSb can cross a single spin-resolved band,
resulting in full spin-orbit polarization. In the fully polarized regime we
observe exotic transport phenomena such as quantum Hall plateaus evolving in
steps and a non-trivial Berry phase
Spin-orbit interaction in a dual gated InAs/GaSb quantum well
Spin-orbit interaction is investigated in a dual gated InAs/GaSb quantum
well. Using an electric field the quantum well can be tuned between a single
carrier regime with exclusively electrons as carriers and a two-carriers regime
where electrons and holes coexist. Spin-orbit interaction in both regimes
manifests itself as a beating in the Shubnikov-de Haas oscillations. In the
single carrier regime the linear Dresselhaus strength is characterized by
28.5 meV and the Rashba coefficient is tuned from 75 to
53 meV by changing the electric field. In the two-carriers regime the spin
splitting shows a nonmonotonic behavior with gate voltage, which is consistent
with our band structure calculations
Decoupling Edge Versus Bulk Conductance in the Trivial Regime of an InAs/GaSb Double Quantum Well Using Corbino Ring Geometry
A Corbino ring geometry is utilized to analyze edge and bulk conductance of InAs/GaSb quantum well structures. We show that edge conductance exists in the trivial regime of this theoretically predicted topological system with a temperature-insensitive linear resistivity per unit length in the range of 2 kΩ/μm. A resistor network model of the device is developed to decouple the edge conductance from the bulk conductance, providing a quantitative technique to further investigate the nature of this trivial edge conductance, conclusively identified here as being of n type
Edge Transport in the Trivial Phase of InAs/GaSb
We present transport and scanning SQUID measurements on InAs/GaSb double quantum wells, a system predicted to be a two-dimensional topological insulator. Top and back gates allow independent control of density and band offset, allowing tuning from the trivial to the topological regime. In the trivial regime, bulk conductivity is quenched but transport persists along the edges, superficially resembling the predicted helical edge-channels in the topological regime. We characterize edge conduction in the trivial regime in a wide variety of sample geometries and measurement configurations, as a function of temperature, magnetic field, and edge length. Despite similarities to studies claiming measurements of helical edge channels, our characterization points to a non-topological origin for these observations
Correction to A Noninvasive Method for Nanoscale Electrostatic Gating of Pristine Materials
Correction to A Noninvasive Method for Nanoscale Electrostatic
Gating of Pristine Material