56 research outputs found
Phonon lineshapes in the vortex state of the phonon-mediated superconductor YNiBC
We present an inelastic neutron scattering study of phonon lineshapes in the
vortex state of the type-II superconductor YNiBC. In a previous study
[Phys. Rev. Lett. \textbf{101}, 237002 (2008)] it was shown that certain
phonons exhibit a clear signature of the superconducting gap on
entering the superconducting state. Our interest was to find out whether or not
the lineshape of such phonons reflects the inhomogeneous nature of the vortex
state induced by a magnetic field smaller than the upper critical field
.We found that this is indeed the case because the observed phonon
lineshapes can be well described by a model considering the phonon as a local
probe of the spatial variation of the superconducting gap. We found that even
at , where the inter-vortex distance is less than \AA, the
phonon lineshape still shows evidence for a variation of the gap
Magnon Bose condensation in symmetry breaking magnetic field
Magnon Bose condensation (BC)in the symmetry breaking magnetic field is a
result of unusual form of the Zeeman energy, which has terms linear in the
spin-wave operators and terms mixing excitations differ in the Wave-vector of
the magnetic structure. The following examples are considered: simple
easy-plane tetragonal antiferromagnets (AF), frustrated AF family
where etc. and cubic magnets with the Dzyaloshinskii-Moriya
interaction ( etc.). In all cases the BC becomes important when the
magnetic field becomes comparable with the spin-wave gap. The theory is
illustrated by existing experimental results.Comment: Submitted to J. of Phys. Condens. Matter (Proceedings of
International Conference "Highly Frustrated Magnets", Osaka (Japan), August
2006). 8 pages, 5 figure
Hysteresis and Anisotropic Magnetoresistance in Antiferromagnetic
The out-of-plane resistivity () and magnetoresistivity (MR) are
studied in antiferromangetic (AF) single crystals, which
have three types of noncollinear antiferromangetic spin structures. The
apparent signatures are observed in measured at the zero-field and
14 T at the spin structure transitions, giving a definite evidence for the
itinerant electrons directly coupled to the localized spins. One of striking
feature is an anisotropy of the MR with a fourfold symmetry upon rotating the
external field (B) within ab plane in the different phases, while twofold
symmetry at spin reorientation transition temperatures. The intriguing thermal
hysteresis in and magnetic hysteresis in MR are observed at spin
reorientation transition temperatures.Comment: 4 pages, 4 figure
Silicon resonant microcantilevers for absolute pressure measurement
This work is focused on the developing of silicon resonant microcantilevers for the measurement of the absolute pressure. The microcantilevers have been fabricated with a two-mask bulk micromachining process. The variation in resonance response of microcantilevers was investigated as a function of pressure 10−1-105 Pa, both in terms of resonance frequency and quality factor. A theoretical description of the resonating microstructure is given according to different molecular and viscous regimes. Also a brief discussion on the different quality factors contributions is presented. Theoretical and experimental data show a very satisfying agreement. The microstructure behavior demonstrates a certain sensitivity over a six decade range and the potential evolution of an absolute pressure sensor working in the same rang
Superexchange coupling and spin susceptibility spectral weight in undoped monolayer cuprates
A systematic inelastic neutron scattering study of the superexchange
interaction in three different undoped monolayer cuprates (La_2CuO_4, Nd_2CuO_4
and Pr_2CuO_4) has been performed using conventional triple axis technique. We
deduce the in-plane antiferromagnetic (AF) superexchange coupling which
actually presents no simple relation versus crystallographic parameters. The
absolute spectral weight of the spin susceptibility has been obtained and it is
found to be smaller than expected even when quantum corrections of the AF
ground state are taken into account.Comment: 13 pages, 1 table, 3 figure
Effect of a magnetic field on the long-range magnetic order in insulating Nd2CuO4, nonsuperconducting and superconducting Nd1.85Ce0.15CuO4
We have measured the effect of a c-axis aligned magnetic field on the
long-range magnetic order of insulating Nd2CuO4, as-grown nonsuperconducting
and superconducting Nd1.85Ce0.15CuO4. On cooling from room temperature, Nd2CuO4
goes through a series of antiferromagnetic (AF) phase transitions with
different noncollinear spin structures. In all phases of Nd2CuO4, we find that
the applied c-axis field induces a canting of the AF order but does not alter
the basic zero-field noncollinear spin structures. Similar behavior is also
found in as-grown nonsuperconducting Nd1.85Ce0.15CuO4. These results contrast
dramatically with those of superconducting Nd1.85Ce0.15CuO4, where a c-axis
aligned magnetic field induces a static, anomalously conducting, long-range
ordered AF state. We confirm that the annealing process necessary to make
superconducting Nd1.85Ce0.15CuO4 also induces epitaxial, three-dimensional
long-range ordered cubic (Nd,Ce)2O3 as an impurity phase. In addition, the
annealing process makes a series of quasi two-dimensional superlattice
reflections associated with lattice distortions of Nd1.85Ce0.15CuO4 in the CuO2
plane. While the application of a magnetic field will induce a net moment in
the impurity phase, we determine its magnitude and eliminate this as a
possibility for the observed magnetic field-induced effect in superconducting
Nd1.85Ce0.15CuO4.Comment: 12 pages, 10 figures, to be published in Phys. Rev.
SU(2)U(1) Gauge Symmetry in High Superconductivity
The square lattice structure of layers and the strongly correlated
property of electrons indicate that the high superconductivity in
cuprates can be described by a SO(5) coherent pairing state in which a
SU(2)U(1) gauge symmetry is embedded. The spin and charge
fluctuations that characterize the low energy magnetic excitations in cuprates
are controlled by this intrinsic SU(2)U(1) gauge symmetry.Comment: 4 pages Revtex fil
SPIN CORRELATIONS IN THE INSULATING SPIN GLASS FexMg1-xCl2
Spin correlations have been studied in the dilute system FexMg1-xCl2 for x = 0.45 and x = 0.55 by neutron scattering. In Fe0.55Mg0.45Cl2, the correlation lengths ξ|| and ξ⊥ are found to decrease abruptly above 30 kG and reach at 50 kG values of 14 Å of the same order of magnitude as those of Fe0.45Mg0.55Cl2
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