Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Two problems in the field of materials-based condensed matter physics, specifically in the field
of superconductivity, are studied theoretically. In both problems, where each is of current exper-
imental interest, an extension of Ginzburg-Landau theory is used to describe a physical system,
with focus on the energy associated to the interface(s) occurring in the respective systems.
The first physical system under consideration is that of a two-band superconductor. Using
Ginzburg-Landau theory for two-band superconductors, the interface energy ¾s between normal
and superconducting states coexisting at the thermodynamic critical magnetic field is determined.
From the theoretical and numerical analysis of the interface energy, it is found that close to the
transition temperature, where the Ginzburg-Landau theory is applicable, the two-band problem
maps onto an effective single band problem. This finding puts into question the possibility of
intermediate, so called type-1.5 superconductivity, in the regime where the Ginzburg-Landau
theory applies.
The second physical system is that of a system with competing superconductivity and anti-
ferromagnetism. From Ginzburg-Landau theory for such competing systems in a thermodynamic
critical magnetic field, it is shown that two possible interfaces can occur: an interface between
a pure anti-ferromagnetic state and a pure superconducting state; and an interface between a
state with coexisting superconductivity and anti-ferromagnetism and a pure anti-ferromagnetic
state. The energy associated to both these interfaces is analysed theoretically and numerically
from which the boundary between type-I and type-II superconductivity is obtained for certain
specific cases. / AFRIKAANSE OPSOMMING: Twee probleme in die veld van materiaal-gebaseerde gekondenseerde materie fisika, spesifiek in
die veld van supergeleiding, word teoreties bestudeer. In beide probleme, albei tans van eksper-
imentele belang, word ’n fisiese sisteem beskryf deur ’n uitbreiding van enkel-band Ginzburg-
Landau teorie, met fokus op die energie geassosieer met die koppelvlak(ke) wat in die onderskeie
sisteme aangetref word.
Die eerste fisiese sisteem wat beskou word is die van ’n twee-band supergeleier. Deur van
Ginzburg-Landau teorie vir twee-band supergeleiers gebruik te maak, word die koppelvlak energie
¾s tussen die gelyktydig bestaande normaal- en supergeleidende toestand in die termodinamiese
kritieke magneetveld bepaal. Deur beide teoretiese en numeriese analieses word bepaal dat na
aan die oorgangstemperatuur, waar Ginzburg-Landau teorie geldig is, die twee-band probleem op
’n effektiewe een-band probleem afbeeld. Hierdie bevinding bevraagteken dus die moontlikheid
van onkonvensionele, of sogenaamde tipe-1.5 supergeleiding, vir gevalle waar Ginzburg-Landau
teorie geldig is.
Die tweede fisiese siteem wat beskou word is ’n sisteem met kompeterende supergeleiding en
anti-ferromagnetisme. Met behulp van Ginzburg-Landau teorie vir sulke sisteme in ’n termod-
inamiese kritiese magneetveld word gewys dat daar twee moontlike koppelvlakke kan ontstaan:
’n koppelvlak tussen ’n uitsluitlik anti-ferromagnetiese toestand en ’n uitsluitlik supergeleidende
toestand; sowel as ’n koppelvlak tussen ’n uitsluitlik anti-ferromagnetiese toestand en ’n toes-
tand van beide supergeleiding en anti-ferromagnetisme. Die energie geassosieer met beide hierdie
koppelvlakke word teoreties en numeries geanaliseer wat lei tot ’n beskrywing van die grenslyn
tussen tipe-I en tipe-II supergeleiding in sekere spesifieke gevalle.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/17916 |
| Date | 12 1900 |
| Creators | Geyer, Jani |
| Contributors | Kastner, Michael, Schmalian, Jorg, Stellenbosch University. Faculty of Science. Dept. of Physics. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 99 p. : ill. |
| Rights | Stellenbosch University |
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