ELFT HÍRADÓ

[tcsaba <tcsaba AT eik.bme.hu>]

                 M E G H Í V Ó - I N V I T A T I O N

    Seminar Series of the Department of Theoretical Physics at the
           Budapest University of Technology and Economics


                          Mircea Trif
                       (Tsinghua Univ.)


    Dynamical Shiba states and bands in s-wave superconductors


Magnetic impurities inserted in an s-wave superconductor give rise to 
spin-polarized in-gap states called Yu-Shiba-Rusinov (YSR) states. When 
a set of such impurities are put in proximity with one another, forming 
for example a chain, they hybridize and they rise to a Shiba band that 
is described by a p-wave, or topological superconductor [1]. Such a 
system can host at its edges zero energy Majorana fermions, which are 
the basic units for topological quantum computing, an extremely 
promising avenue for building up a quantum computer. While all previous 
studies dealt with static magnetic impurities, in this talk, I will 
address the physical manifestations associated with the dynamics of such 
impurities. For the single Shiba state, I will show that the impurity 
spin precession pertains to dc charge and spin currents flowing through 
a normal STM tip tunnel coupled to the superconductor in the vicinity of 
the impurity. The resulting charge current is found to be proportional 
to the difference between the electron and hole wave-functions of the 
Shiba state, being a direct measure for such an asymmetry [2]. In the 
case of a Shiba band, I will show that such a dynamical setup gives rise 
to a Hamiltonian that shows non-trivial topological properties, and 
present the corresponding topological phase diagram. I will show that 
changing precession frequency potentiates control over topological phase 
transitions and the emergence of Majorana bound states. Finally, I will 
show that our proposal could be implemented in an on-chip setup, by 
driving the magnetic impurities or texture by means of the spin-transfer 
torque [3].

[1] Gerbold C. Menard, Sebastien Guissart, Christophe Brun, Mircea Trif, 
et al, arXiv:1607.06353.
[2] Vardan Kaladzhyan, Silas Hoffman, Mircea Trif, arXiv:1611.09722 (to 
appear in PRB).
[3] Vardan Kaladzhyan, Pascal Simon, Mircea Trif, arXiv:1703.01870.


Időpont: 2017. március 31. péntek, 10:15
Helyszín: BME Fizikai Intézet, Elméleti Fizika Tanszék,
Budafoki út 8. F-épület, III lépcsőház, szemináriumi szoba