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Theory of Condensed Matter Elbio Dagotto, Distinguished Professor, UT-ORNL

Theory of Condensed Matter Elbio Dagotto, Distinguished Professor, UT-ORNL. UT. Bulk (Mn,Cu oxides). Organization. UT. Strongly Correlated Electrons. Complex transition metal oxides (high temperature superconductors, manganites, etc) Oxides multilayers.

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Theory of Condensed Matter Elbio Dagotto, Distinguished Professor, UT-ORNL

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  1. 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) Oxides multilayers. Transport in nanoscopic systems. (II) Fe superconductors (Adriana Moreo) UT Nano (Transport, Interfaces)

  3. Our group • 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. • Our group almost full. 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 (E.D., Science 309, 257 (2005)) Materials where Coulombic repulsion and strong e-ph couplings play a key role. One-electron approximation not valid. NON-PERTURBATIVE METHODS NEEDED Many competing tendencies leads to complex behavior!

  5. electrons and spins superexchange t2g lattice distortions + elastic energy self-consistent potential Complicated models! Techniques: Monte Carlo and/or T=0 optimization of classical variables. Exact diagonalization of fermions. CPU time grows like N4. Typical clusters ~ 100 sites.

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

  7. 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.

  8. Theory: Experiments: A S E 12x12, MC, JT distortions same in the three phases Multiferroic manganites can also be studied S. Dong, et al., PRB 78, 155121 (2008)

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

  10. AF Underdoped high-Tc similar to Mn oxides? Patches of SC? 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

  11. 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

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

  13. STO LTO 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?

  14. 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.

  15. 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). (I.c) Effects of strong interactions in molecular conductors and QDs

  16. 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

  17. Time-dependent phenomena in SCES Excitons in Mott insulators and polymers, relevant for solar energy. (Reboredo, Al-Hassanieh, Gonzalez, ED, PRL 2008)

  18. Summary • Complex transition metal oxides • Oxide multilayers • Quantum transport in strongly correlated systems • Lots of fun and challenges doing computational studies of many electrons!

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