1 / 17

2D-MIT as a Wigner-Mott Transition

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)

shlomo
Download Presentation

2D-MIT as a Wigner-Mott Transition

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 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

  2. 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 resistivitydrop! TF ~ 10K Metal destroyed by small parallel field near transition Low density: rs ~ 10 Close to Wigner crystal?

  3. NOTE: strong enhancements seen ONLY close to the critical density nc nc F. L. METAL 2nc INSULATOR STRANGE METAL n STRONG CORRELATION WEAK CORRELATION • 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.

  4. 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 ~ m*T • Entropy per carrier: • Conclusion: • MASS ENHANCEMENT = “ENTROPIC” INSULATOR??!!!

  5. 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

  6. Egap 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: disorderedHubbard-like (charge-transfer)model. • Microscopic modelling (density-dependent parameters)?

  7. Coulomb potential (top view) 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 (U=inf.) constraint • in the lattice orbitals • Remains at half-filling at any density, bands broaden: • bandwith-driven Mott transition

  8. Interstitial band Energy Lower Hubbard band (U=inf.) Use DMFT !! MIT – Mott transition + disorder Density-dependent band structure: results (J. Janik, V.D., 2005) Bands cross around rs ≈ 10

  9. Applications: Mott transition, heavy fermions

  10. Density rs 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

  11. Effects of disorder: The Good, the Bad, and the Ugly

  12. Friend or Foe??? Sir Neville Mott P. W. Anderson

  13. (VD, Pastor, Nikolic, Europhys. Lett. 62, 76 (2003))

  14. Byczuk, Hofstetter, Vollhardt, PRL 2004; NRG impurity solver Disorder W 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

  15. Disordered metallic phase: incoherent transport Tanaskovic, DeOliviera-Aguilar, Miranda, VD, Kotliar, Abrahams (PRL 91, 066603 (2003), cond-mat/0305511) • Strong T-dependence, • factor > 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?)

  16. “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

  17. Nano-Scale Phase Separation Electron/Stripe Glass (can be incorported in DMFT framework) 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 • What’s missing? Lots!

More Related