arXiv subjects

Robson R. da Silva

Publications and source records attributed to Robson R. da Silva.

4 recordsLinked to original sources

arXiv2019

Unconventional Spin-Glass-Like State in AgCo2V3O10, the Novel Magnetically Frustrated Material

Single crystals of a new silver and-cobalt based vanadate AgCo2V3O10 were grown from a melted mixture. The crystal structure determination reveals that this new vanadate crystallizes in triclinic system with space group P-1. The structure of the titled compound is constructed from CoO6octahedra and VO4 tetrahedra sharing edges and vertices leading to an open three-dimensional framework delimiting tunnels along [001], where the Ag cations are located. The bands observed in Raman spectrum were assigned to corresponding vibrations of the VO4 groups. DC and AC magnetization (susceptibility) measurements revealed the spin-glass (SG) -type transition below a frequency-independent temperature Tf(H) that is nearly independent on the applied magnetic field. Magnetic field H> 10 kOe induces the spin glass antiferromagnet. These observations brings AgCo2V3O10 into the class of geometrically frustrated magnetic systems.

cond-mat.mtrl-sci↗

arXiv2015

Unstable and elusive superconductors

We briefly review earlier and report original experimental results in the context of metastable or possible superconducting materials. We show that applied electric field induces conducting state in Copper Chloride (CuCl) whose characteristics resemble behavior of sliding charge-density-wave(s) (CDW). We discuss whether the sliding CDW or collective transport of similar ordered charge phase(s) may account for the problem of "high-temperature superconductivity" observed in this and other materials, including Cadmium Sulfide (CdS), metal-ammonia solutions, polymers, amorphous carbon and tungsten oxides. We also discuss a local superconductivity that occurs at the surface of graphite and amorphous carbon under deposition of foreign atoms/molecules.

cond-mat.supr-con↗

arXiv2011

Local and Global Superconductivity in Bismuth

We performed magnetization M(H,T) and magnetoresistance R(T,H) measurements on powdered (grain size ~ 149 micrometers) as well as highly oriented rhombohedral (A7) bismuth (Bi) samples consisting of single crystalline blocks of size ~ 1x1 mm2 in the plane perpendicular to the trigonal c-axis. The obtained results revealed the occurrence of (1) local superconductivity in powdered samples with Tc(0) = 8.75 \pm 0.05 K, and (2) global superconductivity at Tc(0) = 7.3 \pm 0.1 K in polycrystalline Bi triggered by low-resistance Ohmic contacts with silver (Ag) normal metal. The results provide evidence that the superconductivity in Bi is localized in a tiny volume fraction, probably at intergrain or Ag/Bi interfaces. On the other hand, the occurrence of global superconductivity observed for polycrystalline Bi can be accounted for by enhancement of the superconducting order parameter phase stiffness induced by the normal metal contacts, the scenario proposed in the context of "pseudogap regime" in cuprates [E. Berg et al., PRB 78, 094509 (2008)].

cond-mat.supr-con↗

arXiv2007

Charge Ordering in Amorphous WO$_{x}$ Films

We report on the observation of highly anisotropic viscous electronic conducting phase in amorphous WO$_{1.55}$ films that occurs below a current (I)- and frequency (f)- dependent temperature T*(I, f). At T < T*(I, f) the rotational symmetry of randomly disordered electronic background is broken leading to the appearance of mutually perpendicular metallic- and insulating-like states. A rich dynamic behavior of the electronic matter occurring at T < T*(I, f) provides evidence for an interplay between pinning effects and electron-electron interactions. The results strongly suggest a dynamic crystallization of the disordered electronic matter, viz. formation of sliding Wigner crystal, as well as the occurrence of quantum smectic or stripe phase in the pinning-dominated regime.

cond-mat.str-el↗