Condensed Matter Physics Seminar
2 p.m., Thursday, April 1, 2004
Room 1201, Physics Building
Abnormal normal state in high-Tc superconductors revealed in
60-tesla fields
Fedor F. Balakirev
(National High Magnetic Field Laboratory, Los Alamos, NM)
Abstract: Identification of the mechanism of high-temperature
superconductivity requires understanding of the clearly unconventional nature of
the normal state. The biggest obstacle to the detection of normal state
properties is superconductivity itself, which effectively "conceals" them at low
temperatures. We report on pulsed-magnetic-field experiments that suppress the
superconductivity in high-Tc, cuprates, revealing the
normal-state behavior in the zero temperature limit. The normal-state behavior
is highly abnormal compared to conventional metals: (1) there is an unusual
localization behavior that exhibits a logarithmic divergence of the resistivity
as the temperature approaches zero and (2) whereas the Hall coefficient
typically measures the carrier concentration in a metal, we find that very small
changes of the carrier concentration in cuprates cause dramatic changes in the
Hall coefficient. The Hall coefficient exhibits a pronounced cusp at optimum
doping, possibly indicating a sharp change in the Fermi-surface states. The data
suggest the presence of a zero-temperature phase transition precisely at the
same carrier concentration at which high-temperature superconductivity is most
stable.
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Host: Drew
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