BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Talks.cam//talks.cam.ac.uk// X-WR-CALNAME:Talks.cam BEGIN:VEVENT SUMMARY:High pressure Fermiology studies of YBCO - Audrey Grockowiak\, NHM FL Tallahassee DTSTART:20181221T111500Z DTEND:20181221T123000Z UID:TALK116689@talks.cam.ac.uk CONTACT:Malte Grosche DESCRIPTION:The pnictide\, cuprate and molecular conductor families exhibi t similar phase diagrams\, leading to a great deal of interest in a common mechanism for a “universal phase diagram”. The typical ingredients fo r such phase diagrams include an antiferromagnetic phase\, a supercon- duc ting dome\, and possibly one\, or several quantum critical points (QCP). C hemical doping is one traditional way to look at such materials\, however thermodynamic variables such as magnetic field or hydrostatic pressure hav e proven to be powerful tools to explore this phase diagram\, with very st rong magnetic fields being used to suppress the superconducting dome\, all owing one to investigate the QCP.\nYBCO’s temperature-oxygen doping phas e diagram exhibits a small antiferromagnetic region at lowest dop- ing and charge and spin orders around p=0.1 that com- pete with or induce superco nductivity\, as well as a pseudogap region and a QCP under the SC dome [1] . Over this range of doping\, the Fermi surface changes from small pockets to arcs and finally a large pocket beyond the superconducting dome. Both the QCP and this change in FS are critical to our understanding of the cup rates and the universal phase diagram. Ramshaw\, et al. [2] have found a d ivergence of the effective mass in the region of the CDW that hints at a Q CP around p=0.19. Ideally\, strong fields could also be used to sup- press Hc2\, allowing for the observation of quantum oscil- lations (QOs) in the region around the QCP\, but this would require fields of approximately 15 0 T\, well above the 100 T limit currently available. Instead doping has b een used to suppress the dome to about 30 K [3]\, but doping at this level precludes the observation of QOs. Our group performed high pressure SdH s tudies of YBCO6.5 (p=0.1) at He-3 temperatures in pulsed fields\nto 70T an d 7GPa at HLD and dc fields of 45T and pressures of 24.7 GPa at NHMFL usin g plastic and metal diamond anvil cells (DACs)\, respectively\, that are c ou- pled with an LC tank circuit based on a tunnel diode oscillator. The s mall coil that makes up the inductor of this LC circuit and resides in the high pressure volume of the DAC senses changes in sample resistivity due to variations in temperature\, pressure or magnetic field.\nOur Fermiology studies clearly show a strongly diverg- ing effective mass at 4.5 GPa tha t is associated with a local maximum in frequency and Tc. The high Hc2 in this material limits our study in the low pressure range to pressures belo w 7 GPa. However\,\, at P> 24.7 GPa we are able to once again see quantum oscillations and find that the orbital frequency has increased from 550 T at ambi- ent pressure to 690 T monotonically. Pulsed field high pressure s tudies are currently planned to shed light on the region between 7 and 24 GPa. This now allows us to use pressure to develop a B-P-T phase diagram t hat will permit a more complete picture of HTS to be pursued\, perhaps ans wering how CDWs and the pseudogap play a role in superconductivity and all owing for the investiga- tion of the QCP.\nAcknowledgments: The National H igh Magnetic Field Laboratory is supported by National Science Foundation through NSF/DMR-1157490 and DMR-1644779 and the State of Florida.\n[1] S. Badoux\, et al.\, Nature\, 531\, 210 (2016).\n[2] B. Ramshaw\, et al.\, Sc ience\, 348\, 317 (2015).\n[3] J.L. Tallon\, et al.\, Phys. Rev. Lett.\, 7 9\, 5294 (1997).\n[4] S. Sadewasser\, et al.\, Phys. Rev. B\, 56\, 14168 ( 1997). LOCATION:Mott Seminar Room (531)\, Cavendish Laboratory\, Department of Ph ysics END:VEVENT END:VCALENDAR