Doping dependence of the critical fluctuation regime in the Fe-based superconductor Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$

Abstract

We investigate the importance of superconducting order parameter fluctuations in the 122 family of Fe-based superconductors, using high-resolution specific heat and thermal expansion data of various Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ single crystals covering a large range of the phase diagram from the strongly underdoped to the overdoped regime. By applying scaling relations of the 3d-XY and the 3d-Lowest-Landau-Level (3d-LLL) fluctuation models to data measured in different magnetic fields, we demonstrate that a strong increase of the critical fluctuation regime is responsible for the transition broadening in magnetic fields, which is a direct consequence of a magnetic-field-induced finite size effect due to a reduction of the effective dimensionality by a decreasing magnetic length scale related to the mean vortex separation and the confinement of quasiparticles in low Landau levels. The fluctuations are stronger in the underdoped and overdoped regimes and appear to be weakest at optimal doping.

References in corpus (3)

• Thermodynamic phase diagram and phase competition in BaFe2(As1-xPx)2 studied by thermal expansion
• Thermal fluctuations and vortex melting in the classical superconductor Nb3Sn from high-resolution specific-heat measurements
• Magnetic field induced enlargement of the regime of critical fluctuations in the classical superconductor V3Si from high-resolution specific heat experiments

Cited by in corpus (3)

• Strong Correlations, Strong Coupling and s-wave Superconductivity in Hole-doped BaFe2As2 Single Crystals
• Vortex-lattice melting and paramagnetic depairing in the nematic superconductor FeSe
• Restoration of tetragonal $C_4$ symmetry coexistent with filamentary superconductivity in the pressure induced intermediate phase in the iron-based superconductor Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$