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Уважаемые коллеги,<br>
<br>
На заседании Ученого совета в пятницу 4 декабря будут заслушан
обзорный доклад:<br>
<br>
1) М.В. Фейгельман<br>
<font size="+1"><b>Квантовое разрушение сверхпроводимости в
низкоразмерных системах</b></font><br>
<br>
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.<br>
<div class="abstract tex">
Доклад по обзорной статье:<br>
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
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<br>
<br>
После этого, в 16:00 состоится коллоквиум:<br>
<br>
Katharina Franke (Free University Berlin, Germany)<br>
<font size="+1"><b>Photon-assisted tunneling at the atomic scale:
Probing resonant Andreev reflections from Yu-Shiba-Rusinov
states</b></font><br>
<br>
<div class="abstract tex">
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.<br>
References<br>
[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).<br>
[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). <a class="moz-txt-link-freetext" href="https://doi.org/10.1038/s41567-020-0972-z">https://doi.org/10.1038/s41567-020-0972-z</a>;
arXiv:2001.09534
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<br>
<br>
Доклады на Ученом совете и коллоквиуме будут сопровождаться
онлайн-трансляцией в Zoom. <br>
ID и пароль те же, что и для предыдущих трансляций:<a
class="moz-txt-link-freetext"
href="https://zoom.us/j/93947383544?pwd=QnU4VGVuYVBlSlJSeHBkTlp4QW9HZz09"><br>
</a><a class="moz-txt-link-freetext"
href="https://zoom.us/j/96899364518?pwd=MzBsR2lYT0lYL2x2b1oyNU9LeWlWUT09">https://zoom.us/j/96899364518?pwd=MzBsR2lYT0lYL2x2b1oyNU9LeWlWUT09</a><br>
Meeting ID: 968 9936 4518<br>
Пароль: 250319<br>
<br>
<br>
С. Крашаков<br>
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