Structural Metastability and Fermi Surface Topology of SrAlSi.

SrAlSi crystallizes into either a semimetallic, CaAlSi-type, α phase or a superconducting, BaZnP-type, β phase. We explore possible transformations by employing pressure- and temperature-dependent free-energy calculations, vibrational spectral calculations, and room-temperature synchrotron powder X-ray diffraction (PXRD) measurements up to 14 GPa using a diamond anvil cell. Our theoretical and empirical analyses together with all reported baric and thermal events on both phases allow us to construct a preliminary - diagram of transformations.

Pressure dependence of room-temperature structural properties of CaAlSi.

We investigated the pressure dependence of the crystal structure of CaAlSiby means ofcalculations and room-temperature synchrotron x-ray powder diffraction.calculations reproduce satisfactorily the experimentally observed pressure-dependent structural evolution up to 3 GPa where the title system remains in the trigonalP3¯m1phase. In the pressure range 3-8 GPa, pressure evolution of the calculated in-plane lattice parameters is steeper than the observed.

Quantum conductance-temperature phase diagram of granular superconductor K FeSe.

It is now well established that the microstructure of Fe-based chalcogenide K FeSe consists of, at least, a minor (~15 percent), nano-sized, superconducting K FeSe phase and a major (~85 percent) insulating antiferromagnetic KFeSe matrix. Other intercalated AFeSe (A = Li, Na, Ba, Sr, Ca, Yb, Eu, ammonia, amide, pyridine, ethylenediamine etc.) manifest a similar microstructure.

Linear magnetoresistivity in layered semimetallic CaAlSi.

According to an earlier Abrikosov model, a positive, nonsaturating, linear magnetoresistivity (LMR) is expected in clean, low-carrier-density metals when measured at very low temperatures and under very high magnetic fields. Recently, a vast class of materials were shown to exhibit extraordinary high LMR but at conditions that deviate sharply from the above-mentioned Abrikosov-type conditions. Such deviations are often considered within either classical Parish-Littlewood scenario of random-conductivity network or within a quantum scenario of small-effective mass or low carriers at tiny pockets neighboring the Fermi surface.

A mean-field approach to Kondo-attractive-Hubbard model.

With the purpose of investigating coexistence between magnetic order and superconductivity, we consider a model in which conduction electrons interact with each other, via an attractive Hubbard on-site coupling U, and with local moments on every site, via a Kondo-like coupling, J. The model is solved on a simple cubic lattice through a Hartree-Fock approximation, within a 'semi-classical' framework which allows spiral magnetic modes to be stabilized. For a fixed electronic density, n , the small J region of the ground state (T  =  0) phase diagram displays spiral antiferromagnetic (SAFM) states for small U.