Probing charges and spins in solids at mK temperatures and GHz frequencies

Synopsis

Charges and spins in solids can be probed by electromagnetic radiation, ie. light of different spectral regimes, and the frequency of the light can be adjusted to the energy scales of interest. Several important phenomena in solids, such as superconductivity and quantum criticality, are related to rather small energy scales which go along with rather low temperatures that are required to study these phenomena.

We have recently developed new experimental approaches to probe solids at mK temperatures and GHz frequencies. I will introduce these techniques that are based on planar, on-chip microwave structures, and I will discuss two examples of application. The first one is superconductors with rather low critical temperature, well below 1K, such as doped SrTiO3. The second one is magnetic resonance at very low frequencies, fields, and temperatures, which we apply to explore the magnetic phase diagram of the quantum-critical heavy-fermion material YbRh2Si2.