Volume 2, Issue 1

BiS2-based compounds constitute a new family of layered superconductors. In this article, several experimental findings on the superconductivity and related properties of the BiS2 family are reviewed. In particular, the focus is on the conditions required for the emergence of superconductivity and higher superconducting transition temperature in the BiS2 family: it is shown that optimizing the electron doping and crystal structure are important. Further, a few notable characteristics such as the coexistence of superconductivity and magnetism as well as the relation between the superconductivity and chargedensity- wave instability are introduced in brief.

We report impact of hydrostatic pressure on the newly discovered BiS2 based superconductors. In last couple of years the new BiS2 based superconductor attracted great attention of the condensed matter physics community. These new layered BiS2-based compounds are very sensitive to the concentration of carriers doping and pressure that cause profound changes in their physical properties with appearance of superconductivity in the vicinity of their insulating/semiconducting state. The BiS2-based new compounds are expected to provide us with the next stage of exploring new superconductors and to discuss their exotic superconductivity mechanisms. In current review, we present most of our findings related to impact of hydrostatic pressure on superconductivity of new BiS2 based superconductors at one place.

Recently we reported a new way to manipulate vortices in thin superconducting films by local mechanical contact without magnetic field, current or altering the pinning landscape [1]. We use scanning superconducting interference device (SQUID) microscopy to image the vortices, and a piezo element to push the tip of a silicon chip into contact with the sample. As a result of the stress applied at the contact point, vortices in the proximity of the contact point change their location. Here we study the characteristics of this vortex manipulation, by following the response of individual vortices to single contact events. Mechanical manipulation of vortices provides local view of the interaction between strain and nanomagnetic objects, as well as controllable, effective, localized, and reproducible manipulation technique.

The recent report of superconductivity under high pressure at the record transition temperature of Tc =203 K in pressurized H2S has been identified as conventional in view of the observation of an isotope effect upon deuteration. Here it is demonstrated that conventional theories of superconductivity in the sense of BCS or Eliashberg formalisms cannot account for the pressure dependence of the isotope coefficient. The only way out of the dilemma is a multi-band approach of superconductivity where already small interband coupling suffices to achieve the high values of Tc together with the anomalous pressure dependent isotope coefficient. In addition, it is shown that anharmonicity of the hydrogen bonds vanishes under pressure whereas anharmonic phonon modes related to sulfur are still active.

We investigated the magnetic flux-pinning in iron-based 1111-type (REFeAsO, RE= rare earth) and 11- type (FeSe1−xTex) superconductors by third harmonic acmagnetic susceptibility measurements, a technique sensitive to the dynamics of magnetization, probing non-linear processes in flux pinning transport. Despite the larger thermal fluctuations due to the high critical temperature and large anisotropy, flux dynamics of 1111-type pnictides points out a more efficient pinning mechanism than the one in the 11-type chalcogenides. We have associated the stronger pinning in the 1111-family to the presence of REO (RE=rare earth) spacer layers separating the active FeAslayers unlike the 11-chalcogenides in which no spacer layers are present. Therefore, the disorder in the FeAs layers induced by the misfit strain due to spacer layers has an important role in the enhanced flux pinning of 1111-type superconductors.