For distribution

[CM ICTP - Trieste]

JOINT ICTP/SISSA STATISTICAL PHYSICS SEMINAR

	

Tuesday, 22 January    -    12:30 hrs.



Seminar Room - ICTP Main Building   (first floor)
		


I. NANDORI   ( Institute of Nuclear Physics, Debrecen )


"Field theoretical approach to layered superconductors"


Abstract

Typical high transition temperature superconductors consist of 
copper-oxide superconducting planes separated by insulating layers. The 
superconducting layers are coupled by Josephson and electromagnetic 
interactions. Although, the microscopic theory of high T_c 
superconductivity has not been constructed yet, the phenomenological 
description is well-established. The vortex dynamics of a 2D 
(uncharged) superfluid film can be described by the following models 
which are assumed to belong to the the same universality class: the 
two-dimensional sine--Gordon field theory (2D--SG), the XY spin model 
(2D--XY) and the 2D-Coulomb gas.  For charged 2D films, i.e. for 
superconducting thin films, the vortex behavior is described by the 
massive 2D--SG, the frustrated 2D--XY and the 2D--Yukawa gas. The gas 
of topological excitations and the equivalent spin model of a system of 
coupled layers is known for the Josephson and for the magnetically 
coupled case, however, no field theoretical model has been constructed.

We propose a quantum field theoretical approach to the vortex dynamics 
of magnetically coupled layered superconductors by constructing a 
two-dimensional multi-layer sine-Gordon type model which we map onto a 
gas of topological excitations.  The known interaction potentials of 
magnetically coupled vortices are consistently obtained from our 
field-theoretical analysis.  Originally, this layered SG model has been 
introduced as the bosonised version of the multi-flavor Schwinger 
model, and, consequently, it has been used to study quark confinement.  
We analyze the phase structure of the multi-layer sine--Gordon model by 
functional renormalization group methods.