94 research outputs found
Inflection point in the magnetic field dependence of the ordered moment of URu2Si2 observed by neutron scattering in fields up to 17 T
We have measured the magnetic field dependence of the ordered
antiferromagnetic moment and the magnetic excitations in the heavy-fermion
superconductor URu2Si2 for fields up to 17 Tesla applied along the tetragonal c
axis, using neutron scattering. The decrease of the magnetic intensity of the
tiny moment with increasing field does not follow a simple power law, but shows
a clear inflection point, indicating that the moment disappears first at the
metamagnetic transition at ~40 T. This suggests that the moment m is connected
to a hidden order parameter Phi which belongs to the same irreducible
representation breaking time-reversal symmetry. The magnetic excitation gap at
the antiferromagnetic zone center Q=(1,0,0) increases continuously with
increasing field, while that at Q=(1.4,0,0) is nearly constant. This field
dependence is opposite to that of the gap extracted from specific-heat data.Comment: 10 pages, 5 figures, submitted to PR
Pressure dependence of the magnetization of URu2Si2
The ground state of URu2Si2 changes from so-called hidden order (HO) to
large-moment antiferromagnetism (LMAF) upon applying hydrostatic pressure in
excess of 14 kbar. We report the dc-magnetization M(B,T,p) of URu2Si2 for
magnetic fields B up to 12 T, temperatures T in the range 2 to 100 K, and
pressure p up to 17 kbar. Remarkably, characteristic scales such as the
coherence temperature T*, the transition temperature T0, and the anisotropy in
the magnetization depend only weakly on the applied pressure. However, the
discontinuity in dM/dT at T0, which measures the magnetocaloric effect,
decreases nearly 50 % upon applying 17 kbar for M and B parallel to the
tetragonal c-axis, while it increases 15-fold for the a-axis. Our findings
suggest that the HO and LMAF phases have an astonishing degree of similarity in
their physical properties, but a key difference is the magnetocaloric effect
near T0 in the basal plane
Strain enhancement of superconductivity in CePd2Si2 under pressure
We report resistivity and calorimetric measurements on two single crystals of
CePd2Si2 pressurized up to 7.4 GPa. A weak uniaxial stress induced in the
pressure cell demonstrates the sensitivity of the physics to anisotropy. Stress
applied along the c-axis extends the whole phase diagram to higher pressures
and enhances the superconducting phase emerging around the magnetic
instability, with a 40% increase of the maximum superconducting temperature,
Tc, and a doubled pressure range. Calorimetric measurements demonstrate the
bulk nature of the superconductivity.Comment: 4 pages, 4 figure
Determining the crystal-field ground state in rare earth Heavy Fermion materials using soft-x-ray absorption spectroscopy
We infer that soft-x-ray absorption spectroscopy is a versatile method for
the determination of the crystal-field ground state symmetry of rare earth
Heavy Fermion systems, complementing neutron scattering. Using realistic and
universal parameters, we provide a theoretical mapping between the polarization
dependence of Ce spectra and the charge distribution of the Ce
states. The experimental resolution can be orders of magnitude larger than the
crystal field splitting itself. To demonstrate the experimental
feasibility of the method, we investigated CePdSi, thereby settling an
existing disagreement about its crystal-field ground state
Superconductivity on the threshold of magnetism in CePd2Si2 and CeIn3
The magnetic ordering temperature of some rare earth based heavy fermion
compounds is strongly pressure-dependent and can be completely suppressed at a
critical pressure, p, making way for novel correlated electron states close
to this quantum critical point. We have studied the clean heavy fermion
antiferromagnets CePdSi and CeIn in a series of resistivity
measurements at high pressures up to 3.2 GPa and down to temperatures in the mK
region. In both materials, superconductivity appears in a small window of a few
tenths of a GPa on either side of p. We present detailed measurements of
the superconducting and magnetic temperature-pressure phase diagram, which
indicate that superconductivity in these materials is enhanced, rather than
suppressed, by the closeness to magnetic order.Comment: 11 pages, including 9 figure
Disorder and relaxation mode in the lattice dynamics of PbMgNbO relaxor ferroelectric
The low-energy part of vibration spectrum in PbMgNbO
relaxor ferroelectric was studied by inelastic neutron scattering. We observed
the coexistence of a resolution-limited central peak with strong quasielastic
scattering. The line-width of the quasielastic component follows a
dependence. We find that is temperature-dependent.
The relaxation time follows the Arrhenius law well. The presence of a
relaxation mode associated with quasi-elastic scattering in PMN indicates that
order-disorder behaviour plays an important r\^ole in the dynamics of diffuse
phase transitions
Theoretical study of the dynamic structure factor of superfluid 4He
We study the dynamic structure factor of superfluid 4He
at zero temperature in the roton momentum region and beyond using
field-theoretical Green's function techniques. We start from the
Gavoret-Nozi\`{e}res two-particle propagator and introduce the concept of
quasiparticles. We treat the residual (weak) interaction between quasiparticles
as being local in coordinate space and weakly energy dependent. Our
quasiparticle model explicitly incorporates the Bose-Einstein condensate. A
complete formula for the dynamic susceptibility, which is related to , is derived. The structure factor is numerically calculated
in a self-consistent way in the special case of a momentum independent
interaction between quasiparticles. Results are compared with experiment and
other theoretical approaches.Comment: 17 pages, 16 figure
Neutron Scattering Study on Competition between Hidden Order and Antiferromagnetism in U(Ru_{1-x}Rh_x)_2Si_2 (x <= 0.05)
We have performed elastic and inelastic neutron scattering experiments on the
solid solutions U(Ru_{1-x}Rh_x)_2Si_2 for the Ru rich concentrations: x=0,
0.01, 0.02, 0.025, 0.03, 0.04 and 0.05. Hidden order is suppressed with
increasing x, and correspondingly the onset temperature T_m (~ 17.5 K at x=0)
of weak antiferromagnetic (AF) Bragg reflection decreases. For x=0.04 and 0.05,
no magnetic order is detected in the investigated temperature range down to 1.4
K. In the middle range, 0.02 <= x <= 0.03, we found that the AF Bragg
reflection is strongly enhanced. At x=0.02, this takes place at ~ 7.7 K (=T_M),
which is significantly lower than T_m (~ 13.7 K). T_M increases with increasing
x, and seems to merge with T_m at x=0.03. If the AF state is assumed to be
homogeneous, the staggered moment \mu_o estimated at 1.4 K increases from
0.02(2) \mu_B/U (x=0) to 0.24(1) \mu_B/U (x=0.02). The behavior is similar to
that observed under hydrostatic pressure (\mu_o increases to ~ 0.25 \mu_B/U at
1.0 GPa), suggesting that the AF evolution induced by Rh doping is due to an
increase in the AF volume fraction. We also found that the magnetic excitation
observed at Q=(1,0,0) below T_m disappears as T is lowered below T_M.Comment: 4 pages, 4 figures, submitted to J. Phys. Soc. Jp
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