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