2D-MIT as a Wigner-Mott Transition

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2D-MIT as a Wigner-Mott Transition
Vladimir Dobrosavljevic Department of Physics
and National High Magnetic Field
Laboratory Florida State University
Collaborators John Janik (FSU) Darko Tanaskovic
(FSU) Carol Aguiar (FSU, Rutgers) Eduardo Miranda
(Campinas) Gabi Kotliar (Rutgers) Elihu Abrahams
(Rutgers)
Funding NHMFL/FSU Alfred P. Sloan Foundation NSF
grant DMR-0234215
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2D MIT distinct experimental features
Drastic change of behavior near n nc 1011
cm-2 NOTE behavior seen up to T 0.25 TF
broad density range
Mass enhanced But not the g-factor Large
resistivity drop!
TF 10K
Metal destroyed by small parallel field near
transition Low density rs 10 Close to Wigner
crystal?
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• Experimental puzzles
• On the metallic side
• Origin of small energy scale T TF/m (n-nc)
• Origin of small field scale H c-1 (n-nc)
• Large T-dependence of (drop) resistivity (factor
  10!!),
• but only close to transition.

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What does the mass enhancement mean??

• Lessons from THERMODYNAMIC
• Assume large m (n-nc)-1 !1
• Then coherence temperaure T TF/m! 0
• (Fermi liquid destroyed above T)
• Large specific heat C mT
• Entropy per carrier
• Conclusion
• MASS ENHANCEMENT ENTROPIC INSULATOR??!!!

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• B) On the insulating side
• Nature of the insulator origin of magnetism?
• Near transition
• (Sivan et al.)
• Susceptibility approaches
• FREE SPIN LIMIT!!!
• Local moment magnetism???
• Origin of glassy behavior disorder dependence
• (experiments by D. Popovic)
• My claim all features approach to
  Wigner-Mott glass

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Physical picture Wigner crystal melting as Mott
transition (Analogy with He3 Spivak 2001
Dolgopolov 2002)

• Wigner crystal Mott insulator (magnet)

• Melting Vacancy-Interstitial
• pair formation
• (Phillips, Ceperley 2001)
• Ignore phonons (Giamarchi, le Doussal,...)
• (lattice distortions - pinned by impurities?)

• Low density electrons tightly bound to lattice
  sites (electrostatic repulsion)
• Model disordered Hubbard-like (charge-transfer)
  model.
• Microscopic modelling (density-dependent
  parameters)?

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Charge-transfer (vacancy-interstitial) model
(similar model as in oxides, cuprates)
Interstitial orbital
Coulomb potential (side view)
Quantum Fluctuations
Lattice orbital

• Virtual process hopping in and out of
  interstitial site
• (similar as superexchange through the oxygen
  p-orbital in oxides)
• Correlations single-occupation (Uinf.)
  constraint
• in the lattice orbitals
• Remains at half-filling at any density, bands
  broaden
• bandwith-driven Mott transition

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Density-dependent band structure results (J.
Janik, V.D., 2005)
Bands cross around rs 10
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Applications Mott transition, heavy fermions
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Phase diagram density-driven Wigner-Mott
transition

• Large effective mass
• enhancement near
• transition
• m (n nc)-1
• Correlated metallic
• state wiped out by
• Zeeman effects
• (parallel field)
• First-order finite T
• transition, but only
• BELOW T 0.03TF

Wigner-Mott insulator
Correlated metal
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Effects of disorder The Good, the Bad, and the
Ugly
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Friend or Foe???
Sir Neville Mott
P. W. Anderson
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(VD, Pastor, Nikolic, Europhys. Lett. 62, 76
(2003))
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DMFT-TMT Picture of the Anderson-Mott
Transition VD, Pastor, Nikolic, Europhys. Lett.
62, 76 (2003)
Physical trajectory EF n U n1/2 W
const.
Anomalous metallic phase sandwiched between Mott
and Anderson insulators
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Disordered metallic phase incoherent transport
Tanaskovic, DeOliviera-Aguilar, Miranda, VD,
Kotliar, Abrahams (PRL 91, 066603 (2003),
cond-mat/0305511)

• Strong T-dependence,
• factor gt 10 drop!!!
• (solve full DMFT
• using IPT or slave bosons)
• Enhanced screening at low T
• due to correlations, even as
• compressibility is small
• (approach to Mott transition)
• Strong inelastic scattering
• at higher T

Experiment
Theory
Scattering rate 1/?
T
T/TF

• Incoherent Fermi liquid (low T TF/m
  distribution of local coherence scales)
• (microscopic origin of decoherence?)

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It takes all the running you CAN do, simply to
stay in one place From Alice in
Wonderland as quoted by P.W. Anderson in his
Nobel Lecture
Sir Neville Mott
P. W. Anderson
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Conclusions

• Extended DMFT order-parameter theory for
  Anderson-Mott transition
• Non-perturbative approach to correlations in
  disordered systems
• Non-Fermi liquid behavior as precursor to MIT
  two-fluid behavior
• Intermediate bad-metal phase between Anderson and
  Mott insulators
• New physical picture of MIT in correlated
  disordered systems
• Whats missing? Lots!