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arXiv 1602.06216cond-mat.supr-con
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过掺杂Fe基超导体Ba_(0.35)Rb_(0.65)Fe_(2As)_2中对对称性与hydrostatic pressure的关系

Probing the pairing symmetry in the over-doped Fe-based superconductor Ba_0.35Rb_0.65Fe_2As_2 as a function of hydrostatic pressure

Z. Guguchia, R. Khasanov, Z. Bukowski, F. von Rohr, M. Medarde, P. K. Biswas, H. Luetkens, A. Amato, E. Morenzoni

摘要:

本文报道了过掺杂铁基高温超导体(Fe-HTS)Ba_{1-x} Rb_xFe_2As_2(x = 0.65)中μ子自旋旋转实验,研究了在常压和流体静压下(p = 2.3GPa)的磁穿透深度λ和λ ^{-2}随温度的变化。我们发现,在这个系统中,λ ^{-2}(T)是最好的d波场景描述。这与最佳掺杂x = 0.35系统的情况相反,后者被认为是无节点s^{+-}波超导体。这表明掺杂诱导了Ba_{1-x} Rb_{x} Fe_{2} As_{2}中的配对对称性从s^{+-}到d波的变化。此外,我们发现d波序参量对压力是鲁棒的,这表明d是过掺杂Ba_{1-x} Rb_{x} Fe_{2} As_{2}中常见的和占主导地位的配对对称性。施加p = 2.3GPa的压力导致λ(0)减小小于5%,而在最佳掺杂x = 0.35时,报道了λ(0)的显著减小。超导转变温度T_c和带隙与T_c的比值2Delta/kBT_c随压力的增加而减小。通过结合目前的数据与先前获得的最佳掺杂系统x = 0.35和端员x = 1,我们得出结论,SC间隙的对称性,以及对SC量的压力效应强烈依赖于Rb掺杂水平。根据假定的Lifshitz转变,即,在空穴掺杂时,Ba_{1-x} Rb_{x} Fe_{2} As_{2}的费米表面中的电子袋消失。

英文摘要:

We report muon spin rotation experiments on the magnetic penetration depth lambda and the temperature dependence of lambda^{-2} in the over-doped Fe-based high-temperature superconductor (Fe-HTS) Ba_{1-x}Rb_ xFe_2As_2 (x = 0.65) studied at ambient and under hydrostatic pressures up to p = 2.3 GPa. We find that in this system lambda^{-2}(T) is best described by d-wave scenario. This is in contrast to the case of the optimally doped x = 0.35 system which is known to be a nodeless s^{+-}-wave superconductor. This suggests that the doping induces the change of the pairing symmetry from s^{+-} to d-wave in Ba_{1-x}Rb_{x}Fe_{2}As_{2}. In addition, we find that the d-wave order parameter is robust against pressure, suggesting that d is the common and dominant pairing symmetry in over-doped Ba_{1-x}Rb_{x}Fe_{2}As_{2}. Application of pressure of p = 2.3 GPa causes a decrease of lambda(0) by less than 5 %, while at optimal doping x = 0.35 a significant decrease of lambda(0) was reported. The superconducting transition temperature T_c as well as the gap to T_c ratio 2Delta/k_BT_c show only a modest decrease with pressure. By combining the present data with those previously obtained for optimally doped system x = 0.35 and for the end member x = 1 we conclude that the SC gap symmetry as well as the pressure effects on the SC quantities strongly depend on the Rb doping level. These results are discussed in the light of the putative Lifshitz transition, i.e., a disappearance of the electron pockets in the Fermi surface of Ba_{1-x}Rb_{x}Fe_{2}As_{2} upon hole doping.

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