135 research outputs found

    Solitary waves on finite-size antiferromagnetic quantum Heisenberg spin rings

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    Motivated by the successful synthesis of several molecular quantum spin rings we are investigating whether such systems can host magnetic solitary waves. The small size of these spin systems forbids the application of a classical or continuum limit. We therefore investigate whether the time-dependent Schroedinger equation itself permits solitary waves. Example solutions are obtained via complete diagonalization of the underlying Heisenberg Hamiltonian.Comment: 6 pages, 7 figures, to appear in J. Magn. Magn. Mate

    Anxiety-like behaviour is regulated independently from sex, mating status, and the sex peptide receptor in Drosophila melanogaster

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    Sex differences in anxiety-related behaviours have been documented in many animals and are notable in human populations. A major goal in behaviour research is to understand why and how sex differences in cognitive-emotional states like anxiety arise and are regulated throughout life. Anxiety allows individuals to detect and respond to threats. Mating is a candidate regulator for anxiety because threats are likely to change, often in sex-specific ways, when individuals shift to a postmating reproductive state. However, we know little about how mating mediates anxiety-related behaviour in males and females, or about how males might influence female anxiety via seminal proteins transferred during mating. To address this gap, we examined anxiety-related behaviour in the fruit fly Drosophila melanogaster, an emerging model animal for anxiety, with respect to sex, mating and sex peptide, a seminal protein known to modulate a host of female postmating responses in fruit flies. We assayed anxiety-like behaviour using the open-field assay to assess individual avoidance of the interior of an arena (‘wall-following’ behaviour). We found sex differences in activity level, but no evidence for sex differences in wall-following behaviour. We found no effects of mating in either sex, or of the presence of the sex peptide receptor in females, on wall following. Our results suggest that anxiety is not one of the cognitive-emotional states regulated by mating and sex peptide in fruit flies, and that researchers need an alternative model for sex differences in anxiety

    On the Relationship Between the Critical Temperature and the London Penetration Depth in Layered Organic Superconductors

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    We present an analysis of previously published measurements of the London penetration depth of layered organic superconductors. The predictions of the BCS theory of superconductivity are shown to disagree with the measured zero temperature, in plane, London penetration depth by up to two orders of magnitude. We find that fluctuations in the phase of the superconducting order parameter do not determine the superconducting critical temperature as the critical temperature predicted for a Kosterlitz--Thouless transition is more than an order of magnitude greater than is found experimentally for some materials. This places constraints on theories of superconductivity in these materials.Comment: 5 pages, 1 figur

    Fermiology and superconductivity studies on the non-tetrachalcogenafulvalene structured organic superconductor beta-(BDA-TTP)_2SbF_6

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    The quantum oscillatory effect and superconductivity in a non-tetrachalcogenafulvalene (TCF) structure based organic superconductor beta-(BDA-TTP)_2SbF_6 are studied. Here the Shubnikov-de Haas effect (SdH) and angular dependent magnetoresistance oscillations (AMRO) are observed. The oscillation frequency associated with a cylindrical Fermi surface is found to be about 4050 tesla, which is also verified by the tunnel diode oscillator (TDO) measurement. The upper critical field Hc2 measurement in a tilted magnetic field and the TDO measurement in the mixed state reveal a highly anisotropic superconducting nature in this material. We compared physical properties of beta-(BDA-TTP)_2SbF_6 with typical TCF structure based quasi two-dimensional organic conductors. A notable feature of beta-(BDA-TTP)_2SbF_6 superconductor is a large value of effective cyclotron mass m_c^*=12.4+/1.1 m_e, which is the largest yet found in an organic superconductor. A possible origin of the enhanced effective mass and its relation to the superconductivity are briefly discussed.Comment: 8 pages, 10 figure

    Bose glass behavior in (Yb1x_{1-x}Lux_x)4_4As3_3 representing the randomly diluted quantum spin-1/2 chains

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    The site-diluted compound (Yb1x_{1-x}Lux_x)4_4As3_3 is a scarce realization of the linear Heisenberg antiferromagnet partitioned into finite-size segments and is an ideal model compound for studying field-dependent effects of quenched disorder in the one-dimensional antiferromagnets. It differentiates from the systems studied so far in two aspects - the type of randomness and the nature of the energy gap in the pure sample. We have measured the specific heat of single-crystal (Yb1x_{1-x}Lux_x)4_4As3_3 in magnetic fields up to 19.5 T. The contribution CC_{\perp} arising from the magnetic subsystem in an applied magnetic field perpendicular to the chains is determined. Compared to pure Yb4_4As3_3, for which CC_{\perp} indicates a gap opening, for diluted systems a non-exponential decay is found at low temperatures which is consistent with the thermodynamic scaling of the specific heat established for a Bose-glass phase.Comment: 8 pages, 17 figures, including supplemental material, accepted for PRB rapid communicatio

    Low temperature vortex liquid states induced by quantum fluctuations in the quasi two dimensional organic superconductor kappa-(BEDT-TTF)_{2} Cu(NCS)_{2}

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    We report the transport properties in the vortex liquid states induced by quantum fluctuations at low temperature in the layered organic superconductor kappa-(BEDT-TTF)_{2} Cu(NCS)_{2}. A steep drop of the resistivity observed below about 1 K separates the liquid state into two regions. In the low resistance state at lower temperature, a finite resistivity with weak temperature dependence persists down to 100 mK at least. The finite resistivity in the vortex state at T ~= 0 K indicates the realization of quantum vortex liquid assisted by the strong quantum fluctuations instead of the thermal one. A possible origin for separating these liquid states is a remnant vortex melting line at the original position, which is obscured and suppressed by the quantum fluctuations. A non-linear behavior of the in-plane resistivity appears at large current density in only the low resistance state, but not in another vortex liquid state at higher temperature, where the thermal fluctuations are dominant. The transport properties in the low resistance state are well understood in the vortex slush concept with a short-range order of vortices. Thus the low resistance state below 1 K is considered to be a novel quantum vortex slush state.Comment: 7 pages, 5 figure

    Nuclear Magnetic Resonance in Low-Symmetry Superconductors

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    We consider the nuclear spin-lattice relaxation rate, 1/T1T1/T_1T in superconductors with accidental nodes. We show that a Hebel-Slichter-like peak occurs even in the absence of an isotropic component of the superconducting gap. The logarithmic divergence found in clean, non-interacting models is controlled by both disorder and electron-electron interactions. However, for reasonable parameters, neither of these effects removes the peak altogether.Comment: 10 pages, 5 figure
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