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Theory of Condensed Matter Elbio Dagotto, Distinguished Professor, UT-ORNLPowerPoint Presentation

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

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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

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Theory of Condensed Matter

Elbio Dagotto,

Distinguished Professor, UT-ORNL

UT

Bulk (Mn,Cu oxides)

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)

- 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

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

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.

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

T

x

Phase competition, as in manganites.

Nanoscale inhomogeneities, as in manganites.

Giant responses, as in manganites.

Layered

structure.

AF

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

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, …

Yunoki et al., PRB78, 024405 (2008); PRB76, 064532 (2007). Dong et al.,

Cond-mat/0810.1441.

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).

Current vs. time

Al-Hassanieh et al., PRB73,195304 (2006)

Time unit ~ 10 fs (10^-15) if t=0.1 eV

“1000” = 10 ps

Excitons in Mott insulators

and polymers, relevant for

solar energy.

(Reboredo, Al-Hassanieh,

Gonzalez, ED, PRL 2008)

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