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.
Host:  Drew
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