Heavy fermion superconductivity in the filled skutterudite PrOs4Sb12
M. Brian Maple
Department of Physics and Institute for Pure and Applied Physical Sciences, University of California, San Diego, La Jolla, California 92093, USA
The filled skutterudite compound PrOs4Sb12 was recently found to exhibit heavy fermion behavior and superconductivity below a critical temperature Tc ~ 1.85 K. The jump in specific heat at Tc, the slope of the upper critical field near Tc, and the normal state specific heat yield an electron effective mass of ~ 50 me, where me is the free electron mass. Magnetic susceptibility and inelastic neutron scattering measurements are consistent with a Pr3+ G3 nonmagnetic doublet ground state which carries an electric quadrupole moment in the cubic crystalline electric field. The heavy fermion state in PrOs4Sb12 may originate from Pr3+ electric quadrupole fluctuations, rather than magnetic dipole fluctuations. The unusual normal and superconducting state properties of PrOs4Sb12 are reviewed in this talk.
Possible Type of Heavy-Electron Superconductivity in PrOs4Sb12
Kazumasa Miyakea, Hiroshi Kohnoa, Hisatomo Harimab
aDepartment of Physical Science, Graduate School of Engineering Sience, Osaka University, Toyonaka, Osaka 560-8531, Japan
bThe Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan
Unconventional nature of superconducting state of PrOs4Sb12, Pr-based heavy electron compound with the filled Skutterudite structure, is shown to be explained on the basis of a salient structure of the crystalline-electric-field level and of the Fermi surface determined by the band structure calculation. In particular, the anisotropic pairing with a full gap on the Fermi surface, suggested by the measurement of the NMR relaxation rates 1/T1, is shown to be possible in the manifold of chiral ``p"- or ``d"-pairing symmetry, and to be compatible with the absence of the coherence peak and the pseudo-gap behavior of 1/T1T far above the superconducting transition temperature Tc.
Magnetism and Superconductivity in UT2Al3 (T=Pd, Ni) and UGe2
Noriaki K. Sato
Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
We will present magnetic and superconducting properties of uranium-based heavy fermion compounds. UPd2Al3 and UNi2Al3 shows coexistence of antiferromagnetism (AF) and superconductivity (SC); the superconducting attractive interaction of the former compound with even parity pairing is likely mediated by magnetic excitons,1 and Knight shift measurements of the latter strongly suggests an odd parity SC.2 UGe2 shows coexistence of SC with ferromagnetism; at low temperatures we have observed a unusual staircaselike hysteresis loop.3 These experimental results and a possible interpretation will be described.
Spin dynamics and sliding density-wave in Sr14Cu24O41 ladder compounds
G. Blumberga, P. Littlewoodb, A. Gozara, N. Motoyamac, H. Eisakic, S. Uchidac
aBell Laboratories, Lucent Technologies, Murray Hill, NJ 07974, USA
bUniversity of Cambridge, Cavendish Laboratory, Cambridge, CB3 0HE UK
cThe University of Tokyo, Bunkyo-ku, Tokyo 113, Japan and Stanford University, CA 94305, USA
The undoped spin 1/2 two-leg ladders have short-range magnetic order and a spin gap. The magnetic excitations out of the ground state have been observed as a sharp Raman resonance around 370 meV. Holes doped into these ladders pair and superconduct at high doping concentrations, while competing with the superconductivity insulator is known to result from low hole concentrations. Here, using transport and Raman scattering data, we identify the insulating state of self-doped two-leg spin ladders of Sr14Cu24O41 as a weakly pinned, sliding density wave. This collective density-wave state exhibits a giant dielectric response, non-linear conductivity, and persists to well above room temperature.
Spin fluctuation in Sr2Ca12Cu24O41 under high pressure up to 3.5Gpa
N. FUJIWARAa, Y. Uwatokoa, N. Môri*a, T. Matsumotob, N. Motoyamac, S. Uchidac
aInstitute of Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, Japan
bNational Research Institute for Metal, Tsukuba, Japan
cDepartment of Superconductivity, University of Tokyo, Hongo, Bunkyo-ku, Tokyo, Japan
Nuclear magnetic resonance (NMR) were performed under high pressure up to 3.5Gpa on a spin ladder system, Sr2Ca12Cu24O41. The system is nowadays well established as a low dimensional cuprate where superconducting state is realized by applying pressure of 3Gpa. In the present work, we measured relaxation rate 1/T1 on 63Cu nuclei at the normal state. 1/T1 shows an activated behavior at high temperatures above 50K although the system is metallic. The fact implies breakdown of a scenario that pressure vanishes the spin gap and then superconductivity is induced.
*Present address : Dept. of Physics, Faculty of Science, Saitama Univ., Saitama, Japan
1 N. K. Sato et al. Nature, 410 (2001) 340.
2 K. Ishida et al. to appear in Phys. Rev. Lett.
3 T. Nishioka et al. Phys. Rev. Lett., 88 (2002) 237203, and in this conference.