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arXiv · 1505.01645

Infrared study of the spin reorientation transition and its reversal in the superconducting state in underdoped Ba$ _{1-x} $K$ _{x} $Fe$ _{2} $As$ _{2} $

Ben PP Mallett·Premysl Marsik·Meghdad Yazdi-Rizi·Thomas Wolf·Anna Böhmer·F. Hardy·Christof Meingast·Dominik Munzar·Christian Bernhard
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Abstract

With infrared spectroscopy we investigated the spin-reorientation transition from an orthorhombic antiferromagnetic (o-AF) to a tetragonal AF (t-AF) phase and the reentrance of the o-AF phase in the superconducting state of underdoped Ba$ _{1-x} $K$ _{x} $Fe$ _{2} $As$ _{2} $. In agreement with the predicted transition from a single-$\mathbf{Q}$ to a double-$\mathbf{Q}$ AF structure, we found that a distinct spin density wave (SDW) develops in the t-AF phase. The pair breaking peak of this SDW acquires much more low-energy spectral weight than the one in the o-AF state which indicates that it competes more strongly with superconductivity. We also observed additional phonon modes in the t-AF phase which likely arise from a Brillouin-zone folding that is induced by the double-$\mathbf{Q}$ magnetic structure with two Fe sublattices exhibiting different magnitudes of the magnetic moment.

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Ben PP Mallett, Premysl Marsik, Meghdad Yazdi-Rizi, Thomas Wolf, Anna Böhmer, F. Hardy, Christof Meingast, Dominik Munzar, Christian Bernhard. 2015-05-07. Infrared study of the spin reorientation transition and its reversal in the superconducting state in underdoped Ba$ _{1-x} $K$ _{x} $Fe$ _{2} $As$ _{2} $. https://doi.org/10.1103/physrevlett.115.027003

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