7,339 research outputs found
The S=1/2 chain in a staggered field: High-energy bound-spinon state and the effects of a discrete lattice
We report an experimental and theoretical study of the antiferromagnetic
S=1/2 chain subject to uniform and staggered fields. Using inelastic neutron
scattering, we observe a novel bound-spinon state at high energies in the
linear chain compound CuCl2 * 2((CD3)2SO). The excitation is explained with a
mean-field theory of interacting S=1/2 fermions and arises from the opening of
a gap at the Fermi surface due to confining spinon interactions. The mean-field
model also describes the wave-vector dependence of the bound-spinon states,
particularly in regions where effects of the discrete lattice are important. We
calculate the dynamic structure factor using exact diagonalization of finite
length chains, obtaining excellent agreement with the experiments.Comment: 16 pages, 7 figures, accepted by Phys. Rev.
Phase diagram and spin Hamiltonian of weakly-coupled anisotropic S=1/2 chains in CuCl2*2((CD3)2SO)
Field-dependent specific heat and neutron scattering measurements were used
to explore the antiferromagnetic S=1/2 chain compound CuCl2 * 2((CD3)2SO). At
zero field the system acquires magnetic long-range order below TN=0.93K with an
ordered moment of 0.44muB. An external field along the b-axis strengthens the
zero-field magnetic order, while fields along the a- and c-axes lead to a
collapse of the exchange stabilized order at mu0 Hc=6T and mu0 Hc=3.5T,
respectively (for T=0.65K) and the formation of an energy gap in the excitation
spectrum. We relate the field-induced gap to the presence of a staggered
g-tensor and Dzyaloshinskii-Moriya interactions, which lead to effective
staggered fields for magnetic fields applied along the a- and c-axes.
Competition between anisotropy, inter-chain interactions and staggered fields
leads to a succession of three phases as a function of field applied along the
c-axis. For fields greater than mu0 Hc, we find a magnetic structure that
reflects the symmetry of the staggered fields. The critical exponent, beta, of
the temperature driven phase transitions are indistinguishable from those of
the three-dimensional Heisenberg magnet, while measurements for transitions
driven by quantum fluctuations produce larger values of beta.Comment: revtex 12 pages, 11 figure
Glassy relaxation without freezing in a random dipolar-coupled Ising magnet
We have measured the magnetic susceptibility, χ’+iχ’’, of the dilute dipolar-coupled Ising magnet LiHo_(0.045)Y_(0.955)F_4 over six decades of frequency from 0.02 Hz to 20 kHz. The system behaves as an ideal relaxational glass with Arrhenius behavior in temperature of the peak in χ’’. Scaling data from T=100 mK to T=300 mK by the peak in χ’’ shows an enhanced low-frequency response at high temperatures, in contrast to expectations for spin-glasses and random-field magnets
Extended quantum critical phase in a magnetized spin-1/2 antiferromagnetic chain
Measurements are reported of the magnetic field dependence of excitations in
the quantum critical state of the spin S=1/2 linear chain Heisenberg
antiferromagnet copper pyrazine dinitrate (CuPzN). The complete spectrum was
measured at k_B T/J <= 0.025 for H=0 and H=8.7 Tesla where the system is ~30%
magnetized. At H=0, the results are in quantitative agreement with exact
calculations of the dynamic spin correlation function for a two-spinon
continuum. At high magnetic field, there are multiple overlapping continua with
incommensurate soft modes. The boundaries of these continua confirm
long-standing predictions, and the intensities are consistent with exact
diagonalization and Bethe Ansatz calculations.Comment: 4 pages, 4 figure
A new constant-pressure molecular dynamics method for finite system
In this letter, by writing the volume as a function of coordinates of atoms,
we present a new constant-pressure molecular dynamics method with parameters
free. This method is specially appropriate for the finite system in which the
periodic boundary condition does not exist. Simulations on the carbon nanotube
and the Ni nanoparticle clearly demonstrate the validity of the method. By
using this method, one can easily obtain the equation of states for the finite
system under the external pressure.Comment: RevTex, 5 pages, 3 figures, submitted to Phys. Rev. Let
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