Title: Superconductivity amidst magnetism climbing high in two-dimensional iron-based materials
Abstract
At everyday temperatures, all materials resist electrical flow, causing energy to be lost as heat. Cooling typically does not eliminate this resistance. Superconductors are the rare exemption: below a critical temperature (TC), they carry electric current with zero resistance. This remarkable quantum state arises when electrons pair up and move coherently without scattering. Because of this, superconductors can carry very high currents and enable technologies such as the powerful magnets in MRI systems, synchrotrons, and particle accelerators at scientific user facilities. If materials are designed to remain superconducting at warmer temperatures (cf., above liquid nitrogen), electricity could be transmitted more efficiently, transforming global power systems. Yet conventional theory cannot explain the stronger “glue” that holds electron pairs together at high-temperatures [1].
This gap motivates new experimental platforms to elucidate the complex electron correlations central to our work. I will highlight our research on iron-based high-temperature superconductors whose electron pairing remains stable due to a unique two-dimensional (2D) lattice [2]. We show how intercalation tunes the structure from three to two dimensions, revealing a clear link between enhanced TC and increased spacing between iron planes [3]. With non-traditional techniques using brilliant synchrotron light, we uncover subtle phases that shed light on the interplay between spin fluctuations and itinerant electrons [4], opening new paths for designing layered quantum materials with higher transition temperatures.
Literature
[1] R.M. Fernandes, A.I. Coldea, H. Ding, I.R. Fisher, P. J. Hirschfeld, and G. Kotliar, “Iron pnictides and Chalcogenides: a New Paradigm for Superconductivity”, Nature 2022, 601, 35.
[2] P. Mangelis, R.J. Koch, H. Lei, R.B. Neder, M.T. McDonnell, M. Feygenson, C. Petrovic, A. Lappas, and E.S. Bozin, “Correlated Disorder-to-Order Crossover in the Local Structure of KxFe2-ySe2-zSz”, Phys. Rev. B 2019, 100, 094108.
[3] A. Deltsidis, L. Simonelli, G. Vailakis, I.C. Berdiell, G. Kopidakis, A. Krztoń-Maziopa, E.S. Bozin, and A. Lappas, “Lix(C5H5N)yFe2–zSe2: A Defect Resilient Expanded-Lattice High-Temperature Superconductor”, Inorg. Chem. 2022, 61, 12797.
[4] A. Lappas, M. Kaitatzi, A. Deltsidis. I.C. Berdiell, L. Simonelli, A. Missyul, M. Etter and E.S. Bozin, “Orbital-Selective Instabilities and Spin Fluctuations at the Verge of Superconductivity in Interlayer-Expanded Iron Selenide”, Chem. Mater. 2025, 37, 8581.