3,409 research outputs found
Evidence for incommensurate spin fluctuations in Sr_2RuO_4
We report first inelastic neutron scattering measurements in the normal state
of Sr_2RuO_4 that reveal the existence of incommensurate magnetic spin
fluctuations located at . This
finding confirms recent band structure calculations that have predicted
incommensurate magnetic responses related to dynamical nesting properties of
its Fermi surface
Gap Structure of the Spin-Triplet Superconductor Sr2RuO4 Determined from the Field-Orientation Dependence of Specific Heat
We report the field-orientation dependent specific heat of the spin-triplet
superconductor Sr2RuO4 under the magnetic field aligned parallel to the RuO2
planes with high accuracy. Below about 0.3 K, striking 4-fold oscillations of
the density of states reflecting the superconducting gap structure have been
resolved for the first time. We also obtained strong evidence of multi-band
superconductivity and concluded that the superconducting gap in the active
band, responsible for the superconducting instability, is modulated with a
minimum along the [100] direction.Comment: 4 pages, 4 figure
Muon-spin-relaxation and magnetic-susceptibility studies of effects of the magnetic impurity Ni on the Cu-spin dynamics and superconductivity in La_2-x_Sr_x_Cu_1-y_Ni_y_O_4_ with x = 0.13
Effects of the magnetic impurity Ni on the Cu-spin dynamics and
superconductivity have been studied in La_2-x_Sr_x_Cu_1-y_Ni_y_O_4_ with x =
0.13 changing y finely up to 0.10. Compared with the case of the nonmagnetic
impurity Zn, it has been found from the muon-spin-relaxation measurements that
a large amount of Ni is required to stabilize a magnetic order of Cu spins.
However, the evolution toward the stabilization of the magnetic order with
increasing impurity concentration is qualitatively similar to each other. The
area of the non-superconducting and slowly fluctuating or static region of Cu
spins around Ni has been found to be smaller than that around Zn, suggesting
that the pinning of rather long-ranged dynamical spin correlation such as the
so-called dynamical stripe by Ni is weaker than that by Zn. This may be the
reason why Zn destroys the superconductivity in the hole-doped high-T_c_
cuprates more markedly than Ni.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev.
Tunnelling spectroscopy of the interface between Sr2RuO4 and a single Ru micro-inclusion in eutectic crystals
The understanding of the zero bias conductance peak (ZBCP) in the tunnelling
spectra of S/N junctions involving d-wave cuprate superconductors has been
important in the determination of the phase structure of the superconducting
order parameter. In this context, the involvement of a p-wave superconductor
such as Sr2RuO4 in tunnelling studies is indeed of great importance. We have
recently succeeded in fabricating devices that enable S/N junctions forming at
interfaces between Sr2RuO4 and Ru micro-inclusions in eutectic crystals to be
investigated.3 We have observed a ZBCP and have interpreted it as due to the
Andreev bound state, commonly seen in unconventional superconductors. Also we
have proposed that the onset of the ZBCP may be used to delineate the phase
boundary for the onset of a time reversal symmetry broken (TRSB) state within
the superconducting state, which does not always coincide with the onset of the
superconducting state. However, these measurements always involved two
interfaces between Sr2RuO4 and Ru. In the present study, we have extended the
previous measurements to obtain a deeper insight into the properties of a
single interface between Sr2RuO4 and Ru.Comment: To appear in J. Phys. Soc. Jpn. Vol. 75 No.12 issu
Spin-triplet superconductivity due to antiferromagnetic spin-fluctuation in Sr_2RuO_4
A mechanism leading to the spin-triplet superconductivity is proposed based
on the antiferromagnetic spin fluctuation. The effects of anisotropy in spin
fluctuation on the Cooper pairing and on the direction of d vector are examined
in the one-band Hubbard model with RPA approximation. The gap equations for the
anisotropic case are derived and applied to Sr_2RuO_4. It is found that a
nesting property of the Fermi surface together with the anisotropy leads to the
triplet superconductivity with the d=z(sin{k_x}\pm isin{k_y}), which is
consistent with experiments.Comment: 4 pages, 3 eps figures, revte
The ground state of Sr3Ru2O7 revisited; Fermi liquid close to a ferromagnetic instability
We show that single-crystalline Sr3Ru2O7 grown by a floating-zone technique
is an isotropic paramagnet and a quasi-two dimensional metal as spin-triplet
superconducting Sr2RuO4 is. The ground state is Fermi liquid with very low
residual resistivity (3 micro ohm cm for in-plane currents) and a nearly
ferromagnetic metal with the largest Wilson ratio Rw>10 among paramagnets so
far. This contrasts with the ferromagnetic order at Tc=104 K reported on single
crystals grown by a flux method [Cao et al., Phys. Rev. B 55, R672 (1997)]. We
have also found a dramatic changeover from paramagnetism to ferromagnetism
under applied pressure. This suggests the existence of a substantial
ferromagnetic instability on the verge of a quantum phase transition in the
Fermi liquid state.Comment: 5 pages, 4 figures, to be published in Phys. Rev. B : Rapid co
Spin triplet superconductivity with line nodes in Sr2RuO4
Several possible odd-parity states are listed up group-theoretically and
examined in light of recent experiments on SrRuO. Those include some of
the -wave pairing states, {\mib d}({\mib k})\propto{\hat{\mib z}}
k_xk_y(k_x + {\rm i}k_y) and {\hat{\mib z}} (k_x^2-k_y^2)(k_x + {\rm i}k_y)
and other {\hat{\mib z}} (k_x + {\rm i}k_y)\cos ck_z ( is the -axis
lattice constant) as most plausible candidates. These are time-reversal
symmetry broken states and have line nodes running either vertically (the
former two) or horizontally (the latter), consistent with experiments.
Characterizations of these states and other possibilities are given.Comment: 4 pages, no figure
Interface superconductivity in the eutectic Sr2RuO4-Ru: 3-K phase of Sr2RuO4
The eutectic system Sr2RuO4-Ru is referred to as the 3-K phase of the
spin-triplet supeconductor Sr2RuO4 because of its enhanced superconducting
transition temperature Tc of ~3 K. We have investigated the field-temperature
(H-T) phase diagram of the 3-K phase for fields parallel and perpendicular to
the ab-plane of Sr2RuO4, using out-of-plane resistivity measurements. We have
found an upturn curvature in the Hc2(T) curve for H // c, and a rather gradual
temperature dependence of Hc2 close to Tc for both H // ab and H // c. We have
also investigated the dependence of Hc2 on the angle between the field and the
ab-plane at several temperatures. Fitting the Ginzburg-Landau effective-mass
model apparently fails to reproduce the angle dependence, particularly near H
// c and at low temperatures. We propose that all of these charecteric features
can be explained, at least in a qualitative fashion, on the basis of a theory
by Sigrist and Monien that assumes surface superconductivity with a
two-component order parameter occurring at the interface between Sr2RuO4 and Ru
inclusions. This provides evidence of the chiral state postulated for the 1.5-K
phase by several experiments.Comment: 7 pages and 5 figs; accepted for publication in Phys. Rev.
Multiple Superconducting Phases in New Heavy Fermion Superconductor PrOs4Sb12
The superconducting gap structure of recently discovered heavy fermion
superconductor PrOs4Sb12 was investigated by using thermal transport
measurements in magnetic field rotated relative to the crystal axes. We
demonstrate that a novel change in the symmetry of the superconducting gap
function occurs deep inside the superconducting state, giving a clear
indication of the presence of two distinct superconducting phases with twofold
and fourfold symmetries. We infer that the gap functions in both phases have a
point node singularity, in contrast to the familiar line node singularity
observed in almost all unconventional superconductors.Comment: 4 Pages, 4 Figure
Observation of vortex coalescence in the anisotropic spin-triplet superconductor SrRuO
We present direct imaging of magnetic flux structures in the anisotropic,
spin-triplet superconductor SrRuO using a scanning SQUID
microscope. Individual quantized vortices were seen at low magnetic fields.
Coalescing vortices forming flux domains were revealed at intermediate fields.
Based on our observations we suggest that a mechanism intrinsic to the material
stabilizes the flux domains against the repulsive vortex-vortex interaction.
Topological defects like domain walls can provide this, implying proof for
unconventional chiral superconductivity.Comment: submitted to PR
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