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UID:DSC-16185
DTSTART;TZID=Europe/Berlin:20190617T140000
SEQUENCE:1560809257
TRANSP:OPAQUE
DTEND;TZID=Europe/Berlin:20190617T160000
URL:https://dresden-science-calendar.de/calendar/en/detail/16185
LOCATION:MPI-CPfS\, Nöthnitzer Straße 4001187 Dresden
SUMMARY:Grockowiak: High pressure\, high magnetic field Fermiology studies 
 of YBCO6.50
CLASS:PUBLIC
DESCRIPTION:Speaker: Dr. Audrey Grockowiak\nInstitute of Speaker: National 
 High Magnetic Field Laboratory\, Tallahassee\, USA\nTopics:\nMaterialien\n
  Location:\n  Name: MPI-CPfS (Seminarraum 5 / B3.2.28\, 01187 Dresden\, N
 öthnitzer Straße 40)\n  Street: Nöthnitzer Straße 40\n  City: 01187 Dr
 esden\n  Phone: \n  Fax: \nDescription: The pnictide\, cuprate and molecul
 ar conductor families exhibit similar phase diagrams\, leading to a great 
 deal of interest in a common mechanism for a “universal phase diagram”
 . The typical ingredients for such phase dia- grams include an antiferroma
 gnetic phase\, a supercon- ducting dome\, and possibly one\, or several qu
 antum critical points (QCP). Chemical doping is one traditional way to loo
 k at such materials\, however thermodynamic variables such as magnetic fie
 ld or hydrostatic pressure have proven to be powerful tools to explore thi
 s phase diagram\, with very strong magnetic fields being used to suppress 
 the superconducting dome\, allowing one to investigate the QCP. YBCO’s t
 emperature-oxygen doping phase 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 superconductivity\, as well as a pseudogap region an
 d a QCP under the SC dome [1]. Over this range of doping\, the Fermi surfa
 ce changes from small pockets to arcs and finally a large pocket beyond th
 e superconducting dome. Both the QCP and this change in FS are critical to
  our understanding of the cuprates and the universal phase diagram. Ramsha
 w\, et al. [2] have found a divergence of the effective mass in the region
  of the CDW that hints at a QCP around p=0.19. Ideally\, strong fields cou
 ld also be used to sup- press Hc2\, allowing for the observation of quantu
 m oscil- lations (QOs) in the region around the QCP\, but this would requi
 re fields of approximately 150 T\, well above the 100 T limit currently av
 ailable. Instead doping has been 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 studies of YBCO6.5 (p=0.1) at He-3 temperature
 s in pulsed fields to 70 T and 7 GPa at HLD and dc fields of 45 T and pres
 sures of 25 GPa at NHMFL using plastic and metal diamond anvil cells (DACs
 )\, respectively\, that are cou- pled with an LC tank circuit based on a t
 unnel diode oscillator. The small coil that makes up the inductor of this 
 LC circuit and resides in the high pressure volume of the DAC senses chang
 es in sample resistivity due to   variations in temperature\, pressure or 
 magnetic field. Our high pressure studies show an enhancement of the super
 conducting critical field from 24 to 42T between ambient pressure and 6 GP
 a\, which limits the observation of QO to 5 GPa in the 45T Hybrid. Our Fer
 miology stud- ies clearly show a strongly diverging effective mass at 4.5 
 GPa along with a local maximum in frequency and superconducting critical t
 emperature\, 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 press
 ure and doping are not playing an equivalent role on the CDWs and the supe
 rconducting state as also pointed in other studies [5][6]\, and shows that
  pressure is a new axis in  the YBCO phase diagram which can help understa
 nd the interplay between CDWs and superconductivity in this material.
DTSTAMP:20260505T143830Z
CREATED:20190614T220956Z
LAST-MODIFIED:20190617T220737Z
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