Koichi Izawa

Multiband superconductivity in the heavy fermion compound PrOs4Sb12.

The thermal conductivity of the heavy fermion superconductor Pr(Os(4)Sb(12) was measured down to T(c)/40 throughout the vortex state. At lowest temperatures and for magnetic fields H approximately 0.07H(c2), already 40% of the normal state thermal conductivity is restored. This behavior (similar to that observed in MgB2) is a clear signature of multiband superconductivity in this compound.

Twofold spontaneous symmetry breaking in the heavy-fermion superconductor UPt3.

The field-orientation dependent thermal conductivity of the heavy-fermion superconductor UPt3 was measured down to very low temperatures and under magnetic fields throughout the distinct superconducting phases: B and C phases. In the C phase, a striking twofold oscillation of the thermal conductivity within the basal plane is resolved reflecting the superconducting gap structure with a line of node along the a axis. Moreover, we find an abrupt vanishing of the oscillation across a transition to the B phase, as a clear indication of a change of gap symmetries. We also identify extra two line nodes below and above the equator in both B and C phases. From these results together with the symmetry consideration, the gap function of UPt3 is determined as a E(1u) representation characterized by a combination of two line nodes at the tropics and point nodes at the poles.

The Origin of Magnetic Field Dependence of Specific Heat in Single-Crystalline CeNiSn

The effect of magnetic field on the electronic ground state in CeNiSn has been investigated by means of specific-heat measurement in magnetic fields µ 0 H up to 14 T. A high-quality single crystal allows us to observe a marked field effect on specific heat in the temperature range from 2 to 25 K. The ground state is discussed in terms of a pseudo-gapped density of states in the Kondo resonance band with residual states at the Fermi level inducing the Zeeman splitting.

Transport anomalies across the quantum limit in semimetallic Bi 0.96 Sb 0.04

We report on a study of electronic transport in semimetallic

Verification of the Wiedemann-Franz law in YbRh2Si2 at a quantum critical point.

{text{Bi}}_{0.96}{text{Sb}}_{0.04}

Quadrupole-driven non-Fermi-liquid and magnetic-field-induced heavy fermion states in a non-Kramers doublet system

. At zero field, the system is a very dilute Fermi liquid displaying a

Pairing Symmetry of UPt3 Probed by Thermal Transport Tensors

{T}^{2}

Thermoelectric response near a quantum critical point of β-YbAlB4 and YbRh2Si2: a comparative study.

resistivity with an enhanced prefactor. Quantum oscillations in resistivity as well as in Hall, Nernst, and Seebeck responses of the system are detectable and their period quantifies the shrinking of the Fermi surface with antimony doping. For a field along the trigonal axis, the quantum limit was found to occur at a field as low as 3 T. An ultraquantum anomaly at twice this field was detected in both charge transport and Nernst response. Its origin appears to lie beyond the one-particle picture and linked to unidentified many-body effects.

Anomalous Enhancement of Seebeck Coefficient in Pr-Based 1-2-20 System with Non-Kramers Doublet Ground States

The thermal conductivity measurements are performed on the heavy-fermion compound YbRh(2)Si(2) down to 0.04 K and under magnetic fields through a quantum critical point (QCP) at B(c)=0.66u2009u2009T∥c axis. In the limit as T→0, we find that the Wiedemann-Franz law is satisfied within experimental error at the QCP despite the destruction of the standard signature of Fermi liquid. Our results place strong constraints on models that attempt to describe the nature of the unconventional quantum criticality of YbRh(2)Si(2).

Thermal Conductivity through the Quantum Critical Point in YbRh_{2}Si_{2} at Very Low Temperature.

Orbital degrees of freedom in condensed matters could play important roles in forming a variety of exotic electronic states by interacting with conduction electrons. In 4f electron systems, because of strong intra-atomic spin-orbit coupling, an orbitally degenerate state inherently carries quadrupolar degrees of freedom. The present work has focussed on a purely quadrupole-active system PrIr2Zn20 showing superconductivity in the presence of an antiferroquadrupole order at TQ = 0.11 K. We observed non-Fermi liquid (NFL) behaviors emerging in the electrical resistivity and the 4f contribution to the specific heat, C_4f, in the paramagnetic state at T > TQ. Moreover, in magnetic fields below 6 T, all data set of the electrical resistivity and C_4f(T) are well scaled with characteristic temperatures T0s. This is the first observation of the NFL state in the nonmagnetic quadrupole-active system, whose origin is intrinsically different from that observed in the vicinity of the conventional quantum critical point. It implies possible formation of a quadrupole Kondo lattice resulting from hybridization between the quadrupoles and the conduction electrons. Below 0.13 K, the electrical resistivity and C_4f(T) exhibit anomalies as B approaches 5 T. This is the manifestation of a field-induced crossover toward a Fermi-liquid ground state in the quadrupole Kondo lattice.