[Landau ITP Seminars] Friday 04.12.2020

[Serge Krashakov]

Уважаемые коллеги,

На заседании Ученого совета в пятницу 4 декабря будут заслушан обзорный 
доклад:

1)  М.В. Фейгельман
*Квантовое разрушение сверхпроводимости в низкоразмерных системах*

Будет сделан краткий обзор основных результатов экспериментальных и 
теоретических работ последних ~ 10 лет по квантовым фазовым переходам 
сверхпроводник-изолятор и сверхпроводник-металл. Кроме того, 
предполагается представить некоторый список основных нерешенных проблем 
в этой области.
Доклад по обзорной статье:
Benjamin Sacépé, Mikhail Feigel’man and Teunis M. Klapwijk, Quantum 
breakdown of superconductivity in low-dimensional materials, Nature 
Physics 16, 734-746 (2020); arXiv:2007.15870


После этого, в 16:00 состоится коллоквиум:

Katharina Franke (Free University Berlin, Germany)
*Photon-assisted tunneling at the atomic scale: Probing resonant Andreev 
reflections from Yu-Shiba-Rusinov states*

Exchange coupling of magnetic adsorbates to a superconducting substrate 
leads to Yu-Shiba-Rusinov (YSR) states within the superconducting energy 
gap. These can be probed by scanning tunneling spectroscopy as a pair of 
resonances at positive and negative bias voltage and over a wide range 
of tunnel conductances. At low tunneling rates, the current is carried 
by single-electron processes, where each excitation is sufficiently 
quickly followed by a relaxation into the energetic continuum. Upon 
increasing the junction conductance, the relaxation rates suppress 
single-electron tunneling and resonant Andreev processes start to 
dominate the transport process. The cross-over of these processes is 
expressed in the variation of the ratio of YSR peak height at positive 
and negative bias voltage [1]. Here, we investigate these transport 
processes by photon-assisted tunneling. While applying highfrequency 
radiation to the tunneling junction, we record the differential 
conductance spectra in the low and high-conductance regime. At low 
conductance, the YSR states exhibit symmetrically spaced sidebands with 
their spacing directly evidencing single-electron tunneling. 
Surprisingly, at large junction conductance, the spacing remains the 
same while the patterns become asymmetric. We show that this asymmetry 
is direct evidence of a resonant Andreev reflection with tunneling 
threshold conditions imposed on its electron and hole component [2]. We 
suggest that photon-assisted tunneling can be a powerful tool for the 
determination of the nature of the charge carriers in a single tunneling 
event.
References
[1] M. Ruby, F. Pientka, Y. Peng, F. von Oppen, B.W. Heinrich, and K.J. 
Franke, "Tunneling Processes into Localized Subgap States in 
Superconductors", Phys. Rev. Lett. 115, 087001 (2015).
[2] O. Peters, N. Bogdanoff, S. Acero González, L. Melischek, J. Rika 
Simon, Gaël Reecht, C.B. Winkelmann, Felix von Oppen & K.J. Franke, 
"Resonant Andreev reflections probed by photon-assisted tunnelling at 
the atomic scale", Nat. Phys. (2020). 
https://doi.org/10.1038/s41567-020-0972-z; arXiv:2001.09534


Доклады на Ученом совете и коллоквиуме будут сопровождаться 
онлайн-трансляцией в Zoom.
ID и пароль те же, что и для предыдущих трансляций:
https://zoom.us/j/96899364518?pwd=MzBsR2lYT0lYL2x2b1oyNU9LeWlWUT09
Meeting ID: 968 9936 4518
Пароль: 250319


С. Крашаков
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