[RpL 253] Fwd: [ITP Allothers-landau] Seminar v chetverg 27.01

[Elena Shangina]

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Date: Thursday, January 20, 2011, 8:25:08 PM
Subject: [ITP Allothers-landau] Seminar v chetverg 27.01

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Chetverg 27 yanvarya 2011 g.
Teoreticheskiy seminar v IFP, 11:30.


Peter Armitage  (John Hopkins University, Baltimore, USA)

FAST VORTICES AND SUPERCONDUCTING FLUCTUATIONS
IN THE CUPRATES AND AMORPHOUS SUPERCONDUCTORS

The nature of the underdoped pseudogap regime of the high-temperature 
superconductors has been a matter of long-term debate. On quite general 
grounds, one expects that due to their low superfluid densities and 
short correlation lengths, superconducting fluctuations will be very 
significant for transport and thermodynamic properties in this part of 
the phase diagram. Although there is ample experimental evidence for 
such correlations, there has been disagreement about how high in 
temperature they may persist, their role in the phenomenology of the 
pseudogap, and their significance for understanding high-temperature 
superconductivity.

In this work we use THz time-domain spectroscopy (TTDS) to probe the 
temporal fluctuations of superconductivity above Tc in LSCO thin films 
over a doping range that spans almost the entire superconducting dome 
(x=0.06 to 0.25). Signatures of the fluctuations persist in the 
conductivity in a comparatively narrow temperature range, up to - at 
most - 16 K above Tc. We compare our results with the measurements of 
diamagnetism in a similarly doped crystals of LSCO and show through a 
vortex-plasma model that if the fluctuation diamagnetism solely 
originates in vortices, then they must necessarily exhibit an 
anomalously large vortex diffusion constant, which is more than two 
orders of magnitude larger than the Bardeen-Stephen estimate. This 
points to either an entirely different character to vortex dynamics in 
the underdoped d-wave cuprates or a contribution to the diamagnetic 
response that is not superconducting in origin. I will make a comparison 
to our related work using broadband microwave spectroscopy on amorphous 
superconducting InO thing films.
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-- 
Best regards,
 Elena                            mailto:shangina на rplab.ru