ELFT HÍRADÓ

[Andras Palyi <palyi AT mail.bme.hu>]

Dear Colleagues,

Next Monday the BME Exotic Quantum Phases seminar series continues with this 
talk:

Speaker: Rok Zitko (Ljubljana)
Title: "Yu-Shiba-Rusinov states in superconducting island with finite 
charging energy"
Abstract: below
Time: Sep 14 Monday, 14:15
Location: online in Teams

The link to join the talk in Teams:

https://teams.microsoft.com/l/meetup-join/19%3a8cc7e9ee6d1e483a864d41f638246643%40thread.tacv2/1599670191895?context=%7b%22Tid%22%3a%226a3548ab-7570-4271-91a8-58da00697029%22%2c%22Oid%22%3a%22f8b27e90-dbca-4bb5-813c-d6415577ec35%22%7d
 
<https://teams.microsoft.com/l/meetup-join/19:8cc7e9ee6d1e483a864d41f638246643 AT thread.tacv2/1599670191895?context={%22Tid%22:%226a3548ab-7570-4271-91a8-58da00697029%22,%22Oid%22:%22f8b27e90-dbca-4bb5-813c-d6415577ec35%22}>

Best regards,
Andras Palyi

= = =

Abstract: "Recent advances in the fabrication of nanometer scale hybrid 
semiconductor-superconductor devices as well as in the scanning tunneling 
spectroscopy of adsorbate covered surfaces of superconductors have made 
possible very detailed experimental studies of the old problem of 
paramagnetic impurities in a superconducting host using local probes with 
very high energy and spatial resolution. At the same time, improved 
theoretical tools have been devised to reliably and accurately calculate the 
excitation spectra of the corresponding quantum impurity problems with gapped 
continuum electrons. These developments have enabled very stringent tests 
between experiment and theory. The results demonstrate the importance to 
describe the magnetic impurities as quantum objects with non-trivial internal 
dynamics due to the coupling to their environment.
 
I will discuss the physics of bound states induced by the exchange 
interaction between the magnetic impurities and the Bogoliubov quasiparticles 
in superconductors, known as the Yu-Shiba-Rusinov states. They are observable 
as spectroscopically sharp resonances in the tunneling spectra, located well 
inside the superconducting gap for sufficiently strong exchange coupling. If 
the superconductor is small and has a sizeable charging energy E_c, the 
problem must be described using a model that allows tracking charge on the 
superconductor. I will show that a pairing Hamiltonian with a charging term 
admits a compact matrix-product-operator representation and can be reliably 
solved using the density-matrix renormalization group (DMRG) techniques. I 
will discuss how the properties of the system change as a function of the 
ratio of the charging energy over the superconducting gap, E_c/Delta. The 
method can be generalized to the situation with two superconducting islands 
where two-channel Kondo physics can be explored."