Competing orders and role of fluctuations in FeSe

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Temperature-pressure phase diagram of FeSe from specific heat measurements.
Temperature-pressure phase diagram of FeSe from specific heat measurements.

FeSe is considered as an exceptional member of the family of iron-based superconductors, as it offers the unique possibility to study the interplay of superconductivity with purely nematic as well as magnetic-nematic order by tuning under pressure. Motivated by studying this phase interplay, the authors performed a study of the thermodynamic temperature-pressure phase diagram of FeSe, by measuring the specific heat under pressure up to 2.4 GPa using a recently developed technique optimized for high sensitivity over a wide range of temperatures. This study led to two main findings. First, superconductivity is bulk in FeSe under pressure, and competes with magnetism, whenever present. Second, whenever magnetism is present, fluctuations exist over a wide temperature range above the bulk superconducting and magnetic transitions. The latter result highlights similarities between FeSe and other high-temperature superconductors.

Elena Gati, Anna E. Bohmer, Sergey L. Bud'ko, and Paul C. Canfield, “Bulk superconductivity and role of Fluctuations in the iron-based superconductor FeSe at high pressures” Physical Review Letters, 123, 167002 (2019); DOI: 10.1103/PhysRevLett.123.167002.