In the past decade, strong coupling between light and matter has transitioned from a
theoretical idea to an experimental reality. This represents a new field of quantum light …

It is a remarkable property of BCS theory that the ratio of the energy gap at zero temperature
Ξ and the critical temperature T c is (approximately) given by a universal constant …

the BCS order parameter) at all temperatures 0 Ä T Ä Tc up to the critical one, Tc, and show
that, in the limit of weak coupling, the ratio „. T/= Tc is given by a universal function of the …

We give an overview of operator-theoretic tools that have recently proved useful in the
analysis of boundary-value and transmission problems for second-order partial differential …

We study the BCS energy gap Ξ in the high–density limit and derive an asymptotic formula,
which strongly depends on the strength of the interaction potential V on the Fermi surface. In …

We investigate the BCS critical temperature T c in the high-density limit and derive an
asymptotic formula, which strongly depends on the behavior of the interaction potential V on …

We introduce a multi-band BCS free energy functional and prove that for a multi-band
superconductor the effect of inter-band coupling can only increase the critical temperature …

We prove an abstract criterion on spectral instability of nonnegative selfadjoint extensions of
a symmetric operator and apply this to self-adjoint Neumann Laplacians on bounded …

This thesis consists of two separate parts. In the first part we consider a dilute Fermi gas
interacting through a repulsive interaction in dimensions $ d= 1, 2, 3$. Our focus is mostly on …

Superconductivity has many important applications ranging from levitating trains over qubits
to MRI scanners. The phenomenon is successfully modeled by Bardeen-Cooper-Schrieffer …