176 research outputs found
Ferroelectricity from spin supercurrents in LiCuVO4
We have studied the magnetic structure of the ferroelectric frustrated
spin-1/2 chain material LiCuVO4 in applied electric and magnetic fields using
polarized neutrons. A symmetry and mean-field analysis of the data rules out
the presence of static Dzyaloshinskii-Moriya interaction, while exchange
striction is shown to be negligible by our specific-heat measurements. The
experimentally observed magnetoelectric coupling is in excellent agreement with
the predictions of a purely electronic mechanism based on spin supercurrents.Comment: 4 pages, 3 figures, final versio
Magnetic-field enhanced aniferromagnetism in non-centrosymmetric heavy-fermion superconductor CePtSi
The effect of magnetic field on the static and dynamic spin correlations in
the non-centrosymmetric heavy-fermion superconductor CePtSi was
investigated by neutron scattering. The application of a magnetic field B
increases the antiferromagnetic (AFM) peak intensity. This increase depends
strongly on the field direction: for B[0 0 1] the intensity
increases by a factor of 4.6 at a field of 6.6 T, which corresponds to more
than a doubling of the AFM moment, while the moment increases by only 10 % for
B[1 0 0] at 5 T. This is in strong contrast to the inelastic
response near the antiferromagnetic ordering vector, where no marked field
variations are observed for B[0 0 1] up to 3.8 T. The results
reveal that the AFM state in CePtSi, which coexists with superconductivity,
is distinctly different from other unconventional superconductors.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev.
Low energy spin fluctuations in the heavy fermion compound CeLaRuSi
We report inelastic neutron scattering measurements performed on a single
crystal of the heavy fermion compound CeLaRuSi,
which is at the borderline between an antiferromagnetically ordered and a
paramagnetic ground state. Intensity maps as a function of wavevector and
energy ( meV) were obtained at temperatures and 2 K, using
the time-of-flight spectrometer IRIS. An unexpected saturation of the
relaxation rate and static susceptibility of the spin fluctuations is found at
low temperatures.Comment: 2 pages, 2 figures, SCES'04 Proceeding
Vesignieite: a kagome antiferromagnet with dominant third-neighbor exchange
The spin- kagome antiferromagnet is an archetypal frustrated
system predicted to host a variety of exotic magnetic states. We show using
neutron scattering measurements that deuterated vesignieite
BaCuVO(OD), a fully stoichiometric kagome
magnet with 1% lattice distortion, orders magnetically at
K into a multi-k coplanar variant of the predicted triple-k
octahedral structure. We find this structure is stabilized by a dominant
antiferromagnetic 3-neighbor exchange with minor
1- or 2--neighbour exchange. The spin-wave
spectrum is well described by a -only model including a tiny symmetric
exchange anisotropy
Evidence of a bond-nematic phase in LiCuVO4
Polarized and unpolarized neutron scattering experiments on the frustrated
ferromagnetic spin-1/2 chain LiCuVO4 show that the phase transition at HQ of 8
Tesla is driven by quadrupolar fluctuations and that dipolar correlations are
short-range with moments parallel to the applied magnetic field in the
high-field phase. Heat-capacity measurements evidence a phase transition into
this high-field phase, with an anomaly clearly different from that at low
magnetic fields. Our experimental data are consistent with a picture where the
ground state above HQ has a next-nearest neighbour bond-nematic order along the
chains with a fluid-like coherence between weakly coupled chains.Comment: 5 pages, 4 figures. To appear in Phys. Rev. Let
Low-energy magnetic response of the noncentrosymmetric heavy-fermion superconductor CePt3Si studied via inelastic neutron scattering
The low-energy magnetic excitations of the noncentrosymmetric heavy-fermion
superconductor CePt3Si have been measured with inelastic neutron scattering on
a single crystal. Kondo-type spin fluctuations with an anisotropic wave vector
dependence are observed in the paramagnetic state. These fluctuations do not
survive in the antiferromagnetically ordered state below TN=2.2 K but are
replaced by damped spin waves, whose dispersion is much stronger along the
c-axis than in other directions. No change is observed in the excitation
spectrum or the magnetic order as the system enters the superconducting state
below Tc=0.7 K.Comment: Revised version: 8 pages, 7 figure
Superfluid 4He dynamics beyond quasiparticle excitations
The dynamics of superfluid 4He at and above the Landau quasiparticle regime
is investigated by high precision inelastic neutron scattering measurements of
the dynamic structure factor. A highly structured response is observed above
the familiar phonon-maxon-roton spectrum, characterized by sharp thresholds for
phonon-phonon, maxon-roton and roton-roton coupling processes. The experimental
dynamic structure factor is compared to the calculation of the same physical
quantity by a Dynamic Many-body theory including three-phonon processes
self-consistently. The theory is found to provide a quantitative description of
the dynamics of the correlated bosons for energies up to about three times that
of the Landau quasiparticles.Comment: 5 pages, 3 figure
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