Interplay of stripe and double-Q magnetism with superconductivity in Ba1−xKxFe2As2 under the influence of magnetic fields

Abstract

At x≈0.25Ba1−xKxFe2As2 undergoes a novel first-order transition from a fourfold symmetric double-Q magnetic phase to a twofold symmetric single-Q phase, which was argued to occur simultaneously with the onset of superconductivity [Böhmer et al., Nat. Commun. 6, 7911 (2015)]. Here, by applying magnetic fields up to 10 T, we investigate in more detail the interplay of superconductivity with this magnetostructural transition using a combination of high-resolution thermal-expansion and heat-capacity measurements. We find that a magnetic field suppresses the reentrance of the single-Q orthorhombic phase more strongly than the superconducting transition, resulting in a splitting of the zero-field first-order transition. The suppression rate of the orthorhombic reentrance transition is stronger for out-of-plane than for in-plane fields and scales with the anisotropy of the superconducting state. These effects are captured within a phenomenological Ginzburg-Landau model, strongly suggesting that the suppression of the reentrant orthorhombic single-Q phase is primarily linked to the field-induced weakening of the superconducting order. Not captured by this model is, however, a strong reduction in the orthorhombic distortion for out-of-plane fields, which deserves further theoretical attention.

Source-reported materials — not catalogue approval

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