Robin Nicholas

Abstract:

We find that an InAs/GaSb based electron-hole system exhibits insulating behaviour when the numbers of occupied electron and hole Landau levels are equal. In this insulating state, the Hall resistance becomes symmetric under field reversal, and both the Hall and longitudinal resistances display reproducible fluctuations. A comparison with measurements made on a Corbino disc reveals that these features occur due to conduction at the mesa edge. We propose a simple model based on edge states.

Abstract:

We have studied magnetotransport in a coupled electron-hole system in an InAs/GaSb heterostructure with two-dimensional periodic potential modulations of different strengths. Strong oscillations in low magnetic field longitudinal magnetoresistance have been observed. The amplitude of these oscillations is a function of the magnetic field applied parallel to the two-dimensional system, which modifies the coupling between the electrons and holes.

Abstract:

Electron transport in InAs/GaSb superlattices under intense parallel electric and magnetic fields is investigated. At low electric fields we observe a conduction threshold, which exhibits magnetic field and temperature dependence. At higher biases the superlattice exhibits a large magneto-resistance and in the quantum limit we observe conduction peaks, which satisfy the Stark-Cyclotron-Resonance condition. Eight band k.p calculations show that the miniband width in this system is strongly k dependent.

Abstract:

We report studies of vertical superlattice transport in short period superlattices at high magnetic fields. This shows new magnetophonon resonances can occur in which LO phonons are resonantly scattered between high density of states regions of the superlattice leading to cycling of the carriers through high conductivity regions of the miniband.