Jp Heida

Low temperature current transport of Sn-GaAs contacts

We measure low temperature current transport properties of superconducting Sn contacts to p+-GaAs. For contacts alloyed at 450-degrees-C, the current-voltage characteristics show a strong dependence on alloying time. The critical temperature of Sn near the superconductor-semiconductor interface decreases from 3.8 to 1.8 K as the alloying time increases from 0 to 120 s. On the other hand, a long-time alloying increases the transparency of the interface. Using the Blonder, Tinkham, and Klapwijk model [Phys. Rev. B 25, 4515 (1982) ], we find that the transmission coefficient of the interface increases from 0.2 to 0.7 by alloying. However, the normal state resistance calculated using the model is much smaller than the experimental value.

Superconductors coupled with a two-dimensional electron gas in GaAs/AlGaAs and InAs/AlGaSb heterostructures

Abstract We fabricated superconducting Sn/Pd contacts to a two-dimensional electron gas (2DEG) in GaAs/AlGaAs heterostructures by an alloying technique. A dip around zero bias and peaks at finite voltages have been observed in the differential resistance of a 2DEG between two superconductors. The resistance dip may be a result of Andreev reflection at 2DEG-superconductor interlaces and the peaks are probably due to the Josephson coupling between two very close superconducting islands in a superconducting contact region, which may be formed by alloying. Alternatively, we made superconducting Nb contacts to a 2DEG in an InAs/AlGaSb quantum well structure. The resistance of Nb-2DEG-Nb devices shows a clear indication of Andrccv reflection.

Experiments on Aharonov–Bohm effect under the influence of uniform spin orbit interaction: Possible observation of Berry's phase in electronic transport

We have measured Aharonov–Bohm conductance oscillations in a two-dimensional ring in the presence of strong Rashba spin–orbit interaction. We discuss the experimental procedure that reveals a splitting in the peak of the Fourier spectrum of the above oscillations. The possibility that the splitting originates from a geometric phase acquired by the electron spin is considered.

Quantized conductance and electron focusing spectra of GaAs/AlGaAs point contacts fabricated by optical lithography

Split gate quantum point contacts on a two‐dimensional electron gas (2DEG) of GaAs/AlGaAs heterostructures are fabricated using conventional optical lithography. The typical opening of the split gates ranges from 0.25 to 0.5 μm. Applying negative voltages to the gate introduces horn‐shaped constrictions. In a double point contact device, the point contact conductances are measured as a function of gate voltage, and transverse electron focusing is studied using one point contact to inject electrons ballistically into the 2DEG and the other to collect the electrons. Clear quantized conductance steps in units of 2e2/h are found at temperatures between 0.1 and 2 K. Also, electron focusing spectra are obtained for various point contact widths and some features are characterized by the geometry of the split gate.