Theory of Condensed Matter
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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


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

  • 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.


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!


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.


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


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.


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)


T

x

Phase competition, as in manganites.

Nanoscale inhomogeneities, as in manganites.

Giant responses, as in manganites.

Layered

structure.

High Temperature Superconductors


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


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

New playground in SCES.

Many groups working on this

subject (see E. D., Science 318,

1076 (2007))


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?


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.


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


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

Excitons in Mott insulators

and polymers, relevant for

solar energy.

(Reboredo, Al-Hassanieh,

Gonzalez, ED, PRL 2008)


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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