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SUMMARY:Ferromagnetic insulating state of manganites: Is it an electron gl
 ass? - Prof. Arup Kumar Raychaudhuri\, S.N.Bose National Centre for Basic 
 Sciences
DTSTART:20081001T101500Z
DTEND:20081001T111500Z
UID:TALK13510@talks.cam.ac.uk
CONTACT:Michael Sutherland
DESCRIPTION:Perovskite oxide manganites\, generally known for their Coloss
 al Magnetoresistance (CMR) show a number of interesting ground states depe
 nding on the hole concentration. At optimum hole concentration these mater
 ials show a metallic state that is ferromagnetic. At lower hole concentrat
 ion these materials show a very interesting phase where it is ferromagneti
 c and insulating. This talk is an investigation into the ferromagnetic ins
 ulating (FMI) state.\nWe show that in this phase the material is distinct 
 from a band insulator. It has a finite density of states at the Fermi leve
 l (though it is insulating) as shown by the finite linear heat capacity. U
 nlike the optimal hole doping where the material shows CMR\, in the FMI st
 ate the magnetoresistance collapses even up to a field of 14T. The low tem
 perature transport shows a Shklovskii Efros variable range hopping showing
  existence of a Coulomb gap. The FMI state can be made completely metallic
  by application of high hydrostatic pressure (~7GPa) yet the metallic stat
 e show created is distinct from the metallic state seen in the CMR phase.\
 nWe show\, by measuring the Nyquist Noise (=4kBRTe) which measures the ele
 ctron temperature (Te) that the lattice temperature gets decoupled form th
 e electron temperature when the material is cold through the FMI transitio
 n and below the transition temperature the electrons show a slow response 
 much like a glassy state. We argue that these experiments show that the el
 ectrons in the FMI state get into an electron glass state due to Coulomb i
 nteractions.
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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