1,015 research outputs found
Effect of annealing on the magnetic and superconducting properties of single-crystalline UCoGe
Single-crystals of the new ferromagnetic superconductor UCoGe have been
grown. The quality of as-grown samples can be significantly improved by a
heat-treatment procedure, which increases the residual resistance ratio (RRR)
from ~5 to ~30. Magnetization and resistivity measurements show the annealed
samples have a sharp ferromagnetic transition with a Curie temperature T_C is
2.8 K. The ordered moment of 0.06 mu_B is directed along the orthorhombic
c-axis. Superconductivity is found below a resistive transition temperature T_s
= 0.65 K
Decoupling of Layers in the Three-dimensional Abelian Higgs Model
The Abelian Higgs model with anisotropic couplings in 2+1 dimensions is
studied in both the compact and non-compact formulations. Decoupling of the
space-like planes takes place in the extreme anisotropic limit, so charged
particles and gauge fields are presumably localized within these planes. The
behaviour of the model under the influence of an external magnetic field is
examined in the compact case and yields further characterization of the phases.Comment: 23 pages, 12 figures, plain late
Superconducting and ferromagnetic phase diagram of UCoGe probed by thermal expansion
We report thermal expansion measurements on a single crystal of the
superconducting ferromagnet UCoGe for magnetic fields applied along the main
orthorhombic axes. The thermal expansion cell was mounted on a piezo-electric
rotator in order to fine-tune the magnetic field angle. The superconducting and
magnetic phase diagram has been determined. With our bulk technique we confirm
the -shape of the upper-critical field, , for and
reinforcement of superconductivity above 6 T. At the same time the Curie point
shifts towards lower temperatures on increasing the field along the -axis.
This lends further support to theoretical proposals of spin-fluctuation
mediated reinforcement of superconductivity for .Comment: 7 pages, 7 figure
From bad metal to Kondo insulator:Temperature evolution of the optical properties of SmB6
The recent rekindling of interest in the mixed valent Kondo insulator
SmB as candidate for a first correlated topological insulator has
resulted in a wealth of new experimental observations. In particular,
angle-resolved photoemission experiments have provided completely new insights
into the formation of the low temperature Kondo insulating state starting from
the high temperature correlated metal. Here, we report detailed temperature and
energy dependent measurements of the optical constants of SmB in order to
provide a detailed study from the point of view of a bulk sensitive
spectroscopic probe. We detect a previously unobserved infrared active optical
phonon mode, involving the movement of the Sm ions against the boron cages. The
changes taking place in the free carrier response with temperature and their
connection to changes in optical transitions between different bands are
discussed. We find that the free charge density starts to decrease rapidly
below approximately 200 K. Below 60 K a small amount of spectral weight begins
to accumulate in low lying interband transitions, indicating the formation of
the Kondo insulating state; however, the total integrated spectral weight in
our experimental window ( eV) decreases. This indicates the
involvement of a large Coulomb interaction ( 5 eV) in the formation of the
Kondo insulator.Comment: 10 pages, 7 figures (including supp.). Accepted for publication in
New Journal of Physic
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