arXiv subjects

R. Leturcq

Publications and source records attributed to R. Leturcq.

29 records · Page 2Linked to original sources

arXiv2006

Magnetic field symmetry and phase rigidity of the nonlinear conductance in a ring

We have performed nonlinear transport measurements as a function of a perpendicular magnetic field in a semiconductor Aharonov-Bohm ring connected to two leads. While the voltage-symmetric part of the conductance is symmetric in magnetic field, the voltage-antisymmetric part of the conductance is not symmetric. These symmetry relations are compatible with the scattering theory for nonlinear mesoscopic transport. The observed asymmetry can be tuned continuously by changing the gate voltages near the arms of the ring, showing that the phase of the nonlinear conductance in a two-terminal interferometer is not rigid, in contrast to the case for the linear conductance.

cond-mat.mes-hall↗

arXiv2006

Counting statistics of single-electron transport in a quantum dot

We have measured the full counting statistics (FCS) of current fluctuations in a semiconductor quantum dot (QD) by real-time detection of single electron tunneling with a quantum point contact (QPC). This method gives direct access to the distribution function of current fluctuations. Suppression of the second moment (related to the shot noise) and the third moment (related to the asymmetry of the distribution) in a tunable semiconductor QD is demonstrated experimentally. With this method we demonstrate the ability to measure very low current and noise levels.

cond-mat.mes-hall↗

arXiv2006

Two-subband quantum Hall effect in parabolic quantum wells

The low-temperature magnetoresistance of parabolic quantum wells displays pronounced minima between integer filling factors. Concomitantly the Hall effect exhibits overshoots and plateau-like features next to well-defined ordinary quantum Hall plateaus. These effects set in with the occupation of the second subband. We discuss our observations in the context of single-particle Landau fan charts of a two-subband system empirically extended by a density dependent subband separation and an enhanced spin-splitting g*.

cond-mat.mes-hall↗

arXiv2006

Design of Q-Band loop-gap resonators at frequencies 34-36 GHz for single electron spin spectroscopy in semiconductor nanostructures

We report on the design of loop-gap resonators (LGR) operating in the frequency range 34-36 GHz with the goal to achieve single electron spin resonance (ESR) in quantum dot nanostructures. We present a comprehensive study of the magnetic field strength and the spatial distribution of the electric and magnetic fields in the resonator by means of experiments and numerical simulations.

cond-mat.mes-hall↗

arXiv2005

1/f noise in a dilute GaAs two-dimensional hole system in the insulating phase

We have measured the resistance and the 1/f resistance noise of a two-dimensional low density hole system in a high mobility GaAs quantum well at low temperature. At densities lower than the metal-insulator transition one, the temperature dependence of the resistance is either power-like or simply activated. The noise decreases when the temperature or the density increase. These results contradict the standard description of independent particles in the strong localization regime. On the contrary, they agree with the percolation picture suggested by higher density results. The physical nature of the system could be a mixture of a conducting and an insulating phase. We compare our results with those of composite thin films.

cond-mat.dis-nn↗

arXiv2005

1/f Noise In Low Density Two-Dimensional Hole Systems In GaAs

Two-dimensional electron or hole systems in semiconductors offer the unique opportunity to investigate the physics of strongly interacting fermions. We have measured the 1/f resistance noise of two-dimensional hole systems in high mobility GaAs quantum wells, at densities below that of the metal-insulator transition (MIT) at zero magnetic field. Two techniques voltage and current fluctuations were used. The normalized noise power SR/R2 increases strongly when the hole density or the temperature are decreased. The temperature dependence is steeper at the lowest densities. This contradicts the predictions of the modulation approach in the strong localization hopping transport regime. The hypothesis of a second order phase transition or percolation transition at a density below that of the MIT is thus reinforced.

cond-mat.dis-nn↗

arXiv2005

Probing the Kondo density of states in a three-terminal quantum ring

We have measured the Kondo effect in a quantum ring connected to three terminals. In this configuration non-linear transport measurements allow to check which lead contributes to the Kondo density of states (DOS) and which does not. When the ring is connected to two strongly and one weakly coupled leads, the measurement of the differential conductance through the weakly coupled lead allows to probe directly the Kondo DOS. In addition, by applying a bias between the two strongly coupled leads, we show the splitting of the out-of-equilibrium DOS.

cond-mat.mes-hall↗

arXiv2004

Resistance noise scaling in a 2D system in GaAs

The 1/f resistance noise of a two-dimensional (2D) hole system in a high mobility GaAs quantum well has been measured on both sides of the 2D metal-insulator transition (MIT) at zero magnetic field (B=0), and deep in the insulating regime. The two measurement methods used are described: I or V fixed, and measurement of resp. V or I fluctuations. The normalized noise magnitude SR/R^2 increases strongly when the hole density is decreased, and its temperature (T) dependence goes from a slight increase with T at the largest densities, to a strong decrease at low density. We find that the noise magnitude scales with the resistance, SR /R^2 ~ R^2.4. Such a scaling is expected for a second order phase transition or a percolation transition. The possible presence of such a transition is investigated by studying the dependence of the conductivity as a function of the density. This dependence is consistent with a critical behavior close to a critical density p* lower than the usual MIT critical density pc.

cond-mat.str-el↗

arXiv2004

Multi-terminal transport through a quantum dot in the Coulomb blockade regime

Three terminal tunnelling experiments on quantum dots in the Coulomb blockade regime allow a quantitative determination of the coupling strength of individual quantum states to the leads. Exploiting this insight we have observed independent fluctuations of the coupling strengths as a function of electron number and magnetic field due to changes in the shape of the wave function in the dot. Such a detailed understanding and control of the dot-lead coupling can be extended to more complex systems such as coupled dots, and is essential for building functional quantum electronic systems.

cond-mat.mes-hall↗

arXiv2003

Resistance Noise Scaling in a Dilute Two-Dimensional Hole System in GaAs

We have measured the resistance noise of a two-dimensional (2D)hole system in a high mobility GaAs quantum well, around the 2D metal-insulator transition (MIT) at zero magnetic field. The normalized noise power $S_R/R^2$ increases strongly when the hole density p_s is decreased, increases slightly with temperature (T) at the largest densities, and decreases strongly with T at low p_s. The noise scales with the resistance, $S_R/R^2 \sim R^{2.4}$, as for a second order phase transition such as a percolation transition. The p_s dependence of the conductivity is consistent with a critical behavior for such a transition, near a density p* which is lower than the observed MIT critical density p_c.

cond-mat.str-el↗

arXiv2001

Heating of Two-Dimensional Holes in SiGe and the B = 0 Metal-Insulator Transition

We study the resistivity vs. electric field dependence $ρ(E)$ of a 2D hole system in SiGe close to the B=0 metal-insulator transition. Using $ρ$ as a ``thermometer'' to obtain the effective temperature of the holes $T_e(E)$, we find that the $ρ(E)$ dependence can be attributed to hole heating. The hole-phonon coupling involves weakly screened piezoelectric and deformation potentials compatible with previous measurements. The damping of the Shubnikov-de Haas oscillations gives the same $T_e$ values. Thus the $ρ(E)$ dependence and the $E$-field ``scaling'' do not provide additional evidence for a quantum phase transition (QPT). We discuss how to study, in general, true $E$-field scaling and extract the ratio of the QPT characteristic lengths.

cond-mat↗