A5091395950- Quantum and electron transport phenomena
- Semiconductor Quantum Structures and Devices
- Physics of Superconductivity and Magnetism
- Terahertz technology and applications
- Advancements in Semiconductor Devices and Circuit Design
- Strong Light-Matter Interactions
- Spectroscopy and Laser Applications
- Molecular Junctions and Nanostructures
- Theoretical and Computational Physics
- Quantum, superfluid, helium dynamics
- Photonic and Optical Devices
- Cold Atom Physics and Bose-Einstein Condensates
- Magnetic properties of thin films
- Integrated Circuits and Semiconductor Failure Analysis
- Quantum Information and Cryptography
- Electronic and Structural Properties of Oxides
University of Cambridge
2011-2020
National Physical Laboratory
2015
Cavendish Hospital
2008
We report an experimental technique to measure and manipulate the arrival-time energy distributions of electrons emitted from a semiconductor electron pump, operated as both single-electron source two-electron source. Using energy-selective detector whose transmission we control on picosecond timescales, can directly distribution determine upper-bound width be 30 ps. study effects modifying shape voltage waveform that drives show our results explained by tunneling model emission mechanism....
Recently, it has been possible to design independently contacted electron-hole bilayers (EHBLs) with carrier densities cm 2 in each layer and a separation of 10–20 nm GaAs/AlGaAs system. In these EHBLs, the interlayer interaction can be stronger than intralayer interactions. Theoretical works have indicated possibility very rich phase diagram EHBLs consisting excitonic superfluid phases, charge density waves, Wigner crystals. Experiments revealed that Coulomb drag on hole shows strong...
We present measurements of Coulomb drag in an ambipolar GaAs/AlGaAs double quantum well structure that can be configured as both electron-hole bilayer and a hole-hole bilayer, with insulating barrier only 10 nm between the two wells. resistivity is direct measure strength interlayer particle-particle interactions. explore strongly interacting regime low carrier densities (2D interaction parameter rs up to 14). Our device design allows comparison effects attractive repulsive interactions also...
We report the development of a simple and reliable, front-sided-only fabrication technique for n-type ohmic contacts to two-dimensional electron gases (2DEGs) in undoped GaAs/AlGaAs quantum wells. have adapted well-established recessed contacts/insulated metal gate inducing 2DEG an triangular well also work reliably square Our adaptation involves change procedure etching contact pits optimise etch side-wall profile depth. As application our technique, we present front-side-gated ambipolar...
We present GaAs/AlGaAs double quantum well devices that can operate as both electron-hole (e-h) and hole-hole (h-h) bilayers, with separating barriers narrow 5 nm or 7.5 nm. With such barriers, in the h-h configuration, we observe signs of magnetic-field-induced exciton condensation Hall bilayer regime. In same devices, study zero-magnetic-field e-h states using Coulomb drag. Very strong drag resistivity (up to 10% single layer resistivity) is observed at liquid helium temperatures, but no...
We present observations of an anisotropic resistance state at Landau-level filling factor $\ensuremath{\nu}=5/2$ in a two-dimensional hole system (2DHS), which occurs for certain values density $p$ and average out-of-plane electric field ${E}_{\ensuremath{\perp}}$. The 2DHS is induced by electric-field effect undoped GaAs/AlGaAs quantum well, where front back gates allow independent tuning ${E}_{\ensuremath{\perp}}$, hence the symmetry confining potential. For...
To cool a high mobility two-dimensional electron gas (2DEG) at GaAs–AlGaAs heterojunction to milliKelvin temperatures, we have fabricated low resistance Ohmic contacts based on alloys of Au, Ni, and Ge. The typical contact RC≈0.8 Ω 4.2 K, which drops 0.2 below 0.9 K. Scanning microscope images establish that the same inhomogeneous microstructure has been observed in previous studies. Measurements RC, four-terminal along top single contact, vertical RV all show there is superconductor can be...
An antenna-coupled dual-gated two-dimensional electron gas (2DEG) based on a GaAs-AlGaAs heterostructure shows pronounced response to 2 THz radiation. The device is shown be direct detector, and its photoresponse arises without any source-drain bias. detection novel mechanism that yields substantially stronger than predicted by the classical plasma-wave self-mixing other mechanisms.
This work was funded by EPSRC EP/H017720/1 and EP/J003417/1 European Union Grant INDEX 289968. A.F.C. acknowledges funding from Trinity College, Cambridge, D.T. St. Catherine's Cambridge. I.F. Toshiba Research Europe Limited.
As the ambition behind THz quantum cascade laser based applications continues to grow, abandoning free-space optics in favor of waveguided systems promises major improvements targeted, easy align, and robust radiation delivery. This is especially true cryogenic environments, where illumination traditionally challenging. Although field waveguides rapidly developing, most designs have limitations terms mechanical stability at low temperatures, are costly complicated fabricate lengths > 1 m....