Theory

Abstract

This chapter will give a brief introduction to the most relevant theoretical aspects used in this thesis, with the aim of explaining the most important formulae and ideas. We will start with basic theory of electrons in metals. Moving on from free electron theory we will give the outline to a more realistic theory for our experimental results. We will then describe the theory of quantum oscillations, which is necessary to understand the main results of this thesis. We will then turn to a brief introduction to the fundamental superconducting properties that we will need in the discussion and interpretation of experimental results. One of the main aspects of this thesis is the quantum critical system BaFe$_2$(As$_{1-x}$P$_x$)$_2$. Also in the cuprate superconductor quantum criticality is often discussed as possible origin of high temperature superconductivity. A brief introduction to the topic of quantum criticality shall therefore be given from the starting point of classical phase transition.