468 research outputs found
Fermi surface of the filled-skutterudite superconductor LaRu4P12: A clue to the origin of the metal-insulator transition in PrRu4P12
We report the de Haas-van Alphen (dHvA) effect and magnetoresistance in the
filled-skutterudite superconductor LaRu4P12, which is a reference material of
PrRu4P12 that exhibits a metal-insulator (M-I) transition at T_MI~60 K. The
observed dHvA branches for the main Fermi surface (FS) are well explained by
the band-structure calculation, using the full potential linearized
augmented-plane-wave method with the local-density approximation, suggesting a
nesting instability with q =(1,0,0) in the main multiply connected FS as
expected also in PrRu4P12. Observed cyclotron effective masses of
(2.6-11.8)m_0, which are roughly twice the calculated masses, indicate the
large mass enhancement even in the La-skutterudites. Comparing the FS between
LaRu4P12 and PrRu4P12, an essential role of c-f hybridization cooperating with
the FS nesting in driving the the M-I transition in PrRu4P12 has been
clarified.Comment: Appeared in Physical Review
Specific heat evidence for two-gap superconductivity in ternary-iron silicide LuFeSi
We report low-temperature specific heat studies on single-crystalline
ternary-iron silicide superconductor LuFeSi with = 6.1 K
down to . We confirm a reduced normalized jump in specific heat at
, and find that the specific heat divided by temperature shows
sudden drop at and goes to zero with further decreasing
temperature. These results indicate the presence of two distinct
superconducting gaps in LuFeSi, similar to a typical two-gap
superconductor MgB. We also report Hall coefficients, band structure
calculation, and the anisotropy of upper critical fields for
LuFeSi, which support the anisotropic multiband nature and
reinforce the existence of two superconducting gaps in
LuFeSi.Comment: 5 pages, 5 figure
Role of p-f Hybridization in the Metal-Non-Metal Transition of PrRu4P12
Electronic state evolution in the metal-non-metal transition of PrRu4P12 has
been studied by X-ray and polarized neutron diffraction experiments. It has
been revealed that, in the low-temperature non-metallic phase, two inequivalent
crystal-field (CF) schemes of Pr3+ 4f^2 electrons with Gamma_1 and Gamma_4^(2)
ground states are located at Pr1 and Pr2 sites forming the bcc unit cell
surrounded by the smaller and larger cubic Ru-ion sublattices, respectively.
This modulated electronic state can be explained by the p-f hybridization
mechanism taking two intermediate states of 4f^1 and 4f^3. The p-f
hybridization effect plays an important role for the electronic energy gain in
the metal-non-metal transition originated from the Fermi surface nesting.Comment: 5 pages, 5 figures. Accepted by J. Phys. Soc. Jp
Drastic change in transport of entropy with quadrupolar ordering in PrFeP
The antiferroquadrupolar ordering of PrFeP is explored by
probing thermal and thermoelectric transport. The lattice thermal conductivity
drastically increases with the ordering, as a consequence of a large drop in
carrier concentration and a strong electron-phonon coupling. The low level of
carrier density in the ordered state is confirmed by the anomalously large
values of the Seebeck and Nernst coefficients. The results are reminiscent of
URuSi and suggest that both belong to the same class of aborted
metal-insulator transitions. The magnitude of the Nernst coefficient, larger
than in any other metal, indicates a new route for Ettingshaussen cooling at
Kelvin temperatures.Comment: final published versio
Evidence for ferromagnetic spin-pairing superconductivity in UGe: A Ge-NQR study under pressure
We report that a novel type of superconducting order parameter has been
realized in the ferromagnetic states in UGe via Ge
nuclear-quadrupole-resonance (NQR) experiments performed under pressure ().
Measurements of the nuclear spin-lattice relaxation rate have
revealed an unconventional nature of superconductivity such that the up-spin
band is gapped with line nodes, but the down-spin band remains gapless at the
Fermi level. This result is consistent with that of a ferromagnetic
spin-pairing model in which Cooper pairs are formed among ferromagnetically
polarized electrons. The present experiment has shed new light on a possible
origin of ferromagnetic superconductivity, which is mediated by ferromagnetic
spin-density fluctuations relevant to the first-order transition inside the
ferromagnetic states.Comment: 5 pages, 5 figure
Competition between unconventional superconductivity and incommensurate antiferromagnetic order in CeRh1-xCoxIn5
Elastic neutron diffraction measurements were performed on the quasi-two
dimensional heavy fermion system CeRh1-xCoxIn5, ranging from an incommensurate
antiferromagnet for low x to an unconventional superconductor on the Co-rich
end of the phase diagram. We found that the superconductivity competes with the
incommensurate antiferromagnetic (AFM) order characterized by qI=(1/2, 1/2,
delta) with delta=0.298, while it coexists with the commensurate AFM order with
qc=(1/2, 1/2, 1/2). This is in sharp contrast to the CeRh1-xIrxIn5 system,
where both the commensurate and incommensurate magnetic orders coexist with the
superconductivity. These results reveal that particular areas on the Fermi
surface nested by qI play an active role in forming the superconducting state
in CeCoIn5.Comment: RevTeX4, 4 pages, 4 eps figures; corrected a typo and a referenc
Definitive experimental evidence for two-band superconductivity in MgB2
The superconducting gap of MgB2 has been studied by high-resolution
angle-resolved photoemission spectroscopy (ARPES). The momentum(k)-resolving
capability of ARPES enables us to identify the s- and p-orbital derived bands
predicted from band structure calculations and to successfully measure the
superconducting gap on each band. The results show that superconducting gaps
with values of 5.5 meV and 2.2 meV open on the s-band and the p-band,
respectively, but both the gaps close at the bulk transition temperature,
providing a definitive experimental evidence for the two-band superconductivity
in MgB2. The experiments validate the role of k-dependent electron-phonon
coupling as the origin of multiple-gap superconductivity in MgB2.Comment: PDF file onl
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
Elastic properties of the Non-Fermi liquid metal and the Dense Kondo semiconductor
We have investigated the elastic properties of the Ce-based filled
skutterudite antimonides CeRuSb and CeOsSb by means
of ultrasonic measurements. CeRuSb shows a slight increase around
130 K in the temperature dependence of the elastic constants ,
(-)/2 and . No apparent softening toward low
temperature due to a quadrupolar response of the 4-electronic ground state
of the Ce ion was observed at low temperatures. In contrast CeOsSb
shows a pronounced elastic softening toward low temperature in the longitudinal
as a function of temperature () below about 15 K, while a slight
elastic softening was observed in the transverse below about 1.5 K.
Furthermore, CeOsSb shows a steep decrease around a phase
transition temperature of 0.9 K in both and. The elastic
softening observed in below about 15 K cannot be explained
reasonably only by the crystalline electric field effect. It is most likely to
be responsible for the coupling between the elastic strain and the
quasiparticle band with a small energy gap in the vicinity of Fermi level. The
elastic properties and the 4 ground state of Ce ions in CeRuSb
and CeOsSb are discussed from the viewpoint of the crystalline
electric field effect and the band structure in the vicinity of Fermi level.Comment: 9 pages, 11 figures, regular pape
Metallic mean-field stripes, incommensurability and chemical potential in cuprates
We perform a systematic slave-boson mean-field analysis of the three-band
model for cuprates with first-principle parameters. Contrary to widespread
believe based on earlier mean-field computations low doping stripes have a
linear density close to 1/2 added hole per lattice constant. We find a
dimensional crossover from 1D to 2D at doping followed by a breaking
of particle-hole symmetry around doping 1/8 as doping increases. Our results
explain in a simple way the behavior of the chemical potential, the magnetic
incommensurability, and transport experiments as a function of doping. Bond
centered and site-centered stripes become degenerate for small overdoping.Comment: submitted to PR
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