Symmetry breaking and restoring under high pressure: the amazing behaviour of the "simple" alkali metals

We argue that an ionic lattice surrounded by a Fermi liquid changes phase several times under pressure, oscillating between the symmetric phase and a low-symmetry dimerized structure, as a consequence of Friedel oscillations in the pair potential. Phase oscillations explain the tendency towards dimerization which has been recently reported for the light alkali metals under high pressure. Moreover, a restoring of the symmetric phase is predicted for such elements at an even higher density.Comment: accepted in Eur. Phys. J.

Scaling of the superconducting transition temperature in underdoped high-Tc cuprates with a pseudogap energy: Does this support the anyon model of their superfluidity?

In earlier work, we have been concerned with the scaling properties of some classes of superconductors, specifically with heavy Fermion materials and with five bcc transition metals of BCS character. Both of these classes of superconductors were three-dimensional but here we are concerned solely with quasi-two-dimensional high-Tc cuprates in the underdoped region of their phase diagram. A characteristic feature of this part of the phase diagram is the existence of a pseudogap (pg). We therefore build our approach around the assumption that kB Tc / E_pg is the basic dimensionless ratio on which to focus, where the energy E_pg introduced above is a measure of the pseudogap. Since anyon fractional statistics apply to two-dimensional assemblies, we expect the fractional statistics parameter allowing `interpolation' between Fermi-Dirac and Bose-Einstein statistical distribution functions as limiting cases to play a significant role in determining kB Tc / E_pg and experimental data are analyzed with this in mind.Comment: Phys. Chem. Liquids, to be publishe

Resonant modes in strain-induced graphene superlattices

We study tunneling across a strain-induced superlattice in graphene. In studying the effect of applied strain on the low-lying Dirac-like spectrum, both a shift of the Dirac points in reciprocal space, and a deformation of the Dirac cones is explicitly considered. The latter corresponds to an anisotropic, possibly non-uniform, Fermi velocity. Along with the modes with unit transmission usually found across a single barrier, we analytically find additional resonant modes when considering a periodic structure of several strain-induced barriers. We also study the band-like spectrum of bound states, as a function of conserved energy and transverse momentum. Such a strain-induced superlattice may thus effectively work as a mode filter for transport in graphene

Exploring the mechanism of formation of native-like and precursor amyloid oligomers for the native acylphosphatase from Sulfolobus solfataricus

Over 40 human diseases are associated with the formation of well-defined proteinaceous fibrillar aggregates. Since the oligomers precursors to the fibrils are increasingly recognized to be the causative agents of such diseases, it is important to elucidate the mechanism of formation of these early species. The acylphosphatase from Sulfolobus solfataricus is an ideal system as it was found to form, under conditions in which it is initially native, two types of prefibrillar aggregates: (1) initial enzymatically active aggregates and (2) oligomers with characteristics reminiscent of amyloid protofibrils, with the latter originating from the structural reorganization of the initial assemblies. By studying a number of protein variants with a variety of biophysical techniques, we have identified the regions of the sequence and the driving forces that promote the first aggregation phase and show that the second phase consists in a cooperative conversion involving the entire globular fol

Dynamical polarization of graphene under strain

We study the dependence of the plasmon dispersion relation of graphene on applied uniaxial strain. Besides electron correlation at the RPA level, we also include local field effects specific for the honeycomb lattice. As a consequence of the two-band character of the electronic band structure, we find two distinct plasmon branches. We recover the square-root behavior of the low-energy branch, and find a nonmonotonic dependence of the strain-induced modification of its stiffness, as a function of the wavevector orientation with respect to applied strain.Comment: Phys. Rev. B, accepte