201 research outputs found
Antiferromagnetism and hot spots in CeIn
Enormous mass enhancement at ''hot spots'' on the Fermi surface (FS) of
CeIn has been reported at strong magnetic field near its antiferromagnetic
(AFM) quantum critical point [T. Ebihara et al., Phys. Rev. Lett. 93, 246401
(2004)] and ascribed to anomalous spin fluctuations at these spots. The ''hot
spots'' lie at the positions on FS where in non-magnetic LaIn the narrow
necks are protruded. In paramagnetic phase CeIn has similar spectrum. We
show that in the presence of AFM ordering its FS undergoes a topological change
at the onset of AFM order that truncates the necks at the ''hot spots'' for one
of the branches. Applied field leads to the logarithmic divergence of the dHvA
effective mass when the electron trajectory passes near or through the neck
positions. This effect explains the observed dHvA mass enhancement at the ''hot
spots'' and leads to interesting predictions concerning the spin-dependence of
the effective electron mass. The (T,B)-phase diagram of CeIn, constructed
in terms of the Landau functional, is in agreement with experiment.Comment: 4 pages, 1 figur
Further analysis of the quantum critical point of CeLaRuSi
New data on the spin dynamics and the magnetic order of
CeLaRuSi are presented. The importance of the Kondo
effect at the quantum critical point of this system is emphasized from the
behaviour of the relaxation rate at high temperature and from the variation of
the ordered moment with respect to the one of the N\'eel temperature for
various .Comment: Contribution for the Festschrift on the occasion of Hilbert von
Loehneysen 60 th birthday. To be published as a special issue in the Journal
of Low Temperature Physic
New Superconducting and Magnetic Phases Emerge on the Verge of Antiferromagnetism in CeIn
We report the discovery of new superconducting and novel magnetic phases in
CeIn on the verge of antiferromagnetism (AFM) under pressure () through
the In-nuclear quadrupole resonance (NQR) measurements. We have found a
-induced phase separation of AFM and paramagnetism (PM) without any trace
for a quantum phase transition in CeIn. A new type of superconductivity
(SC) was found in GPa to coexist with AFM that is magnetically
separated from PM where the heavy fermion SC takes place. We propose that the
magnetic excitations such as spin-density fluctuations induced by the
first-order magnetic phase transition might mediate attractive interaction to
form Cooper pairs.Comment: 4 pages, 4 EPS figures, submitted to J. Phys. Soc. Jp
Superconductivity mediated by a soft phonon mode: specific heat, resistivity, thermal expansion and magnetization of YB6
The superconductor YB6 has the second highest critical temperature Tc among
the boride family MBn. We report measurements of the specific heat,
resistivity, magnetic susceptibility and thermal expansion from 2 to 300 K,
using a single crystal with Tc = 7.2 K. The superconducting gap is
characteristic of medium-strong coupling. The specific heat, resistivity and
expansivity curves are deconvolved to yield approximations of the phonon
density of states, the spectral electron-phonon scattering function and the
phonon density of states weighted by the frequency-dependent Grueneisen
parameter respectively. Lattice vibrations extend to high frequencies >100 meV,
but a dominant Einstein-like mode at ~8 meV, associated with the vibrations of
yttrium ions in oversized boron cages, appears to provide most of the
superconducting coupling and gives rise to an unusual temperature behavior of
several observable quantities. A surface critical field Hc3 is also observed.Comment: 29 pages, 5 tables, 17 figures. Accepted for publication in Phys.
Rev.
Avpr1a variant associated with preschoolers' lower altruistic behavior
10.1371/journal.pone.0025274PLoS ONE69
Orbital-based Scenario for Magnetic Structure of Neptunium Compounds
In order to understand a crucial role of orbital degree of freedom in the
magnetic structure of recently synthesized neptunium compounds NpTGa_5 (T=Fe,
Co, and Ni), we propose to discuss the magnetic phase of an effective
two-orbital model, which has been constructed based on a j-j coupling scheme to
explain the magnetic structure of uranium compounds UTGa_5. By analyzing the
model with the use of numerical technique such as exact diagonalization, we
obtain the phase diagram including several kinds of magnetic states. An
orbital-based scenario is discussed to understand the change in the magnetic
structure among C-, A-, and G-type antiferromagnetic phases, experimentally
observed in NpFeGa_5, NpCoGa_5, and NpNiGa_5.Comment: 18 pages, 8 figures, to appear in New Journal of Physic
Dichotomy between the hole and electrons behavior in the multiband FeSe probed by ultra high magnetic fields
Magnetoresistivity \r{ho}xx and Hall resistivity \r{ho}xy in ultra high
magnetic fields up to 88T are measured down to 0.15K to clarify the multiband
electronic structure in high-quality single crystals of superconducting FeSe.
At low temperatures and high fields we observe quantum oscillations in both
resistivity and Hall effect, confirming the multiband Fermi surface with small
volumes. We propose a novel and independent approach to identify the sign of
corresponding cyclotron orbit in a compensated metal from magnetotransport
measurements. The observed significant differences in the relative amplitudes
of the quantum oscillations between the \r{ho}xx and \r{ho}xy components,
together with the positive sign of the high-field \r{ho}xy , reveal that the
largest pocket should correspond to the hole band. The low-field
magnetotransport data in the normal state suggest that, in addition to one hole
and one almost compensated electron bands, the orthorhombic phase of FeSe
exhibits an additional tiny electron pocket with a high mobility.Comment: Latex, 4 pages (2 figures, 1 table), and supplemental materia
Pressure Evolution of the Magnetic Field induced Ferromagnetic Fluctuation through the Pseudo-Metamagnetism of CeRu2Si2
Resistivity measurements performed under pressure in the paramagnetic ground
state of CeRu2Si2 are reported. They demonstrate that the relative change of
effective mass through the pseudo metamagnetic transition is invariant under
pressure. The results are compared with the first order metamagnetic transition
due to the antiferromagnetism of Ce0.9La0.1Ru2Si2 which corresponds to the
"negative" pressure of CeRu2Si2 by volume expansion. Finally, we describe the
link between the spin-depairing of quasiparticles on CeRu2Si2 and that of
Cooper pairs on the unconventional heavy fermion superconductor CeCoIn5.Comment: 5 pages, 6 figures, accepted for publication in J. Phys. Soc. Jp
Unconventional Superconductivity in Heavy Fermion Systems
We review the studies on the emergent phases of superconductvity and
magnetism in the -electron derived heavy-fermion (HF) systems by means of
the nuclear-quadrupole-resonance (NQR) under pressure. These studies have
unraveled a rich variety of the phenomena in the ground state of HF systems. In
this article, we highlight the novel phase diagrams of magnetism and
unconventional superconductivity (SC) in CeCuSi, HF antiferromagnets
CeRhIn, and CeIn. A new light is shed on the difference and common
features on the interplay between magnetism and SC on the magnetic criticality.Comment: 15 pages, 13 figures, to appear in J. Phys. Soc. JPN, 74, No.1
(2005), special issue "Kondo Effect- 40 Years after the Discovery
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