Study of TAFF and vortex phase of Fe_xTe_0.60Se_0.40 (0.970 ≤ x ≤ 1.030) single crystals

Abstract

Single crystalline samples with starting compositions FexTe0.60Se0.40 (x = 0.970, 0.985, 1, 1.015 and 1.030) have been grown using the self-flux method to study the effect of Fe variation (x) on the structural and superconducting properties of the grown single crystalline samples. All the grown samples are found superconducting and among all, the FeTe0.60Se0.40 (x = 1) sample shows the highest superconducting transition temperature (TC). For the samples with x other than 1, a decrease in the superconducting properties, such as TC, activation energy (U0) and upper critical field (HC2(0)), has been observed. The thermal activation energy (TAE) of the flux flow has been calculated using the conventional method and modified thermally activated flux flow (TAFF) model. The values of U0(H) show transition from the single vortex pinning regime to the collective vortex pinning regime at 2T. Also, the presence of planer defects has been estimated via both models. Furthermore, the modified TAFF model suggests three dimentional (3D) behaviour for all the grown single crystals. The vortex phase diagrams have been established by analysing the magnetoresistance data. The analysis reveals the transitions from unpinned to pinned vortex liquid region and also from the pinned vortex liquid state to vortex glass state. In the vortex phase diagram, below the critical temperature (T*), the critical exponent (s) is in a good agreement with the ‘q’ values for the 3D behaviour of vortex states for all the grown samples.

Thermally activated flux flow and inter-granular coupling properties in (Bi, Pb)-2223 superconductor added with ZnO nanoparticles

“…( 9), the vortex glass temperature T g and critical exponent s were evaluated. According to the vortex-glass theory, s ≤ 2.7 corresponds to the 2D vortex glass state while the values of s in between 2.7 to 8.5 correspond to the 3D vortex glass state [14,17,58]. As represented in Table 2, the obtained s values for different composites are smaller than 2.7, which indicates the 2D vortex glass state for the prepared composites.…”

“…It had been shown that introducing arti cial pinning centers in the superconducting matrices, apart from those which occur naturally, is a very effective method to avoid vortex motion and improve the ux pinning capability and superconducting transport properties [8,10,[27][28][29][30][31]. Different techniques such as chemical doping [17,[32][33][34], high energy ions irradiation [31,35], and different types of additives [1,2,[36][37][38][39][40][41][42][43] were used in the literature for this purpose. It has been proved that the appropriate amount of nanosized additives could improve the microstructure, intergranular coupling, and ux pining capability of the high-temperature ceramic superconductors [2, 36-39, 42, 44, 45].…”

“…Strong thermal uctuations give a rich variety of vortex phases and vortex dynamics in ceramic superconductors [15]. The vortex liquid (VL) and vortex glass (VG) phases indicate the resistive and pure superconducting states, respectively [17].…”

“…As can be observed, however, the plateau is not seen but rather increases as temperature decreases. Such behavior has been observed in cuprates and iron-based superconductors[14,17,31, 61]. To solve this contradiction in the TAFF model,Zhang et al [63, 64] established a new model, called the modi ed TAFF model, by suggesting non-linear activated energy of the form U(T, B) = U 0 (B)(1 − T /T C ) q .…”

Effects of Thallium fluoride substitution on the flux pinning energies of (Cu0.5, Tl0.5)Ba2Ca2Cu3O10-δ superconductors

“…As a result, substantial thermal fluctuations in high-temperature superconductors (HTSCs), vortex phases, and dynamics vary [5,6]. The two distinct vortex phases, such as the liquid and glass phases, respectively, determine the normal and superconducting states [7]. Most of the dynamical complexity of the vortices is due to the battle between thermal fluctuations, arbitrary pinning, and the interaction of vortices [8].…”