arXiv subjects

X. G. Feng

Publications and source records attributed to X. G. Feng.

7 recordsLinked to original sources

arXiv2002

Effects of a Parallel Magnetic Field on the Metal-Insulator Transition in a Dilute Two-Dimensional Electron System

The temperature dependence of conductivity $σ(T)$ of a two-dimensional electron system in silicon has been studied in parallel magnetic fields B. At B=0, the system displays a metal-insulator transition at a critical electron density $n_c(0)$, and $dσ/dT >0$ in the metallic phase. At low fields ($B\lesssim 2$ T), $n_c$ increases as $n_c(B) - n_c(0) \propto B^β$ ($β\sim 1$), and the zero-temperature conductivity scales as $σ(n_s,B,T=0)/σ(n_s,0,0)=f(B^β/δ_n)$ (where $δ_n=(n_s-n_c(0))/n_c(0)$, and $n_s$ is electron density) as expected for a quantum phase transition. The metallic phase persists in fields of up to 18 T, consistent with the saturation of $n_c$ at high fields.

cond-mat.str-el↗

arXiv2000

Novel metallic behavior in two dimensions

Experiments on a sufficiently disordered two-dimensional (2D) electron system in silicon reveal a new and unexpected kind of metallic behavior, where the conductivity decreases as σ(n_s,T)=σ(n_s,T=0)+A(n_s)T^2 (n_s-carrier density) to a non-zero value as temperature T->0. In 2D, the existence of a metal with dσ/dT>0 is very surprising. In addition, a novel type of a metal-insulator transition obtains, which is unlike any known quantum phase transition in 2D.

cond-mat↗

arXiv2000

Effects of a parallel magnetic field on the novel metallic behavior in two dimensions

Magnetoconductance (MC) in a parallel magnetic field B has been measured in a two-dimensional electron system in Si, in the regime where the conductivity decreases as σ(n_s,T,B=0)=σ(n_s,T=0) + A(n_s)T^2 (n_s -- carrier density) to a non-zero value as temperature T->0. Very near the B=0 metal-insulator transition, there is a large initial drop in σwith increasing B, followed by a much weaker σ(B). At higher n_s, the initial drop of MC is less pronounced.

cond-mat.str-el↗

arXiv1999

Suppression of metallic behavior in two dimensions by spin flip scattering

We study the effect of the disorder on the metallic behavior of a two-dimensional electron system in silicon. The temperature dependence of conductivity $σ(T)$ was measured for different values of substrate bias, which changes both potential scattering and the concentration of disorder-induced local magnetic moments. We find that the latter has a much more profound effect on $dσ/dT$. In fact, the data suggest that in the limit of $T\to 0$ the metallic behavior, as characterized by $dσ/dT < 0$, is suppressed by an arbitrarily small amount of spin flip scattering by local magnetic moments.

cond-mat.str-el↗

arXiv1999

Effect of Local Magnetic Moments on the Metallic Behavior in Two Dimensions

The temperature dependence of conductivity $σ(T)$ in the metallic phase of a two-dimensional electron system in silicon has been studied for different concentrations of local magnetic moments. The local moments have been induced by disorder, and their number was varied using substrate bias. The data suggest that in the limit of $T\to 0$ the metallic behavior, as characterized by $dσ/dT < 0$, is suppressed by an arbitrarily small amount of scattering by local magnetic moments.

cond-mat.dis-nn↗

arXiv1998

Many-body correlations probed by plasmon-enhanced drag measurements in double quantum well structures

Electron drag measurements of electron-electron scattering rates performed close to the Fermi temperature are reported. While evidence of an enhancement due to plasmons, as was recently predicted [K. Flensberg and B. Y.-K. Hu, Phys. Rev. Lett. 73, 3572 (1994)], is found, important differences with the random-phase approximation based calculations are observed. Although static correlation effects likely account for part of this difference, it is argued that correlation-induced multiparticle excitations must be included to account for the magnitude of the rates and observed density dependences.

cond-mat.mes-hall↗

arXiv1998

Negative Electron Drag and Hole-Like behavior in the Integer Quantum Hall Regime

Electron drag between two two-dimensional electron gases in magnetic fields has been observed with a polarity opposite that for zero field. This negative drag requires that the electrons have a hole-like dispersion. Density dependence measurements in the integer quantum Hall regime show that drag is negative only when the upper Landau level of one layer is more than half filled while the other is less than half filled, indicating that hole-like dispersion is present in a half of each Landau level. Negative drag is argued to be a consequence of disorder.

cond-mat.mes-hall↗