Scott Dietrich

Quantum lifetime of 2D electron in magnetic field

The lifetime of two dimensional electrons in GaAs quantum wells, placed in weak quantizing magnetic fields, is measured using a simple transport method in broad range of temperatures from 0.3 K to 20 K. The temperature variations of the electron lifetime are found to be in good agreement with conventional theory of electron-electron scattering in 2D systems.

Transport relaxation time and quantum lifetime in selectively doped GaAs/AlAs heterostructures

Low-temperature dependences of the transport relaxation time (τtr) and quantum lifetime (τq) on the density of the two-dimensional electron gas (ne) in GaAs quantum wells with AlAs/GaAs lateral superlattice barriers have been studied. An exponential increase in the quantum lifetime with increasing electron density has been observed. It has been shown that the sharp increase in the quantum lifetime correlates with the appearance of X electrons in the AlAs/GaAs lateral superlattice barriers. It has been established that the ratio of the transport relaxation time to the quantum lifetime in the studied structures nonmonotonically depends on the density: the ratio τtr/τq first increases linearly with ne and then decreases. This behavior is not described by the existing theories.

Quantum oscillations of nonlinear response in electron systems with variable density

Quantum oscillations of dissipative resistance are observed in response to electric current applied to a GaAs quantum well with variable two dimensional electron density placed in quantizing magnetic fields. At a fixed magnetic field, the period of the current induced oscillations depends linearly on the electron density. The observed behavior is in accord with a recently proposed model that considers the DC bias-induced spatial re-population of Landau levels as the origin of the resistance oscillations. It indicates the important role of the electron screening in the vicinity of the quantum well, which significantly enhances the nonlinear response.

Inter-subband resistance oscillations in crossed electric and magnetic fields

Quantum oscillations of nonlinear resistance are investigated in response to electric current and magnetic field applied perpendicular to single GaAs quantum wells with two populated subbands. At small magnetic fields current-induced oscillations appear as Landau-Zener transitions between Landau levels inside the lowest subband. Period of these oscillations is proportional to the magnetic field. At high magnetic fields different kind of quantum oscillations emerges with a period,which is independent of the magnetic field. At a fixed current the oscillations are periodic in inverse magnetic field with a period that is independent of the dc bias. The proposed model considers these oscillations as a result of spatial variations of the energy separation between two subbands induced by the electric current.

Quantum oscillations of dissipative resistance in crossed electric and magnetic fields

Oscillations of dissipative resistance of two-dimensional electrons in GaAs quantum wells are observed in response to an electric current I and a strong magnetic field applied perpendicular to the two-dimensional systems. Period of the current-induced oscillations does not depend on the magnetic field and temperature. At a fixed current the oscillations are periodic in inverse magnetic fields with a period that does not depend on dc bias. The proposed model considers spatial variations of electron filling factor, which are induced by the electric current, as the origin of the resistance oscillations.

Frequency dispersion of nonlinear response of thin superconducting films in the Berezinskii-Kosterlitz-Thouless state

The effects of microwave radiation on transport properties of atomically thin La2-xSrxCuO₄ films were studied in the 0.1-20 GHz frequency range. Resistance changes induced by microwaves were investigated at different temperatures (8–15 K) near the superconducting transition. A strong decrease of the nonlinear response is observed within a few GHz of a cutoff frequency νcut ≈ 2GHz. The expected frequency dependence vastly underestimates the sharpness of this drop. Numerical simulations that assume ac response to follow dc V-I characteristics of the films reproduce well the low frequency behavior, but fail above νcut. Thus, high-frequency radiation is much less effective in inducing vortex-antivortex dissociation in the oscillating superconducting condensate.