Ryuji Higashinaka

Superconductivity in Layered Pnictides BaRh2P2 and BaIr2P2

Bulk superconductivity was discovered in BaRh2P2 (Tc = 1.0 K) and BaIr2P2 (Tc = 2.1 K), which are isostructural to (Ba,K)Fe2As2, indicative of the appearance of superconductivity over a wide variety of layered transition metal pnictides. The electronic specific heat coefficient gamma in the normal state, 9.75 and 6.86 mJ/mol K2 for BaRh2P2 and BaIr2P2 respectively, indicate that the electronic density of states of these two compounds are moderately large but smaller than those of Fe pnictide superconductors. The Wilson ratio close to 1 indeed implies the absence of strong electron correlations and magnetic fluctuations unlike Fe pnictides.

Anisotropic release of the residual zero-point entropy in the spin ice compound Dy2Ti2O7: Kagome ice behavior

We report the specific heat and entropy of single crystals of the spin ice compound

Pronounced −Log T Divergence in Specific Heat of Nonmetallic CeOBiS2: A Mother Phase of BiS2-Based Superconductor

{\mathrm{Dy}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}

Anomalously Field-Insensitive Correlated Electron Behaviors in SmTa2Al20

at temperatures down to 0.35 K. We apply magnetic fields along the four characteristic directions [100], [110], [111], and [112]. Because of Ising anisotropy, we observe anisotropic release of the residual zero-point entropy, attributable to the difference in frustration dimensionality. In the high magnetic field along these four directions, the residual entropy is almost fully released and the activation entropy reaches

Single Crystal Growth and Low Temperature Properties of PrNb2Al20

R\mathrm{ln}2.

Fermi surfaces and orbital polarization in superconducting CeO0.5 F0.5BiS2 revealed by angle-resolved photoemission spectroscopy

However, in the intermediate-field region, the entropy in the fields along the [111] direction is different from those for the other three field directions. For the [111] direction, the frustration structure changes from that of the three-dimensional pyrochlore to that of a two-dimensional Kagome-like lattice with constraint due to the ice rule, leading to different values of the zero-point entropy.

Magnetodielectric response of the spin-ice Dy2Ti2O7

The low-temperature properties of CeOBiS2 single crystals are studied by electrical resistivity, magnetization, and specific heat measurements. Ce 4f-electrons are found to be in a well-localized state split by crystalline-electric-field (CEF) effects. The CEF ground state is a pure Jz = ±1/2 doublet, and excited doublets are located far above. At low temperatures in zero field, we observe pronounced −log T divergence in the specific heat, revealing the presence of quantum critical fluctuations of 4f magnetic moments near a quantum critical point (QCP). Considering that CeOBiS2 is a nonmetal, this phenomenon cannot be attributed to the competition between Kondo and the Ruderman–Kittel–Kasuya–Yosida (RKKY) interactions as in numerous f-electron-based strongly correlated metals, indicating an unconventional mechanism. We suggest that CeOBiS2 is the first material found to be located at a QCP among geometrically frustrated nonmetallic magnets.

Low Temperature Specific Heat of Dy2Ti2O7 in the Kagome Ice State

The low-temperature properties of single crystals of SmTa2Al20 have been studied by electrical resistivity, magnetization, and specific heat measurements. A λ-type peak structure, indicating a phase transition, was found in the specific heat at \(T_{\text{x}} = 2.0\) K. From an analysis of the nuclear specific heat contribution, the ordered moment is estimated to be 0.22 µB/Sm, which is largely suppressed from 0.84 µB/Sm for a free Sm3+ ion. The Kondo-like \(-{\log T}\) dependence of resistivity and the suppressed effective magnetic moment of 0.09 µB/Sm above \(T_{\text{x}}\) indicate strong \(c\)–\(f\) hybridization. The largely enhanced specific heat divided by temperature of about 3 J/(mol K2) below 0.4 K suggests the formation of extremely heavy quasiparticles in the ordered state. A notable feature commonly observed in all of these behaviors is robustness against magnetic fields. We discuss the possible relevance of multipole moments in the quartet ground state to the robustness against magnetic fields.

Field-induced transition on a triangular plane in the spin-ice compound Dy2Ti2O7

Magnetization, electrical resistivity and specific heat measurements were performed on single crystals of PrNb 2 Al 20 grown by Al self-flux method. No evident anomalies suggesting phase transitions has been found down to 0.6 K. In all measurements, there appear features indicative of crystalline electric field levels with the energy splitting of ∼ 50 K. The monotonically increasing M – H curve at 2 K suggests a nonmagnetic Γ 1 singlet or a non-Kramers Γ 3 doublet ground state. In addition, low-lying excitations in 4 f -electron system remain down to 2 K remain and the associated features (a low temperature upturn in C / T and a non-Fermi liquid behavior in ρ) are observed.

Strong Effect of Yb Filling Fraction on the Magnetic Ground Sate of the Filled Skutterudite YbFe4Sb12

We have investigated the electronic structure of BiS