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DESCRIPTION:Utpal Chatterjee\, Argonne National Laboratory\n\nHigh Temperat
ure Superconductors (HTSCs) were discovered more than 25 years ago.\nHowev
er\, a microscopic theory of them is yet to be realized. In order to ident
ify the\nmechanism behind superconductivity in these systems\, we must und
erstand the normal\nstate from which superconductivity emerges. From our d
etailed Angle Resolved\nPhotoemission Spectroscopy (ARPES) measurements on
Bi2Sr2CaCu2O8+δ\; (BISCO 2212) HTSCs we have found that unlike conventional superconduct
ors\, where there is a single temperature scale Tc separating t
he normal from the superconducting state\, HTSCs\nare associated with two
additional temperature scales. One is the so-called pseudogap\nscale T*\,
below which electronic states are partially gapped\, while the second one
is the\ncoherence scale Tcoh\, characterizing the onset of a si
gnificant enhancement in electronic\nlifetime. We have observed that both
T* and Tcoh change strongly with carrier\nconcentration and the
y cross each other near optimal doping\, i.e. the carrier concentration\na
t which an HTSC attains its maximum Tc. Furthermore\, there is
an unusual phase in the\nnormal state where the electronic excitations are
gapped as well as coherent. Quite\nremarkably\, this is the phase from wh
ich the superconductivity with maximum Tc\nemerges. Our experim
ental finding that T* and Tcoh intersect is not compatible with
the\ntheories invoking “single quantum critical” point near optimal d
oping\, rather it is more\nnaturally consistent with the theories of super
conductivity for doped Mott insulators.
DTSTART:20120126T203000Z
LOCATION:Physics Building\, Room 204
SUMMARY:Characterizing phase diagram of High Temperature Superconductors vi
a Angle Resolved Photoemission Spectroscopy
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