[institut] IPB Colloquium: Rok Zitko, Monday, 17 October, 14:00

[Darko Tanaskovic]

Dear colleagues,

You are cordially invited to the IPB COLLOQUIUM which will be held on 
Monday, 17 October 2016 at 14:00 in “Dr. Dragan Popović” library reading 
room of the Institute of Physics Belgrade. The talk entitled

Magnetic nanostructures in contact with superconductors: from Shiba to 
Majorana states

will be given by Dr. Rok Žitko (Institute "Jozef Stefan", Ljubljana, 
Slovenia)


Abstract of the talk:

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. These are known in different research 
communities either as the Yu-Shiba-Rusinov states or the Andreev bound 
states. They are observable as spectroscopically sharp resonances in the 
tunneling spectra, located well inside the superconducting gap for 
sufficiently strong exchange coupling. In more general cases (such as 
high impurity spin, magnetic anisotropy, coupling to vibrational modes, 
presence of multiple screening channels or multiple impurities) the 
spectra of the sub-gap excitations become complex with multiple 
excitations that reveal the strongly correlated nature of the problem. 
When multiple impurities form a long ferromagnetically ordered chain and 
provided that there is sufficiently strong spin-orbit coupling, the 
system is predicted to enter a topologically nontrivial state 
characterized by fractional Majorana modes localized on the chain ends. 
The signatures of such zero-energy modes have now been observed in 
several experiments.



Best regards,
Darko Tanaskovic

Institute of Physics Belgrade
Pregrevica 118, 11080 Belgrade, Serbia
http://www.ipb.ac.rs/