350 research outputs found
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
Pressure induced effects on the Fermi surface of superconducting 2H-NbSe
The pressure dependence of the critical temperature and upper critical
field has been measured up to 19 GPa in the layered superconducting
material 2H-NbSe. Relating the behavior of to Fermi surface
parameters, we find that the electron phonon coupling of the 2D Nb 4d derived
bands shows a peak at 5 GPa when the charge density wave (CDW) order is
suppressed. On the other hand, shows a bell shaped curve with a
maximum at 10.5 GPa, well above the pressure for the suppression of the CDW
order. Changes in the band structure produce this shift in the maximum of
, demonstrating that 2H-NbSe shows important differences with
respect to other compounds where has a maximum in the temperature-density
phase diagram shaped by the suppression of another, non-superconducting, ground
state.Comment: 5 pages, 4 figures. Small changes in discussion. Typos correcte
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
Superconducting Gap of UCoGe probed by Thermal Transport
Thermal conductivity measurements in the superconducting state of the
ferromagnet UCoGe were performed at very low temperatures and under magnetic
field on samples of different qualities and with the heat current along the
three crystallographic axis. This allows to disentangle intrinsic and extrinsic
effects, confirm the situation of multigap superconductivity and shed new light
on the situation expected or claimed for the gap in these ferromagnetic
superconductors, like evidences of absence of "partially gapped" Fermi
surfaces.Comment: 6 pages, 5 figures. To be appeared in Physical Review Rapid
Communicatio
Evolution of crystalline electric field effects, superconductivity, and heavy fermion behavior in the specific heat of Pr(OsRu)Sb
Specific heat measurements were made on single crystals of the
superconducting filled skutterudite series Pr(OsRu)Sb
down to 0.6 K. Crystalline electric field fits in the normal state produced
parameters which were in agreement with previous measurements. Bulk
superconductivity was observed for all values of the Ru concentration with
transition temperatures consistent with previous experiments, confirming a
minimum in at . The data below appear to be more
consistent with power law behavior for (PrOsSb), and with
exponential behavior for . An enhanced electronic
specific heat coefficient was observed for , further
supporting as a critical concentration where the physical
properties abruptly change. Significant enhancement of above
the weak coupling value was only observed for and .Comment: 16 pages, 5 figures, submitted to Physical Review B. v2: text added
and figures modifie
Thermoelectric response near a quantum critical point of beta-YbAlB4 and YbRh2Si2: A comparative study
The thermoelectric coefficients have been measured on the Yb-based heavy
fermion compounds beta-YbAlB4 and YbRh2Si2 down to a very low temperature. We
observe a striking difference in the behavior of the Seebeck coefficient, S in
the vicinity of the Quantum Critical Point (QCP) in the two systems. As the
critical field is approached, S/T enhances in beta-YbAlB4 but is drastically
reduced in YbRh2Si2. While in the former system, the ratio of
thermopower-to-specific heat remains constant, it drastically drops near the
QCP in YbRh2Si2. In both systems, on the other hand, the Nernst coefficient
shows a diverging behavior near the QCP. The results provide a new window to
the way various energy scales of the system behave and eventually vanish near a
QCP
Crystal growth and characterization of the ruthenate superconducting compound: Sr2RuO4
International audienceSr2RuO4 is a copper-free layered perovskite superconductor with the tetragonal K2NiF4-type structure. The precise nature of the pairing in the superconducting state of this material is still under debate. In this paper, we report about crystal growth and characterization of this compound. The crystals were grown by a floating zone technique using a light furnace equipped with double elliptical mirrors starting from off-stoichiometric Sr2RuO4. The crystals have been checked by X-ray diffraction and microanalysis. The superconducting properties were measured by AC-susceptibility, magnetization and specific heat. High crystalline quality centimetre-sized crystals have been grown and best crystals exhibit superconducting transitions at View the MathML source (typical dimensions : 4.5 mm diameter and 70 mm length with the (0 0 1) axis perpendicular to growth direction). The unconventional superconductors are characterized by a drastic impurity effect on the superconducting properties. We try to establish a correlation between the defect concentration and the physical properties of Sr2RuO4
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