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Elastocaloric evidence for a multicomponent superconductor stabilized within the nematic state in Ba(Fe1−xCox)2As2

Cornell Affiliated Author(s)

Author

Sayak Ghosh
Matthias Ikeda
Anzumaan Chakraborty
Thanapat Worasaran
Florian Theuss
Luciano Peralta
P.~M. Lozano
Jong-Woo Kim
Philip Ryan
Linda Ye
Aharon Kapitulnik
Steven Kivelson
B.~J. Ramshaw
Rafael Fernandes
Ian Fisher

Abstract

The iron-based high-Tc superconductors exhibit rich phase diagrams with intertwined phases, including magnetism, nematicity and superconductivity. The superconducting Tc in many of these materials is maximized in the regime of strong nematic fluctuations, making the role of nematicity in influencing the superconductivity a topic of intense research. Here, we use the AC elastocaloric effect (ECE) to map out the phase diagram of Ba(Fe1−xCox)2As2 near optimal doping. The ECE signature at Tc on the overdoped side, where superconductivity condenses without any nematic order, is quantitatively consistent with other thermodynamic probes that indicate a single-component superconducting state. In contrast, on the slightly underdoped side, where superconductivity condenses within the nematic phase, ECE reveals a second thermodynamic transition proximate to and below Tc. We rule out magnetism and re-entrant tetragonality as the origin of this transition, and find that our observations strongly suggest a phase transition into a multicomponent superconducting state. This implies the existence of a sub-dominant pairing instability that competes strongly with the dominant s± instability. Our results thus motivate a re-examination of the pairing state and its interplay with nematicity in this extensively studied iron-based superconductor, while also demonstrating the power of ECE in uncovering strain-tuned phase diagrams of quantum materials.

Date Published

Journal

arXiv e-prints

Number of Pages

arXiv:2402.17945

DOI

10.48550/arXiv.2402.17945

Group (Lab)

Brad Ramshaw Group

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