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Superconductivity in CeRh 1-x Ir x In 5

Superconductivity in CeRh 1-x Ir x In 5. M. Nicklas et al ., Physical Review B 70 , 020505(R) (2004). Kitaoka Laboratory Yoichi Mugino. Contents. Introduction ■ Superconductivity in metals ■ Heavy-fermion systems and superconductivity

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Superconductivity in CeRh 1-x Ir x In 5

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  1. Superconductivity in CeRh1-xIrxIn5 M. Nicklas et al., Physical Review B 70, 020505(R) (2004) Kitaoka Laboratory Yoichi Mugino

  2. Contents • Introduction ■Superconductivityin metals ■Heavy-fermion systems and superconductivity • Experimental data about CeRh1-xIrxIn5 • Summary

  3. ＋ ＋ ＋ ＋ ＋ ＋ ＋ ＋ ＋ ＋ ＋ ＋ ＋ ＋ ＋ ＋ ＋ ＋ ＋ ＋ ＋ ＋ - - - - - ＋ ＋ ＋ ＋ ＋ - ＋ ＋ ＋ ＋ Superconductivity in metals BCS theory Superconductivity is caused by the formation of Cooper-pairs mediated by electron-phonon interaction. ・Electrons near the Fermi level can travel in the crystal ionseven atvery low temperatures and attract ions around them in a time scale of lattice vibration. ・This interaction makes plus charged cloud left as a result of phonon emission. ・The delayed lattice vibration is responsible for attracting an electron through phonon absorption. ・As a result, two electrons are bounded, forming the Cooper pair. Superconductivity

  4. ・ ・ ・ Superconducting state Normal state Superconducting state Energy gap A quantum ground state for the Cooper pairs with an energy gap The formation of energy gap keeps current permanent and perfect diamagnetism, called as Meissner effect.

  5. Heavy-fermion systems Heavy-fermion compounds CePd2Si2 CeIn3 CeRh2Si2CeCu2Si2 CeRhIn5 Ce3+ : [Xe] 4f1 Conventional metals Electrons move freely f electrons Electrons don’t move freely due to the electron correlation Heavy fermion system : 重い電子系

  6. conduction electrons Polarization Jcf Jcf 4ｆ electrons The indirect f-f interaction is mediated by conduction electrons. c-f Interaction RKKY interaction Kondo effect Localization Itinerancy Jcf: exchange interaction conduction electrons 4ｆ electrons Magnetic moment is screened by hybridization between conduction electrons and f electrons Localization : 局在 Itinerancy : 遍歴

  7. TK TRKKY : RKKY interaction : Kondo effect Temperature (K) AFM QCP HF 0 Pressure Jcf Phase diagram for heavy fermion systems Doniach model indicate competition between RKKY interaction and Kondo effect QCP : Quantum critical point (量子臨界点)

  8. (a) (b) (c) Phase diagram for strongly correlated electron systems (a) heavy-fermion system (b) organic compound (c) high-Tc cuprates

  9. Magnetically mediated superconductivity Magnetic interaction plays role for forming the Cooper pairs instead of electron-phonon interaction.

  10. SC2 SC1 New superconducting phase in CeCu2Si2 New type of superconducting phase was found ! SC2 appears where antiferromagnetism disappears Another mechanism for SC is suggested. The origin of this SC phase is still unknown QCP H.Q.Yuan et al., New Journal 6 (2004) 132

  11. Phase diagram for CeRh1-xIrxIn5 & CeIrIn5 SC2 appears in CeIrIn5 under pressure like CeCu2Si2 !

  12. Crystal structure CeRh1-xIrxIn5 Quasi-2D structure ● CeRhIn5 TN=3.8K (ambient pressure) Antiferromagnet CeIrIn5 Ir(Rh) TC=0.4K (ambient pressure) Superconductor

  13. CeRhIn5 M. Yashima et al. T. Muramatsu et al. Rh→Ir pressure effect Chemical substitution and pressure CeRh1-xIrxIn5 CeRhIn5 TN = 3.8 K CeIrIn5 Tc = 0.4 K P. G. Pagliuso et al., PRB 64, 100503(R) (2001)

  14. About resistance normal metal magnet Magnetic fluctuation enhances resistance at low temperature.

  15. x=0 x=1 Normal stateproperty T AFM SC1 SC2 P x=0 Pressure enhances the scattering rate as magnetic order is replaced by superconductivity. Pressure x=1 Application of pressure suppresses the scattering rates as these become far from quantum critical point. The mechanism of SC2 is different from that of SC1 !

  16. Summary • There are two superconducting phases in CeRh1-xIrxIn5. • One is the superconducting phase which is mediated by magnetic interaction. • Another one is yet unknown. • My future works are devoted to unravel this new SC phenomenon

  17. Ir concentration The ratio of tetragonal lattice parameter c/a varies linearly with pressure. pressure c b a c/a varies with Ir concentration as pressure is applied.

  18. 1/T1

  19. Introduction Heavy fermion system(2) Specific heat Susceptibility Resistance

  20. Examples In the case of CeIn3 law out of Near the QCP, the magnetic scattering increases due to magnetic instability. G. Knebel et al., Physical Review vol.64 024425

  21. Experimental Data Pressure effect on CeRh1-xIrxIn5 According to resistance measurements, Superconducting dome is separated with pressure. Two types of superconductivity exist ! pressure SC1 is superconductivity which is mediated by magnetic moment. What’s the mechanism for cooper pair in SC2?

  22. Introduction interaction ε*F εF interaction Fermi liquid Fermi gas Heavy fermion system “Heavy” means that the electrons move strictly

  23. ・ ・ ・ Fermion and Boson

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