Heavy fermion

In a heavy fermion compound Yb MnSbn, the dephasing rate of the coherent optical phonons decreased with lowering temperature above Curie temperature Tc, but increased below Tc- The results were attributed to the coupling between an optical phonon mode and the Kondo effect [100]. 

On the other hand, recent measurements on UBcis have shown this intermetallic to be a very special species of superconductor with a large density of electronic states at Ep ( 1000 mJ/mol K ). Such results will certainly motivate both theoreticians and experimentalists and the so called heavy-fermion superconductors family is already developing . ... 

In addition, there are certain metals involving 4f- or 5f-states, formerly called Kondo metals and now described as heavy-fermion materials, which have a very large electronic specific heat and may be described as crystals in which every rare-earth metal is envisaged, coherently, in a Kondo-type spin flip. 

The Hall effect has been studied only for some borocarbides. The normal state Hall coefficients / h were found to be negative and only weakly temperature dependent for polycrystalline borocarbides based on R = Y (Fisher et al. 1995 Narozhnyi et al. 1996 Mandal and Winzer 1997), La (Fisher et al. 1995), Ho (Fisher et al. 1995 Mandal and Winzer 1997) and Gd (Mandal and Winzer 1997). A negative but strongly temperature dependent R was found for the heavy-fermion compound YbNi2B2C (Narozhnyi et al. 1999b). 

A. C. Hewson, The Kondo Problem to Heavy Fermions (Campridge University Press, Cambridge, 1993). 

ADP atomic displacement parameters HFSC heavy-fermion superconductor... 

FIHFM field-induced heavy-fermion metal QCP quantum critical point... 

HFS heavy-fermion state RRR residual resistance ratio... 

FIHFM, field-induced heavy-fermion metal FMM, ferromagnetic metal ... 

Fig. 12. Total heat capacity of a single crystal of PrFe4Pi2 vs. temperature in various applied magnetic fields (a) low fields and (b) high fields. The dashed fines in (b) correspond to the best fit of the heavy fermion state to die resonant level model (Crlm)-Cph is the estimate of die phonon contribution to the heat capacity (Aoki et al., 2002).

Fig. 13. Magnetic field vs. temperature phase diagram of single crystal PrFe4Pi2 with the magnetic fields applied along the (100) direction. The labels ODS and HFS refer to ordered state and heavy fermion state, respectively. The ordered state is probably due to quadrupolar ordering of the Pr 4f ground state. The solid and broken lines represent second-order and first-order phase boundaries, respectively (Aoki et al., 2002).

Preliminary results on low temperature transport properties in YbPdSb system with MgAgAs type structure are presented by Aliev et al. (1988). Resistivity shows a maximum at T = 50-100 K and the Fermi-liquid decrease of q go + AT2 at helium temperatures. The high value of the A coefficient 5 p 2 cm/K2 indicates the possibility of the heavy fermion behavior with y about 300MOO mJ/molK2. The Seebeck coefficient S is positive and shows a maximum Smax 22 pV/K at T 200 K. 

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