Metal-Insulator Transition in a Disordered Two-Dimensional Electron Gas in GaAs-AlGaAs at Zero Magnetic Field

Abstract

A metal-insulator transition in two-dimensional electron gases at B = 0 is found in Ga[Al]As heterostructures, where a high density of self-assembled InAs quantum dots is incorporated just 3 nm below the heterointerface. The transition occurs at resistances around h/e 2 and critical carrier densities of 1.2 · 10 11 cm −2 . Effects of electron-electron interactions are expected to be rather weak in our samples, while disorder plays a crucial role. 71.30.+h, 73.20.Jc 73.40.Kp

Quantum phase transitions in two-dimensional systems

“…The concentration n c corresponding to a change in the sign of the derivative dR/dT , varied widely from sam- ple to sample, depending on the disorder in the electron system under investigation. A similar change in the sign of the derivative dR/dT , corresponding to the critical carrier concentration n c (p c ), was subsequently found in AlGaAs/GaAs heterostructures with two-dimensional electron 71,72 and hole 73,74,75,76,77,78,79,80 gas, quantum wells AlAs with two-dimensional electron gas 81 , as well as quantum SiGe wells with electron 82 and hole 83,84 gas. However, the temperature dependence of the resistance of these low-dimensional systems in the temperature range T < 1K turned out to be much less than that in silicon MOS structures (Fig.…”

“…Further cooling of these systems results in, at first, saturation of some (previously 'metallic') temperature dependencies of resistance, and then their transformation to the regime with dR/dT < 0. Such an effect was observed in AlGaAs/GaAs heterostructures with two-dimensional electron 72 and hole 79 gas, as well as for two-dimensional holes in SiGe 90 and for two-dimensional electron gas of Si-MOSFET for vicinal orientations of the interface between Si and SiO 2 91 . In numerous experiments on Si-MOSFET 69,70,85,86,87,88,89 it was established that the critical carrier concentration corresponding to the change in the sign of the derivative dR/dT is determined by the quality of the sample.…”

“…In experiments studying the lowtemperature transport in Si-MOSFET with varying peak mobility, a dependence of the zν on the momentum relaxation time of electrons and critical concentration n c has been observed 87 . In AlGaAs/GaAs heterostructures with two-dimensional electron gas, the analysis of scaling in temperature and electric field allowed the determination of the critical indices z = 1.4 ± 1.0 and ν = 1.9 ± 0.9 72 . In AlGaAs/GaAs with p-type conductance, the product of critical indices equals to zν = 7.0 ± 1.5 and zν = 3.8 ± 0.4 for systems with a concentration of two-dimensional holes p > p c and p < p c , correspondingly 74 .In SiGe quantum wells involving twodimensional electron gas with a concentration n s < n c the product of critical indices is equal zν = 1.6 ± 0.2 82 .…”

Making Massless Dirac Fermions from a Patterned Two-Dimensional Electron Gas

“…We show through exact numerical calculations within an independent particle picture that applying an appropriate nanometerscale periodic potential with hexagonal symmetry onto conventional two-dimensional electron gases (2DEGs) will generate massless Dirac fermions at the corners of the supercell Brillouin zone (SBZ). We find that the potential configurations needed should be within or close to current laboratory capabilities, and this approach could benefit from the highly developed experimental techniques of 2DEG physics 20 including recent advances in self-assembly nanostructures 21,22,23 .…”

Scattering-assisted tunneling: Energy dependence, magnetic field dependence, and use as an external probe of two-dimensional transport

“…Once the electrons are strongly localized, the system is said to have undergone a metal-insulator transition. 31,33 If the electrons are localized to effectively zero-dimensional quantum dots, then the density of states available for scattering will be restricted and scattering will be quenched, leading to a large decrease in the tunneling rate through the barrier. In this case, τ s should increase greatly as the QW is depleted.…”