Elastocaloric evidence for a multicomponent superconductor stabilized within the nematic state in Ba(Fe1−xCox)2As2
The iron-based high-Tc superconductors exhibit rich phase diagrams with intertwined phases, including magnetism, nematicity and superconductivity. We use the AC elastocaloric effect (ECE), which is a highly sensitive, thermodynamic probe of phase transitions under uniaxial strain, 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 highlight the significant role of nematic order in determining the pairing symmetry close to optimal doping in this extensively studied iron-based superconductor, while also demonstrating the power of ECE in uncovering strain-tuned phase diagrams of quantum materials.
Dr. Sayak obtained his PhD. from Cornell University where studied the ultrasonic and electronic properties of quantum materials at cryogenic temperatures and high magnetic fields. Presently, he is a postdoctoral fellow at Stanford university.
About the QSQM: The EFRC-QSQM center aims to develop and apply nontrivial quantum sensing to measure and correlate local and nonlocal quantum observables in exotic superconductors, topological crystalline insulators, and strange metals. The center is led by the University of Illinois at Urbana-Champaign in partnership with the University of Illinois at Chicago and the SLAC National Accelerator Laboratory.
