Superconductivity-enhanced nematicity and “s+d” gap symmetry in Fe(Se_1−xS_x)

详细信息    查看全文

• 作者：Liran Wang ; Fr&eacute ; d&eacute ; ric Hardy ; Thomas Wolf ; Peter Adelmann ; Rainer Fromknecht ; Peter Schweiss and Christoph Meingast
• 刊名：physica status solidi (b)
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：254
• 期：1
• 全文大小：734K
• ISSN：1521-3951

文摘

Superconducting iron chalcogenide FeSe has the simplest crystal structure among all the Fe-based superconductors. Unlike other iron pnictides, FeSe exhibits no long-range magnetic order accompanying the tetragonal-to-orthorhombic structural distortion, which raises the fundamental question about the role of magnetism and its associated spin fluctuations in mediating both nematicity and superconductivity. The extreme sensitivity of FeSe to external pressure suggests that chemical pressure, induced by substitution of Se by the smaller ion S, could also a be good tuning parameter to further study the coupling between superconductivity and nematicity and to obtain information on both the Fermi-surface changes and the symmetry of the superconducting state. Here, we study the thermodynamic properties of Fe(Se1−xSx) for three compositions, x=0, 0.08, and 0.15, using heat-capacity and thermal-expansion measurements. With increasing S content, we observe a significant reduction of the tetragonal-to-orthorhombic transition temperature Ts. However, this suppression of Ts is counterintuitively accompanied by an enhancement of the orthorhombic distortion δ below Tc, which clearly indicates that superconductivity favors the nematic state. In parallel, the superconducting transition temperature Tc is sizeably enhanced, whereas the increase of the Sommerfeld coefficient γn is quite moderate. In the T→0 limit, an unusually large residual density of states is found for x>0 indicative of significant substitution-induced disorder. We discuss these observations in the context of “s+d” superconducting-state symmetry.