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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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Theory of condensed matter elbio dagotto distinguished professor ut ornl

Theory of Condensed Matter

Elbio Dagotto,

Distinguished Professor, UT-ORNL


Organization

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)


Our group

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.


Strongly correlated electronic materials e d science 309 257 2005

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!


Complicated models

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.


I a colossal magneto resistance cmr

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


Theory of condensed matter elbio dagotto distinguished professor ut ornl

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.


Multiferroic manganites can also be studied s dong et al prb 78 155121 2008

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)


High temperature superconductors

T

x

Phase competition, as in manganites.

Nanoscale inhomogeneities, as in manganites.

Giant responses, as in manganites.

Layered

structure.

High Temperature Superconductors


Theory of condensed matter elbio dagotto distinguished professor ut ornl

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


Theory of condensed matter elbio dagotto distinguished professor ut ornl

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


I b oxide interfaces and superlattices

(I.b) Oxide interfaces and superlattices

New playground in SCES.

Many groups working on this

subject (see E. D., Science 318,

1076 (2007))


Correlated electron multilayers applications of complex oxides oxide electronics

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?


Smo lmo smo lmo

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.


I c effects of strong interactions in molecular conductors and qds

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


Transport in sces systems t dmrg s r white and a feiguin 2004

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


Time dependent phenomena in sces

Time-dependent phenomena in SCES

Excitons in Mott insulators

and polymers, relevant for

solar energy.

(Reboredo, Al-Hassanieh,

Gonzalez, ED, PRL 2008)


Summary

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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