1,737 research outputs found
Minimum Detection Efficiencies for a Loophole-Free Bell-type Test
We discuss the problem of finding the most favorable conditions for closing
the detection loophole in a test of local realism with a Bell inequality. For a
generic non-maximally entangled two-qubit state and two alternative measurement
bases we apply Hardy's proof of non-locality without inequality and derive an
Eberhard-like inequality. For an infinity of non-maximally entangled states we
find that it is possible to refute local realism by requiring perfect detection
efficiency for only one of the two measurements: the test is free from the
detection loophole for any value of the detection efficiency corresponding to
the other measurement. The maximum tolerable noise in a loophole-free test is
also evaluated.Comment: 4 pages, 2 figure
Theoretical search for superconductivity in Sc3XB perovskites and weak ferromagnetism in Sc3X (X = Tl, In, Ga, Al)
A possibility for a new family of intermetallic perovskite superconductors
Sc3XB, with X = Tl, In, Ga and Al, is presented as a result of KKR electronic
structure and pseudopotential phonon calculations. The large values of computed
McMillan--Hopfield parameters on scandium suggest appearance of
superconductivity in Sc3XB compounds. On the other hand, the possibility of
weak itinerant ferromagnetic behavior of Sc3X systems is indicated by the small
magnetic moment on Sc atoms in two cases of X =~ l and In. Also the electronic
structure and resulting superconducting parameters for more realistic case of
boron--deficient systems Sc3XB_x are computed using KKR--CPA method, by
replacing boron atom with a vacancy. The comparison of the calculated
McMillan--Hopfield parameters of the Sc3XB series with corresponding values in
MgCNi3 and YRh3B superconductors is given, finding the favorable trends for
superconductivity.Comment: 13 pages, 13 figures. v3 - revise
Pressure effects in the triangular layered cobaltites NaxCoO2
We have measured transport properties as a function of temperature and
pressure up to 30GPa in the NaxCoO2 system. For the x=0.5 sample the transition
temperature at 53K increases with pressure, while paradoxically the sample
passes from an insulating to a metallic ground state. A similar transition is
observed in the x=0.31 sample under pressure. Compression on the x=0.75 sample
transforms the sample from a metallic to an insulating state. We discuss our
results in terms of interactions between band structure effects and Na+ order.Comment: 18 pages, 5 figure
Evidences of a consolute critical point in the Phase Separation regime of La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single crystals
We report on DC and pulsed electric field sensitivity of the resistance of
mixed valent Mn oxide based La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single
crystals as a function of temperature. The low temperature regime of the
resistivity is highly current and voltage dependent. An irreversible transition
from high (HR) to a low resistivity (LR) is obtained upon the increase of the
electric field up to a temperature dependent critical value (V_c). The
current-voltage characteristics in the LR regime as well as the lack of a
variation in the magnetization response when V_c is reached indicate the
formation of a non-single connected filamentary conducting path. The
temperature dependence of V_c indicates the existence of a consolute point
where the conducting and insulating phases produce a critical behavior as a
consequence of their separation.Comment: 5 pages, 6 figures, corresponding author: C. Acha ([email protected]
Evidence for polarons in iron pnictides of the Ln-1111 and AE-122 families
Examination of the electrical resistivities of iron pnictides shows that they
can be accounted by conduction by polarons. Their activation energies show a
linear behaviour with the critical temperatures of the spin density waves
(SDW), T*, as both vary with pressure. The slope matches the ratio SDW gap to
T*, while the intercept can be related to the transition temperature of the
lattice distortion, T0. An adapted Landau free energy predicts the observed
order of the transitions, according to which is higher, T* or T0. Simple
arguments favour combined Jahn-Teller antiferromagnetic bipolarons.Comment: 14 pages with 4 Figure
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