Dresden 2026 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 95: Fe-based Superconductors

TT 95.2: Talk

Friday, March 13, 2026, 09:45–10:00, HSZ/0103

Measuring Nematic Fluctuations in FeSe under Hydrostatic and Chemical Pressure — •Adrian Merritt¹, Amir Haghighirad², Dmitry Reznik³, Ayman Said⁴, Ahmet Alatas⁴, Alexei Bosak⁵, Michaela Souliou^2,5, and Frank Weber² — ¹Karlsruher Institut für Technologie - PHI, 76049 Karlsruhe, Germany — ²Karlsruher Institut für Technologie - IQMT, 76344 Eggenstein-Leopoldshafen, Germany — ³University of Colorado, 80309, Boulder, Colorado, USA — ⁴Advanced Photon Source, Argonne National Laboratory, 60439, Illinois, USA — ⁵European Synchrotron Radiation Facility (ESRF), 38043 Grenoble, France

Nematic correlations in iron-based superconductors have been widely studied through phonon softening measured by INS and IXS. Softening of the transverse acoustic phonons near the tetragonal-orthorhombic transition reflects growing nematic fluctuations, which also appear near the superconducting transition, highlighting the competition between nematicity and superconductivity. Our earlier IXS work on FeSe and Co-doped Ba122 showed similar behavior with and without magnetism and across the superconducting transition, suggesting that nematicity may hinder superconductivity.

Our most recent FeSe studies examine the effects of pressure, using both hydrostatic pressure and isoelectronic chemical pressure via S substitution. Both methods introduce magnetic phases and modify the structural transition order, opening a rich, otherwise inaccessible phase diagram. We present these results and compare how nematic fluctuations evolve across the different pressure-induced phases of FeSe.

Keywords: FeSe; nematicity; high pressure; phonons; IXS