1,346 research outputs found
Strong Coupling between Antiferromagnetic and Superconducting Order Parameters in CeRhIn Studied by In-NQR Spectroscopy
We report on a novel pressure ()-induced evolution of magnetism and
superconductivity (SC) in a helical magnet CeRhIn with an incommensurate
wave vector through the In nuclear quadrupole
resonance (NQR) measurements under . Systematic measurements of the
In-NQR spectrum reveal that the commensurate antiferromagnetism (AFM)
with is realized above 1.7 GPa. An
important finding is that the size of SC gap and increase as the
magnitude of the AFM moment decreases in the region, where SC uniformly
coexists with the commensurate AFM. This result provides evidence of strong
coupling between the commensurate AFM order parameter (OP) and SC OP.Comment: 5 pages, 5 figure
Density of States and NMR Relaxation Rate in Anisotropic Superconductivity with Intersecting Line Nodes
We show that the density of states in an anisotropic superconductor with
intersecting line nodes in the gap function is proportional to for , where is the maximum value of
the gap function and is constant, while it is proportional to if
the line nodes do not intersect. As a result, a logarithmic correction appears
in the temperature dependence of the NMR relaxation rate and the specific heat,
which can be observed experimentally. By comparing with those for the heavy
fermion superconductors, we can obtain information about the symmetry of the
gap function.Comment: 7 pages, 4 PostScript Figures, LaTeX, to appear in J. Phys. Soc. Jp
Universal behavior at discontinuous quantum phase transitions
Discontinuous quantum phase transitions besides their general interest are
clearly relevant to the study of heavy fermions and magnetic transition metal
compounds. Recent results show that in many systems belonging to these classes
of materials, the magnetic transition changes from second order to first order
as they approach the quantum critical point (QCP). We investigate here some
mechanisms that may be responsible for this change. Specifically the coupling
of the order parameter to soft modes and the competition between different
types of order near the QCP. For weak first order quantum phase transitions
general results are obtained. In particular we describe the thermodynamic
behavior at this transition when it is approached from finite temperatures.
This is the discontinuous equivalent of the non-Fermi liquid trajectory close
to a conventional QCP in a heavy fermion material.Comment: 7 pages, 3 figure
High-Tc Nodeless s_\pm-wave Superconductivity in (Y,La)FeAsO_{1-y} with Tc=50 K: 75As-NMR Study
We report 75As-NMR study on the Fe-pnictide high-Tc superconductor
Y0.95La0.05FeAsO_{1-y} (Y0.95La0.051111) with Tc=50 K that includes no magnetic
rare-earth elements. The measurement of the nuclear-spin lattice-relaxation
rate 75(1/T1) has revealed that the nodeless bulk superconductivity takes place
at Tc=50 K while antiferromagnetic spin fluctuations (AFSFs) develop moderately
in the normal state. These features are consistently described by the multiple
fully-gapped s_\pm-wave model based on the Fermi-surface (FS) nesting.
Incorporating the theory based on band calculations, we propose that the reason
that Tc=50 K in Y0.95La0.051111 is larger than Tc=28 K in La1111 is that the FS
multiplicity is maximized, and hence the FS nesting condition is better than
that in La1111.Comment: 4 pages, 3 figures, accepted for publication in Phys Rev. Let
Novel phase diagram for antiferromagnetism and superconductivity in pressure-induced heavy-fermion superconductor CeRhIn probed by In-NQR
We present a novel phase diagram for the antiferromagnetism and
superconductivity in CeRhIn probed by In-NQR studies under pressure
(). The quasi-2D character of antiferromagnetic spin fluctuations in the
paramagnetic state at = 0 evolves into a 3D character because of the
suppression of antiferromagnetic order for 1.36 GPa (QCP:
antiferromagnetic quantum critical point). Nuclear-spin-lattice-relaxation rate
measurements revealed that the superconducting order occurs in the
range 1.36 -- 1.84 GPa, with maximum 0.9 K around
1.36 GPa.Comment: 5 pages, 5 figures, submitted to PR
Orbital degeneracy as a source of frustration in LiNiO
Motivated by the absence of cooperative Jahn-Teller effect and of magnetic
ordering in LiNiO, a layered oxide with triangular planes, we study a
general spin-orbital model on the triangular lattice. A mean-field approach
reveals the presence of several singlet phases between the SU(4) symmetric
point and a ferromagnetic phase, a conclusion supported by exact
diagonalizations of finite clusters. We argue that one of the phases,
characterized by a large number of low-lying singlets associated to dimer
coverings of the triangular lattice, could explain the properties of LiNiO,
while a ferro-orbital phase that lies nearby in parameter space leads to a new
prediction for the magnetic properties of NaNiO.Comment: 18 pages, 17 figure
Two-Staged Magnetoresistance Driven by Ising-like Spin Sublattice in SrCo6O11
A two-staged, uniaxial magnetoresistive effect has been discovered in
SrCo6O11 having a layered hexagonal structure. Conduction electrons and
localized Ising spins are in different sublattices but their interpenetration
makes the conduction electrons sensitively pick up the stepwise
field-dependence of magnetization. The stepwise field-dependence suggests two
competitive interlayer interactions between ferromagnetic Ising-spin layers,
i.e., a ferromagnetic nearest-layer interaction and an antiferromagnetic
next-nearest-layer interaction. This oxide offers a unique opportunity to study
nontrivial interplay between conduction electrons and Ising spins, the coupling
of which can be finely controlled by a magnetic field of a few Tesla.Comment: 14 pages, 4 figures, accepted for publication in Phys. Rev. Let
Spin Susceptibility of Noncentrosymmetric Heavy-fermion Superconductor CeIrSi3 under Pressure: 29Si-Knight Shift Study on Single Crystal
We report 29Si-NMR study on a single crystal of the heavy-fermion
superconductor CeIrSi3 without an inversion symmetry along the c-axis. The
29Si-Knight shift measurements under pressure have revealed that the spin
susceptibility for the ab-plane decreases slightly below Tc, whereas along the
c-axis it does not change at all. The result can be accounted for by the spin
susceptibility in the superconducting state being dominated by the strong
antisymmetric (Rashba-type) spin-orbit interaction that originates from the
absence of an inversion center along the c-axis and it being much larger than
superconducting condensation energy. This is the first observation which
exhibits an anisotropy of the spin susceptibility below Tc in the
noncentrosymmetric superconductor dominated by strong Rashba-type spin-orbit
interaction.Comment: 4 pages, 4 figures, Accepted for publication in Phys. Rev. Let
Emergent Phases of Nodeless and Nodal Superconductivity Separated by Antiferromagnetic Order in Iron-based Superconductor (Ca4Al2O6)Fe2(As1-xPx)2: 75As- and 31P-NMR Studies
We report P- and As-NMR studies on
(CaAlO)Fe(AsP) with an isovalent substitution
of P for As. We present the novel evolution of emergent phases that the
nodeless superconductivity (SC) in 00.4 and the nodal one around
=1 are intimately separated by the onset of a commensurate stripe-type
antiferromagnetic (AFM) order in 0.5 0.95, as an isovalent
substitution of P for As decreases a pnictogen height measured from
the Fe plane. It is demonstrated that the AFM order takes place under a
condition of 1.32\AA1.42\AA, which is also the case for other
Fe-pnictides with the Fe state in (Fe) layers. This novel
phase evolution with the variation in points to the importance of
electron correlation for the emergence of SC as well as AFM order.Comment: 5pages, 4figures; accepted for publication as a Rapid Communication
in Phys. Rev.
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