Insights from specific heat measurements and beyond*

Understanding the phase interplay in iron-based superconductors is considered to be crucial for unravelling the mechanism behind their superconductivity. In this talk, we focus on new insights into the phase interplay under pressure of two members, FeSe and BaFe₂As₂, from specific heat under pressures [1] up to ~ 2.5 GPa.
For FeSe [2], we show that superconductivity is bulk and competes with magnetism, whenever present. In addition, we conclude that, whenever magnetism is present, magnetic and superconducting fluctuations exist across wide ranges of pressure above their respective, bulk transition temperatures.
For Ba(Fe_1-xCo_x)₂As₂ [3], we argue that the behavior of the nematic transition under pressure is intimately linked to changes of the Fermi surface topology. We complement these data by presenting the first study of elastoresistance under pressure [4] on BaFe₂As₂, which might allow to study the interplay of nematicity and superconductivity under pressure.
[1] Gati et al., Rev. Sci. Instrum. 90, 023911 (2019); [2] Gati et al., PRL 123, 167002 (2019); [3] Gati et al., PRB 100, 064512 (2019); [4] Gati et al., in preparation.