Upper critical field of isoelectron substituted SrFe2(As1−xPx<

Abstract

The upper critical field Hc2 of optimally doped iron-based superconductor SrFe2(As1−xPx)2 (x = 0.35, Tc = 25 K) was measured as a function of temperature down to 1.6 K for two principal directions of magnetic field H c and H a. Measurements were performed in pulsed magnetic fields up to 65 T using a tunnel-diode resonator technique on as-grown and heavy-ion irradiated single crystals, with columnar defect density corresponding to a matching field Bφ = 25 T. The Hc2,c(T ) is close to T -linear, while clear saturation is observed for Hc2,a(T ), leading to a strongly temperature dependent anisotropy parameter γ. The linear shape of Hc2,c(T ) is very similar to that observed in nodal KFe2As2 but very different from full-gap LiFeAs. Irradiation does not introduce any additional features on Hc2(T ) line corresponding to the matching field. Instead, it suppresses uniformly both Tc and Hc2, keeping their ratio constant.

Tunnel diode resonator for precision magnetic susceptibility measurements in a mK temperature range and large DC magnetic fields

“…The tunnel diode resonator (TDR) technique 1 of radio frequency magnetic susceptibility measurements is broadly used for the studies of magnetic and superconducting materials. [2][3][4][5][6][7][8][9] The technique detects the changes in the inductance, L, of an LC tank circuit due to the variation of sample magnetic susceptibility via the shift of the resonant frequency, 2πf 0 = 1/…”

“…4 The TDR technique is recognized as a powerful probe for resistivity and magnetic susceptibility measurements, and it is used routinely in both DC and pulsed high magnetic field experiments to detect qualitative features in the fielddependent measurements, such as quantum oscillations, 16 energy level crossings, 6,7 or the upper critical fields of superconductors. 8,[16][17][18][19][20][21] Furthermore, TDR measurements of superconductors in a magnetic field can be used to study the elastic properties of the vortex lattice as well as the critical currents. [21][22][23] For a superconductor in the mixed state, the measured quantity, λ m , is related to the Campbell penetration depth λ C by a relation λ 2 m = λ 2 L + λ 2 C .…”

Observation of lock-in phenomena in heavy-ion-irradiated single crystal ofBa(Fe0.93Co0.07)2Taen1, Yagyuda2, Nakajima3 et al. 2014Phys. Rev. B6041View full textAdd to dashboardCite

“…A recent numerical study shows that different angular dependencies of J c may be obtained by changing ε ξ and ε λ , even in the case of spherical pinning sites [25]. For the particular case of the IBSs of the BaFe 2 As 2 family (so-called "122"), ε ξ estimated from H c2 is ∼ 2 near T c and almost unity in the low temperature limit [26][27][28]. In addition, single crystals of 122 superconductors with optimal doping are free from twin boundaries, in contrast to YBCO, so that the effect of CDs can be purely investigated.…”

Upper critical field of high-quality single crystals of KFe2As2

“…[20][21][22] Recently, we found similar T -linear dependence in the optimally doped SrFe 2 (As 1−x P x ) 2 , x = 0.35. 23 Because of the nodal superconducting gap of this compound, 24 we speculated a possible link between the nodal superconducting gap and the T -linear dependence of H c2 . On the other hand, the T -linear dependence of H c2,c (T ) observed in dirty iron pnictides 25 and doped MgB 2 (Ref.…”