2,439 research outputs found
New Josephson Plasma Modes in Underdoped YBa2Cu3O6.6 Induced by Parallel Magnetic Field
The c-axis reflectivity spectrum of underdoped YBa2Cu3O6.6 (YBCO) is measured
below Tc=59K in parallel magnetic fields H//CuO2 up to 7T. Upon application of
a parallel field, a new peak appears at finite frequency in the optical
conductivity at the expense of suppression of c-axis condensate weight. We
conclude that the dramatic change originates from different Josephson coupling
strengths between bilayers with and without Josephson vortices. We find that
the 400cm^-1 broad conductivity peak in YBCO gains the spectral weight under
parallel magnetic field; this indicates that the condensate weight at \omega =0
is distributed to the intra-bilayer mode as well as to the new optical
Josephson mode.Comment: 4 pages, 3 figure
Thermodynamic properties of quadrupolar states in the frustrated pyrochlore magnet TbTiO
The low-temperature thermodynamic properties of the frustrated pyrochlore
TbTiO have been studied using the single crystal of
sitting in a long range ordered phase in the - phase diagram.
We observed that the specific heat exhibits a minimum around 2 K and slightly
increases on cooling, similar to a Schottky-like anomaly for canonical spin
ices. A clear specific-heat peak observed at K is ascribable
to the phase transition to a quadrupolar state, which contributes to a
relatively large change in entropy, J Kmol.
However, it is still smaller than for the ground state doublet of the
Tb ions. The entropy release persists to higher temperatures, suggesting strong
fluctuations associated with spin ice correlations above . We
discuss the field dependence of the entropy change for and
.Comment: 6 pages, 2 figure
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
Accelerated Sampling of Boltzmann distributions
The sampling of Boltzmann distributions by stochastic Markov processes, can
be strongly limited by the crossing time of high (free) energy barriers. As a
result, the system may stay trapped in metastable states, and the relaxation
time to the equilibrium Boltzmann distribution may be very large compared to
the available computational time. In this paper, we show how, by a simple
modification of the Hamiltonian, one can dramatically decrease the relaxation
time of the system, while retaining the same equilibrium distribution. The
method is illustrated on the case of the one-dimensional double-well potential
Quantum Critical Point of Itinerant Antiferromagnet in Heavy Fermion
A quantum critical point (QCP) of the heavy fermion Ce(Ru_{1-x}Rh_x)_2Si_2 (x
= 0, 0.03) has been studied by single-crystalline neutron scattering. By
accurately measuring the dynamical susceptibility at the antiferromagnetic wave
vector k_3 = 0.35 c^*, we have shown that the energy width Gamma(k_3), i.e.,
inverse correlation time, depends on temperature as Gamma(k_3) = c_1 + c_2
T^{3/2 +- 0.1}, where c_1 and c_2 are x dependent constants, in a low
temperature range. This critical exponent 3/2 +- 0.1 proves that the QCP is
controlled by that of the itinerant antiferromagnet.Comment: 4 pages, 3 figure
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