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“Strongly correlated electrons in bulk and nanoscopic systems” Theory of Condensed Matter

“Strongly correlated electrons in bulk and nanoscopic systems” Theory of Condensed Matter Elbio Dagotto, Distinguished Professor, UT-ORNL. UT. Bulk (Mn,Cu oxides). Organization. UT. Strongly Correlated Electrons.

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“Strongly correlated electrons in bulk and nanoscopic systems” Theory of Condensed Matter

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  1. “Strongly correlated electrons in bulk and nanoscopic systems” Theory of Condensed Matter Elbio Dagotto, Distinguished Professor, UT-ORNL

  2. UT Bulk (Mn,Cu oxides) Organization UT Strongly Correlated Electrons • Complex transition metal oxides (high temperature superconductors, manganites, etc) (II) Oxides multilayers. (III) Transport in nanoscopic systems. UT Nano (Transport, Interfaces)

  3. Publications • Check http://sces.phys.utk.edu • 2004-2008: 17 papers in Physical Review Letters; 28 in Physical Review B; 2 in Science; 1 in Physics World. • Support provided by NSF and DOE. • 4 students graduated during Summer 2007. Currently at BNL, LANL, UC, and Boston College. 5 new students arrived. • 5 postdocs + many visitors. • We will consider hiring new students. Ideal candidates should have the comprehensive exam approved, and at least Solid State I approved. • Work is computationally intense; strong competition with other groups; definitely a full time job.

  4. Manganites Strongly Correlated Electronic Materials (rich phase diagrams, nanoscale inhomogeneities, giant responses)(E.D., Science 309, 257 (2005)) Materials where Coulombic repulsion and strong e-ph couplings play a key role. NON-PERTURBATIVE METHODS “Strongly correlated electrons is the new frontier” (A. Cho, Science 314, 1072 (2006)) Risky but potentially rewarding business!

  5. Potential applications in read sensors, but critical temperatures must increase. (I) Colossal Magneto Resistance (CMR) Resistivity of Mn-oxides changes by 10 orders of magnitude at low T

  6. C. Sen, G. Alvarez, E.D., PRL 98, 127202 (2007). Resistance vs. temperature, Monte Carlo simulations. Shape very similar to CMR Experiments. Large magneto-resistance observed. Summary: CMR appears in a tiny cluster! We can easily ask “questions” to the computer. Similar to experimental physics.

  7. Origin of CMR? Short-range charge order; i.e. small regions of competing CO phase below a T*. Typical MC snapshot. Nanoscale structures are spontaneously formed (“self organization”). See also S. Yunoki et al., PRL 80, 845 (1998); A. Moreo et al., Science 283, 2034 (1999); ED et al, Phys. Rep. 344, 1 (2001); J. Burgy et al., PRL 87, 277202 (2001) and PRL 92, 097202 (2004).

  8. T x Phase competition, as in manganites. Nanoscale inhomogeneities, as in manganites. Giant responses, as in manganites. Layered structure. High Temperature Superconductors

  9. T T* mixed Af FM W AF Underdoped high-Tc similar to Mn oxides? Patches of SC? Non-interacting fermions + classical AF and SC order parameters; Alvarez et al., PRB 71, 014514 (2005); M. Mayr et al., PRB 73, 014509 (2006) Main result: clean clean True phase diagram of cuprates in clean limit? dirty clean SC D=|D| eif Region of giant responses? Vortex liquid? (Ong)

  10. AF Recent STM results for BSCCO above Tc (Gomes et al., Nature 447, 569 (2007)) 80a x 80a Region of SC clusters, as predicted by theory in 2005 Optimal Tc=93K

  11. (II) Oxide interfaces and superlattices New playground in SCES. Many groups working on this subject (see E. D., Science 318, 1076 (2007))

  12. LaTiO3 SrTiO3 z Ohtomo et al, Nature 419 (‘02) See also Mannhart, Triscone, Hwang, Tokura, Ramesh, Okamoto, … Correlated electron multilayers:Applications of complex oxides?Oxide electronics? STO LTO

  13. Yunoki et al., PRB78, 024405 (2008); PRB76, 064532 (2007). Dong et al., Cond-mat/0810.1441. SMO/LMO/SMO/LMO … MC, DMRG, Poisson Eq.,… LaMnO3/CaMnO3 layers. Both AF insulating, but combination is FM metallic.

  14. Interactions are important at low T: Kondo effect observed in molecules with net spin (peak in conductance) Nature 391, 156 (98); 417, 722 (02); 417, 725 (02); Science 280, 567 (98); 281, 540 (98). (III) Effects of strong interactions in molecular conductors and QDs

  15. One Dot Current vs. time Transport in SCES systems (t-DMRG, S. R. White and A. Feiguin 2004) Al-Hassanieh et al., PRB73,195304 (2006) Time unit ~ 10 fs (10^-15) if t=0.1 eV “1000” = 10 ps

  16. Interferences in dots and molecules (G. Martins et al., PRL 96, 066802 (2006); PRL 94, 026804 (2005); K. Al-Hassanieh et al., PRL 95, 256807 (2005);Lanczos + embedding)

  17. Breaking of a Mott insulator by strong bias (Al-Haasanieh, Dias, ED, …) Time-dependent phenomena in SCES (in progress) Excitons in Mott insulators and polymers, relevant for solar energy. (Reboredo, Al-Hassanieh, Gonzalez, ED, PRL 2008)

  18. Summary • Nanoscale self-organization and complex oxides: Solution of the CMR puzzle at hand. SC puddles in underdoped cuprates. • Oxide multilayers: New phases? New functionalities? • Quantum transport in strongly correlated systems: Another novel playground.

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