13,021 research outputs found
Understanding the small business sector: reflections and confessions
No description supplie
Incoherent superconductivity well above in high- cuprates - harmonizing the spectroscopic and thermodynamic data
Cuprate superconductors have long been known to exhibit an energy gap that
persists high above the superconducting transition temperature (). Debate
has continued now for decades as to whether it is a precursor superconducting
gap or a pseudogap arising from some competing correlation. Failure to resolve
this has arguably delayed explaining the origins of superconductivity in these
highly complex materials. Here we effectively settle the question by
calculating a variety of thermodynamic and spectroscopic properties, exploring
the effect of a temperature-dependent pair-breaking term in the self-energy in
the presence of pairing interactions that persist well above . We start by
fitting the detailed temperature-dependence of the electronic specific heat and
immediately can explain its hitherto puzzling field dependence. Taking this
same combination of pairing temperature and pair-breaking scattering we are
then able to simultaneously describe in detail the unusual temperature and
field dependence of the superfluid density, tunneling, Raman and optical
spectra, which otherwise defy explanation in terms a superconducting gap that
closes conventionally at . These findings demonstrate that the gap above
in the overdoped regime likely originates from incoherent superconducting
correlations, and is distinct from the competing-order "pseudogap" that appears
at lower doping.Comment: 15 pages, 6 figure
Hall effect and Fermi surface reconstruction via electron pockets in the high- cuprates
The mechanism by which the Fermi surface of high- cuprates undergoes a
dramatic change from a large hole-like barrel to small arcs or pockets on
entering the pseudogap phase remains a question of fundamental importance. Here
we calculate the normal-state Hall coefficient from the resonating-valence-bond
spin-liquid model developed by Yang, Rice and Zhang. In this model,
reconstruction of the Fermi surface occurs via an intermediate regime where the
Fermi surface consists of both hole- and electron-like pockets. We find that
the doping dependence of the Hall number transitions from to
over this narrow doping range. At low temperatures, a switch from a downturn to
an upturn in the Hall coefficient signals the departure of the electron-like
pockets from the Fermi surface.Comment: 5 pages, 5 figure
Closing the pseudogap quietly
The physical properties of hole-doped cuprate high-temperature
superconductors are heavily influenced by an energy gap known as the pseudogap
whose origin remains a mystery second only to that of superconductivity itself.
A key question is whether the pseudogap closes at a temperature T*. The absence
of a specific heat anomaly, together with persistent entropy losses up to 300K,
have long suggested that the pseudogap does not vanish at T*. However, amid a
growing body of evidence from other techniques pointing to the contrary we
revisit this question. Here we investigate if, by adding a temperature
dependence to the pseudogap energy and quasiparticle lifetime in the
resonating-valence-bond spin-liquid model of Yang Rice and Zhang, we can close
the pseudogap quietly in the specific heat.Comment: 5 pages, 4 figure
Collision strengths and transition probabilities for Co III forbidden lines
In this paper we compute the collision strengths and their thermally-averaged
Maxwellian values for electron transitions between the fifteen lowest levels of
doubly-ionised cobalt, Co^{2+}, which give rise to forbidden emission lines in
the visible and infrared region of spectrum. The calculations also include
transition probabilities and predicted relative line emissivities. The data are
particularly useful for analysing the thermodynamic conditions of supernova
ejecta.Comment: 9 pages, 2 figures, 11 table
- …