Multiband effects on the upper critical field angular dependence of 122-family iron pnictide superconductors

Abstract

Detailed measurements of the in-plane resistivity were performed in a high-quality Ba($$\hbox {Fe}_{1-x}\hbox {Co}_{{x}}$$ Fe 1 - x Co x )$$_2\hbox {As}_2$$ 2 As 2 ($$x=0.065$$ x = 0.065 ) single crystal, in magnetic fields up to 9 T and with different orientations $$\theta$$ θ relative to the crystal c axis. A significant $$\rho (T)_{H,\theta }$$ ρ ( T ) H , θ rounding is observed just above the superconducting critical temperature $$T_c$$ T c due to Cooper pairs created by superconducting fluctuations. These data are analyzed in terms of a generalization of the Aslamazov-Larkin approach, that extends its applicability to high reduced-temperatures and magnetic fields. This method allows us to carry out a criterion-independent determination of the angular dependence of the upper critical field, $$H_{c2}(\theta )$$ H c 2 ( θ ) . In spite of the relatively small anisotropy of this compound, it is found that $$H_{c2}(\theta )$$ H c 2 ( θ ) presents a significant deviation from the single-band 3D anisotropic Ginzburg-Landau (3D-aGL) approach, particularly for large $$\theta$$ θ (typically above $$\sim 60^o$$ ∼ 60 o ). These results are interpreted in terms of the multiband nature of these materials, in contrast with other proposals for similar $$H_{c2}(\theta )$$ H c 2 ( θ ) anomalies. Our results are also consistent with an effective anisotropy factor almost temperature independent near $$T_c$$ T c , a result that differs from the ones obtained by using a single-band model.

Unveiling intrinsic material and extrinsic pinning dimensionality in superconductors: Why Fe(Se,Te) is able to mimic YBCO

“…Llovo et al. 11 estimated the upper critical field of 122 type iron pnictide superconductor by using different xR N criteria and anticipated that the upper critical field is unaffected by choosing different criteria. Likewise, in the case of (Ba,K)Fe 2 As 2 superconductor, when the different x R N criteria are used to estimate the angular behavior of the upper critical field, the results are also unaffected.…”

“… 8 Nonetheless, the depairing current is linked to the upper critical field but the critical current density is associated with the irreversibility field, which is an essential property for applications. 9 , 10 , 11 …”

Effective Magnetic Field Dependence of the Flux Pinning Energy in FeSe0.5Te0.5 Superconductor

“…which Llovo et al observe a deviation of the Hc2(θ) from the ε (θ) scaling [35]. A further step is to test the scaling approach followed by Xiao et al in the case of the layered HTS BiSCCO compound [36], an approach which already has been proven effective to describe the angular dependence of another physical quantity strongly dependent on material pinning properties, which is the Flux Flow Instability critical voltage V* [37].…”

Enhancement of the critical current by surface irregularities in Fe-based superconductors

“…FeSC also present a multiband electronic structure [2][3][4], which leads to unconventional behavior of observables such as the magnetic penetration depth [6], the Seebeck coefficient [7], the specific heat [8,9], or the upper critical field [10][11][12][13]. On the other hand, these materials present some properties that make them interesting from an applications perspective, such as high critical and irreversibility magnetic fields [14][15][16][17][18], and a relatively low anisotropy.…”