Optimization of Coplanar Waveguide Resonators for ESR Studies on Metals

TL;DR

This paper investigates the electromagnetic properties of coplanar waveguide resonators near metallic samples to optimize their design for electron spin resonance studies at very low temperatures.

Contribution

It provides simulations and analytic calculations to determine optimal sample placement for enhanced microwave magnetic fields in CPW resonators used in ESR experiments.

Findings

Identified an optimal sample distance for maximum microwave magnetic field

Demonstrated the impact of metallic samples on resonator performance

Provided guidelines for designing CPW resonators for ESR in metals

Abstract

We present simulations and analytic calculations of the electromagnetic microwave fields of coplanar waveguide (CPW) resonators in the vicinity of highly conducting metallic samples. The CPW structures are designed with the aim of investigating electron spin resonance (ESR) in metallic heavy-fermion systems, in particular YbRh$_2$Si$_2$, close to the quantum critical point. Utilizing CPW resonators for ESR experiments allows for studies at mK temperatures and a wide range of freely selectable frequencies. It is therefore of great interest to evaluate the performance of resonant CPW structures with nearby metallic samples. Here we study the microwave fields at the sample surface as a function of sample distance from the waveguide structure and analyze the implications of the sample on the performance of the resonator. The simulation results reveal an optimum sample distance for which the microwave magnetic fields at the sample are maximized and thus best suited for ESR studies.