1 / 17

Coherent Kondo State in a Dense Kondo Substance : Ce x La 1-x Cu 6

Coherent Kondo State in a Dense Kondo Substance : Ce x La 1-x Cu 6. A.Sumiyama et al., J.Phys.Soc.Jpn. 55 (1986) Shimizu-group Katsuya TOKUOKA. Contents. Introduction ■ Dilute Kondo effect ■ Coherent Kondo effect Experimental data about Ce x La 1-x Cu 6 Summary.

aderyn
Download Presentation

Coherent Kondo State in a Dense Kondo Substance : Ce x La 1-x Cu 6

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. Coherent Kondo State in a Dense Kondo Substance : CexLa1-xCu6 A.Sumiyama et al., J.Phys.Soc.Jpn.55(1986) Shimizu-group Katsuya TOKUOKA

  2. Contents • Introduction■ Dilute Kondo effect■ Coherent Kondo effect • Experimental data about CexLa1-xCu6 • Summary

  3. The simple metallic resistivity potassium The resistivity decreases monotonically as the temperature decreases. 102 R / R290K Residual resistivity（残留抵抗） T (K) Impurity scattering C.Kittel Introduction to Solid State Physics

  4. Kondo effect Discovery of the resistivity minimum in dilute magnetic alloys(希薄磁性合金).(1930’s) The electrical resistivity increases steeply as the temperature decreases In the low temperature region. Jun Kondo has derived the logarithmic increase of the resistivity in the low temperature region. (1964) → 40th anniversary in 2004 ! de Haas et al., Physica 1 (1934) 1115 http://www.aist.go.jp/aist_j/information/emeritus_advisor/index.html

  5. Dilute Kondo effect(希薄系近藤効果) T > TK T < TK Spin singlet (スピン一重項)S = 0 de Haas et al., Physica 1 (1934) 1115 But this Kondo effect does not appear if the metal contains a large amount of magnetic impurities. TK : 近藤温度

  6. A new type Kondo effect In Ce compounds, although it contains a large amount of magnetic impurities (>10%), Kondo effect appeared. Temperature dependence of resistivity in CeCu6 Y.Ōnuki et al., J.Phys.Soc.Jpn. 53 (1984) 1210-1213

  7. f - electron Lanthanoides La3+ Ce3+ Pr3+ … 4f-electrons 0 1 2 |r R(r)|2 Closed shell 5s25p6 r (a.u.) http://www.phy.saitama-u.ac.jp/~saso/saso.html f - electron is localized.

  8. Coherent (Dense) Kondo effect(高濃度近藤効果) In Ce compounds,the Kondo effect appears. T > TK f-localized(局在) Dilute T < TK f-itinerant (遍歴 ) Y.Ōnuki et al., J.Phys.Soc.Jpn. 53 (1984) 1210-1213 Heavy fermion state(重い電子状態)

  9. Coherent Kondo substance CeCu6 • Coherent Kondo substance • Pauli paramagnet (パウリ常磁性)(no magnetic ordering) • Large specific heat coefficient(電子比熱係数) γ= 1.6 J / mole·K2 Crystal structure of CeCu6 Y.Onuki et al., J.Phys.Soc.Jpn. 54 (1985) 1964-1974 The effective mass (有効質量) is 1000 times or more as large as the free electron mass !

  10. Motivation LaCu6 is a normal metal which has the same structure. (no f – electrons) To clarify the process from the incoherent Kondo state to the coherent Kondo state, we can investigate the compound : CexLa1-xCu6 (x=0-1). Dilute (incoherent) Dense(Coherent) Ce density x : 0 1

  11. Experiment Single crystals of CexLa1-xCu6 were grown by the Czochralski pulling method. a large single crystal ! Measurements ・electrical resistivityfrom 300 K~ 18 mK ・magnetoresistance (磁気抵抗効果)

  12. Temperature dependence of electrical resistivity Electrical resistivity increasesas temperature increases in the low temperature region. A maximum appeared around 5-15 K for an x value of 0.73-1.0. Temperature dependence of electrical resistivity in CexLa1-xCu6 f-electrons are itinerant in the low temperature region.

  13. Magnetic resistivity The normal metal ρ( T ) = ρ0 + ρe-e(T) (Matthiessen’s rule) The magnetic substance ρ( T ) = ρ0 + ρe-e(T) + ρm(T) ρm= ρCexLa1-xCu6- ρLaCu6 (magnetic resistivity)

  14. Magnetic resistivity Dilute x = 0.094 – 0.50 Coherent x = 0.73 – 1.0 Consecutive change from dilute to coherent Temperature dependence of magnetic resistivity in CexLa1-xCu6

  15. Magnetoresistance A effective method to investigate heavy fermion system In normal metalCyclotron motion → The resistivity increases. Heavy fermion systemmagnetization→ The resistivity decreases due to magnetic ordering. Ｉ H c a b

  16. Magnetic field dependence of resistivity Magnetoresistance at 1.5 K Dilute Kondo system ρhas a Maximum around 20 kOe. Because of the suppression of the coherent Kondo effect, the resistivity increases. Itinerant localized The coherent Kondo effect is suppressed by applied magnetic field. Magnetic field dependence of resistivity in CeCu6

  17. Summary • Dilute Kondo effect appears for x = 0.096 – 0.50.Coherent Kondo effect appears for x = 0.73 – 1.0. • Consecutive change from dilute Kondo state to coherent Kondo state occurs. • The coherent Kondo effect is suppressed by applying a magnetic field.

More Related