Superconductivity-induced nematicity

Abstract

The role of nematic order for the mechanism of high-temperature superconductivity is highly debated. In most iron-based superconductors (IBS) the tetragonal symmetry is broken already in the normal state, resulting in orthorhombic lattice distortions, static stripe magnetic order, or both. Superconductivity then emerges, at least at weak doping, already from the state with broken $C_4$ rotational symmetry. One of the few stoichiometric IBS, lithium iron arsenide, superconducts below 18 K and does not display either structural or magnetic transition in the normal state. Here we demonstrate, using angle-resolved photoemission, that even superconducting state in LiFeAs is also a nematic one. We observe spontaneous breaking of the rotational symmetry in the gap amplitude on all Fermi surfaces, as well as unidirectional distortion of the Fermi pockets. Remarkably, these deformations disappear above superconducting $T_c$. Our results demonstrate the realization of a novel phenomenon of superconductivity-induced nematicity in IBS, emphasizing the intimate relation between them. We suggest a theoretical explanation based on the emergence of a secondary instability inside the superconducting state, which leads to the nematic order and s-d mixing in the gap function.

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• Superconducting Arcs
• Chiral to Nematic Crossover in the Superconducting State of 4Hb-TaS${}_2$
• Two distinct superconducting states controlled by orientation of local wrinkles in LiFeAs
• Nematicity and superconductivity: Competition versus cooperation
• Electron and Superconducting Properties of the AFeAs (A= Li, Na) Family Alkali-Metal Pnictides: Current Stage of the Research (mini-review)
• Fermi surface tomography
• Phonon-induced rotation of the electronic nematic director in superconducting Bi${}_2$Se${}_3$
• Local Structure of Mott Insulating Iron Oxychalcogenides La${}_2$O${}_2$Fe${}_2$O$M$${}_2$ ($M$ = S, Se)
• Absence of hexagonal to square structural transition in LiFeAs vortex matter
• Stronger quantum fluctuation with larger spins: Emergent magnetism in the pressurized high-temperature superconductor FeSe
• The role of electromagnetic gauge-field fluctuations in the selection between chiral and nematic superconductivity
• Absence of nematic instability in LiFeAs
• Ubiquity of rotational symmetry breaking in superconducting films, from Fe(Te,Se)/Bi${}_2$Te${}_3$ to Nb, and the effect of measurement geometry
• On the existence of nematic-superconducting states in the Ginzburg-Landau regime
• Dynamical vortices in electron-phonon superconductors
• Specific Heat and the gap structure of a Nematic Superconductor, application to FeSe