108 research outputs found
Magnetic order in Ce0.95Nd0.05CoIn5: the Q-phase at zero magnetic field
We report neutron scattering experiment results revealing the nature of the
magnetic order occurring in the heavy fermion superconductor Ce0.95Nd0.05CoIn5,
a case for which an antiferromagnetic state is stabilized at a temperature
below the superconducting transition one. We evidence an incommensurate order
and its propagation vector is found to be identical to that of the magnetic
field induced antiferromagnetic order occurring in the stoichiometric
superconductor CeCoIn5, the so-called Q-phase. The commonality between these
two cases suggests that superconductivity is a requirement for the formation of
this kind of magnetic order and the proposed mechanism is the enhancement of
nesting condition by d-wave order parameter with nodes in the nesting area.Comment: submitted to Phys. Rev. Lett. on June 30th, 201
Assessment of the U and Co magnetic moments in UCoGe by X-ray magnetic circular dichroism
The ferromagnetic superconductor UCoGe has been investigated by high field
X-ray magnetic circular dichroism (XMCD) at the U-M and Co/Ge-K edges.
The analysis of the branching ratio and XMCD at the U-M edges reveals
that the U-5 electrons count is close to 3. The orbital ()
and spin () moments of U at 2.1K and 17T (H//c) have been
determined. Their ratio () suggests a significant delocalization of
the 5 electron states. The similar field dependences of the local U/Co and
the macroscopic magnetization indicate that the Co moment is induced by the U
moment. The XMCD at the Co/Ge-K edges reveal the presence of small Co-4 and
Ge-4 orbital moments parallel to the macroscopic magnetization. In addition,
the Co-3 moment is estimated to be at most of the order of 0.1 at
17T. Our results rule out the possibility of an unusual polarisability of the U
and Co moments as well as their antiparallel coupling. We conclude that the
magnetism which mediates the superconductivity in UCoGe is driven by U.Comment: 4 figures + supplementary materia
Optical conductivity of URuSi in the Kondo Liquid and Hidden-Order Phases
We measured the polarized optical conductivity of URuSi from room
temperature down to 5 K, covering the Kondo state, the coherent Kondo liquid
regime, and the hidden-order phase. The normal state is characterized by an
anisotropic behavior between the ab plane and c axis responses. The ab plane
optical conductivity is strongly influenced by the formation of the coherent
Kondo liquid: a sharp Drude peak develops and a hybridization gap at 12 meV
leads to a spectral weight transfer to mid-infrared energies. The c axis
conductivity has a different behavior: the Drude peak already exists at 300 K
and no particular anomaly or gap signature appears in the coherent Kondo liquid
regime. When entering the hidden-order state, both polarizations see a dramatic
decrease in the Drude spectral weight and scattering rate, compatible with a
loss of about 50 % of the carriers at the Fermi level. At the same time a
density-wave like gap appears along both polarizations at about 6.5 meV at 5 K.
This gap closes respecting a mean field thermal evolution in the ab plane.
Along the c axis it remains roughly constant and it "fills up" rather than
closing.Comment: 10 pages, 7 figure
Upper critical field of CeCoIn5
We present a detailed analysis of the upper critical field for CeCoIn5 under
high pressure. We show that, consistently with other measurements, this system
shows a decoupling between maximum of the superconducting transition
temperature Tc and maximum pairing strength. This puts forward CeCoIn5 as an
important paradigm for this class of unconventional, strongly correlated
superconductors.Comment: 15 pages, 5 figures, author version, published in New J. Phy
Thermal conductivity through the quantum critical point in YbRh2Si2 at very low temperature
The thermal conductivity of YbRh2Si2 has been measured down to very low
temperatures under field in the basal plane. An additional channel for heat
transport appears below 30 mK, both in the antiferromagnetic and paramagnetic
states, respectively below and above the critical field suppressing the
magnetic order. This excludes antiferromagnetic magnons as the origin of this
additional contribution to thermal conductivity. Moreover, this low temperature
contribution prevails a definite conclusion on the validity or violation of the
Wiedemann-Franz law at the field-induced quantum critical point. At high
temperature in the paramagnetic state, the thermal conductivity is sensitive to
ferromagnetic fluctuations, previously observed by NMR or neutron scattering
and required for the occurrence of the sharp electronic spin resonance
fracture.Comment: 11 pages + Supplementary Material
Comment on ``Texture in the Superconducting Order Parameter of CeCoIn Revealed by Nuclear Magnetic Resonance''
The study of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state has been of
considerable recent interest. Below the temperature which is believed to
be the transition temperature () to the FFLO phase in CeCoIn, K.
Kakuyanagi et al. (Phys. Rev. Lett. 94, 047602 (2005)) reported a composite NMR
spectrum with a tiny component observed at frequencies corresponding to the
normal state signal. The results were interpreted as evidence for the emergence
of an FFLO state. This result is inconsistent with two other NMR studies of V.
F. Mitrovi{\'c} et al. (Phys. Rev. Lett. 97, 117002 (2006)) and B.-L. Young et
al. (Phys. Rev. Lett. 98, 036402 (2007)). In this comment we show that the
findings of K. Kakuyanagi et al. do not reflect the true nature of the FFLO
state but result from excess RF excitation power used in that experiment.Comment: 1 page, to appear in PR
Phase Diagram of CeCoIn_5 in the Vicinity of H_{c2} as Determined by NMR
We report ^{115}In nuclear magnetic resonance (NMR) measurements in the
heavy-fermion superconductor CeCoIn_5 as a function of temperature in different
magnetic fields applied parallel to the plane. The
measurements probe a part of the phase diagram in the vicinity of the
superconducting critical field H_{c2} where a possible inhomogeneous
superconducting state, Fulde-Ferrel-Larkin-Ovchinnikov (FFLO), is stabilized.
We have identified clear NMR signatures of two phase transitions occurring in
this part of the phase diagram. The first order phase transitions are
characterized by the sizable discontinuity of the shift. We find that a
continuous second order phase transition from the superconducting to the FFLO
state occurs at temperature below which the shift becomes temperature
independent. We have compiled the first phase diagram of CeCoIn_5 in the
vicinity of H_{c2} from NMR data and found that it is in agreement with the one
determined by thermodynamic measurements.Comment: 4 pages, submitted to Proceedings of SCES'0
Reentrant valence transition in EuO at high pressures: beyond the bond-valence model
The pressure-dependent relation between Eu valence and lattice structure in
model compound EuO is studied with synchrotron-based x-ray spectroscopic and
diffraction techniques. Contrary to expectation, a 7% volume collapse at
45 GPa is accompanied by a reentrant Eu valence transition into a
\emph{lower} valence state. In addition to highlighting the need for probing
both structure and electronic states directly when valence information is
sought in mixed-valent systems, the results also show that widely used
bond-valence methods fail to quantitatively describe the complex electronic
valence behavior of EuO under pressure.Comment: 5 pages, 4 figure
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