Heavy Fermi-liquid State Research Articles

Kondo-lattice formation in cubic-phaseYbCu5

The ${\mathrm{YbCu}}_{5}$ phase with $C15b$ structure has been prepared by a high-pressure technique, and its physical properties have been investigated. The temperature dependence of magnetic susceptibility, electrical resistivity, and specific heat show Kondo-lattice formation. Furthermore, a heavy Fermi-liquid state without magnetic ordering down to 2.0 K is found to evolve below about 6 K. The electronic specific heat coefficient \ensuremath{\gamma} is enhanced to values as large as to 550 mJ/mol ${\mathrm{K}}^{2}$. The magnetization measured up to 40 T at 1.6 K has a field dependence which is expected for a Kondo system when the total angular momentum is $J>1.$ All results are in good agreement with the extrapolation of the previous results of ${\mathrm{YbCu}}_{5\ensuremath{-}x}{\mathrm{Ag}}_{x} (0.125<~x<~1.0)$ for $x\ensuremath{\rightarrow}0$. The concentration dependence of characteristic temperatures of ${\mathrm{YbCu}}_{5\ensuremath{-}x}{\mathrm{Ag}}_{x}$ can be quantitatively explained by the chemical pressure effect within the compressible Kondo model for the full range of Ag concentration ( $0.0<~x<~1.0).$ The origins of Kondo-lattice formation in ${\mathrm{YbCu}}_{4}$Ag and the valence transition in ${\mathrm{YbCu}}_{4}$In are discussed.

Non-Unitary Triplet Pairing State in UPt3

A pairing mechanism for a heavy Fermion superconductor UPt 3 is proposed on the basis of spin fluctuation theory. The main attractive interaction comes from the ferromagnetic fluctuation while the antiferromagnetic fluctuation is also involved into the pair formation. The proposed mechanism gives a new interpretation to the double transitions, lending further support to our previous spin space degenerate scenario where the order parameter is characterized by a non-unitary triplet pairing belonging to one-dimensional representation in weak spin-orbit coupling. Based on the derived free energy functional the phase diagrams for two principal field orientations of hexagonal crystal are constructed. We analyze the recent Knight shift experiment in detail. It is pointed out that a novel heavy Fermi liquid state whose band width T K ∼10 K almost isotropic in spin space must exist at the Fermi surface. Several decisive experiments are proposed to check our proposals.

Possible Pairing Mechanism and Double Transitions in UPt3

In response to the recent remarkable Knight shift and the neutron scattering experiments on UPt 3 , a pairing mechanism is proposed on the basis of spin fluctuation theory. The proposed mechanism gives a new interpretation of the double transitions, lending further support to our previous spin space degenerate scenario where the order parameter is characterized by a nonunitary triplet pairing belonging to one-dimensional representation in weak spin-orbit coupling. It is found that a novel heavy Fermi liquid state with a bandwidth of ∼10 K almost isotropic in spin space must exist near the Fermi surface. Several decisive experiments are pointed out to check our proposals.

Elastic anomaly of heavy fermion systems in a crystalline field

An elastic anomaly, observed in the heavy Fermi liquid state of Ce alloys (for example, CeCu6 and CeTe), is analysed by using the infinite-U Anderson lattice model. Four atomic energy levels are assumed for f-electrons. Two of them are mutually degenerate. A small crystalline splitting 2 Delta is assumed between two energy levels. The fourfold degenerate conduction bands are also considered in the model. The authors solve the model using the mean-field approximation to slave bosons, changing the Fermi energy in order to keep the total electron number constant. The non-zero value of the mean field of the slave bosons persists over temperatures much higher than the Kondo temperature. This is an effect of the constant electron number. Next, the linear susceptibility with respect to Delta is calculated in order to obtain the renormalized elastic constant. The resulting temperature dependence of the constant shows a downward dip. The authors discuss the relation of their findings to experimental data.

Theory of magnetic instabilities in heavy fermion compounds

The author calculates the magnetic interactions between f electrons in the heavy fermion compounds using the slave boson approach to the periodic Anderson model. He shows that at high temperatures the RKKY interaction between local moments which may produce a magnetic transition with TN>T* is recovered. At low temperatures there is an additional part to the interaction which acts between the quasi-particles and allows magnetic transitions from within the heavy Fermi liquid state. The magnetic moment in the SDW state can be calculated and the possibility of small magnetic moments is discussed.

Low Temperature Magnetoresistance of UPt3, U3Fe and U6Co

The transverse magnetoresistance Δρ(T,H)≡ρ(T,H)-ρ(T,0) has been measured at fixed temperatures in the range 0.5K \\leqslant T \\leqslant 40K as a function of magnetic field H \\leqslant 15T for polycrystalline samples of U6Fe and U6Co, and a single crystal of UPt3 (\\overrightarrowH||\\overrightarrowa and \\overrightarrowH||\\overrightarrowc, \\overrightarrowJ||\\overrightarrowb). The sign of Δρ(T,H) changes from positive to negative as T increases through ∼25K for U6Fe and U6Co, and \\i∼18K for UPt3. At low temperatures the data obey a novel universal form Δρ=AH2/B+H for all three materials, where A and B are T- and H-independent constants. Such behavior is postulated as typical of materials entering a heavy Fermi liquid state at low temperatures.