Conduction channels of superconducting quantum point contacts

Abstract

Esta es la versión de autor del artículo publicado en: This is an author produced version of a paper published in: El acceso a la versión del editor puede requerir la suscripción del recurso Access to the published version may require subscription Atomic quantum point contacts accommodate a small number of conduction channels. Their number N and transmission coefficients {Tn} can be determined by analyzing the subgap structure due to multiple Andreev reflections in the current-voltage (IV ) characteristics in the superconducting state.With the help of mechanically controllable break-junctions we have produced Al contacts consisting of a small number of atoms. In the smallest stable contacts, usually three channels contribute to the transport. We show here that the channel ensemble {Tn} of few atom contacts remains unchanged up to temperatures and magnetic fields approaching the critical temperature and the critical field, respectively, giving experimental evidence for the prediction that the conduction channels are the same in the normal and in the superconducting state.

Subgap structure in resistively shunted superconducting atomic point contacts

“…Carefully designed resistive environments were shown to cause a superconductor-insulator quantum phase transition in a single tunnel junction. In accord to preceding studies of aluminum QPC, 23 we found that the PIN code is temperature independent. 22 Finally, thermal stability of shunted and unshunted Nb QPCs was investigated.…”

Superconducting properties of lithographic lead break junctions

“…Temperature dependent DOS broadening Examples of tunnel spectra for sample C at various temperatures are plotted in figure 5. Beside a reduction of the gap D. -+ D.(T)when approaching Tc, as expected, we observe a pronounced broadening of the coherence peak that goes beyond mere thermal broadening of the Fermi functions, as a tentative fitting reveals (seefigure S3).This observation is distinctly different from the behavior of AI where only negligible broadening was observed[21).…”

Subharmonic gap structure in superconducting scanning tunneling microscope junctions

“…For moderate junction transparencies [19] we observe the Josephson effect and the subgap structures at eV = 2∆/2 and eV = 2∆/3. In contrast with the break junction experiments [7,8,10], where thermal and noise induced phase fluctuations were kept minimal [20] and their effect on the SGS was negligible, the noise temperature in the present work is quite high. With the observation of a smeared SGS in the current-voltage characteristics of our junctions, and a measurement of the noise temperature based on the Josephson effect, this work represents a first attempt at studying the effects of phase fluctuations on the SGS, which so far has been only qualitative.…”

“…The phenomenon is termed the subharmonic gap structure (SGS) and is characterized by temperature independent excess current onsets at these voltages. Renewed interest in this effect over the last decade [2,3,4,5,6,7,8,9,10,11,12] was driven in part by advances in fabrication of controllable superconducting point contacts. The emergence of new systems, such as Josephson junction qubits where quasiparticle currents play a role in the decoherence of the qubit state [13], also calls for a better understanding of subgap quasiparticle tunneling processes.…”