S. Nishizaki

Detailed topography of the fermi surface of Sr2RuO4

We apply a novel analysis of the field and angle dependence of the quantum-oscillatory amplitudes in the unconventional superconductor Sr2RuO4 to map its Fermi surface (FS) in unprecedented detail and to obtain previously inaccessible information on the band dispersion. The three quasi-2D FS sheets not only exhibit very diverse magnitudes of warping, but also entirely different dominant warping symmetries. We use the data to reassess recent results on c-axis transport phenomena.

Anisotropic superconductivity of Sr2RuO4

Abstract We report the upper critical field H c2 of single crystalline Sr 2 RuO 4 , which is the only known layered-perovskite superconductor without copper. The ratio H c2∥ ab / H c2∥ c = 26 indicates that the ruthenate is a highly anisotropic superconductor. In addition, we found a peculiar second dissipation peak only when the flux lines, as well as their induced motions, are within the ab -planes.

Calculation of thermodynamic and transport properties of Sr2RuO4 at low temperatures using known fermi surface parameters

Abstract We report the results of a study of quantum oscillations in the layered perovskite superconductor Sr 2 RuO 4 . All three predicted sheets of the Fermi surface have been observed, and we show how the measured Fermi surface parameters and quasiparticle cyclotron masses can be used to make successful quantitative predictions of a number of physical properties that can be measured independently.

Redistribution of the spectral intensity in a layered 4d-electron superconductor Sr2RuO4 observed by the photoemission spectroscopy

Abstract Spectra from photoemission spectroscopy (PES) of a recently discovered layered-perovskite superconductor Sr2RuO4 are reported. The PES spectrum of Sr2RuO4 around the Fermi level (EF) is apparently different from the non-interacting density of states obtained by a band calculation, suggesting the importance of strong electron correlation in this system.

Crossover from 3D to 2D metallic conduction in Sr2RuO4

We have investigated the normal-state conduction of superconducting Sr2RuO4 (Tc ∼ 1K), which is isostructural to La2−xSrxCuO4. The resistivity of single crystals shows a crossover at TM∼130K from 3D metallic conduction at lower temperatures to 2D one at higher temperatures. Concerning the temperature dependence of the out-of-plane resistivity, we present a systematic interpretation based on competition between the life time of the quasiparticles and the time for the quasiparticles to travel between the adjacent RuO2 planes.

Electronic Raman scattering spectra of Sr2RuO4 single crystals

Abstract Electronic Raman scattering has been measured in Sr 2 RuO 4 single crystals. We observe that the electronic Raman scattering exhibits a structureless continuum spectrum extending to beyond 4000 cm −1 . The scattering rate Γ of charge carriers, estimated from the observed Raman spectrum, shows an ω-linear increase in the higher-energy region above 500 cm −1 . This indicates strong correlation between charge carriers. In the lower-energy region the scattering rate is almost constant, Γ (0) ∼ 300 cm −1 . This value is essentially the same as that observed in high- T c copper oxides.

Spectral weight redistribution in Ca1−x Sr x VO3 and Sr2RuO4

Quasiparticle spectra of the Ca1−xSrxVO3 and Sr2RuO4 single-crystals are reported. The spectra have been measured around 14K for Ca1−xSrxVO3 and 80K for Sr2RuO4 by high-resolution angle-integrated photoemission spectroscopy. Large spectral weight redistribution has been observed in both systems, suggesting an importance of the electron correlation.

Structural and transport properties of detwinned crystals of La2−xSrxCuO4

Abstract We studied a process of detwinning of La 2− x Sr 2 CuO 4 ( x =0.14) by X-ray diffraction measurements between 5 and 300K. Detwinned crystals are obtained by cooling under a small uniaxial pressure of about 2MPa along the tetragonal 〈110〉 T direction. We also report on the effect of twin formation on the inplane transport properties.

Thermal Expansion of La2-xSrxCuO4 Single Crystals

We report on the thermal expansion coefficient α of La2−x Sr x CuO4 (x=0.14) single crystals between 5 and 300 K measured by both a capacitive method and a strain-gauge method. We have observed anomalies in α at the tetragonal-orthorhombic structural phase transition (T d1=200 K) and at the superconducting transition (T c=34 K). A thermodynamic analysis using the Ehrenfest relation shows that the pressure effects of both T d1 and T c observed in hydrostatic-pressure experiments are actually determined by the sum of compensating in-plane and c-axis uniaxial pressure coefficients with opposite signs. Using additional results obtained by X-ray diffraction at low temperatures, we will also discuss how to obtain nearly untwinned crystals below T d1.

Spin fluctuation and unconventional pairing in Sr2RuO4

Abstract Sr2RuO4 with Tc = 0.7 K with the same layered perovskite structure as La2CuO4 is the exchange-enhanced Pauli paramagnet with the two dimensional (2D) electronic structure. The superconductivity of has been found to be unconventional from the nuclear relaxation behavior exhibiting a sharp decrease with no coherence peak just below Tc and the T1T=constant behavior well below Tc. In comparison with the high-Tc Bi2Sr2CaCu2O8+y (Bi2212) and the 3D analogue of exchange-enhanced Pauli paramagnet CeCo2, the similarity and dissimilarity are presented on the normal and superconducting states.