5,037 research outputs found
Out-of-plane thermopower of strongly correlated layered systems: an application to Bi_2(Sr,La)_2CaCu_2O_{8+\delta}
We calculate the out-of-plane thermopower in a quasi-two dimensional system,
and argue that this quantity is an effective probe of the asymmetry of the
single-particle spectral function. We find that the temperature and doping
dependence of the out-of-plane thermopower in Bi_2(Sr,La)_2CaCu_2O_{8+\delta}
single crystals is broadly consistent with the behavior of the spectral
function determined from ARPES and tunneling experiments. We also investigate
the relationship between out-of-plane thermopower and entropy in a quasi-two
dimensional material. We present experimental evidence that at moderate
temperatures, there is a qualitative correspondence between the out-of-plane
thermopower in Bi_2(Sr,La)_2CaCu_2O_{8+\delta}, and the entropy obtained from
specific heat measurements. Finally, we argue that the derivative of the
entropy with respect to particle number may be the more appropriate quantity to
compare with the thermopower, rather than the entropy per particle.Comment: 11 pages, 5 figures. v2: substantially rewritten, including a more
detailed analysis of the relationship between thermopower and entrop
Editorial: Assessment of pain in the older population
For many years now we have proposed that pain is regularly assessed and fundamental to the management process. To date, there has been a great deal of research exploring the most appropriate pain assessment tools and great strides have been made in their implementation. Assessment of pain in the older population has presented challenges, especially when there are communication difficulties, as seen in adults with dementia or other communication issues. Pain is not a natural part of the ageing process and people should not be expected to live with it. In recent years, there has been recognition that stoicism does not mean there is no pain and a number of behavioural pain assessment tools have been developed, evaluated, and introduced widely, with widespread implementation of validated pain assessment. The papers in this collection examine the issues of pain assessment in older adults and those with dementia, moving forward thinking on these subjects and presenting innovative ways of implementing pain management using technology. The COVID 19 pandemic resulted in many older adults being isolated at home, so they consequently became more isolated. Furthermore, many services were disbanded in the UK and staff were reallocated to COVID areas which resulted in a reduced number of pain services and therefore increased waiting times
Interaction Correction of Conductivity Near a Ferromagnetic Quantum Critical Point
We calculate the temperature dependence of conductivity due to interaction
correction for a disordered itinerant electron system close to a ferromagnetic
quantum critical point which occurs due to a spin density wave instability. In
the quantum critical regime, the crossover between diffusive and ballistic
transport occurs at a temperature ,
where is the parameter associated with the Landau damping of the spin
fluctuations, is the impurity scattering time, and is the Fermi
energy. For a generic choice of parameters, is few orders of
magnitude smaller than the usual crossover scale . In the ballistic
quantum critical regime, the conductivity has a temperature
dependence, where is the dimensionality of the system. In the diffusive
quantum critical regime we get dependence in three dimensions, and
dependence in two dimensions. Away from the quantum critical regime
we recover the standard results for a good metal.Comment: 15 pages, 8 figure
Effect of disorder on a Pomeranchuk instability
We study the effect of disorder on the order parameter equation and
transition temperature of a Pomeranchuk-type Fermi-surface instability using
replica mean field theory. We consider the example of a phase transition to a
type Fermi surface distortion, and show that, in the regime
where such a transition is second order, the transition temperature is reduced
by disorder in essentially the same way as that for a d-wave superconductor. We
argue that observing this disorder dependence of metal-to-metal transition
might be a useful indicator of a finite angular momentum Fermi surface
distortion.Comment: 4.1 pages, 3 figs. Version as published in EPL. Added data of
Sr3Ru2O7 to theory curves of Fig.2, and some clarification of derivation of
result
A study of inner zone electron data and their comparison with trapped radiation models
A summary and intercomparison of recent inner radiation zone electron data are presented. The morphology of the inner radiation zone is described and the data compared with the current generation of inner zone trapped electron models. An analytic representation of the inner zone equatorial pitch angle distribution is presented. This model was based upon data from eight satellites and was used to reduce all data to the form of equatorial flux. Although no Starfish-free high energy electron measurements were available from the inner portion of the inner radiation zone, it was found that the AE-6 model provided a good description of the present solar maximum environment
Fe K-edge X-ray Absorption Spectroscopy of corrosion phases of archaeological iron: results, limitations, and the need for complementary techniques
Data analysis methods for iron X-ray Absorption Spectroscopy (XAS) can provide extensive information about the oxidation state and co-ordination of an Fe-species. However, the extent to which techniques developed using a single-phase iron sample may be applied to complex, mixed-phase samples formed under real-world conditions is not clear. This work uses a combination of pre-edge fitting and linear combination analysis (LCA) to characterise the near edge region of the X-ray absorption spectrum (XANES) for a set of archaeological iron corrosion samples from a collection of cast iron cannon shot excavated from the Mary Rose shipwreck and compares the data with phase compositions determined by Synchrotron X-ray Powder Diffraction (SXPD). Archaeological powder and cross-section samples were compared to a library of iron standards and diffraction data. The XANES are consistent with previous observations that generation of the chlorinated phase akaganeite, β-FeO(OH,Cl), occurs in those samples which have been removed form passive storage and subjected to active conservation. However, the results show that if any metallic species is present in the sample, the contribution from Fe(0) to the spectral region containing a pre-edge for oxidised iron - Fe(II) and Fe(III) - causes the analysis to be less effective and the conclusions unreliable. Consequently, while the pre-edge fitting methodology may be applied to a mixture of iron oxides or oxyhydroxides, the procedure is inappropriate for a mixed metal-oxide sample without the application of a complimentary technique, such as SXPD
Probing spin-charge separation in a Tomonaga-Luttinger liquid
In a one-dimensional (1D) system of interacting electrons, excitations of
spin and charge travel at different speeds, according to the theory of a
Tomonaga-Luttinger Liquid (TLL) at low energies. However, the clear observation
of this spin-charge separation is an ongoing challenge experimentally. We have
fabricated an electrostatically-gated 1D system in which we observe spin-charge
separation and also the predicted power-law suppression of tunnelling into the
1D system. The spin-charge separation persists even beyond the low-energy
regime where the TLL approximation should hold. TLL effects should therefore
also be important in similar, but shorter, electrostatically gated wires, where
interaction effects are being studied extensively worldwide.Comment: 11 pages, 4 PDF figures, uses scicite.sty, Science.bs
Probing e-e interactions in a periodic array of GaAs quantum wires
We present the results of non-linear tunnelling spectroscopy between an array
of independent quantum wires and an adjacent two-dimensional electron gas
(2DEG) in a double-quantum-well structure. The two layers are separately
contacted using a surface-gate scheme, and the wires are all very regular, with
dimensions chosen carefully so that there is minimal modulation of the 2DEG by
the gates defining the wires. We have mapped the dispersion spectrum of the 1D
wires down to the depletion of the last 1D subband by measuring the conductance
\emph{G} as a function of the in-plane magnetic field \emph{B}, the interlayer
bias and the wire gate voltage. There is a strong suppression of
tunnelling at zero bias, with temperature and dc-bias dependences consistent
with power laws, as expected for a Tomonaga-Luttinger Liquid caused by
electron-electron interactions in the wires. In addition, the current peaks fit
the free-electron model quite well, but with just one 1D subband there is extra
structure that may indicate interactions.Comment: 3 pages, 3 figures; formatting correcte
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