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Using ultra-high magnetic fields to explore high-temperature superconductors

Brad Ramshaw, Los Alamos National Laboratory
Monday, December 8, 2014 - 4:00pm to 5:00pm
PAA A-110

The family of
copper-oxides collectively known as the "cuprates" exhibits the remarkable
phenomenon of high-temperature superconductivity (high-Tc). In some cuprates
this macroscopic quantum-mechanical state, with the zero electrical resistance,
extends more than half way to room temperature (164 K). Despite almost 30 years
of intensive research in this field---research that has driven fantastic
developments in techniques like scanning-tunneling-microscopy, angle-resolved
photoemission, and neutron and x-ray scattering, to name a few---the mechanism
of high-Tc is still unknown, and the mere "factor of two" that we
need for room-temperature superconductivity has remained elusive. We use
magnetic fields of up to 100 tesla to suppress superconductivity and examine
the properties of the underlying metal that gives rise to high-Tc. I will
review how magnetic fields give Fermi surface information, telling us about
broken symmetries and interactions in the system. I will then present my latest
research that uncovers the signature of quantum criticality---where
ground-state quantum fluctuations dominate the interactions in a
system---in the high-Tc cuprate YBa2Cu3O6+x, and discuss the relevance of
quantum criticality to superconductivity. I will conclude with a discussion of
future directions for high-Tc research, including what else we can learn in
high magnetic fields, and ultrasonic measurements that can reveal broken
symmetries in the ground-state.

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