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

• 成果类型: Article
• 署名作者: Ghosh, Sayak; Ikeda, Matthias S.; Chakraborty, Anzumaan R.; Worasaran, Thanapat; Theuss, Florian; Peralta, Luciano B.; Lozano, P. M.; Kim, Jong-Woo; Thompson, P. J.; Ryan, Philip J.; Ye, Linda; Kapitulnik, Aharon; Kivelson, Steven A.; Ramshaw, B. J.; Fernandes, Rafael M.; Fisher, Ian R.
• 署名单位: Stanford University; Stanford University; University of Minnesota System; University of Minnesota Twin Cities; Cornell University; Universidad de los Andes (Colombia); United States Department of Energy (DOE); Argonne National Laboratory; University of Liverpool; Stanford University; Canadian Institute for Advanced Research (CIFAR); University of Illinois System; University of Illinois Urbana-Champaign; University of Illinois System; University of Illinois Urbana-Champaign
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-10751
• DOI: 10.1073/pnas.2424833122
• 发表日期: 2025-09-16
• 关键词: order-parameter

摘要

The iron-based high-Tc superconductors (SCs) 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 reentrant 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 subdominant pairing instability that competes strongly with the dominant s +/- instability. Our results highlight the significant role of nematic order in determining the pairing symmetry close to optimal doping in this extensively studied iron-based SC, while also demonstrating the power of ECE in uncovering strain-tuned phase diagrams of quantum materials.