The influence of Si on the superconducting properties of LiFeAs single crystals

Abstract

The results of Si doping on the superconducting transition temperature, critical current density, irreversibility field, upper critical field, coherence length and magnetic relaxation of LiFeAs single crystals are reported for H c. The superconducting transition temperature of the Si doped sample decreases by about of 6.4 K/at.%, which is likely due to the pair breaking effect. The presence of a secondary high-field fishtail maximum, which shifts progressively with temperature, is associated with the extrinsic pinning centers created by Si. The increase of the critical current densities in intermediate magnetic fields of about three times as compared to our undoped material indicates that very small amounts of Si act as effective pinning sites for the flux pinning enhancement in the material. Pinning force curves measured at different temperatures obey a normalized form of Kramer's law, which indicates that the critical current density is limited by one predominant flux pinning mechanism. Analysis of the temperature and field dependences of the magnetic relaxation is consistent with the collective pinning model. The magnetic relaxation measurements combined with the peak position of the critical current density in the B-T phase diagram suggest an elastic-plastic transition of the vortex lattice at higher temperatures and fields.

Crystal structure and superconducting properties of hole-doped Ca0.89Na0.11FFeAs single crystals

“…The observed behavior might be dominated by the presence of a crossover from elastic vortex creep at low temperatures to plastic creep at elevated temperatures. A similar flux dynamics, leading to a substantial decrease or even to negative µ values, has been observed in a number of superconducting cuprates and pnictides [41][42][43][44]. In contrast, for Ca 0.6 Na 0.4 Fe 2 As 2 we found a single value for µ = 0.58, which could fit the whole temperature range satisfactorily.…”

Fabrication and critical current density analysis of YBa2Cu3O7+(BaSnO3)′/YBa2Cu3O7+(BaSnO3)″ multilayer films

“…Possible explanation of the vortex dynamics along weak pinning layers is vortex cutting [25,26] or vortex-bow-out [27], but further studies are needed to understand detailed vortex behavior in this system. Temperature and magnetic field dependences of J c have been analyzed to understand vortex pinning in superconductors [28][29][30][31]. Although the ML-structure dependence of J c is discussed mainly at 77 K in the present study, detailed J c -B analysis at various temperatures is needed for more detailed understanding of vortex behavior in the MLs.…”

Flux pinning and magnetic relaxation in Ga-doped LiFeAs single crystals

“…We have observed a very similar situation for LiFeAs doped with other p-elements. 37 The most likely interpretation might be either occupation of additional sites within the LiAs-layer or partial substitution of the Li-site by the extremely small amount of Ga with different size (r(Li þ ) ¼ 73 pm, r(Ga 3þ ) ¼ 61 pm 31 ). A substitution of Li in LiFeAs by additional Fe in the sense of a solid solution Li 1-x Fe 1þx As was earlier discussed 33 after it was already indicated in the original communication describing the first synthesis and structure determination by Juza and Langer in 1968.…”