arXiv subjects

S. M. Loureiro

Publications and source records attributed to S. M. Loureiro.

4 recordsLinked to original sources

arXiv2006

ARPES Study of the Metal-Insulator Transition in Bismuth Cobaltates

We present an angle-resolved photoemission spectroscopy (ARPES) study of a Mott-Hubbard-type bismuth cobaltate system across a metal-insulator transition. By varying the amount of Pb substitution, and by doping with Sr or Ba cation, a range of insulating to metallic properties is obtained. We observe a systematic change in the spectral weight of the coherent and incoherent parts, accompanied by an energy shift of the incoherent part. The band dispersion also shows the emergence of a weakly dispersing state at the Fermi energy with increasing conductivity. These changes correspond with the changes in the temperature-dependent resistivity behavior. We address the nature of the coherent-incoherent parts in relation to the peak-dip-hump feature seen in cuprates superconductors.

cond-mat.str-el↗

arXiv2002

Coherence-Incoherence and Dimensional Crossover in Layered Strongly Correlated Metals

Correlations between electrons and the effective dimensionality are crucial factors that shape the properties of an interacting electron system. For example, the onsite Coulomb repulsion, U, may inhibit, or completely block the intersite electron hopping, t, and depending on the ratio U/t, a material may be a metal or an insulator. The correlation effects increase as the number of allowed dimensions decreases. In 3D systems, the low energy electronic states behave as quasiparticles (QP), while in 1D systems, even weak interactions break the quasiparticles into collective excitations. Dimensionality is particularly important for a class of new exotic low-dimensional materials where 1D or 2D building blocks are loosely connected into a 3D whole. Small interactions between the blocks may induce a whole variety of unusual transitions. Here, we examine layered systems that in the direction perpendicular to the layers display a crossover from insulating-like, at high temperatures, to metallic-like character at low temperatures, while being metallic over the whole temperature range within the layers. We show that this change in effective dimensionality correlates with the existence or non-existence of coherent quasiparticles within the layers.

cond-mat.str-el↗

arXiv2001

Absence of a structural transition up to 40 Gpa in MgB2 and the relevance of magnesium non-stoichiometry

We report measurements on MgB2 up to ~40GPa. Increasing pressure yields a monotonous decrease of the lattice parameters and of the c/a ratio, but no structural transition down to parameters smaller than those of AlB2. The transition superconducting temperature also decreases with temperature in a sample dependent way. The results are explained by an increase of the filling of the 2D pxy bands with pressure, the Mg stoichiometry determining the starting position of the Fermi level. Our measurements indicate that these hole bands are the relevant ones for superconductivity.

cond-mat.supr-con↗

arXiv2001

Optical studies of charge dynamics in the optimally-doped Bi2212 and the non-superconducting cobaltate single crystals

An analysis of the frequency-dependent scattering rate reveals signatures of the superconducting gap as well as the pseudogap in high-T_c cuprates. These features can be identified in the temperature-dependent spectral function W(omega), inverted from the optical data of the optimally-doped Bi2212 using an experimentally unambiguous method that shows the behavior of both the maxima and minima in the spectral function.

cond-mat.supr-con↗