Signatures of Phase Transitions in the Microwave Response of YbRh2Si2

Abstract

We used a spectroscopic microwave technique utilizing superconducting stripline resonators at frequencies between 3 GHz and 15 GHz to examine the charge dynamics of YbRh2Si2 at temperatures and magnetic fields close to the quantum critical point. The different electronic phases of this heavy-fermion compound, in particular the antiferromagnetic, Fermi-liquid, and non-Fermi-liquid regimes, were probed with temperature-dependent microwave measurements between 40 mK and 600 mK at a set of different magnetic fields up to 140 mT. Signatures of phase transitions were observed, which give information about the dynamic response of this peculiar material that exhibits field-tuned quantum criticality and pronounced deviations from Fermi-liquid theory.

Angle-dependent electron spin resonance of YbRh2Si2 measured with planar microwave resonators and in-situ rotation

“…3 for different sample orientations. Q is generally decreasing with increasing field due to field-induced losses in the superconducting resonator [17,30,31,32,33] and due to the microwave charge response of the heavy fermions [14,26,34,35,36], and additionally it has a dip at the resonance magnetic field B 0 , indicating ESR absorption and thus the spin response of YbRh 2 Si 2 . As can be seen in Fig.…”

“…As the ESR response of YbRh 2 Si 2 is a very interesting topic on its own [7] and as its possible relation to quantum criticality is not settled [12,13], ESR studies close to the quantum-critical point are also desired from a fundamental perspective of magnetic resonance. Planar microwave resonators can be used as ESR probes [14,15,16] for YbRh 2 Si 2 to overcome the limitations of conventional ESR spectrometers: as such resonators [17,18,19,20] can be operated with a multimode measurement technique [14,21,22,23], they can simultaneously address multiple ESR frequencies and thus multiple magnetic magnetic fields in the phase diagram [14], and they can also be employed at mK temperatures [23,17,24,25,26,27].…”

Metallic coplanar resonators optimized for low-temperature measurements

“…Our metallic CPW resonators were successfully employed in several low-temperature and low-frequency ESR experiments. If performed in a dilution refrigerator we expect even more interesting physics of exotic behavior of materials such as YbRh 2 Si 2 [45,50,51].…”

Characterization of harmonic modes and parasitic resonances in multi-mode superconducting coplanar resonators

“…[1][2][3][4][5][6][7][8][9] In astronomy and particle physics, highly sensitive kinetic inductance detectors (KIDs) can easily be multiplexed. [10][11][12][13] In solid state spectroscopy, [14][15][16] planar superconducting resonators probe the microwave properties of numerous material classes of interest, ranging from conventional [17][18][19][20][21][22][23][24][25] and unconventional superconductors [26][27][28][29][30][31][32][33][34] to heavy-fermion metals, 14,35 quantum paraelectrics, 36,37 various magnetic and spin systems, [38][39][40][41][42][43][44] and dielectric thin films. [45][46][47] Realization of on-chip superconducting...…”