279 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
Diffraction from Ordered States of Higher Multipoles
Possible ways of identification are discussed of an electronic order of
higher multipoles such as octupoles and hexadecapoles. A particularly powerful
method is resonant X-ray scattering (RXS) using quadrupolar resonance processes
called E2.The characteristic azimuthal angle dependence of
CeLaB is interpreted as evidence of antiferro-octupole
order. For PrRuP, eightfold pattern against azimuthal angle is
predicted if its metal-insulator transition is a consequence of a hexadecapole
order. In non-resonant superlattice Bragg scattering, hexadecapole contribution
may also be identified because of absence of quadrupole component.Comment: Invited paper to be published in Proc. Hiroshima Workshop on Novel
Functional Materials with Multinary Freedoms (Physica B, 2006
Anomalous Anisotropic Magnetoresistance in Heavy-Fermion PrFe4P12
We have investigated the anisotropy of the magnetoresistance in the Pr-based
HF compound PrFe4P12. The large anisotropy of effective mass and its strong
field dependence have been confirmed by resistivity measurements. Particularly
for H||[111], where the effective mass is most strongly enhanced, the non-Fermi
liquid behavior has been observed. Also, we have found the angular dependence
of the magnetoresistance sharply enhanced at H||[111], which is evidently
correlated with both the non-Fermi liquid behavior and the high-field ordered
state (B-phase).Comment: 3 pages, 3 figures. J. Phys. Soc. Jpn. Vol.77, No.8, in pres
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
On the origin of multiple ordered phases in PrFe4P12
The nature of multiple electronic orders in skutterudite PrFe_4P_{12} is
discussed on the basis of a model with antiferro-quadrupole (AFQ) interaction
of \Gamma_3 symmetry. The high-field phase can be reproduced qualitatively
provided (i) ferro-type interactions are introduced between the dipoles as well
as between the octupoles of localized f-electrons, and (ii) separation is
vanishingly small between the \Gamma_1-\Gamma_4^{(1)} crystalline electric
field (CEF) levels. The high-field phase can have either the same ordering
vector q=(1,0,0) as in the low-field phase, or a different one q=0 depending on
the parameters. In the latter case, distortion of the crystal perpendicular to
the (111) axis is predicted. The corresponding anomaly in elastic constants
should also appear. The electrical resistivity is calculated with account of
scattering within the CEF quasi-quartet. It is found that the resistivity as a
function of the direction of magnetic field shows a sharp maximum around the
(111) axis at low temperatures because of the level crossing.Comment: 16 pages, 5 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
Field-angle-dependent specific heat measurements and gap determination of a heavy fermion superconductor URu2Si2
To identify the superconducting gap structure in URu2Si2 we perform
field-angle-dependent specific heat measurements for the two principal
orientations in addition to field rotations, and theoretical analysis based on
microscopic calculations. The Sommerfeld coefficient \gamma(H)'s in the mixed
state exhibit distinctively different field-dependence. This comes from point
nodes and substantial Pauli paramagnetic effect of URu2Si2. These two features
combined give rise to a consistent picture of superconducting properties,
including a possible first order transition of Hc2 at low temperatures.Comment: 4 pages, 5 figures, to appear in Phys. Rev. Let
High magnetic field phase diagram of PrOs4Sb12
The magnetic phase diagram of PrOsSb has been investigated by
specific heat measurements between 8 and 32 T. A new Schottky anomaly due to
excitations between two lowest crystalline-electric-field (CEF) singlets, has
been found for both and above the field
where the field-induced ordered phase (FIOP) is suppressed. The constructed
phase diagram shows weak magnetic anisotropy and implies a crossing of
the two CEF levels at about 8 - 9 T for both field directions. These results
provide an unambiguous evidence for the singlet being the CEF ground
state and suggest the level crossing (involving lowest CEF levels) as the
driving mechanism of FIOP.Comment: Submitted to Phys. Rev. Let
Charge Kondo effect toward a non-Fermi-liquid fixed point in the orbitally degenerate exchange model
We show that a Kondo-type model with an orbital degeneracy has a new
non-Fermi-liquid fixed point. Near the fixed point the spin degrees of freedom
are completely quenched, and the residual charge degrees of freedom lead to the
multi-channel Kondo effect. Anomalous behavior appears in electric and thermal
properties, but the magnetic susceptibility should show the local Fermi-liquid
behavior. The non-Fermi-liquid fixed point becomes unstable against
perturbations breaking the particle-hole symmetry. We derive these results
using the third-order scaling for a spherically symmetric model with a
fictitious spin. In contrast to the Coqblin-Schrieffer model, the present model
respects different time-reversal properties of multipole operators.Comment: 4 pages, 2 eps figures, to appear in J. Phys. Soc. Jpn. 68 No.
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