135 research outputs found
Solitary waves on finite-size antiferromagnetic quantum Heisenberg spin rings
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
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
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
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 (YbLu)As representing the randomly diluted quantum spin-1/2 chains
The site-diluted compound (YbLu)As 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
(YbLu)As in magnetic fields up to 19.5 T. The contribution
arising from the magnetic subsystem in an applied magnetic field
perpendicular to the chains is determined. Compared to pure YbAs, for
which 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}
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
We consider the nuclear spin-lattice relaxation rate, 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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