Y. Echizen

Ce- and Yb-based Kondo semiconductors

Abstract Kondo semiconductors are a class of strongly correlated f-electron materials whose low-energy excitations exhibit a (pseudo)gap at low temperatures. The significant difference between the pseudogap in orthorhombic CeNiSn and CeRhSb and the real gap in cubic Ce 3 Bi 4 Pt 3 and YbB 12 is highlighted by a comparison of transport properties. Low-temparature measurements of the magnetoresistance, Hall coefficient and specific heat of CeNiSn have revealed a field-induced excitation of the coherent low-carrier state. A systematic study of CeNi 1− x T x Sn ( T = Co, Cu and Pt ) has shown that the residual carriers in CeNiSn are immobilized by 1% substitution irrespective of the substitutes. Further substitution with 5% Cu induces a magnetic instability at T = 0.

Large thermoelectric power in several metallic compounds of cerium and uranium

Abstract The thermoelectric power S was measured from 1.5 to 500 K for CePdSb, CeRhSn, CeIrSn, UNi4B, UPt2In and UCu3+xGa2−x. The value of S at 300 K ranges from 16 to 70 μV/K. The rather large S is attributed to the strong scattering of conduction electrons by the 4f or 5f electrons in the vicinity of the Fermi level. A Lorentzian 4f-band model, which was previously proposed for valence fluctuating compounds, reproduces the temperature dependence of S for CeRhSn and CeIrSn. However, it can not reproduce the upward curvature of S(T) at low temperatures for the U compounds. We propose here a two-5f-bands model, which consists of a narrow (5–20 meV) and a wide (37–82 meV) Lorentzian density of states. The good fitting to the data of S(T) for the above U compounds suggests the presence of two energy scales.

Superzone gap formation in UCu2Sn

Abstract Electrical resistivity, magnetic susceptibility and Hall effect were measured on a hexagonal antiferromagnet UCu 2 Sn. Below T N = 16K, the resistivity ρ sharply increases along all the a -, b - and c -axis. The anisotropic behavior, ρ b > ρ a > ρ c , suggests that the magnetic superzone gap is larger in the c -plane than along the c -axis. However, anisotropy in the magnetization for H‖a and H‖c is weak even in the antiferromagnetically ordered state. The magnetization curve of a powdered sample exhibits a spin-flop like behavior at 230 kOe.

Anisotropic transport and magnetic properties of frustrated CeRhSn

Abstract The resistivity ρ, magnetic susceptibility χ, and specific heat C were measured for a single crystal of the valence-fluctuating hexagonal system CeRhSn. Strong anisotropy in both the resistivity (ρa>ρc) and magnetic susceptibility (χc>χa) was found. A hump appears in ρc(T) below 7 K , where both C/T and χ exhibit strong upturns. Power-law behaviors χc∝T−1.1 and χa∝T−0.35 were found below 4 and 16 K , respectively, down to 0.4 K . These results suggest the presence of unquenched moments in the quasi-Kagome lattice.

Thermoelectric Properties of Single-Crystal CeRhSn with Valence Fluctuations

The thermoelectric power S, electrical resistivity ρ and thermal conductivity κ have been measured for single crystals of CeRhSn and LaRhSn with the hexagonal ZrNiAl-type structure. For CeRhSn, a broad maximum of 60 µV/K appears in S(T) along both the a- and c-axes at 160 K, being typical of a valence-fluctuating Ce compound. The ρa(T) exhibits a high maximum of 350 µΩcm at 70 K, whereas ρc(T) decreases monotonically on cooling from 300 to 1.3 K. Although the measured κ(T) for CeRhSn is smaller than that for LaRhSn, the phonon contribution κph for the former is approximately twofold that for the latter. The relation κph(LaRhSn) < κph(CeRhSn) < κph(LaRhIn) suggests that the phonon scattering induced by atomic disorder is most significant in LaRhSn. The thermoelectric figure of merit Z for CeRhSn has the maxima of 3×10-4 K-1 at 160 K and 7×10-4 K-1 at 130 K along the a- and c-axes, respectively.

Resistivity, Hall effect, and Shubnikov–de Haas oscillations in CeNiSn

The resistivity and Hall effect in CeNiSn are measured at temperatures down to 35 mK and in magnetic fields up to 20 T with the current applied along the b axis. The resistivity at zero field exhibits a quadratic temperature dependence below

Thermoelectric and magnetic properties of CeRh1−xMxSn (M=Co, Ni, Ru)

\ensuremath{\sim}0.16\mathrm{K}

Electrical resistivity of CeNiSn under uniaxial and hydrostatic pressures

with a huge coefficient of the

A study of the first-order valence transition in single crystals by magnetic susceptibility measurements

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The Fermi surface in the “Kondo semiconductor” CeNiSn

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