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${}_2$

Abstract

The hole doped Fe-based superconductors Ba${}_{1-x}$A${}_x$Fe${}_2$As${}_2$ (where A=Na or K) show a particular rich phase diagram. It was observed that an intermediate re-entrant tetragonal phase forms within the orthorhombic antiferromagnetically-ordered stripe-type spin density wave state above the superconducting transition [S. Avci et al., Nature Comm. 5, 3845 (2014), A. E. Böhmer et al., arXiv:1412.7038v2]. A similar intermediate phase was reported to appear if pressure is applied to underdoped Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ [E. Hassinger et al., Phys. Rev. B 86, 140502(R) (2012)]. Here we report data of the electric resistivity, Hall effect, specific heat, and the thermoelectrical Nernst and Seebeck coefficients measured on a Ba${}_{0.85}$K${}_{0.15}$Fe${}_2$As${}_2$ single crystal under pressure up to 5.5 GPa. The data reveals a coexistence of the intermediate phase with filamentary superconductivity. The Nernst coefficient shows a large signature of nematic order that coincides with the stripe-type spin density wave state up to optimal pressure. In the pressure-induced intermediate phase the nematic order is removed, thus confirming that its nature is a re-entrant tetragonal phase.

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• Expansion of the tetragonal magnetic phase with pressure in the iron-arsenide superconductor Ba{1-x}KxFe2As2
• Emergent magnetic degeneracy in iron pnictides due to the interplay between spin-orbit coupling and quantum fluctuations
• Spin-Orbit Coupling and Magnetic Anisotropy in Iron-Based Superconductors
• Trapping Majorana Zero Modes in Vortices of Magnetic Texture Crystals Coupled to Nodal Superconductors
• Antiferromagnetic chiral spin density wave and strain-induced Chern insulator in the square lattice Hubbard model with frustration
• Possible coexistence of double-Q magnetic order and chequerboard charge order in the re-entrant tetragonal phase of Ba0.76K0.24Fe2As2
• Predictability as a probe of manifest and latent physics: The case of atomic scale structural, chemical, and polarization behaviors in multiferroic Sm-doped BiFeO3