The role of spin fluctuations in quantum materials. – (Caitlin Duffy / LNCMI / Seminar). – 15/01/2026, 14H

Seminar LNCMI

Caitlin Duffy  

Seminar LNCMI, 15/01/2026, 14H, seminar room and Visio

Summary
Spin fluctuations are seen as crucial in a wealth of quantum materials and have been theoretically shown to give rise to non-Fermi liquid behaviour and unconventional superconductivity [1,2]. However, their direct observation is a significant challenge, particularly in high magnetic fields where many correlated systems exhibit unusual behaviour.

These fluctuations can be indirectly seen in high fields using techniques such as ultrasound and magnetotransport. Direct observation has recently been made possible using resonant torsion magnetometry (RTM) – a cantilever-based technique that measures spin fluctuations through the anisotropic magnetic susceptibility of a sample. RTM was developed at the NHFML in Los Alamos and has been used to observe transverse magnetic fluctuations preceding the field-induced superconducting phase of UTe2 [3], and to provide support in favour of the quantum spin liquid state in RuCl3 [4].

In this seminar I will introduce this novel and powerful technique that I would like to bring the LNCMI. I will discuss how I aim to complement RTM studies with ultrasound and magnetotransport measurements to answer several long-standing questions about the iron pnictides and iron selenides. These two classes of strange metal both host unconventional superconductivity and quantum criticality. However, the magnetically-ordered phase present in the pnictides, and theoretically assumed to induce its unconventional behaviour, is absent in the selenides.

Additionally, I will briefly mention how this technique can be of interest within the wider community of the LNCMI and the EMFL.

[1] Kontani, Rep. Prog. Phys. 71, 026501 (2009)
[2] Scalapino, J. Low Temp. Phys. 117, 179-188 (1999)
[3] Zambra et al., arXiv:2506.08984
[4] Modic et al., Nat. Phys. 17, pages 240–244 (2021)

Zoom: https://univ-grenoble-alpes-fr.zoom.us/j/94228207316?pwd=khTdznxeFy1ZUYkYftQ0QSox6Fz3iK.1