Fermiology Study of YBCO*

We report on high pressure SdH studies of YBCO6.5 (p=0.1) at He-3 temperatures in pulsed fields to 85 T and 7 GPa at HLD and dc fields of 45 T and pressures of 25 GPa at NHMFL using plastic and metal diamond anvil cells (DACs), respectively, that are coupled with an LC tank circuit based on a tunnel diode oscillator.
Our high pressure studies show an enhancement of the superconducting critical field from 24 to 42T between ambient pressure and 6 GPa, which limits the observation of QO to 5 GPa in the 45T Hybrid. Our Fermiology studies clearly show a strongly diverging effective mass at 4.5 GPa along with a local maximum in frequency and superconducting critical temperature, attributed to the effect of various charge orders present in this material. For pressures greater than 15 GPa we are able to measure a critical field of the order of 30T and to measure again QOs. We find that the orbital frequency has increased from 550 T at ambient pressure to 690 T at 15 GP and above. Assuming that the samples are driven by pressure to the overdoped state, those results do not match the reported frequency of 18kT observed for the overdoped analog Tl-2201. This indicates that pressure and doping are not playing an equivalent role on the CDWs and the superconducting state as also pointed in other studies, and shows that pressure is a new axis in the YBCO phase diagram which can help understand the interplay between CDWs and superconductivity in this material.