173 research outputs found
Total suppression of superconductivity by high magnetic fields in YBa2 Cu3O6.6
We have studied in fields up to 60T the variation of the transverse
magnetoresistance (MR) of underdoped YBCO6.6 crystals either pure or with Tc
reduced down to 3.5K by electron irradiation. We evidence that the normal state
MR is restored above a threshold field H'c(T), which is found to vanish at
T'c>>Tc. In the pure YBCO6.6 sample a 50 Tesla field is already required to
completely suppress the superconducting fluctuations at Tc. While disorder does
not depress the pseudogap temperature, it reduces drastically the phase
coherence established at Tc and weakly H'c(0), T'c and the onset Tnu of the
Nernst signal which are more characteristic of the 2D local pairing.Comment: 4 pages, 4 figure
Nernst effect and disorder in the normal state of high-T_{c} cuprates
We have studied the influence of disorder induced by electron irradiation on
the Nernst effect in optimally and underdoped YBa2Cu3O(7-d) single crystals.
The fluctuation regime above T_{c} expands significantly with disorder,
indicating that the T_{c} decrease is partly due to the induced loss of phase
coherence. In pure crystals the temperature extension of the Nernst signal is
found to be narrow whatever the hole doping, contrary to data reported in the
low-T_{c} cuprates families. Our results show that the presence of "intrinsic"
disorder can explain the enhanced range of Nernst signal found in the pseudogap
phase of the latter compounds.Comment: revised version. to be published in Physical Review Letter
Observation of two species of vortices in the anisotropic spin-triplet superconductor
Magnetic flux structures in single crystals of the layered spin triplet
superconductor SrRuO are studied by scanning micro SQUID Force
microscopy. Vortex chains appear as the applied field is tilted along the
in-plane direction of the superconductor. The vortex chains align along the
direction of the in-plane component of the applied magnetic field. The
decoration of in-plane vortices by crossing Abrikosov vortices is observed: two
vortex orientations are apparent simultaneously, one along the layers and the
other perpendicular to the layers. The crossing vortices appear preferentially
on the in-plane vortices
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
Magnetic order in the frustrated Ising-like chain compound SrNiIrO
We have studied the field and temperature dependence of the magnetization of
single crystals of Sr3NiIrO6. These measurements evidence the presence of an
easy axis of anisotropy and two anomalies in the magnetic susceptibility.
Neutron powder diffraction realized on a polycrystalline sample reveals the
emergence of magnetic reflections below 75 K with magnetic propagation vector k
~ (0, 0, 1), undetected in previous neutron studies [T.N. Nguyen and H.-C zur
Loye, J. Solid State Chem., 117, 300 (1995)]. The nature of the magnetic ground
state, and the presence of two anomalies common to this family of material, are
discussed on the basis of the results obtained by neutron diffraction,
magnetization measurements, and symmetry arguments
Flows driven by Banach space-valued rough paths
We show in this note how the machinery of C^1-approximate flows devised in
the work "Flows driven by rough paths", and applied there to reprove and extend
most of the results on Banach space-valued rough differential equations driven
by a finite dimensional rough path, can be used to deal with rough differential
equations driven by an infinite dimensional Banach space-valued weak geometric
Holder p-rough paths, for any p>2, giving back Lyons' theory in its full force
in a simple way.Comment: 8 page
Observation of vortex coalescence in the anisotropic spin-triplet superconductor SrRuO
We present direct imaging of magnetic flux structures in the anisotropic,
spin-triplet superconductor SrRuO using a scanning SQUID
microscope. Individual quantized vortices were seen at low magnetic fields.
Coalescing vortices forming flux domains were revealed at intermediate fields.
Based on our observations we suggest that a mechanism intrinsic to the material
stabilizes the flux domains against the repulsive vortex-vortex interaction.
Topological defects like domain walls can provide this, implying proof for
unconventional chiral superconductivity.Comment: submitted to PR
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