355 research outputs found
Unusual Higgs or Supersymmetry from Natural Electroweak Symmetry Breaking
This review provides an elementary discussion of electroweak symmetry
breaking in the minimal and the next-to-minimal supersymmetric models with the
focus on the fine-tuning problem -- the tension between natural electroweak
symmetry breaking and the direct search limit on the Higgs boson mass. Two
generic solutions of the fine-tuning problem are discussed in detail: models
with unusual Higgs decays; and models with unusual pattern of soft
supersymmetry breaking parameters.Comment: 23 pages, 6 figures; invited review by MPL
Fulde-Ferrell-Larkin-Ovchinnikov Superconducting State in CeCoIn5
We report specific heat measurements of the heavy fermion superconductor
CeCoIn5 in the vicinity of the superconducting critical field H_{c2}, with
magnetic field in the [110], [100], and [001] directions, and at temperatures
down to 50 mK. The superconducting phase transition changes from second to
first order for field above 10 T for H || [110] and H || [100]. In the same
range of magnetic field we observe a second specific heat anomaly within the
superconducting state. We interpret this anomaly as a signature of a
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) inhomogeneous superconducting state. We
obtain similar results for H || [001], with FFLO state occupying a smaller part
of the phase diagram.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Letter
Nanoscale structuring of tungsten tip yields most coherent electron point-source
This report demonstrates the most spatially-coherent electron source ever
reported. A coherence angle of 14.3 +/- 0.5 degrees was measured, indicating a
virtual source size of 1.7 +/-0.6 Angstrom using an extraction voltage of 89.5
V. The nanotips under study were crafted using a spatially-confined,
field-assisted nitrogen etch which removes material from the periphery of the
tip apex resulting in a sharp, tungsten-nitride stabilized, high-aspect ratio
source. The coherence properties are deduced from holographic measurements in a
low-energy electron point source microscope with a carbon nanotube bundle as
sample. Using the virtual source size and emission current the brightness
normalized to 100 kV is found to be 7.9x10^8 A/sr cm^2
Anisotropy of Thermal Conductivity and Possible Signature of the Fulde-Ferrell-Larkin-Ovchinnikov state in CeCoIn_5
We have measured the thermal conductivity of the heavy-fermion superconductor
CeCoIn_5 in the vicinity of the upper critical field, with the magnetic field
perpendicular to the c axis. Thermal conductivity displays a discontinuous jump
at the superconducting phase boundary below critical temperature T_0 ~ 1 K,
indicating a change from a second to first order transition and confirming the
recent results of specific heat measurements on CeCoIn_5. In addition, the
thermal conductivity data as a function of field display a kink at a field H_k
below the superconducting critical field, which closely coincides with the
recently discovered anomaly in specific heat, tentatively identified with the
appearance of the spatially inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) superconducting state. Our results indicate that the thermal
conductivity is enhanced within the FFLO state, and call for further
theoretical investigations of the order parameter's real space structure (and,
in particular, the structure of vortices) and of the thermal transport within
the inhomogeneous FFLO state.Comment: 19 pages, 6 figures, submitted to Prhys. Rev.
Mixed-State Thermodynamics of Superconductors with Moderately Large Paramagnetic Effects
Effects of Pauli paramagnetism on thermodynamic quantities in a vortex state,
such as the specific heat and magnetization , are studied using the
quasiclassical Eilenberger formalism. We demonstrate that with an increase of
paramagnetic depairing effect, the sigh of the curvature of the field
dependence of changes from negative to positive, and that the Maki
parameter becomes an increasing function of temperature. Our results
provide a natural explanation for the unusual field dependence of seen in
CeCoIn in terms of the paramagnetic effect.Comment: Published in J. Phys. Soc. Jpn. 74, 2181 (2005
Antivortices due to competing orbital and paramagnetic pair-breaking effects
Thermodynamically stable vortex-antivortex structures in a
quasi-two-dimensional superconductor in a tilted magnetic field are predicted.
For this geometry, both orbital and spin pair-breaking effects exist, with
their relative strength depending on the tilt angle \Theta. The spectrum of
possible states contains as limits the ordinary vortex state (for large \Theta)
and the Fulde-Ferrell-Larkin-Ovchinnikov state (for \Theta=0). The
quasiclassical equations are solved near H_{c2} for arbitrary \Theta and it is
shown that stable states with coexisting vortices and antivortices exist in a
small interval close to \Theta=0. The results are compared with recent
predictions of antivortices in mesoscopic samples.Comment: 11 pages, 3 figure
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