Superconducting properties in filled-skutterudite PrOs4Sb12 Kitaoka Lab. M1 Takayuki Nagai references ・H.Kotegawa et al,Phys.Rev.Lett. 90,027001 (2003) ・M.Yogi et al,Phys.Rev. B 67,180501(R) (2003) Filled-skutterudite : 充填スクッテルダイト Abstract abstract ・Filled-skutterudite compounds show rich properties metal-insulator transition, heavy fermion behavior,and superconductivity etc. (LaOs4Sb12,PrOs4Sb12, PrRu4Sb12 etc.) ・PrOs4Sb12 shows heavy-fermion-like behavior and anomalous superconductivity in many experiments. ・The related compounds, LaOs4Sb12 ,LaRu4Sb12 and PrRu4Sb12 have been reported as conventional BCS superconductors. Metal-insulator transition : 金属-絶縁体転移 Heavy-fermion (HF) compound : 重い電子系化合物 Outline Outline • Introduction - Filled-skutterudite structure - Crystal electric field - Nuclear Quadrupole Resonance technique • Experiments • Summary Introduction : Filled-skutterudite / Crystal structure Crystal structure Thermoelectric effect Higher temperature Lower temperature Application ・refrigerator ・waste heat recovery etc. Filled-skutterudite compounds show rich properties. rare earth ・metal-insulator transition transition metal ・heavy-fermion (HF) behavior pnictogen ・superconducting (SC) transition The cage made by a rare earth atom and 12 pnictogen atoms forms bcc-type crystal lattice Thermoelectric effect : 熱電効果 IntroductionIntroduction : Crystal electric field : Crystal electric field PrOs4Sb12 L-S coupling Crystal electric field effect J=6 (13) (111K , doublet) Pr3+-4f2 J=5 (11) (65K , triplet) J=4 (9) (6K , triplet) magnetic (0K , singlet) non-magnetic Very small split Crystal electric field : 結晶場 Interaction between electrons and ions. L-S coupling : スピン-軌道相互作用 L S L : orbital angular momentum S : spin angular momentum → Magnetic fluctuations T.Hotta et al,Phys. Rev.Letter. 94 (2005) 067003 Magnetic fluctuation : 磁気揺らぎ Introduction : Filled-skutterudite compounds / PrOs4Sb12 Introduction : Filled-skutterudite compounds PrOs4Sb12 ・zero resistivity ・Meissner effect ・Jump of specific heat ・ First Pr-based heavy-fermion superconductor PrOs4Sb12 E.D.Bauer et al,Phys. Rev. B 65 (2002) 100506 PrRu4Sb12 ？ BCS TC=1.85K TC=1.3K LaOs4Sb12 LaRu4Sb12 BCS BCS TC=0.74K TC=3.58K Introduction : Nuclear Quadrupole Resonance Introduction : Nuclear Quadrupole Resonance Q Q 6 e+ 3I 2 Z I 2 I 1 3 5 I , , ... 2 2 2 3 2 m 3 2 m 1 2 Q 0 Q 0 Charge distribution is not spherical symmetry. Sb-NQR spectrum of PrOs4Sb12 ・123Sb (I=7/2) ・121Sb (I=5/2) 7 2 5 2 3νQ 2νQ 5 2 νQ 3 2 1 2 Intensity(arb.unit) 1.0 0.8 123 121 0.6 0.4 Sb Sb 121Sb (123Sb) has 2 (3) NQR transitions. 0.2 2νQ 3 2 νQ 1 2 50 60 70 80 Frequency(MHz) Nuclear Quadrupole Resonance : 核四重極共鳴 Experiments : Nuclear spin-lattice relaxation m H AI S 3 2 AI S m T1 1 e 1 2 t T1 Nuclear spin-lattice relaxation 核スピン－格子緩和 Experiments : Nuclear spin-lattice relaxation BCS superconductor : LaOs4Sb12 Normal state 1 N ( E ) N ( E ) f ( E )(1 f ( E ))dEdE T1 N 2 ( EF )T TT const 1 La Experiments : Nuclear spin-lattice relaxation BCS superconductor : LaOs4Sb12 SC state 100 TC TT 1 const -1 1/T1 (sec ) 10 1 Coherence peak 0.1 e k BT 0.01 2 NMR can detect low energy excitation around the Fermi surface. LaOs4Sb12 0.001 0.1 1 H.Kotegawa et al (2003) 10 Temperature (K) 100 Experiments :Gapof structure of anisotropic Experiments: Gap structure anisotropic superconductors rsuperconductor Observed in HF superconductors. Line-node Gap equation ( ) 0 cos 1/T1∝T3 Point-node Gap equation TC T3 ( ) 0 sin 1/T1∝T5 G.-q.Zheng et al,PRL 86 4664(2001) Anisotropic superconductor : 異方的超伝導体 Experiments : Spin-lattice-relaxation time T1 4 f 0 LaOs4Sb12 vs. 4 f 2 PrOs4Sb12 TC 100 TC LaOs4Sb12 10 -1 1/T1 (sec ) ・Normal State →T1T : const. LaOs4Sb12 1 ・SC State → Coherence peak at TC 0.1 and Exponential T dependence of 1/T1 PrOs4Sb12 Conventional BCS superconductor. 0.01 PrOs4Sb12 LaOs4Sb12 0.001 0.1 1 H.Kotegawa et al (2003) H.Kotegawa et al (2003) 10 Temperature (K) 100 Experiments : Spin-lattice-relaxation time T1-2 1 CeCu2Si2 , CeIrIn5 vs. 4 f PrOs4Sb12 2 CeIrIn5 CeCu2Si2 100 TC T3 10 TC -1 TC PrOs4Sb12 1/T1 (sec ) 4 f T3 T3 1 0.1 T5 0.01 PrOs4Sb12 0.001 0.1 Y.Kawasaki et al,PRB 66 (2002) 224502 G.-q.Zheng et al,PRL 86 4664(2001) 1 H.Kotegawa et al (2003) 10 100 Temperature (K) CeCu2Si2 , CeIrIn5 ・SC state 1/T1 is proportional to T3 → anisotropic HF superconductor Isotropic HF superconductor? Experiments : Spin-lattice-relaxation time T1-3 TC 2 4 f PrRu4Sb12 100 4 f PrOs4Sb12 PrOs4Sb12 -1 1/T1 (sec ) 10 vs. 2 1 0.1 0.01 PrOs4Sb12 0.001 0.1 1 H.Kotegawa et al (2003) 10 100 M.Yogi et al, PRL 90 027001 (2003) Temperature (K) T<<70K H. Kotegawa et al, PRL 90 027001 (2003) T<<6K T>>6K magnetic TC=1.85K magnetic 6K non-magnetic : Electrons 70K TC=1.3K non-magnetic T>>70K Results TC 100 Crystal electric field plays an important role. -1 1/T1 (sec ) 10 1 0.1 0.01 PrOs4Sb12 H.Kotegawa et al (2003) PrOs 4Sb1210isn’t a 1 conventional BCS Temperature (K) superconductor. 0.001 0.1 100 100 TC PrRu4Sb12 Isotropic-HF super conductor BCS TC=1.85K TC=1.3K -1 1/T1 (sec ) 10 PrOs4Sb12 1 0.1 0.01 LaOs4Sb12 0.001 0.1 1 LaOs4Sb12 LaRu4Sb12 BCS BCS TC=0.74K TC=3.58K H.Kotegawa et al (2003) 10 Temperature (K) 100 Summary Summary • From temperature dependence of nuclear-spin-relaxation time T1, PrOs4Sb12 is not conventional BCS superconductor but HF-like-isotropic superconductor. • Crystal electric field plays an important role in the superconductivity of PrOs4Sb12 .
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