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SUMMARY:Magnetic order in the pseudogap phase of the high-T_c superconduct
 or YBCO - Benoît Fauqué\; \, Laboratoire Léon Brillouin CEA/Saclay\, Fr
 ance
DTSTART:20070530T101500Z
DTEND:20070530T111500Z
UID:TALK7455@talks.cam.ac.uk
CONTACT:Michael Sutherland
DESCRIPTION:One of the leading issues in the understanding of high-T_c sup
 erconductivity is the origin of the pseudo-gap phase. This phenomenon occu
 rs typically in the low hole doping side (underdoped region) of the copper
  oxide superconductoring phase diagram. This phase is remarkable as all ph
 ysical properties display\, below a characteristic temperature T^*\, anoma
 lies from the behavior expected for a standard metal\, although no symmetr
 y breaking has been evidenced so far. The pseudo-gap state is usually desc
 ribed in two ways: either it represents a precursor of the superconducting
  (SC) state or it is related to an order parameter competing with the SC o
 ne. Using polarized elastic neutron diffraction\, we report signature of a
  spontaneous magnetic order in YBa_2Cu_3O_{6+x} only in its\nunderdoped ph
 ase. To date\, it is the first direct evidence of a hidden order parameter
  characterizing the pseudo-gap phase in high-T_c cuprates. Magnetic intens
 ity occurs only on top of nuclear Bragg peaks with no additionnal Bragg pe
 aks indicating no translational breaking symmetry of the lattice. The magn
 etic order basically exhibits the pattern\nof the orbital moments expected
  from the circulating currents (CC) theory of the pseudo-gap state\, being
  more\nspecifically only compatible with the CC phase with two currents pe
 r CuO_2 plaquette.
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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