1 / 22

F. Kagawa (Univ. Tokyo)

Mott Transition and Its Novel Criticality in k -(ET) 2 Cu[N(CN) 2 ]Cl Investigated by Transport and NMR measurements. F. Kagawa (Univ. Tokyo). Collaborators. K. Miyagawa (Univ. Tokyo & CREST) K. Kanoda (Univ. Tokyo & CREST). Outline. 1. Introduction.

elda
Download Presentation

F. Kagawa (Univ. Tokyo)

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. Mott Transition and Its Novel Criticality in k-(ET)2Cu[N(CN)2]Cl Investigated by Transport and NMR measurements F. Kagawa (Univ. Tokyo) Collaborators K. Miyagawa (Univ. Tokyo & CREST) K. Kanoda (Univ. Tokyo & CREST)

  2. Outline 1. Introduction Bandwidth controlled Mott transition Organic conductor k-(ET)2X 2. 1st-order Mott transition and critical endpoint demonstrated by transport and NMR measurements 3. Mott criticality in two dimensions 4. Conclusions

  3. the basic problem for the physics of strongly correlated electrons Introduction to the Mott Transition competition between kinetic energy and correlation energy in a half-filled band marginal insulator marginal metal Mott ins. Metal ？ U >> W U << W （itinerant electrons） （localized electrons） particlelike wavelike （bandwidth controlled）Mott transition U : local Coulomb repulsion W : bandwidth

  4. S S S S S S S S side view ET molecule Organic conductor k-(ET)2Cu[N(CN)2]Cl insulating anion layer : Cu[N(CN)2]Cl conducting ET layer quasi-2D system

  5. Band-filling dimer t t’ conducting layer equivalent model side view top view one hole (ET)2 Cu[N(CN)2]Cl + +1 -1 (ET)2 Cu[N(CN)2]Cl conducting layer closed shell (insulating layer) half-filled band one hole/one dimer H. Kino and H. Fukuyama, JPSJ 65, 2158 (1996)

  6. Outline 1. Introduction 2. 1st-order Mott transition and critical endpoint demonstrated by transport and NMR measurements 3. Mott criticality in two dimensions 4. Conclusions

  7. X= 1. k-Cl 2. k-Br (deuterated） 3. k-Br 4. k-NCS Phase diagram ofk-(BEDT-TTF)2X 1 3 4 2 1st-order transition and 2nd-order critical endpoint S. Lefebvre et al. (NMR) PRL 85, 5420 (2000) D. Fournier et al. (ultrasonic) PRL 90, 127002 (2003) P. Limelette et al. (resistivity) PRL 91, 016401 (2003) FK et al. (resistivity) PRB 69, 064511 (2004) K. Kobashi et al. (resistivity) k-Cl is a Mott insulator at ambient pressure unpublished

  8. 1st-order Mott transition driven by temperature, pressure, or magnetic field temperature pressure magnetic field Mott ins. Mott ins. Mott ins. R (W) R (W) R (W) metal metal metal T = 32.1 K (22.7 MPa, 22.2 K) P = 22.3 MPa T (K) H (T) P (MPa) FK, PRB 69, 064511 (2004) FK, PRB 69, 064511 (2004) FK, PRL 93, 127001 (2004) H. Taniguchi, PRB 67, 014510 (2003) H. Taniguchi, PRB 67, 014510 (2003) metal Mott ins. metal metal Mott ins. Mott ins. lowering temperature applying magnetic field applying pressure Pressure-sweep (i.e., bandwidth-control) is the most useful for the systematic study of the Mott transition.

  9. Mott’s original idea; bandwidth-control in a half-filled band Metal Mott ins. ？ U >> W U << W (low pressure) (high pressure) Bandwidth-controlled Mott transition U : local Coulomb repulsion W : bandwidth Isothermal pressure sweep is a quite natural way to investigate the Mott transition.

  10. Mott insulator Phase diagram ofk-(BEDT-TTF)2X k-Cl Pressure medium; Helium Isothermal pressure sweep at various temperatures

  11. Pressure-Temperature phase diagram of k-Cl Discontinuous nature vanishes at the critical endpoint (TC ~ 40 K) Mott transition without additional symmetry breaking FK, PRB 69, 064511 (2004)

  12. fluctuation of the Mott transition Critical endpoint is of the second order Critical phenomena should be present around the endpoint

  13. Outline 1. Introduction 2. 1st-order Mott transition and critical endpoint demonstrated by transport and NMR measurements 3. Mott criticality in two dimensions 4. Conclusions

  14. magnetic susceptibility T > TC Ising Ferromag. c c ~ (T – TC)-g Criticality of phase transitions spontaneous magnetization M g T < TC M ~ (TC – T)b T H M TC 0 T magnetization vs magnetic field TC T T b crossover M ~ H1/d M T = TC TC Singularities are characterized by “critical exponents” d 1st-order d, b, g …. H H 0

  15. Mott examples of phase transitions Phase transitions and universality classes universality class ? Ising Ising spin liquid-gas binary-alloy superconductivity superfluid XY spin XY Heisenberg Heisenberg spin Mott insulator metal Castellani et al., (1979) dynamical mean-field theory Kotliar, Georges, (1996 ~) ‘gas’ phase ‘liquid’ phase Which universality class does Mott criticality belong to? Identical with the classical liquid-gas criticality?

  16. “magnetic susceptibility” “magnetization curve” “spontaneous magnetization” Critical phenomena of conductance FK et al., Nature 436, 534 (2005) above Tc

  17. Divergence of pressure derivative max g ~ 1 dP dG ~ (T – TC)-g | T-TC| / TC Singular pressure dependence Gmet-GC Conductance jump d ~ 2 Gmet-GC b ~ 1 ~ (P – PC)1/d ~ (TC – T)b P-PC | TC-T | / TC unconventional exponents are found Critical exponents (d, b, g) ~ (2, 1, 1) Note; the scaling law d = 1 + (g/b) is satisfied. crossover 2 = 1 + (1/1) conductance G reflects the singularity of the order parameter (DMFT)

  18. FK et al., Nature 436, 534 (2005) Mott Scaling in two dimensions universal form of equation of states () DP f± = (DP)1/d Gmet(P, T) -GC | DT |bd T < TC This plot assures the validity of … TC ~ 39.7 K critical exponents d ~ 2 (Gmet- GC)/DP(1/d) b ~ 1 simple analysis based on (P-PC) and (T-TC) g ~ 1 the correspondence between the order parameter and the conductance T > TC Relevant theoretical work; DP/DTbg M. Imada, PRB 72, 075113 (2005)

  19. Thus DC-conductivity is expected to reflect the singularity of O.P. order parameterf ;thermodynamic quantity Conductivity and the order parameter conductance G ; not thermodynamic quantity From theoretical point of view… O.P. of Mott transition Low-w spectral weight Drude weight r (w) DC-conductivity w A. Georges N. Nagaosa G. Kotliar S. Onoda G. Kotliar et al., PRL 84, 5180 (2000) D. Vollhardt A. Georges, cond-mat/0403123

  20. () h f± ・ = h1/d | e |bd : Conductance measured from the C.P. Gmet(P, T) -GC From experimental point of view… Conductivity and the order parameter g(Ly e, Lx h) = Ld g(e, h) Scaling hypothesis : g(e, h) :Gibbs free energy measured from the C.P., (e, h) = (0, 0), i.e., singular part of Gibbs free energy Universal form of equation of states : f Consistency with the scaling hypothesis appears to assure that the conductance reflect the singularity of Gibbs free energy, i.e., O.P.

  21. Conductance satisfies ‘Mott scaling’ 3D system (V1-xCrx)2O3 T < TC Quasi-2D system 3D system k-(ET)2Cu[N(CN)2]Cl (V1-xCrx)2O3 d ~ 2 d ~ 3 b ~ 1 b ~ 0.5 d ~ 3 g ~ 1 g ~ 1 b ~ 0.5 g ~ 1 T > TC Conductance satisfies the scaling properties in (V1-xCrx)2O3, too. P. Limelette et al., Science 302, 89 (2003)

  22. Conclusions The first-order Mott transition and the second-order critical endpoint the Mott transition without additional symmetry breaking occurs in k-Cl. (ideal Mott transition) FK et al., PRB 69, 064511 (2004) PRL 93, 127001 (2004) Novel critical exponents (d, b, g) ~ (2, 1, 1) the Mott criticality in a quasi-two-dimensional system belongs to a novel universality class. FK et al., Nature 436, 534 (2005)

More Related