Effects of a single magnetic impurity on superconductivity
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Date
2008
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Degree Level
Masters
Abstract
Electronic structure of a conventional superconductor in the vicinity of a single, iso-
lated magnetic impurity has been probed experimentally with scanning tunneling
spectroscopy by Yazdani et al.. Motivated by their experiment, we study the ef-
fects of a single magnetic impurity on superconductivity by means of the mean-¯eld
Bogoliubov-de Gennes theory. The Bogoliubov-de Gennes equations are solved di-
rectly and numerically, utilizing parallel computation on a CFI-founded 128-CPU
Beowulf-class PC cluster here at the University of Saskatchewan. As a preliminary
study, we also examine the electronic structure around a magnetic vortex. The local
magnetic field around a vortex breaks up Cooper pairs and suppresses superconduc-
tivity locally. Quasiparticle excitations are created and bound in the vortex core area
due to repeated Andreev scattering. A magnetic impurity tends to align the spins of
the neighboring electrons and break up Cooper pairs, and has similar effects of lo-
cally suppressing superconductivity. A striking difference, however, from the vortex
problem is that around a magnetic impurity there is particle-hole asymmetry in the
tunneling conductance. This is due to different probability amplitudes in the spin-up
branch and the spin-down branch of quasiparticle excitations. Furthermore, for the
spin potential strength larger than a certain critical value, the nature of quasiparticle
excitations is changed dramatically. Within a model of classical spin, we propose an
explanation of the measured tunneling conductance of the experiment. This work
is significant in that it gives us insight into superconductivity and magnetism{two
complementary manifestation of strong electron correlations.
Description
Keywords
NbSe_2, Nb, spin potential, vortex
Citation
Degree
Master of Science (M.Sc.)
Department
Physics and Engineering Physics
Program
Physics and Engineering Physics