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We present a detailed investigation of the stoichiometric CeRh$_4$Al$_{15}$ single crystal compound using the temperature dependence of the heat capacity [$C_{\text{P}}$($T$)], electrical resistivity [$\rho$($T$)], magnetic susceptibility [$\chi$($T$)], and magnetization [$M$($H$)] measurements for a magnetic field ($H$) applied in the basal plane and along the $c$-axis. The low temperature power-law behavior of $C$/$T$ $\propto$ $\chi$ $\propto$ $T^{-1+\alpha}$, the isotherm magnetization, $M \sim H^{\alpha}$ with the exponent $\alpha$ = 0.45 - 0.55, and the $T$-linear resistivity $\Delta \rho$ $\sim$ $T^\epsilon$ with $\epsilon \sim$ 1 are found to be consistent with the formation of quantum Griffiths singularities in the non-Fermi-liquid (NFL) regime. We further investigated the spin dynamics of a polycrystalline sample of CeRh$_4$Al$_{15}$, using zero-field (ZF) and longitudinal-field (LF) muon spin relaxation ($\mu$SR) measurements. ZF-$\mu$SR measurements do not reveal any sign of long-range magnetic ordering down to 70~mK. The electronic relaxation rate ($\lambda$) below 0.5~K increases rapidly and shows a thermal activation-like characteristic [$T$log($\lambda$)$\sim$ $T$] over the entire measured temperature range between 70~mK to 4~K, indicating the presence of low energy spin fluctuations in CeRh$_4$Al$_{15}$. LF-$\mu$SR measurements show a time-field ($t/H^{\eta}$) scaling of the $\mu$SR asymmetry indicating a quantum critical behavior of this compound. Furthermore, inelastic neutron scattering study on the polycrystalline sample reveals two crystal field excitations near 19 and 33~meV. These features collectively provide strong evidence of NFL behavior in CeRh$_4$Al$_{15}$ due to the formation of Griffiths phase close to a $T$ $\rightarrow$ 0~K quantum critical point., Comment: 12 pages, 5 figures

The low-carrier ordered phase below the metal-non-metal transition temperature T_MI ~ 63 K of PrRu4P12 is explored by probing magnetoresistance, magnetic susceptibility, thermoelectric power, and Hall effect on high quality single crystals. All the measured properties exhibit the signature of decimation of the Fermi surface below T_MI and anomalous behaviors below 30 K including a large thermoelectric power ~-200 uV/K and a giant negative magnetoresistance (93% at ~0.4 K). The results indicate an additional structure below 30 K and a semimetal-like ground state. The observed anomalous behaviors are most likely associated with the novel role of c-f hybridization between conduction electrons and Pr 4f electrons, whose crystalline electric field level schemes show drastic change below T_MI., Comment: 7 pages, 5 figures

We have investigated the anisotropy of the magnetoresistance in the Pr-based HF compound PrFe4P12. The large anisotropy of effective mass and its strong field dependence have been confirmed by resistivity measurements. Particularly for H||[111], where the effective mass is most strongly enhanced, the non-Fermi liquid behavior has been observed. Also, we have found the angular dependence of the magnetoresistance sharply enhanced at H||[111], which is evidently correlated with both the non-Fermi liquid behavior and the high-field ordered state (B-phase)., Comment: 3 pages, 3 figures. J. Phys. Soc. Jpn. Vol.77, No.8, in press

We report on systematic study of superconducting characteristics and Pr crystalline-electric-field (CEF) levels of filled-skutterudite \pra ($T_{\rm c}$ = 2.33 K). The temperature dependences of the upper critical field $H_{\rm c2}$ and the Ginzburg-Landau (Maki) parameter $\kappa_2$ suggest an s-wave clean-limit superconductivity. The electronic specific heat coefficient $\gamma \sim 95$ mJ/K$^2$mol, being $\sim 1.5$ times larger than that for \lra, indicates $4f$-originating quasiparticle mass enhancement. Magnetic susceptibility $\chi(T)$ indicates that the CEF ground state is a $\Gamma_1$ singlet and a $\Gamma_4^{(1)}$ triplet first excited state lies at $\Delta_{\rm CEF}\sim 30$ K above. Systematic comparison among \pos, \prs, \pra and La-based reference compounds suggests that inelastic exchange- and aspherical-charge-scatterings of conduction electrons from CEF-split $4f$ levels play an essential role for the quasiparticle mass enhancement and the value of $T_{\rm c}$ in the Pr-based filled skutterudites., Comment: 4 pages, 6 figures

We have measured the electrical resistivity, thermoelectric power, Hall coefficient, and magnetoresistance (MR) on single crystals of PrOs$_{4}$Sb$_{12}$, LaOs$_{4}$Sb$_{12}$ and NdOs$_{4}$Sb$_{12}$. All the transport properties in PrOs$_{4}$Sb$_{12}$ are similar to those in LaOs$_{4}$Sb$_{12}$ and NdOs$_{4}$Sb$_{12}$ at high temperatures, indicating the localized character of 4$f$-electrons. The transverse MR both in LaOs$_{4}$Sb$_{12}$ and PrOs$_{4}$Sb$_{12}$ tends to saturate for wide field directions, indicating these compounds to be uncompensated metals with no open orbit. We have determined the phase diagram of the field induced ordered phase by the MR measurement for all the principle field directions, which indicates an unambiguous evidence for the $\Gamma_{\rm 1}$ singlet crystalline electric field ground state., Comment: 7 pages, 10 figures, to appear in Physical Review B

We have measured both magnetoresistance and Hall effect in CeOs$_4$Sb$_{12}$ to clarify the large resistivity state ascribed to the Kondo insulating one and the origin of the phase transition near 0.9 K reported in the specific heat measurement. We found unusual temperature ($T$) dependence both in the electrical resistivity $\rho\sim T^{-1/2}$ and the Hall coefficient $R_{\rm H}\sim T^{\rm -1}$ over the wide temperature range of about two order of magnitude below $\sim30$ K, which can be explained as a combined effect of the temperature dependences of carrier density and carrier scattering by spin fluctuation. An anomaly related with the phase transition has been clearly observed in the transport properties, from which the $H-T$ phase diagram is determined up to 14 T. Taking into account the small entropy change, the phase transition is most probably the spin density wave one. Both the electrical resistivity and Hall resistivity at 0.3 K is largely suppressed about an order of magnitude by magnetic fields above $\sim3$ T, suggesting a drastic change of electronic structure and a suppression of spin fluctuations under magnetic fields., Comment: 7 pages, 6 figures

Rare 4f^2-based heavy-fermion behaviors have been revealed recently in Pr-based filled skutterudites PrFe4P12 and PrOs4Sb12. Recent studies on the thermal properties on both compounds are reported, putting emphasis on the field-induced ordered phase found in PrOs4Sb12., Comment: 4 pages, 1 eps figure, Proceedings of SCES2002 conference in Krakow/Poland

We report measurements of low-temperature specific heat on the 4f^2-based heavy-fermion superconductor PrOs4Sb12. In magnetic fields above 4.5 T in the normal state, distinct anomalies are found which demonstrate the existence of a field-induced ordered phase (FIOP). The Pr nuclear specific heat indicates an enhancement of the 4f magnetic moment in the FIOP. Utilizing a Maxwell relation, we conclude that anomalous entropy, which is expected for a single-site quadrupole Kondo model, is not concealed below 0.16 K in zero field. We also discuss two possible interpretations of the Schottky-like anomaly at ~3 K, i.e., a crystalline-field excitation or a hybridization gap formation., Comment: 5 pages with 5 figures, a note with two references added in proof

The effect of uniaxial pressure (P_u) on the magnetic susceptibility (X), magnetization (M), and magnetoresistance (MR) of the heavy-fermion metamagnet CeRu2Si2 has been investigated. For the magnetic field along the tetragonal c axis, it is found that characteristic physical quantities, i.e., the temperature of the susceptibility maximum (T_max), the pagamagnetic Weiss temperature (Q_p), 1/X at 2 K, and the magnetic field of the metamagnetic anomaly (H_M), scale approximately linearly with P_u, indicating that all the quantities are related to the same energy scale, probably of the Kondo temperature. The increase (decrease) of the quantities for P_u || c axis (P_u || a axis) can be attributed to a decrease (increase) in the nearest Ce-Ru distance. Consistently in MR and X, we observed a sign that the anisotropic nature of the hybridization, which is believed to play an important role in the metamagnetic anomaly, can be controlled by applying the uniaxial pressure. PACS numbers: 75.20.Hr, 71.27.+a, 74.62.Fj, Comment: 7 pages, ReVTeX, 6 EPS figures : Will appear in Phys. Rev. B

Specific heat and magnetization measurements have been performed on high-quality single crystals of filled-skutterudite PrFe_4P_{12} in order to study the high-field heavy-fermion state (HFS) and low-field ordered state (ODS). From a broad hump observed in C/T vs T in HFS for magnetic fields applied along the <100> direction, the Kondo temperature of ~ 9 K and the existence of ferromagnetic Pr-Pr interactions are deduced. The {141}-Pr nuclear Schottky contribution, which works as a highly-sensitive on-site probe for the Pr magnetic moment, sets an upper bound for the ordered moment as ~ 0.03 \mu_B/Pr-ion. This fact strongly indicates that the primary order parameter in the ODS is nonmagnetic and most probably of quadrupolar origin, combined with other experimental facts. Significantly suppressed heavy-fermion behavior in the ODS suggests a possibility that the quadrupolar degrees of freedom is essential for the heavy quasiparticle band formation in the HFS. Possible crystalline-electric-field level schemes estimated from the anisotropy in the magnetization are consistent with this conjecture., Comment: 7 pages and 7 figures. Accepted for publication in Phys. Rev. B

We show mathematical structure of the function dynamics, i.e., the dynamics of interval maps $f_{n+1} = (1-\e)f_n + \e f_n\circ f_n$ and clarify the types of fixed points, the self-referential structure and the hierarchical structure., Comment: 16 pages, 14 figures