arXiv subjects

V. Bayot

Publications and source records attributed to V. Bayot.

24 records · Page 2Linked to original sources

arXiv2002

Long dephasing time and high temperature ballistic transport in an InGaAs open quantum dot

We report on measurements of the magnetoconductance of an open circular InGaAs quantum dot between 1.3K and 204K. We observe two types of magnetoconductance fluctuations: universal conductance fluctuations (UCFs), and 'focusing' fluctuations related to ballistic trajectories between openings. The electron phase coherence time extracted from UCFs amplitude is larger than in GaAs/AlGaAs quantum dots and follows a similar temperature dependence (between T^-1 and T^-2). Below 150K, the characteristic length associated with 'focusing' fluctuations shows a slightly different temperature dependence from that of the conductivity.

cond-mat.mes-hall↗

arXiv1999

NMR Determination of 2D Electron Spin Polarization at $ν=1/2$

Using a `standard' NMR spin-echo technique we determined the spin polarization of two-dimensional electrons, confined to GaAs quantum wells, from the hyperfine shift of Ga nuclei in the wells. Concentrating on the temperature and magnetic field dependencies of spin polarization at Landau level filling factor $ν=1/2$, we find that the results are described well by a simple model of non-interacting composite fermions, although some inconsistencies remain when the two-dimensional electron system is tilted in the magnetic field.

cond-mat.mes-hall↗

arXiv1998

Heat Capacity Evidence for the Suppression of Skyrmions at Large Zeeman Energy

Measurements on a multilayer two-dimensional electron system (2DES) near Landau level filling $ν$=1 reveal the disappearance of the nuclear spin contribution to the heat capacity as the ratio $\tilde{g}$ between the Zeeman and Coulomb energies exceeds a critical value $\tilde{g}_c \approx$0.04. This disappearance suggests the vanishing of the Skyrmion-mediated coupling between the lattice and the nuclear spins as the spin excitations of the 2DES make a transition from Skyrmions to single spin-flips above $\tilde{g}_c$. Our experimental $\tilde{g}_c$ is smaller than the calculated $\tilde{g}_c$=0.054 for an ideal 2DES; we discuss possible origins of this discrepancy.

cond-mat.mes-hall↗

arXiv1997

Critical Behavior of Nuclear-Spin Diffusion in GaAs/AlGaAs Heterostructures near Landau Level Filling ν=1

Thermal measurements on a GaAs/AlGaAs heterostructure reveal that the state of the confined two-dimensional electrons dramatically affects the nuclear-spin diffusion near Landau level filling factor ν=1. The experiments provide quantitative evidence that the sharp peak in the temperature dependence of heat capacity near ν=1 is due to an enhanced nuclear-spin diffusion from the GaAs quantum wells into the AlGaAs barriers. We discuss the physical origin of this enhancement in terms the possible Skyrme solid-liquid phase transition.

cond-mat.mes-hall↗

arXiv1996

Giant Low Temperature Heat Capacity of GaAs Quantum Wells near Landau Level Filling $ν$=1

We report low temperature ($T$) heat capacity ($C$) data on a multiple-quantum-well GaAs/AlGaAs sample in the quantum Hall regime. Relative to its low field magnitude, $C$ exhibits up to 10^5-fold enhancement near $ν$=1 where Skyrmions arethe ground state of the confined two-dimensional electrons. We attribute the large $C$ to a Skyrmion-induced, strong coupling of the nuclear spin system to the lattice. The data are consistent with the Schottky nuclear heat capacity of Ga and As atoms in the quantum wells, except at very low $T$ where $C$ vs $T$ exhibits a remarkably sharp peak suggestive of a phase transition in the electronic system.

cond-mat↗

arXiv1995

Quantum transport in a multiwalled carbon nanotube

We report on electrical resistance measurements of an individual carbon nanotube down to a temperature T=20 mK. The conductance exhibits a ln T dependence and saturates at low temperature. A magnetic field applied perpendicular to the tube axis, increases the conductance and produces aperiodic fluctuations. The data find a global and coherent interpretation in terms of two-dimensional weak localization and universal conductance fluctuations in mesoscopic conductors. The dimensionality of the electronic system is discussed in terms of the peculiar structure of carbon nanotubes.

cond-mat↗