Harima Hisatomo

Novel Kondo Behaviors Realized in the Filled Skutterudite Structure

Novel Kondo-like behaviors realized in the Pr-based filled skutterudites are reviewed based on the electronic transport properties, specific heat and de Haas–van Alphen (dHvA) experiments, along wi...

Novel Features Realized in the Filled Skutterudite Structure

Full varieties of strongly correlated electron phenomena have been found in the filled skutterudite systems, by changing the constituent elements. The unique crystal structure leads to novel features even in the systems containing rare earth elements with plural number of 4 f -electrons. According to the intensive competitions and cooperation among experimental and theoretical research works, remarkable progress has been made in sorting out several basic origins that bring about the variety of this system, such as the strong c – f hybridization, the small CEF level splitting, the orbital degree of freedom (multipoles), and the positional degree of freedom within a pnictogen cage. However, there still remain many attractive questions to be answered.

Specific heat and de haas-van alphen experiments on the heavy-fermion superconductor CePt3Si

Specific heat and de Haas–van Alphen (dHvA) measurements were performed on a high-quality single crystal of CePt 3 Si without inversion symmetry in the tetragonal crystal structure. We observed distinct peaks in the specific heat C at the superconducting transition temperature T c =0.46 K and the antiferromagnetic ordering temperature T N =2.25 K, compared to the previous data, indicating an improvement of the sample quality. The temperature dependence of the electronic specific heat coefficient C e / T below about 0.3 K is well described by the equation of C e / T =γ s +β s T with γ s =34.1 mJ/(K 2 ·mol) and β s =1290 mJ/(K 3 ·mol), evidencing the existence of line nodes in the superconducting energy gap. Furthermore, the electronic specific heat coefficient γ s in the superconducting state indicates a nonlinear magnetic field dependence \(\gamma_{\text{s}}(H)\propto\sqrt{H}\), which also supports the presence of line nodes. We did not observe a discontinuous change of the Fermi surface at P AF =0.6 GPa ...

Heavy Fermions in YbAl 3 Studied by the de Haas-van Alphen Effect

We carried out the de Haas-van Alphen (dHvA) experiment in YbAl 3 with the cubic crystal structure. One of the six dHvA branches, named β with a dHvA frequency of 4.5×10 7 Oe, is nearly spherical in topology and has a large cyclotron mass of 23.9 m 0 . The other branches were observed only in small angular regions centered at symmetrical directions. Their cyclotron masses are in the range from 13.5 to 17.4 m 0 . The topology of the Fermi surface cannot be explained by the conventional band model because the fully occupied 4 f -levels in YbAl 3 are below the Fermi level. A small alteration so as to shift upwards the 4 f -levels is necessary to fit to the experimental dHvA data. These give a direct evidence that the 4 f -electrons form heavy fermions at low temperatures, which is most likely related to the many-body Kondo effect.

Fermi surface and Yamaji effect in Sr2RuO4

We have observed the de Haas-van Alphen (dHvA) oscillation of Sr 2 RuO 4 , the layered perovskite superconductor not based on copper. The Fermi surface was confirmed to be a corrugated cylinder. This characteristic feature of the Fermi surface brings about a large angular dependence of the dHvA amplitude, which is explained by the spin-splitting zero in the dHvA oscillation and the Yamaji effect.

Split Fermi Surface Properties of LaTGe3 (T: Transition Metal) and PrCoGe3 with the Non-centrosymmetric Crystal Structure

We succeeded in growing single crystals of LaTGe 3 (T: Fe, Co, Rh, Ir) and PrCoGe 3 with the non-centrosymmetric tetragonal crystal structure, and studied the split Fermi surface properties and the magnitude of the antisymmetric spin–orbit interaction 2|α p ⊥ |. The 2|α p ⊥ | value is found to vary when LaTGe 3 is changed from T = Co, Rh to Ir, but remains unchanged in LaIrX 3 from X = Si to Ge. It is found that this 2|α p ⊥ | value is large in LaIrSi 3 and LaIrGe 3 : 2|α p ⊥ | = 460 K in LaCoGe 3 , 510 K in LaRhGe 3 , 1100 K in LaIrSi 3 , and 1090 K in LaIrGe 3 for the main outer orbits named α of bands 69 and 70 electron Fermi surfaces, for example. This is due to the large effective atomic number of Ir and a large distribution of the radial wave function of Ir-5 d electrons close to the nuclear center, compared with those of Co and Rh. In the case of a paramagnet PrCoGe 3 and LaFeGe 3 with the relatively large cyclotron mass, the corresponding 2|α p ⊥ | value is found to become small: 2|α p ⊥ | = 280 a...

Fermi Surface Meets Multipoles in Skutterudites

In many trivalent filled skutterudites physical properties are characterized by the nesting property of the main Fermi surface and the mutipole orderings. The main conduction band consists of Pnictogen p -orbitals with the symmetry of x y z , and the Fermi surface shows a good nesting property with q =(1, 0, 0). The Coulomb potential up to the sixth order term can couple with such the Pnictogen molcular orbital, as it is the third order term symmetry x y z . Therefore, the orbital multipoles up to rank 6 (hexacontatetrapole moment), originating in 4 f electrons affect the main conduction band in the filled skutterudites. Anti-ferromagnetically ( q =(1, 0, 0)) higher multipole ordering can be assisted by the Fermi surface nesting, to open a gap at the Fermi level, as typically realized in PrRu 4 P 12 . In other many skutterudites, there exist other Fermi surfaces to suppress the anti-ferromagnetically ordering, however multipole moments may change the Fermi surface volumes, because it affects only the main...

Magnetoresistance and de Haas-van Alphen Effect in UPt3

We have done the transverse magnetoresistance and the de Haas-van Alphen (dHvA) experiments in UPt 3 . The magnetoresistance increases in the whole field direction. UPt 3 is thus a compensated metal, possessing no open orbits. As for the dHvA experiment, we have observed at least three new branches. One of them is in the basal plane and the others are around the [0001] direction. The branches with dHvA frequencies of 2.7×10 7 Oe and 4.9×10 7 Oe in the field along [0001] possess large masses of 40–50 m 0 . These results have been discussed on the basis of the 5 f -itinerant Fermi surface model.

Theory of Metal–Insulator Transition in Praseodymium Skutterudite Compounds

The metal–insulator transition of PrRu 4 P 12 and the non-magnetic phase transition of PrFe 4 P 12 are theoretically investigated. The nesting property of the Fermi surface with q =(1,0,0) is coupled, through Fe/Ru displacements, with anti-quadrupolar ordering at the phase transitions. Coupling between phonon modes of the displacements of the Fe/Ru ions and the Pr 4 f 2 ground state doublet leads to a symmetry lowering (1,1,-2) type distortion of the Fe/Ru positions and a simultaneous splitting of the 4 f 2 doublet into eigenstates with quadrupole moments ±8. The sign of both the distortion and the quadrupole moment alternate from site to site, resulting in anti-quadrupolar ordering. The difference between these two compounds stems from another small Fermi surface in PrFe 4 P 12 ; the presence of this band would suppress the metal-insulator transition in PrFe 4 P 12 , even after the nesting effect is taken into account. Therefore, the low temperature state of PrFe 4 P 12 is expected to remain metallic.

Rattling and Superconducting Properties of the Cage Compound GaxV2Al20

Low-energy rattling modes and their effects on superconductivity are studied in the cage compound Ga x V 2 Al 20 . A series of polycrystalline samples of 0 < x ≤0.6 are examined through resistivity...