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SUMMARY:Superfluid density\, universal scaling of critical current and the
  quest for room-temperature superconductivity - Jeffery Tallon\, Robinson 
 Research Institute\, Victoria University of Wellington and MacDiarmid Inst
 itute for Advanced Materials &amp\; Nanotechnology\, New Zealand.
DTSTART:20170531T101500Z
DTEND:20170531T111500Z
UID:TALK71796@talks.cam.ac.uk
CONTACT:Helen Verrechia
DESCRIPTION:The superfluid density is a key parameter in describing the th
 ermodynamic and electrodynamic properties of superconductors and governs f
 or example the fluctuation amplitude near Tc. If fluctuations are sufficie
 ntly strong the transition temperature Tc can be reduced below its mean-fi
 eld value. Firstly\, it is shown that the transport critical current densi
 ty of all superconductors in zero external field is\, rather surprisingly\
 , a universal parameter governed only by the superfluid density. Using wha
 t must be close to the entire inventory of available data (98 data sets)\,
  this is demonstrated for all superconductors of any type\, symmetry or an
 isotropy\, including single atomic-layer superconductors. This leads to a 
 remarkable scaling behaviour as a function of sample size for both films a
 nd round wires which is found to be applicable over some eight orders of m
 agnitude in sample dimension – from single atomic layer to mm scale. The
  superfluid density is determined in this way for highly compressed H2S wi
 th Tc = 203 K (~150 GPa) and the fluctuation temperature scale is estimate
 d. It is ~1400 K for phase fluctuations but as low as 300 K for amplitude 
 fluctuations suggesting that already the mean-field Tc value exceeds the o
 bserved 203 K and any attempts to raise Tc further are likely to be increa
 singly hampered by strong fluctuations.\n
LOCATION:Small Lecture Theatre (Bragg Building)\, Cavendish Laboratory
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