975 research outputs found
Large magnetic field-induced spectral weight enhancement of high-energy spin excitations in
We report electronic Raman scattering experiments on a superconducting single crystal in a magnetic field. At low
temperatures, the spectral weight of the high-energy two-magnon peak increases
linearly with field and is amplified by a factor of more than two at 14 T. The
effect disappears at elevated temperatures and is not present in undoped . This observation is discussed in terms of an electronically
inhomogeneous state in which the field enhances the volume fraction of a phase
with local antiferromagnetic order at the expense of the superconducting phase.Comment: to appear in PR
Spin-Wave Lifetimes Throughout the Brillouin Zone
We use a neutron spin-echo method with eV resolution to determine the
lifetimes of spin waves in the prototypical antiferromagnet MnF over the
entire Brillouin zone. A theory based on the interaction of magnons with
longitudinal spin fluctuations provides an excellent, parameter-free
description of the data, except at the lowest momenta and temperatures. This is
surprising, given the prominence of alternative theories based on magnon-magnon
interactions in the literature. The results and technique open up a new avenue
for the investigation of fundamental concepts in magnetism. The technique also
allows measurement of the lifetimes of other elementary excitations (such as
lattice vibrations) throughout the Brillouin zone.Comment: 12 pages, 4 figure
Magnetic structure of the edge-sharing copper oxide chain compound NaCu2O2
Single-crystal neutron diffraction has been used to determine the
incommensurate magnetic structure of NaCu2O2, a compound built up of chains of
edge-sharing CuO4 plaquettes. Magnetic structures compatible with the lattice
symmetry were identified by a group-theoretical analysis, and their magnetic
structure factors were compared to the experimentally observed Bragg
intensities. In conjunction with other experimental data, this analysis yields
an elliptical helix structure in which both the helicity and the polarization
plane alternate among copper-oxide chains. This magnetic ground state is
discussed in the context of the recently reported multiferroic properties of
other copper-oxide chain compounds
Coherent Modulation of the YBa2Cu3O6+x Atomic Structure by Displacive Stimulated Ionic Raman Scattering
We discuss the mechanism of coherent phonon generation by Stimulated Ionic
Raman Scattering, a process different from conventional excitation with near
visible optical pulses. Ionic Raman scattering is driven by anharmonic coupling
between a directly excited infrared-active phonon mode and other Raman modes.
We experimentally study the response of YBa2Cu3O6+x to the resonant excitation
of apical oxygen motions at 20 THz by mid-infrared pulses, which has been shown
in the past to enhance the interlayer superconducting coupling. We find
coherent oscillations of four totally symmetric (Ag) Raman modes and make a
critical assessment of the role of these oscillatory motions in the enhancement
of superconductivity.Comment: 12 pages, 4 figure
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