arXiv subjects

T. M. Klapwijk

Publications and source records attributed to T. M. Klapwijk.

114 records · Page 7Linked to original sources

arXiv1998

Classical versus Quantum Effects in the B=0 Conducting Phase in Two Dimensions

In the dilute two-dimensional electron system in silicon, we show that the temperature below which Shubnikov-de Haas oscillations become apparent is approximately the same as the temperature below which an exponential decrease in resistance is seen in B=0, suggesting that the anomalous behavior in zero field is observed only when the system is in a degenerate (quantum) state. The temperature dependence of the resistance is found to be qualitatively similar in B=0 and at integer Landau level filling factors.

cond-mat.str-el↗

arXiv1997

Suppression of the Coulomb interaction contribution to the conductance by a parallel magnetic field

The Coulomb interaction contribution to the conductance is investigated in a phase-coherent disordered 2-dimensional electron gas, which resistance can be varied by an overall gate electrode. Its magnitude of dGeei=-0.3 e^2/h is obtained by applying a bias voltage to suppress the Coulomb anomaly. In contrast to theoretical predictions, dGeei is suppressed by a parallel magnetic field. The zero-bias magnetoresistance exhibits reproducible fluctuations in perpendicular magnetic fields on a field scale much larger than that expected for universal conductance fluctuations, which might be attributed to fluctuations in the Coulomb interaction contribution.

cond-mat.mes-hall↗

arXiv1997

Reentrant behavior in the superconducting phase-dependent resistance of a disordered 2-dimensional electron gas

We have investigated the bias-voltage dependence of the phase-dependent differential resistance of a disordered T-shaped 2-dimensional electron gas coupled to two superconducting terminals. The resistance oscillations first increase upon lowering the energy. For bias voltages below the Thouless energy, the resistance oscillations are suppressed and disappear almost completely at zero bias voltage. We find a qualitative agreement with the calculated reentrant behavior of the resistance and discuss quantitative deviations.

cond-mat.mes-hall↗

arXiv1997

Observation of Andreev Reflection Enhanced Shot Noise

We have experimentally investigated the quasiparticle shot noise in NbN/MgO/NbN superconductor - insulator - superconductor tunnel junctions. The observed shot noise is significantly larger than theoretically expected. We attribute this to the occurrence of multiple Andreev reflection processes in pinholes present in the MgO barrier. This mechanism causes the current to flow in large charge quanta (Andreev clusters), with a voltage dependent average value of m = 1+ 2 Delta/eV times the electron charge. Because of this charge enhancement effect, the shot noise is increased by the factor m.

cond-mat.supr-con↗

arXiv1995

Experimental determination of the quasi-particle decay length $ξ_{\text{Sm}}$ in a superconducting quantum well

We have investigated experimentally the electronic transport properties of a two-dimensional electron gas (2DEG) present in an AlSb/InAs/AlSb quantum well, where part of the toplayer has been replaced by a superconducting Nb strip, with an energy gap $Δ_0$. By measuring the lateral electronic transport underneath the superconductor, and comparing the experimental results with a model based on the Bogoliubov-de Gennes equation and the Landauer-Büttiker formalism, we obtain a decay length $ξ_{\text{Sm}} \approx 100~\text{nm}$ for electrons. This decay length corresponds to an interface transparency $T_{\text{SIN}}=0.7$ between the Nb and InAs. Using this value, we infer an energy gap in the excitation spectrum of the SQW of $Δ_{\text{eff}} = 0.97 Δ_0 = 0.83~\text{meV}$.

cond-mat↗

arXiv1994

Proximity and Josephson effects in superconductor - two dimensional electron gas planar junctions

The DC Josephson effect is theoretically studied in a planar junction in which a two dimensional electron gas (2DEG) infinite in lateral directions is in contact with two superconducting electrodes placed on top of the 2DEG. An energy gap in the excitation spectrum is created in the 2DEG due to the proximity effect. It is shown that under certain conditions, the region of the 2DEG underneath the superconductors is analogous to a superconducting region with an order parameter $\varepsilon_g\exp(iϕ)$\/, where $\varepsilon_g~(\varepsilon_g<Δ)$\/ depends on the interface transmittance and the Fermi velocity mismatch between the superconductors and the 2DEG.

cond-mat↗