12,210 research outputs found
Field-dependent diamagnetic transition in magnetic superconductor
The magnetic penetration depth of single crystal
was measured down to 0.4 K in dc fields up
to 7 kOe. For insulating , Sm spins order at the
N\'{e}el temperature, K, independent of the applied field.
Superconducting ( K) shows a
sharp increase in diamagnetic screening below which varied from
4.0 K () to 0.5 K ( 7 kOe) for a field along the c-axis. If the
field was aligned parallel to the conducting planes, remained
unchanged. The unusual field dependence of indicates a spin freezing
transition that dramatically increases the superfluid density.Comment: 4 pages, RevTex
Discrimination between pure states and mixed states
In this paper, we discuss the problem of determining whether a quantum system
is in a pure state, or in a mixed state. We apply two strategies to settle this
problem: the unambiguous discrimination and the maximum confidence
discrimination. We also proved that the optimal versions of both strategies are
equivalent. The efficiency of the discrimination is also analyzed. This scheme
also provides a method to estimate purity of quantum states, and Schmidt
numbers of composed systems
Two spatially separated phases in semiconducting RbFeS
We report neutron scattering and transport measurements on semiconducting
RbFeS, a compound isostructural and isoelectronic to the
well-studied FeSe K, Rb, Cs, Tl/K) superconducting
systems. Both resistivity and DC susceptibility measurements reveal a magnetic
phase transition at K. Neutron diffraction studies show that the 275 K
transition originates from a phase with rhombic iron vacancy order which
exhibits an in-plane stripe antiferromagnetic ordering below 275 K. In
addition, interdigitated mesoscopically with the rhombic phase is an ubiquitous
phase with iron vacancy order. This phase has a
magnetic transition at K and an iron vacancy order-disorder
transition at K. These two different structural phases are closely
similar to those observed in the isomorphous Se materials. Based on the close
similarities of the in-plane antiferromagnetic structures, moments sizes, and
ordering temperatures in semiconducting RbFeS and
KFeSe, we argue that the in-plane antiferromagnetic order
arises from strong coupling between local moments. Superconductivity,
previously observed in the FeSeS system, is absent
in RbFeS, which has a semiconducting ground state. The
implied relationship between stripe/block antiferromagnetism and
superconductivity in these materials as well as a strategy for further
investigation is discussed in this paper.Comment: 7 pages, 5 figure
Antiferromagnetic critical pressure in URu2Si2 under hydrostatic conditions
The onset of antiferromagnetic order in URu2Si2 has been studied via neutron
diffraction in a helium pressure medium, which most closely approximates
hydrostatic conditions. The antiferromagnetic critical pressure is 0.80 GPa,
considerably higher than values previously reported. Complementary electrical
resistivity measurements imply that the hidden order-antiferromagnetic
bicritical point far exceeds 1.02 GPa. Moreover, the redefined
pressure-temperature phase diagram suggests that the superconducting and
antiferromagnetic phase boundaries actually meet at a common critical pressure
at zero temperature.Comment: 5 pgs, 4 figs; AFM ordered moment revised to 0.5 muB, added and
corrected citations and reference
Optimal Eavesdropping in Quantum Cryptography. II. Quantum Circuit
It is shown that the optimum strategy of the eavesdropper, as described in
the preceding paper, can be expressed in terms of a quantum circuit in a way
which makes it obvious why certain parameters take on particular values, and
why obtaining information in one basis gives rise to noise in the conjugate
basis.Comment: 7 pages, 1 figure, Latex, the second part of quant-ph/970103
Landau quantization effects in the charge-density-wave system (Per)(mnt) (where Au and Pt)
A finite transfer integral orthogonal to the conducting chains of a
highly one-dimensional metal gives rise to empty and filled bands that simulate
an indirect-gap semiconductor upon formation of a commensurate
charge-density-wave (CDW). In contrast to semiconductors such as Ge and Si with
bandgaps eV, the CDW system possesses an indirect gap with a greatly
reduced energy scale, enabling moderate laboratory magnetic fields to have a
major effect. The consequent variation of the thermodynamic gap with magnetic
field due to Zeeman splitting and Landau quantization enables the electronic
bandstructure parameters (transfer integrals, Fermi velocity) to be determined
accurately. These parameters reveal the orbital quantization limit to be
reached at T in (Per)(mnt) salts, making them highly
unlikely candidates for a recently-proposed cascade of field-induced
charge-density wave states
Scaling of the elastic contribution to the surface free energy of a nematic on a sawtoothed substrate
We characterize the elastic contribution to the surface free energy of a
nematic in presence of a sawtooth substrate. Our findings are based on
numerical minimization of the Landau-de Gennes model and analytical
calculations on the Frank-Oseen theory. The nucleation of disclination lines
(characterized by non-half-integer winding numbers) in the wedges and apexes of
the substrate induces a leading order proportional to qlnq to the elastic
contribution to the surface free energy density, q being the wavenumber
associated with the substrate periodicity.Comment: 7 pages, 6 figures, accepted for publication in Physical Review
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