M.S. Daly

“Intrinsic” quantum Hall effect in InAs/Ga1−xInxSb crossed gap heterostructures in high magnetic fields

Abstract We report a study of the quantum Hall effect and Shubnikov-dc Haas oscillations in semimctallic type II heterostructures of the strained layer system InAs/Ga1−xInxSb which are almost intrinsic. In high magnetic fields up to 50 T, ρxy has large peaks, demonstrating the high degree of charge compensation in the system. Between these peaks, intrinsic quantum Hall minima arc observed, where ρxy approaches zero.

The dependence of the Composite Fermion effective mass on carrier density and Zeeman energy

Measurements of the temperature-dependent resistivity of high-mobility GaAs/GaAlAs heterojunctions are used to measure the effective mass of Composite Fermions (CF). The CF effective mass is found to increase approximately linearly with the effective field up to effective fields of 14 T. Data from all fractions around are unified by the single parameter for samples studied over a wide range of temperature. The energy gap is found to increase as at high fields. Hydrostatic pressure is used to reduce the value of the electron g-factor, and this is shown to have a large effect on the relative strengths of different fractions. By 13.4 kbar, where the Zeeman energy is only 1/4 of its value at 0 bar, fractions with odd numerators are found to be strongly suppressed, and new features with even numerators appear. The energy gaps measured for 5/3 as a function of carrier density and pressure are consistent with a g-factor equal to the bulk value enhanced by a factor of two due to exchange interactions.

Optical and magnetotransport properties of semimetallic InAs/(In,Ga)Sb superlattices

Abstract Semimetallic superlattices and double heterojunctions of the system InAs / In x Ga 1− x Sb have been studied by cyclotron resonance and magnetotransport in the magnetic field range 10–100 T. The cyclotron resonance is used to show that there is a magnetic field induced transition from semimetallic to semiconducting behaviour, at which almost all the carriers in the system disappear. The magnetotransport shows that large oscillatory Hall voltages occur in the quantised regime, and these are strongly temperature dependent. The field positions of the Hall resistivity peaks are related to the crossing of the electron and hole Landau levels. Hydrostatic pressure is used to achieve a controlled decrease of the band overlap, and to show that the Hall peaks and minima move to zero field as the zero overlap condition is approached. Both the cyclotron resonance and the magnetotransport show that the magnitude of the band overlap is orientation. dependent, being ≈ 60 meV larger for (1 1 1) oriented structures. This is attributed to the presence of a large interface dipole for this orientation.

Pressure investigation of the quantum Hall effect in intrinsic semimetallic InAs/(Ga,In)Sb heterostructures

Abstract We have performed magnetotransport measurements on InAs/(Ga,In)Sb heterostructures under hydrostatic pressure. The system has a cross gap band alignment which leads to the formation of co-existent 2D electron-hole gases. The amount of overlap and thus the electron and hole concentrations can be tuned by the application of hydrostatic pressure. The samples studied here have nearly equal electron and hole concentrations and show large oscillatory quantum Hall features. Measurements of the band overlap Δ and its rate of change with pressure d(Δ) dP provides evidence that both the growth direction and also the composition of the interface layer play an important role in determining the band line-up.

Interface composition dependence of the band offset in InAs/GaSb

Abstract We have performed 4 K magnetotransport measurements on intrinsic InAs/GaSb multi quantum wells (MQWs) under hydrostatic pressure. Through careful configuration of the growth we are able to produce samples that have differing interface monolayers (either InSb or GaAs). Analysing the data to calculate the band overlap (Δ), we find that InSb-like samples have an overlap 30 meV larger than GaAs-like in good agreement with recent theoretical predictions.

Observation of the zero Hall resistance state in a semimetallic superlattice

Abstract The quantum Hall effect has been measured in an intrinsic semimetallic superlattice with almost equal electron and hole densities. Giant oscillations are seen in the Hall resistivity, and at high fields and pressures a zero-resistance state is observed where the Hall resistivity goes to zero due to compensation of the Hall fields of the two carrier types. This behaviour is interpreted in terms of the limiting properties of ρ xx and ρ xy

Zeeman splitting in the extreme quantum limit through cyclotron resonance on two-dimensional GaAs at high pressure

Abstract Cyclotron resonance measurements on a GaAs heterojunction in the extreme quantum limit are presented. It has been reported recently that a new splitting appears for filling factors less than 1 6 . We have applied hydrostatic pressure in order to investigate the dependence on electron g-factor, since a pressure of ~8 kbar halves the g-factor, yet changes the effective mass by only ~ 5%. The critical filling factor, defined as the point where the two split resonances have equal intensity, is found to be strongly reduced with pressure. A general relationship is presented for the dependence of the critical filling factor on the Zeeman splitting.