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Field-Induced Quantum Critical Point in CeCoIn 5

Field-Induced Quantum Critical Point in CeCoIn 5. J.Paglione et al,Phys.Rev.Lett. 91.246405 (2003) F. Ronning et al,Phys.Rev. B 71, 104528 (2005) Kitaoka Laboratory Takuya Fujii. Contents. Introduction - QCP - Heavy Fermion & Fermi Liquid Experimental Data

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Field-Induced Quantum Critical Point in CeCoIn 5

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  1. Field-Induced Quantum Critical Point in CeCoIn5 J.Paglione et al,Phys.Rev.Lett. 91.246405 (2003) F. Ronninget al,Phys.Rev. B 71, 104528 (2005) KitaokaLaboratory Takuya Fujii

  2. Contents • Introduction - QCP - Heavy Fermion & Fermi Liquid • Experimental Data - Resistivity and specific heat of CeCoIn5 under fields - Phase diagram • Summary

  3. Metal Semiconductor Insulator Superconductor Material The ground states are changed ! Magnetism Physical properties around QCP Parameter Magnetic field(H) Material Pressure(P) Carrier doping

  4. High-Tc cuprates Heavy-fermionsystem QCP by carrier doping QCP by Pressure QCP (Quantum Critical Point): Phase transition of ground state (T=0K) (ex) magnetic order-disorder, normal phase-SC QCP (Quantum Critical Point) Unconventional SC around QCP

  5. Physical properties around QCP Non Fermi liquid Temperature (K) Magnetic fluctuations happen. magnetic order QCP Fermi Liquid 0 Parameters Physical properties around QCP are not described by Fermi Liquid theory.

  6. RKKY interaction conduction electron f-electron Heavy Fermion & Fermi Liquid <Heavy electron systems> f-electron: (RKKY interaction)  localize at the atom. (Kondo effect)    become itinerant by the hybridization between conduction electrons and f-electrons. localize : 局在する itinerant :遍歴した Kondo effect conduction electron rare earth ion Magnetic order Fermi liquid state by heavy electrons

  7. H // ab Normal SC H // c Crystalstructure of CeCoIn5 Tc=2.3K Heavy fermions superconductor • Tc=2.3 K at P=0. • C/T=350 mJ/mol K2 • H//abc2 ~ 11.8 T, H//cc2 ~ 5 T S. Ikeda et al., J. Phys. Soc. Jpn. 71 (2002) 1023.

  8. QCP of CeCoIn5 Comparison with isostructural CeRhIn5 isostructural AFM compound: CeRhIn5(TN=3.8K) CeCoIn5is in the vicinity of QCP at ambient pressure. M. Yashima et al.

  9. FL and NFL behavior Non Fermi-liquid 2D AFM r=r0+AT, C/T~ -log T 3D AFM r= r0+AT3/2, C/T=r0-aT1/2 Fermi-liquid (3D, 2D) r =r0+AT2 C/T=const A(slope): interaction between electrons

  10. Resistivity in high fields ( H // c) Temperature range of wider Hex Fermi liquid: A decreases as increasing field. By applying magnetic field, a FL regime is recovered !

  11. Field dependence of T2 coefficient • critical behavior • divergence close to H* (H*=5.1,α=-1.37)

  12. High-Hex C/T=const C/T=const Fermi liquid: Hex isclose to H* C/T~ -log T C/T~ -log T Non Fermi liquid: Specific heat in high fields ( H // c )

  13. H-T phase diagram H // c FL H* SC H* coincides with the critical field of SC Hc2(0).

  14. QCP in H // ab H // c H // ab Hc2ab~11.8 T Hc2c~5 T Cel/T= FLNFL was also observed around Hc2.

  15. H // ab + ×Tc ●TFL H // c +Tc + FL: H // c ○TFL FL: H // ab H-T phase diagram SC

  16. QCP SC FL QCP AF FL What is unique about CeCoIn5 ? comparison with YbRh2Si2 Hex approaches tocritical field value H* . critical behavior ! In CeCoIn5 : H*Hc2(0) H-T phase diagram of YbRh2Si2 FL AF NFL T (K) H* SC FL 0 H(T) H* P.Gegenwart el et al. (2002)

  17. Summary • We observed a suppression of the non-Fermi liquid behaviors with increasing field, and the development of a Fermi liquid state. • It was a field-induced quantum critical point. • It coincides with the superconducting critical field Hc2(0).

  18. The end THE END

  19. FL: H // c H*Hc2(0) FL: H // ab SC

  20. Motivation • Motivation Quantum critical behavior in the H-T phase diagram ? • Measurements Specific heat and resistivity in high magnetic field.

  21. QCP at negative P? - the QCP of CeCoIn5 under Pressure V.A.Sidorov et al. 2002

  22. ・ ・ ・ ・ ・ ・ ・ ・ ・ Interaction ・ Fermi liquid ・ Fermi gas Heavy Fermion & Fermi Liquid No dynamic interaction between particles. Fermi gas : The interaction between electrons becomes very strong. itinerancy The electrons can’t move easily. The effective mass seems heavy. Fermi liquid : Heavy fermion is described by Fermi Liquid theory.

  23. QCP by the competition between RKKY interaction and Kondo effect

  24. - Resistivity of CeCoIn5under fields resistivity of metal at low temperature ( scattering by the phonon vibration) ( scattering between conduction electrons)

  25. - Resistivity of CeCoIn5under fields Tc NFL

  26. Resistivity of CeCoIn5under fields MR:magnetoresistance

  27. - Resistivity of CeCoIn5under fields Crossover from positive to negative MR T(K)=16 14.5 initial increase  an increase of spin disorder 13 a suppression of AF correlations 11.5 10 8.5 7 5.5 polarization of spins by increasing field strength a field-aligned state 4 T>Tc 2 0.1

  28. Hex : London penetration depth : Coherence length Hc2(//ab)=11.8T,(//c)=5T ab< c

  29. Non Fermi liquid behavior • The single-impurity multichannel Kondo model theory • Disorder-induced theory • Spin-fluctuation theory Non Femi-liquid 2D AFM r=r0+AT, C/T~ -log T 3D AFM r= r0+AT3/2, C/T=r0-aT1/2 Landau Fermi-liquid (3D, 2D) r =r0+AT2, C/T=const.c=const.

  30. NFL:near QCP,due to spin critical fluctuations, FL SC - H-T phase diagram of CeCoIn5

  31. H*

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