Sergey Vitkalov

Small-angle shubnikov-de haas measurements in a 2D electron system: the effect of a strong In-plane magnetic field

Measurements in magnetic fields applied at small angles relative to the electron plane in silicon MOSFETs indicate a factor of 2 increase of the frequency of Shubnikov-de Haas oscillations at H>H(sat). This signals the onset of full spin polarization above H(sat), the parallel field above which the resistivity saturates to a constant value. For H<H(sat), the phase of the second harmonic of the oscillations relative to the first is consistent with scattering events that depend on the overlap instead of the sum of the spin-up and spin-down densities of states. This unusual behavior may reflect the importance of many-body interactions.

Scaling of the Magnetoconductivity of Silicon MOSFETs: Evidence for a Quantum Phase Transition in Two Dimensions

For a broad range of electron densities n and temperatures T, the in-plane magnetoconductivity of the two-dimensional system of electrons in silicon MOSFETs can be scaled onto a universal curve with a single parameter H(sigma)(n,T), where H(sigma) obeys the empirical relation H(sigma) = A(n) [Delta(n)(2)+T2](1/2). The characteristic energy k(B)Delta associated with the magnetic field dependence of the conductivity decreases with decreasing density, and extrapolates to 0 at a critical density n(0), signaling the approach to a zero-temperature quantum phase transition. We show that H(sigma) = AT for densities near n(0).

Zero-Differential Resistance State of Two-Dimensional Electron Systems in Strong Magnetic Fields

We report the observation of a zero-differential resistance state (ZDRS) in response to a direct current above a threshold value I>I th applied to a two-dimensional system of electrons at low temperatures in a strong magnetic field. Entry into the ZDRS, which is not observable above several Kelvins, is accompanied by a sharp dip in the differential resistance. Additional analysis reveals an instability of the electrons for I>I th and an inhomogeneous, nonstationary pattern of the electric current. We suggest that the dominant mechanism leading to the new electron state is a redistribution of electrons in energy space induced by the direct current.

Spin polarization of strongly interacting two-dimensional electrons : The role of disorder

In high-mobility silicon metal-oxide-semiconductor field-effect transistors, the g*m* inferred indirectly from magnetoconductance and magnetoresistance measurements with the assumption that g*μ B H s =2E F are in surprisingly good agreement with g*m* obtained by direct measurement of Shubnikov-de Haas oscillations. The enhanced susceptibility Χ*α(g*m*) exhibits critical behavior of the form Χ*α(n-n 0 ) We examine the significance of the field scale H s derived from transport measurements, and show that this field signals the onset of full spin polarization only in the absence of disorder. Our results suggest that disorder becomes increasingly important as the electron density is reduced toward the transition.

Spin polarization of two-dimensional electrons determined from Shubnikov–de Haas oscillations as a function of angle

Recent experiments in the two-dimensional electron systems in silicon metal‐oxide‐semiconductor field effect transistors have shown that the in-plane magnetic field Hsat required to saturate the conductivity to its high-field value, and the magnetic fieldHs needed to completely align the spins of the electrons, are comparable. By small-angle Shubnikov-de Haas oscillation measurements that allow separate determinations of the spin-up and spin-down subband populations, we show to an accuracy 5% that Hsat5Hs .

Nonlinear resistance of two-dimensional electrons in crossed electric and magnetic fields

The longitudinal resistivity of two dimensional (2D) electrons placed in strong magnetic field is significantly reduced by applied electric field, an effect which is studied in a broad range of magnetic fields and temperatures in GaAs quantum wells with high electron density. The data are found to be in good agreement with theory, considering the strong nonlinearity of the resistivity as result of non-uniform spectral diffusion of the 2D electrons. Inelastic processes limit the diffusion. Comparison with the theory yields the inelastic scattering time of the two dimensional electrons. In the temperature range T=2-10(K) for overlapping Landau levels, the inelastic scattering rate is found to be proportional to T^2, indicating a dominant contribution of the electron-electron scattering to the inelastic relaxation. In a strong magnetic field, the nonlinear resistivity demonstrates scaling behavior, indicating a specific regime of electron heating of well-separated Landau levels. In this regime the inelastic scattering rate is found to be proportional to T^3, suggesting the electron-phonon scattering as the dominant mechanism of the inelastic relaxation.

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.

Temperature dependence of the resistivity of a dilute two-dimensional electron system in high parallel magnetic field

We report measurements of the resistance of silicon metal-oxide-semiconductor field-effect transistors as a function of temperature in high parallel magnetic fields where the two-dimensional system of electrons has been shown to be fully spin polarized. In a field of 10.8 T, insulating behavior is found for densities up to n{sub s}{approx}1.35x10{sup 11}cm{sup -2}{approx}1.5n{sub c}; above this density the resistance is a very weak function of temperature, varying less than 10% between 0.25 and 1.90 K. At low densities {rho}{yields}{infinity} more rapidly as the temperature is reduced than in zero field and the magnetoresistance {Delta}{rho}/{rho} diverges as T{yields}0.

Hall coefficient of a dilute two-dimensional electron system in a parallel magnetic field

Measurements in magnetic fields applied at a small angle with respect to the two-dimensional plane of the electrons of low-density silicon metal-oxide--semiconductor field-effect transistors indicate that the Hall coefficient is independent of parallel field from