Honda Fuminori

Field-Induced Antiferromagnetism and Upper Critical Field in Pressure-Induced Superconductor CeRhIn5

An antiferromagnet CeRhIn 5 is well known to be changed into a superconductor by applying pressure P . Its electronic state is also clarified to be changed at the critical pressure P c ≃2.5 GPa under magnetic fields. We measured the low-temperature electrical resistivity of CeRhIn 5 in magnetic fields up to 17 T and at pressures up to 2.45 GPa, and constructed phase diagrams. At P = 2.45 GPa, which is close to P c ≃2.5 GPa, there are four kinds of phases, namely, the paramagnetic, superconducting, superconducting and antiferromagnetic, and antiferromagnetic phases in the temperature vs magnetic field phase diagram. The antiferromagnetic phase is found to be induced in the superconducting phase under magnetic fields and expanded in magnetic fields higher than the upper critical field in superconductivity. Interestingly, the anisotropy of the upper critical field in CeRhIn 5 is found to be different from that in a similar non-magnetic heavy-fermion superconductor CeCoIn 5 , revealing the anisotropic paramag...

Pressure-Induced Superconductivity in Antiferromagnet CePd5Al2

A layered compound CePd 5 Al 2 , which is an analog of a heavy fermion superconductor NpPd 5 Al 2 , is found to be an antiferromagnet with an easy-axis along the tetragonal [001] direction but becomes superconductive in the pressure region from 9 to 12 GPa, with the superconducting transition temperature, T sc = 0.57 K and the upper critical field at 0 K, H c2 (0) = 2.5 kOe, at 10.8 GPa. The quasi-two dimensional Fermi surfaces are also theoretically calculated for CePd 5 Al 2 on the basis of the 4 f -itinerant band model.

Field-Induced Quadrupolar Ordered Phase for H∥ in Heavy-Fermion Compound YbCo2Zn20

Magnetic susceptibility, high-field magnetization up to 500 kOe, and specific heat in a wide temperature range from 0.06 to 300 K were measured for single crystals of the cubic heavy-fermion compound YbCo 2 Zn 20 in order to elucidate the electronic states of the compound at low temperatures. A strong increase in the magnetic specific heat in the form of C mag / T below ∼1 K is approximately explained by the resonant level model for S = 1/2 with the Kondo temperature T K = 1 K, and an extremely large C mag / T ≃8 J/(K 2 ·mol) below about 0.2 K is explained by considering the magnetic entropy of the doublet ground state in the 4 f crystalline electric field (CEF) scheme of an Yb 3+ ion, which corresponds to an extremely large electronic specific heat coefficient. The field-induced ordered phase for H ∥ , which has recently been found by low-temperature magnetization measurements, was precisely studied by electrical resistivity and specific heat measurements, and was observed in a limited angular range ...

Effect of Pressure and Magnetic Field on the Superconducting State of a Heavy Fermion Superconductor NpPd5Al2

We have carried out the electrical resistivity measurements under high pressures and high magnetic fields in NpPd 5 Al 2 in order to investigate a quantum critical behavior and the stability of the superconducting phase. A T -linear dependence of the electrical resistivity is changed into the Fermi liquid relation of ρ∼ A T 2 under the magnetic fields, and A value indicates a divergent feature around the upper critical field H c2 , indicating the existence of a field-tuned quantum critical point (QCP) around H c2 . With increasing pressure, the superconducting transition temperature T sc decreases and becomes zero above 5.7 GPa, together with a decrease of the upper critical field, indicating that the electronic state of NpPd 5 Al 2 is located in the vicinity of QCP at ambient pressure and deviates from QCP with increasing pressure. Furthermore, we have constructed the superconducting phase diagram at 3.71 GPa.

Pressure-Induced Valence Transition and Characteristic Electronic States in EuRh2Si2

EuRh2Si2 is well known to show a valence transition at a pressure of about 1 GPa from a Eu-divalent (antiferromagnetic) state to a nearly Eu-trivalent (paramagnetic) state, which was clarified using polycrystalline samples. We have succeeded in growing single crystals of EuRh2Si2 by the Bridgman method and studied their electronic properties measuring the electrical resistivity under pressure. EuRh2Si2 indicates a first-order valence transition in the pressure range from 1 to 2 GPa, distinguished by a sharp transition and a prominent hysteresis in the temperature dependence of the electrical resistivity. A critical end point in the valence transition is estimated as \(P_{\text{CEP}} \simeq 2.05\) GPa and \(T_{\text{CEP}} \simeq 170\) K. In the pressure range from 2 to 3 GPa, the electrical resistivity is found to exhibit a characteristic behavior for a moderately heavy-fermion compound such as EuIr2Si2. At pressures higher than 3 GPa, the resistivity reveals a normal metallic behavior in a nearly trivalen...

High-Quality Single Crystal Growth and Unique Electronic States under Magnetic Field and Pressure in Rare Earth and Actinide Compounds

The f electrons in rare earth and actinide compounds exhibit variety of characteristic properties including heavy fermions and unconventional superconductivity. Fermi surface properties in rare earth and actinide compounds such as CeSn 3 , USi 3 , NpGe 3 and PuIn 3 are clarified by the de Haas–van Alphen experiments on the basis of the results of energy band calculations. An abrupt nonlinear increase of magnetization, namely metamagnetic behavior is found in the heavy fermion compounds including YbT 2 Zn 20 (T: Co, Rh, Ir). An effect of pressure on the electronic state of YbIr 2 Zn 20 and antiferromagnets CeRhIn 5 and CeIrSi 3 are also studied in magnetic fields. The electronic instability including unconventional superconductivity occurs at about 2.4 GPa in CeRhIn 5 and 2.6 GPa in CeIrSi 3 .

Characteristic Heavy Fermion Properties in YbCu2Si2 and YbT2Zn20 (T: Co, Rh, Ir)

We studied the Fermi surface properties of YbCu 2 Si 2 and YbCu 2 Ge 2 with the tetragonal structure by measuring the de Haas–van Alphen (dHvA) oscillations, together with the energy band calculations. It was clarified that 4 f electrons contribute to the Fermi surface of a valence fluctuating compound YbCu 2 Si 2 , but not to that of a divalent compound YbCu 2 Ge 2 . Namely, the Fermi surface of YbCu 2 Si 2 contains the 4 f -components considerably and the corresponding cyclotron effective mass m c * of the main Fermi surface is large, m c * =30–40 m 0 ( m 0 : rest mass of an electron). We also studied the heavy fermion properties of YbT 2 Zn 20 (T: Co, Rh, Ir) with the cubic caged structure. The metamagnetic behavior or an abrupt nonlinear increase of magnetization was observed at 6 kOe in YbCo 2 Zn 20 , 63 kOe in YbRh 2 Zn 20 , and 97 kOe in YbIr 2 Zn 20 for H ∥ , which was measured at 60 mK in YbCo 2 Zn 20 and 1.3 K in YbRh 2 Zn 20 and YbIr 2 Zn 20 . The metamagnetic field is found to be a good pa...

Electronic and Magnetic Properties in Heavy Fermion Ferromagnet YbPdGe

The crystal structure of YbPdGe is orthorhombic, with a large lattice constant for the b -axis. Reflecting this crystal structure, the electronic state is well conductive in the a – c plane. Magnetically YbPdGe is a ferromagnet with a Curie temperature T C = 11.4 K, and ferromagnetic moments are most likely oriented along the b -axis. The electronic specific heat coefficient γ=150 mJ/(K 2 ·mol) and a reduced magnetic entropy at T C suggest that YbPdGe is a heavy fermion ferromagnet.

Multiple Metamagnetic Transitions in Antiferromagnet Yb2Pt2Pb with the Shastry–Sutherland Lattice

From the magnetization and magnetoresistance measurements, we constructed the magnetic phase diagram of Yb 2 Pt 2 Pb with the Shastry–Sutherland lattice, which consists of characteristic two phases below 1 K with many metamagnetic transitions, revealing magnetic frustrations.

Split Fermi Surface Properties of VSi2 without Mirror Planes in the Chiral Crystal Structure

VSi2 is hexagonal in the crystal structure, and the basal plane stacks along the [0001] direction. Interestingly, each plane is rotated by 60\circ relative to the neighboring one. Therefore, there exist no mirror planes in this chiral structure. We carried out a de Haas–van Alphen (dHvA) experiment and clarified the Fermi surface properties. Each dHvA branch was found to be split into two branches on the basis of the antisymmetric spin–orbit interaction. The magnitude of the antisymmetric spin–orbit interaction in this chiral structure was determined for the first time to be 19 K for dHvA branch α (dHvA frequency \(F = 7.9 \times 10^{7}\) Oe and cyclotron mass \(m^{*}_{\text{c}} = 1.6\) \(m_{0}\)), 39 K for branch β (\(F = 4.1 \times 10^{7}\) Oe and \(m^{*}_{\text{c}} = 3.4\) \(m_{0}\)), and 110 K for branch γ (\(F = 1.8 \times 10^{7}\) Oe and \(m^{*}_{\text{c}} = 2.3\) \(m_{0}\)). These dHvA branches correspond to the main Fermi surfaces, which are well explained by the results of the energy band calcula...