arXiv subjects

D. A. Ritchie

Publications and source records attributed to D. A. Ritchie.

240 records · Page 14Linked to original sources

arXiv1996

Possible Spin Polarization in a One-Dimensional Electron Gas

In zero magnetic field, conductance measurements of clean one-dimensional (1D) constrictions defined in GaAs/AlGaAs heterostructures show twenty-six quantized ballistic plateaux, as well as a structure close to $0.7(2e^2/h)$. In an in-plane magnetic field all the 1D subbands show Zeeman splitting and in the wide channel limit the $g$-factor is $\mid g \mid = 0.4$, close to that of bulk GaAs. For the last subband spin-splitting originates from the structure at $0.7(2e^2/h)$, indicating spin polarization at $B=0$. The measured enhancement of the $g$-factor as the subbands are depopulated suggests that the ``0.7 structure'' is induced by electron-electron interactions.

cond-mat↗

arXiv1996

Re-entrant resonant tunneling

We study the effect of electron-electron interactions on the resonant-tunneling spectroscopy of the localized states in a barrier. Using a simple model of three localized states, we show that, due to the Coulomb interactions, a single state can give rise to two resonant peaks in the conductance as a function of gate voltage, G(Vg). We also demonstrate that an additional higher-order resonance with Vg-position in between these two peaks becomes possibile when interactions are taken into account. The corresponding resonant-tunneling process involves two-electron transitions. We have observed both these effects in GaAs transistor microstructures by studying the time evolution of three adjacent G(Vg) peaks caused by fluctuating occupation of an isolated impurity (modulator). The heights of the two stronger peaks exibit in-phase fluctuations. The phase of fluctuations of the smaller middle peak is opposite. The two stronger peaks have their origin in the same localized state, and the third one corresponds to a co-tunneling process.

cond-mat↗

arXiv1996

Ballistic Composite Fermions in Semiconductor Nanostructures

We report the results of two fundamental transport measurements at a Landau level filling factor $ν$ of 1/2. The well known ballistic electron transport phenomena of quenching of the Hall effect in a mesoscopic cross-junction and negative magnetoresistance of a constriction are observed close to B~=~0 and $ν~=~ 1/2$. The experimental results demonstrate semi-classical charge transport by composite fermions, which consist of electrons bound to an even number of flux quanta.

cond-mat↗

arXiv1995

The Aharonov-Bohm Effect in the Fractional Quantum Hall Regime

We have investigated experimentally resonant tunnelling through single-particle states formed around an antidot by a magnetic field, in the fractional quantum Hall regime. For 1/3 filling factor around the antidot, Aharonov-Bohm oscillations are observed with the same magnetic field period as in the integer quantum Hall regime. All our measurements are consistent with quasiparticles of fractional charge e*. However, the results are also consistent with particles of any charge (>= e*) as the system must rearrange every time the flux enclosed increases by h/e.

cond-mat↗

arXiv1995

Tunneling Between Two-Dimensional Electron Gases in a Weak Magnetic Field

We have measured the tunneling between two two-dimensional electron gases (2DEGs) in weak magnetic fields, when the carrier densities of the two electron layers are matched. At zero magnetic field, B=0, the lineshape of the equilibrium tunneling resonance is best fit by a Lorentzian, with a linewidth which is determined by the roughness of the tunnel barrier. For $B\not=0$ with filling factors $ν\gg 1$, there is a suppression of the resonant tunneling conductance about zero bias, $V_{\text{sd}}=0$. This low field signature of the high field Coulomb gap shows the same linear $B$ dependence as previously measured for $ν<1$.

cond-mat↗

arXiv1994

Tunneling Between Two-Dimensional Electron Gases in a Strong Magnetic Field

We have measured the tunneling between two two-dimensional electron gases at high magnetic fields $B$, when the carrier densities of the two electron layers are matched. For filling factors $ν<1$, there is a gap in the current-voltage characteristics centered about $V=0$, followed by a tunneling peak at $\sim 6$~mV. Both features have been observed before and have been attributed to electron-electron interactions within a layer. We have measured high field tunneling peak positions and fitted gap parameters that are proportional to $B$, and independent of the carrier densities of the two layers. This suggests a different origin for the gap to that proposed by current theories, which predict a $\sqrt{B}$ dependence.

cond-mat↗