ELFT HÍRADÓ

[Janos Asboth <asboth AT phy.bme.hu>]

Meghívó

BME Elméleti Fizika Szeminárium,

december 4. péntek 10h15,
online a Microsoft Teamsben,
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Rózsa Levente (University of Konstanz):

Extended and interacting Yu-Shiba-Rusinov states on the surface of
elemental superconductors

Magnetic impurities in conventional superconductors locally break Cooper
pairs, leading to the emergence of Yu-Shiba-Rusinov (YSR) bound states.
Chains of YSR impurities have been theoretically predicted to give rise to
Majorana bound states, representing promising building blocks of
topological quantum computers. Revealing the topological properties of YSR
bands necessitates a fundamental understanding of the extension of
individual YSR states, as well as of the interactions between the states.

Here, a theoretical explanation of recent scanning tunneling microscopy and
spectroscopy experiments on YSR bound states in elemental superconductors
is presented. On the La(0001) surface, YSR states are found to extend up to
30-40 nm distance along certain crystallographic directions, approximately
one order of magnitude longer than what has been previously observed in
similar setups [1]. This is explained by an effectively reduced
dimensionality of the electronic structure, with the scattering processes
dominated by surface states with a strongly anisotropic Fermi surface. The
presence of multi-orbital YSR states has been observed in the vicinity of
Mn adatoms on the Nb(110) surface, with a hybridization and energy
splitting of the states in both ferromagnetically and antiferromagnetically
aligned dimers [2]. In the antiferromagnetic dimer, such a splitting of the
YSR states has been ruled out in theoretical considerations so far, since
their degeneracy is protected by Kramers' theorem via an effective
time-reversal symmetry. It is shown that this degeneracy is lifted if
spin-orbit coupling is taken into account, together with the breaking of
inversion symmetry at the surface.

[1] H. Kim, L. Rózsa, D. Schreyer, E. Simon, and R. Wiesendanger, Nat.
Commun. 11, 4573 (2020).
[2] P. Beck, L. Schneider, L. Rózsa, K. Palotás, A. Lászlóffy, L. Szunyogh,
J. Wiebe, and R. Wiesendanger, arXiv:2010.04031.

Minden érdeklődőt szeretettel várunk.

Asbóth János
szemináriumi koordinátor