Florian Theuss

All Publications

• Disorder-Induced Suppression of Superconductivity in Infinite-Layer Nickelates. Physical review letters Ranna, A., Grasset, R., Gonzalez, M., Lee, K., Wang, B. Y., Abarca Morales, E., Theuss, F., Filipiak, Z. H., Moravec, M., Konczykowski, M., Hwang, H. Y., Mackenzie, A. P., Goodge, B. H. 2025; 135 (12): 126501

  Abstract

  The pairing symmetry of superconducting infinite-layer nickelates is a fundamental yet experimentally challenging question. We employ high-energy electron irradiation to induce disorder in superconducting Nd_{0.825}Sr_{0.175}NiO_{2} thin films, examine the impact of pair-breaking defects on superconductivity, and elucidate the nature of the superconducting gap. Our measurements reveal a complete suppression of superconductivity with increasing disorder, suggesting an unconventional, sign-changing order parameter.

  View details for DOI 10.1103/7lqb-pjkm

  View details for PubMedID 41046393

• Elastocaloric evidence for a multicomponent superconductor stabilized within the nematic state in Ba(Fe1-xCox)2As2. Proceedings of the National Academy of Sciences of the United States of America Ghosh, S., Ikeda, M. S., Chakraborty, A. R., Worasaran, T., Theuss, F., Peralta, L. B., Lozano, P. M., Kim, J. W., Thompson, P. J., Ryan, P. J., Ye, L., Kapitulnik, A., Kivelson, S. A., Ramshaw, B. J., Fernandes, R. M., Fisher, I. R. 2025; 122 (37): e2424833122

  Abstract

  The iron-based high-[Formula: see text] superconductors (SCs) exhibit rich phase diagrams with intertwined phases, including magnetism, nematicity, and superconductivity. The superconducting [Formula: see text] 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 [Formula: see text] 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 [Formula: see text]. 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 [Formula: see text] 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.

  View details for DOI 10.1073/pnas.2424833122

  View details for PubMedID 40920926

• Disorder-Induced Suppression of Superconductivity in Infinite-Layer Nickelates PHYSICAL REVIEW LETTERS Ranna, A., Grasset, R., Gonzalez, M., Lee, K., Wang, B., Morales, E., Theuss, F., Filipiak, Z. H., Moravec, M., Konczykowski, M., Hwang, H. Y., Mackenzie, A. P., Goodge, B. H. 2025; 135 (12)

  View details for DOI 10.1103/7lqb-pjkm

  View details for Web of Science ID 001576223300006

• Absence of a bulk thermodynamic phase transition to a density wave phase in UTe2 PHYSICAL REVIEW B Theuss, F., Shragai, A., Grissonnanche, G., Peralta, L., Simarro, G., Hayes, I. M., Saha, S. R., Eo, Y., Suarez, A., Salinas, A., Pokharel, G., Wilson, S. D., Butch, N. P., Paglione, J., Ramshaw, B. J. 2024; 110 (14)

  View details for DOI 10.1103/PhysRevB.110.144507

  View details for Web of Science ID 001333139000005

• Single-component superconductivity in UTe₂ at ambient pressure NATURE PHYSICS Theuss, F., Shragai, A., Grissonnanche, G., Hayes, I. M., Saha, S. R., Eo, Y., Suarez, A., Shishidou, T., Butch, N. P., Paglione, J., Ramshaw, B. J. 2024

  View details for DOI 10.1038/s41567-024-02493-1

  View details for Web of Science ID 001221052200003

• Resonant Ultrasound Spectroscopy for Irregularly Shaped Samples and Its Application to Uranium Ditelluride PHYSICAL REVIEW LETTERS Theuss, F., Simarro, G., Shragai, A., Grissonnanche, G., Hayes, I. M., Saha, S., Shishidou, T., Chen, T., Nakatsuji, S., Ran, S., Weinert, M., Butch, N. P., Paglione, J., Ramshaw, B. J. 2024; 132 (6): 066003

  Abstract

  Resonant ultrasound spectroscopy (RUS) is a powerful technique for measuring the full elastic tensor of a given material in a single experiment. Previously, this technique was practically limited to regularly shaped samples such as rectangular parallelepipeds, spheres, and cylinders [W. M. Visscher et al. J. Acoust. Soc. Am. 90, 2154 (1991)JASMAN0001-496610.1121/1.401643]. We demonstrate a new method for determining the elastic moduli of irregularly shaped samples, extending the applicability of RUS to a much larger set of materials. We apply this new approach to the recently discovered unconventional superconductor UTe_{2} and provide its elastic tensor at both 300 and 4 kelvin.

  View details for DOI 10.1103/PhysRevLett.132.066003

  View details for Web of Science ID 001182351400005

  View details for PubMedID 38394590