Shimizu-group (M1) Shuei Kayama

1. High pressure studies of physical properties for Eu compounds by electrical resistivity measurements Shimizu-group (M1) Shuei Kayama

2. Contents • Introduction • Lanthanide • Pressure effect to lanthanide compounds • (Ce, Yb) • Motivation • Experiment • Setting • Results • Summary

3. Introduction n(r) r/rB n(r) : Distribution of electrons rB : Bohr radius（ボーア半径） Ce 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f x 5s2 5p6 5d1 6s2 x = 0 ~ 14 Localized or conduction electron ? Conduction electrons

4. Introduction Lanthanide Pm La Ce Pr Nd Sm Eu Gd Tb Dy Ho Tm Yb Lu Yb2+ Ce3+ Yb3+ Ce4+ • Heavy fermion • Spin fluctuation • Mixed valency ~7.7 mB 0 mB Eu2+ Eu3+ Eu2+ Eu3+

5. Introduction RKKY interaction and Kondo effect Doniachphase diagram Kondo effect RKKYinteraction Conduction electron Conduction electron 4f 4f 4f Kondo effect quenches spin. RKKY interaction makes spin stable. |Jcf D(eF)| Jcf : Exchange interaction of conductive electron and the 4f electron D(eF) : Electron density in the Fermi surface We can control antagonism of RKKY interaction and Kondo effect by pressure.

6. Introduction Lanthanide Pm La Ce Pr Nd Sm Eu Gd Tb Dy Ho Tm Yb Lu CeCu2Si2 Z. Phys. B - Condensed Matter 60, (1985)379-386 Yb2+ Yb3+ Heavy fermion superconductivity 0 mB Ce3+ Eu2+ Eu3+ Ce4+ Counter system ~7.7 mB Eu2+ Eu3+

7. Introduction Pm La Ce Pr Nd Sm Eu Gd Tb Dy Ho Tm Yb Lu [1] CeCu2Ge2 YbCo2Zn20 [2] Co [1] Ce Cu Ge [4] [3] CeCu2Ge2 YbCo2Zn20 [1] J. Phys. Soc. Jpn. 80 (2011) [2] J. Phys. Chem., 89 (1985) [3] J. Phys. Soc. Jpn. 67 (1998) [4] J. Phys. Soc. Jpn. 77 (2008)

8. Introduction Motivation Eu compounds has not studied well under high pressure. We are measuring the electrical resistance under high pressure to study physical properties of various Eu compounds. (EuGa4, EuRu2P2, EuCd11)

9. High pressure studies of physical properties for Eu compounds by electrical resistivity measurements Shimizu-group (M1) Shuei Kayama

10. Contents • Introduction • Lanthanide • Pressure effect to lanthanide compounds • (Ce, Eu, Yb) • Motivation • Experiment • Setting • Results • Summary

11. Introduction n(r) r/rB n(r) : Distribution of electrons rB : Bohr radius（ボーア半径） Ce 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f x 5s2 5p6 5d1 6s2 x = 0 ~ 14 Localized or conduction electron ? Conduction electrons

12. Introduction Lanthanide Pm La Ce Pr Nd Sm Eu Gd Tb Dy Ho Tm Yb Lu Yb2+ Ce3+ Yb3+ Ce4+ • Heavy fermion • Spin fluctuation • Mixed valency ~7.7 mB 0 mB Eu2+ Eu3+ Eu2+ Eu3+

13. Introduction RKKY interaction and Kondo effect Doniachphase diagram Kondo effect RKKYinteraction Conduction electron Conduction electron 4f 4f 4f Kondo effect quenches spin. RKKY interaction makes spin stable. |Jcf D(eF)| Jcf : Exchange interaction of conductive electron and the 4f electron D(eF) : Electron density in the Fermi surface We can control antagonism of RKKY interaction and Kondo effect by pressure.

14. Introduction Lanthanide Pm La Ce Pr Nd Sm Eu Gd Tb Dy Ho Tm Yb Lu CeCu2Si2 Z. Phys. B - Condensed Matter 60, (1985)379-386 Yb2+ Yb3+ Heavy fermion superconductivity 0 mB Ce3+ Eu2+ Eu3+ Ce4+ Counter system ~7.7 mB Eu2+ Eu3+

15. Introduction Pm La Ce Pr Nd Sm Eu Gd Tb Dy Ho Tm Yb Lu [1] CeCu2Ge2 YbCo2Zn20 [2] Co [1] Ce Cu Ge [4] [3] CeCu2Ge2 YbCo2Zn20 [1] J. Phys. Soc. Jpn. 80 (2011) [2] J. Phys. Chem., 89 (1985) [3] J. Phys. Soc. Jpn. 67 (1998) [4] J. Phys. Soc. Jpn. 77 (2008)

16. Introduction Motivation Eu compounds has not studied well under high pressure. We are measuring the electrical resistance under high pressure to study physical properties of various Eu compounds. (EuGa4, EuRu2P2, EuCd11)

17. Experiment ・Setting 3 cm 6 cm ～ 350 GPa (≒ the center of the earth) Diamond Anvil Cell (DAC)

18. ruby ruby Experiment - Settings Ruby Sample Electric probe (Cu) 500 μm Insulation layer (c-BN+epoxy) + Gasket (Re or SUS310S)

19. Experiment ρ vs T Eu ・Previous (EuGa4) BaAl4 type Ga

20. Experiment Eu ・Result (EuGa4) ρ vs T Ga ρ vs T ρcurves (low T region) suddenly change their features at P≈ 10.5 GPa. ρ in the low T suddenly drops at P≈ 16.8 GPa.

21. Experiment ・Result (EuGa4) ρ vs T (EuGa4) ρ vs T (EuNi2Ge2)

22. Experiment ・Result (EuGa4) EuNi2Ge2 EuNi2Ge2 TV Eu2+ TN Eu3+

23. Experiment EuGa4 ρ vs T ・Zero resistivity is not observed. ・Critical magnetic field is about 200 mT. 17 GPa The superconductivity is characteristic property of EuGa4? Tc≒ 6 K (Ga)

24. Experiment ・Result (EuRu2P2) ThCr2Si2 type ρ vs T Eu Ru P

25. Experiment ・Result (EuRu2P2) EuRu2P2 dp-p 8 GPa C. Huhnt et al. Physica B 252 (1998) 51

26. Experiment ・Result (EuCd11) BaHg11 type Eu Cd ρ vs T

27. Summary • EuGa4 is showed that There is a possibility of new pressure induced valence transition material. • Kondo effect behavior is observed under high pressure in EuRu2P2 • Neel temperature increases with increasing pressure.

29. 比較

30. n(r) r/rB n(r) : Distribution of electrons rB : Bohr radius（ボーア半径） Ce

31. Introduction ρ/ρ (280 K) vs T YbB12 Kondo insulator NaCl type Yb

32. Introduction ThCr2Si2 type

33. Introduction ・Motivation Eu compounds has not studied well. We are measuring the electric resistance under high pressure to study physical properties of various Eu compounds.

34. Introduction ρ vs T Eu ・Previous work of Eu compound (BaAl4 type) BaAl4 type Ga EuGa4

35. Experiment ・Setting 3 cm 6 cm ～ 350 GPa (≒ the center of the earth) Diamond Anvil Cell (DAC)

36. Introduction CeCu2Ge2 ThCr2Si2 type Tatsuo C. Kobayashi et al., J. Phys. Soc. Jpn. 67 (1998) Increasing pressure.

37. Summary • As for RKKY interaction and Kondo effect, Ce and Yb compounds has been studied in paticular. • We are measuring the electric resistance under high pressure to study physical properties of various Eu compounds. • My study • Electrical resistivity was measured under high pressure.

38. Experiment - +

39. Introduction YbCo2Zn20 CeCr2Al20 type Increasing pressure.

40. Introduction Lanthanide Pm Lu La Ce Pr Nd Sm Eu Gd Tb Dy Ho Tm Yb Stably valence +3 +3 +2 +3 +2 Eu2+ [Xe]4f75d06s2 Eu3+ [Xe]4f65d16s2 Average valence Eu2+X (4f7-X) J = 7/2 J = 0 Magnetic state Non magnetic state The valence of Eu was investigated up to 34GPa. The valence saturates at v=2.64 throughout the hcp’-phase. Valence fluctuation J. Rohler, Physica B 144, 27(1986)

41. Introduction ・Physical property of Eu Antiferromagnetic transition Pressure-induced super conductivity superconductivity is controlled by localized magnetic moment due to 4f electron in ambient pressure. However, the magnetism of the pressure region that Eu becomes the superconductivity doesn’t still understand. M. Debessai et al., Phys. Rev. Lett. 102, 197002 (2009).

42. How to estimate pressure Experiment ・Ruby fluorescence Put the powder of Ruby (Al2O3) in DAC with sample. Ruby (Al2O3) produce fluorescence when irradiated by laser. The color of fluorescense is change by applying pressure. http://geoweb.princeton.edu/research/MineralPhy/labtour/Ruby.html

43. Introduction Eu ・Physical property of various Eu compounds Ga TN: Neel temperature qP : Cury temperature mB : Magnetic moment kB : Boltzman constant Hc : Cryticalfeild Two sublattice model TN – qP = (3mB/kB) Hc EuGa4 EuBi3, EuPb3 Eu Bi, Pb J. Am. Chem. Soc., 126 (21) 2004, ・Studies of these compounds are not conducted under high pressure.

44. Introduction ・Motivation Various studies of the Eu have been performed. However, There are many problems that have not been yet understood. We think about physics of the Eu in a broad vision by observing the physical property of various Eu compounds.

45. Experiment Four probe method To detect the electrical resistance, I used four probe method V+ sample I+ I- V- insulated gasket

46. D. Jaccard et al. / Physica B 259-261 (1999)