Vortex dynamics inβ-FeSe single crystals: effects of proton irradiation and small inhomogeneous stress

Abstract

Abstract.We report on the critical current density Jc and the vortex dynamics of pristine and 3 MeV proton irradiated (cumulative dose equal to 2×10 16 cm −2 ) β-FeSe single crystals.We also analyze a remarkable dependence of the superconducting critical temperature Tc, Jc and the flux creep rate S on the sample mounting method. Free-standing crystals present Tc=8.4(1)K, which increases to 10.5(1)K when they are fixed to the sample holder by embedding them with GE-7031 varnish. On the other hand, the irradiation has a marginal effect on Tc. The pinning scenario can be ascribed to twin boundaries and random point defects. We find that the main effect of irradiation is to increase the density of random point defects, while the embedding mainly reduces the density of twin boundaries. Pristine and irradiated crystals present two outstanding features in the temperature dependence of the flux creep rate: S(T ) presents large values at low temperatures, which can be attributed to small pinning energies, and a plateau at intermediate temperatures, which can be associated with glassy relaxation. From Maley analysis, we observe that the characteristic glassy exponent µ changes from ∼ 1.7 to 1.35-1.4 after proton irradiation.

Anomalous reduction in the long-time flux creep relaxation in superconducting Ca10(Pt4As8)((Fe1−x Pt x )2As2)5 (x ≈ 0.05) single crystals

“…The self-field J c at 1.8 K is around 0.42 MA cm −2 , which corresponds to ∼0.7% of the J 0 (T=0 K). Similar (J c /J 0 ) ratio is usually observed in pristine single crystals of other IBS such as FeSe (≈0.6%) [5] and Co-doped BaFe 2 As 2 (≈1%) [2,24]. Low J c /J 0 is expected for vortex pinning dominated by random disorder [1].…”

“…The parameter t 0 obtained in the different fits is in the range 10 −8 -10 −10 [23]. Usually μ values which ranges between 0.7 and ≈1.6 are observed in pristine single crystals of different IBS, which include FeSe [4,5], FeTe 0.6 Se 0.4 [30] and Co-doped BaFe 2 As 2 [14], among others. At low fields, μ is larger than that predicted for the SVR (μ=1/7), but comparable with that obtained in YBCO single crystals [11].…”

“…The concept of glassy relaxation governed by vortex bundles has been largely applied to the study of different families of Fe-based superconductors with anisotropy ranging from low γ (i.e., FeSe) [4,5] to high γ (i.e., SmFeAsO 0.85 F 0.15 ) [6]. The field dependence of the magnetization is characterized by a second peak in the magnetization (SPM) or fishtail [7][8][9][10].…”

Microstructural control of the transport properties of β-FeSe films grown by sputtering

“…From these curves the lattice parameters of these single-phase samples are obtained, showing enlarged a = 3.788 Å and contracted c = 5.463 Å lattice parameters. This implies a distortion of ∆a /a = +0.64 % and ∆c /c = −1.03 %, with reference to a bulk single crystal (a = 3.771 Å and c = 5.521 Å) 37 .…”

Vortex phase diagram in 1111-type CaFe0.89Co0.11AsF single crystal

“…The vortex dynamics and the vortex phase diagram have been systematically investigated in many IBSs, such as the 11 system [14][15][16][17][18][19], 112 system [11,20], 122 system [21][22][23], 111 system [24], oxygen-based 1111 system [10,25], and 12 442 system [26]. Meanwhile, some novel phenomena, i.e.…”