SNS%20picture

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SNS picture
March 2005
SNS 2006-8, HFIR
Recent Developments in the Study of Strongly
Correlated Electronic Systems E. Dagotto,
UT-ORNL
Nanocenter (CNMS)
Joint Institutes (JIAM,JINS)
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Organization

• Strong correlation in nanoscopic systems
  transport in molecules and quantum dots.
• Manganites recent simulations of realistic
  models. Cuprates recent simulations of
  phenomenological models.

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(1) Molecular conductorsand quantum dots
Key role of phonons in molecular conductors
Kondo effect observed in molecules with net spin
via enhancement in conductance (Coulombic effects
cannot be neglected in small molecules)
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DMRG/Lanczos for Transport in SCES systems
(Al-Hassanieh et al., PRB B73, 195304 (2006)
Schneider and Schmitteckert, preprint.)
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New results quantum interferences
Anomalous cancellation of conductance in arrays
of quantum dots, Center of Mass phonons in
molecules, and in T-geometries. In progress
finite bias -gt currents in Mott insulators, etc.
G. Martins et al., PRL 05 K. Al-Hassanieh et
al., PRL 05 G. Martins et al., PRL 06 A.
Feiguin, C. Busser, et al.
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(2,3) Complex materials, phase competition
vast evidence of inhomogeneous states in
manganites and cuprates (Cheong, De Teresa,
Fernandez-Baca, Dusenhofer, Hennion, Fischer,,
Zheng, Khomskii, Argyriou, Perring, Radaelli, )
Intrinsic softness!! E.D., Science 2005
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Colossal Magneto Resistance (CMR)
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Special Case CMR
(1) Phase competition FM Metal vs. CO/AF
Insulator is the basis of the
phenomenon. (2) Simulations of simple models
(resistor networks) show CMR. (3) Both strong
Hund coupling and JT phonons needed.
S. Yunoki et al., PRL 98, A. Moreo et al. Science
99 E.D. et al., Phys.Rep. 01
Very recent effort at UT/ORNL aims to observe CMR
in double exchange models of Mn oxides. It
exploits (i) ORNL computers facilities with
thousands of processors for parallel computing,
(ii) new algorithms TPEM.
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Final attack realistic models, one- and
two-orbital DE with phonons (C. Sen, G. Alvarez,
et al., PRB, to appear)
Importance of Coulomb, phonons, and disorder!
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Recent results, involving two phases with
different spin/charge order.
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Origin of glassy state? Patches of SC above Tc?
(Alvarez et al., PRB 71, 014514 (2005) M. Mayr
et al., PRB 06).
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Conclusions

• Strong interactions are important in transport in
  small molecules and dots. Bulk ? Nano?
• Interesting physics arises from a combination of
  Coulombic, phononic, and disordering effects. We
  need a Theory of Everything.
• Electronic softness, self-organization, several
  d. of f. simultaneously active Cause of CMR?
  Yes. Cause of high-Tc?