282 research outputs found
Metamagnetic Quantum Criticality Revealed by 17O-NMR in the Itinerant Metamagnet Sr3Ru2O7
We have investigated the spin dynamics in the bilayered perovskite Sr3Ru2O7
as a function of magnetic field and temperature using 17O-NMR. This system sits
close to a metamagnetic quantum critical point (MMQCP) for the field
perpendicular to the ruthenium oxide planes. We confirm Fermi-liquid behavior
at low temperatures except for a narrow field region close to the MMQCP. The
nuclear spin-lattice relaxation rate divided by temperature 1/T1T is enhanced
on approaching the metamagnetic critical field of 7.9 T and at the critical
field 1/T1T continues to increase and does not show Fermi- liquid behavior down
to 0.3 K. The temperature dependence of T1T in this region suggests the
critical temperature Theta to be 0 K, which is a strong evidence that the spin
dynamics possesses a quantum critical character. Comparison between uniform
susceptibility and 1/T1T reveals that antiferromagnetic fluctuations instead of
two-dimensional ferromagnetic fluctuations dominate the spin fluctuation
spectrum at the critical field, which is unexpected for itinerant
metamagnetism.Comment: 5 pages, 4 figures, Accepted by Phys. Rev. Let
Eastward traverse of equatorial plasma plumes observed with the Equatorial Atmosphere Radar in Indonesia
The zonal structure of radar backscatter plumes associated with Equatorial Spread F (ESF), probably modulated by atmospheric gravity waves, has been investigated with the Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (0.20° S, 100.32° E; dip latitude 10.1° S) and the FM-CW ionospheric sounders on the same magnetic meridian as the EAR. The occurrence locations and zonal distances of the ESF plumes were determined with multi-beam observations with the EAR. The ESF plumes drifted eastward while keeping distances of several hundred to a thousand kilometers. Comparing the occurrence of the plumes and the F-layer uplift measured by the FM-CW sounders, plumes were initiated within the scanned area around sunset only, when the F-layer altitude rapidly increased. Therefore, the PreReversal Enhancement (PRE) is considered as having a zonal variation with the scales mentioned above, and this variation causes day-to-day variability, which has been studied for a long time. Modulation of the underlying E-region conductivity by gravity waves, which causes inhomogeneous sporadic-E layers, for example, is a likely mechanism to determine the scale of the PRE
Microscopic Mechanism for Staggered Scalar Order in PrFe4P12
A microscopic model is proposed for the scalar order in PrFe4P12 where f2
crystalline electric field (CEF) singlet and triplet states interact with two
conduction bands. By combining the dynamical mean-field theory and the
continuous-time quantum Monte Carlo, we obtain an electronic order with
staggered Kondo and CEF singlets with the total conduction number being unity
per site. The ground state becomes semimetallic provided that the two
conduction bands have different occupation numbers. This model naturally
explains experimentally observed properties in the ordered phase of PrFe4P12
such as the scalar order parameter, temperature dependence of the resistivity,
field-induced staggered moment, and inelastic features in neutron scattering.
The Kondo effect plays an essential role for ordering, in strong contrast with
ordinary magnetic orders by the RKKY interaction.Comment: 4 pages, 4figure
Anisotropic low field behavior and the observation of flux jumps in CeCoIn5
The magnetic behavior of the heavy fermion superconductor CeCoIn5 has been
investigated. The low field magnetization data show flux jumps in the mixed
state of the superconducting phase in a restricted range of temperature. These
flux jumps begin to disappear below 1.7 K, and are completely absent at 1.5 K.
The magnetization loops are asymmetric, suggesting that surface and geometrical
factors dominate the pinning in this system. The lower critical field (Hc1),
obtained from the magnetization data, shows a linear temperature dependence and
is anisotropic. The calculated penetration depth is also anisotropic, which is
consistent with the observation of an anisotropic superconducting gap in
CeCoIn5. The critical currents, determined from the high field isothermal
magnetization loops, are comparatively low (around 4000 A/cm2 at 1.6 K and 5
kOe).Comment: 4 pages 3 figure
Phenomenological theory of a scalar electronic order: application to skutterudite PrFe4P12
By phenomenological Landau analysis, it is shown that a scalar order
parameter with the point-group symmetry explains most properties
associated with the phase transition in PrFeP at 6.5 K. The
scalar-order model reproduces magnetic and elastic properties in
PrFeP consistently such as (i) the anomaly of the magnetic
susceptibility and elastic constant at the transition temperature, (ii)
anisotropy of the magnetic susceptibility in the presence of uniaxial pressure,
and (iii) the anomaly in the elastic constant in magnetic field. An Ehrenfest
relation is derived which relates the anomaly of the magnetic susceptibility to
that of the elastic constant at the transition.Comment: 16 pages, 9 figure
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