Y. Fudamoto

Time-reversal symmetry-breaking superconductivity in Sr2RuO4

We report muon spin relaxation measurements on the superconductor Sr2RuO4 that reveal the spontaneous appearance of an internal magnetic field below the transition temperature: the appearance of such a field indicates that the superconducting state in this material is characterized by the breaking of time-reversal symmetry. These results, combined with other symmetry considerations, suggest that superconductivity in Sr2RuO4 is of p-wave (odd-parity) type, analogous to superfluid 3He.Although the properties of most superconducting materials are well described by the theory of Bardeen, Cooper and Schrieffer (BCS), considerable effort has been devoted to the search for exotic superconducting systems in which BCS theory does not apply. The transition to the superconducting state in conventional BCS superconductors involves the breaking of gauge symmetry only, whereby the wavefunction describing the Cooper pairs—the paired electron states responsible for superconductivity—adopt a definite phase. In contrast, a signature of an unconventional superconducting state is the breaking of additional symmetries, which can lead to anisotropic pairing (such as the ‘d-wave’ symmetry observed in the copper oxide superconductors) and the presence of multiple superconducting phases (as seen in UPt3 and analogous behaviour in superfluid 3He; refs 3–5). Here we report muon spin-relaxation measurements on the superconductor Sr2RuO4 that reveal the spontaneous appearance of an internal magnetic field below the transition temperature: the appearance of such a field indicates that the superconducting state in this material is characterized by the breaking of time-reversal symmetry. These results, combined with other symmetry considerations, suggest that superconductivity in Sr2RuO4 is of ‘p-wave’ (odd-parity) type, analogous to superfluid 3He.

Reduction of Ordered Moment and Néel Temperature of Quasi-One-Dimensional Antiferromagnets Sr2CuO3 and Ca2CuO3

We report elastic neutron diffraction and muon spin relaxation ({mu}SR) measurements of the quasi-one-dimensional antiferromagnets Sr{sub 2}CuO{sub 3} and Ca{sub 2}CuO{sub 3}, which have extraordinarily reduced T{sub N}/J ratios. We observe almost resolution-limited antiferromagnetic Bragg reflections in Sr{sub 2}CuO{sub 3} and obtain a reduced ordered moment size of {approximately}0.06{mu}{sub B}. We find that the ratio of ordered moment size {mu}(Ca{sub 2}CuO{sub 3})/{mu}(Sr{sub 2}CuO{sub 3})=1.5(1) roughly scales with their N{acute e}el temperatures, which suggests that the ordered moment size of quasi-one-dimensional antiferromagnets decreases continuously in the limit of vanishing interchain interactions. {copyright} {ital 1997} {ital The American Physical Society}

μSR studies of intercalated HfNCl superconductor

Abstract Muon spin relaxation measurements of the magnetic field penetration depth λ have been performed in a quasi two-dimensional (2-d) superconductor based on HfNCl intercalated with Li and organic molecules. The relaxation rate σ(T→0)∼0.5 μs −1 was obtained with transverse fields applied perpendicular to the aligned HfN planes. Using the relation σ∝λ −2 ∝n s2d /m ∗ (2-d superconducting carrier density/effective mass), we deduced the 2-d Fermi temperature TF2d. The ratio Tc/TF2d for the HfNCl-(Li) system is very close to those in two other quasi-2-d superconductors, YBa2Cu3O7 and (BEDT-TTF)2-X. Compared to the Kosterlitz–Thouless (KT) transition temperature TKT=TF2d/8 for the limit of strong coupling, Tcs of these systems are reduced by a factor of 3–4, indicating the importance of carrier overlapping and/or 3-d coupling.

New Josephson plasma modes in underdoped YBa2Cu3O6.6 induced by a parallel magnetic field.

The c-axis reflectivity spectrum of underdoped YBa2Cu3O6.6 (YBCO) is measured below T(c)=59 K in parallel magnetic fields H parallel CuO2 up to 7 T. Upon application of a parallel field, a new peak appears at finite frequency in the optical conductivity at the expense of suppression of c-axis condensate weight. We conclude that the dramatic change originates from different Josephson coupling strengths between bilayers with and without Josephson vortices. We find that the 400 cm(-1) broad conductivity peak in YBCO gains the spectral weight under parallel magnetic field; this indicates that the condensate weight at omega=0 is distributed to this peak as well as to the new optical Josephson mode.

Muon spin relaxation and susceptibility studies of the pure and diluted spin 1/2 kagomé-like lattice system (CuxZn(1-x))3V2O7(OH2) 2H2O.

Muon spin relaxation and magnetic susceptibility measurements have been performed on the pure and diluted spin 1/2 kagomé system (CuxZn(1-x))3V2O7(OH)2 2H2O. In the pure x=1 system we found a slowing down of Cu spin fluctuations with decreasing temperature towards T approximately 1 K, followed by slow and nearly temperature-independent spin fluctuations persisting down to T=50 mK, indicative of quantum fluctuations. No indication of static spin freezing was detected in either of the pure (x=1.0) or diluted samples. The observed magnitude of fluctuating fields indicates that the slow spin fluctuations represent an intrinsic property of kagomé network rather than impurity spins.

In-plane optical conductivity of La 2 − x Sr x Cu O 4 : Reduced superconducting condensate and residual Drude-like response

Temperature dependencies of the optical spectra of

Superfluid density and volume fraction of static magnetism in stripe-stabilized La1.85−yEuySr0.15CuO4

{\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}

Susceptibility inhomogeneity and non-Fermi-liquid behavior in nominally ordered UCu 4 Pd

with

Static magnetism in superconducting stage-4 La2CuO4+y(y=0.12)

x=0.12

Muon spin relaxation measurements of magnetic-field penetration depth in Ba8Si46

and 0.15 were carefully examined for a polarization parallel to the