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arXiv · 1502.06051

Spin liquid polymorphism in a correlated electron system on the threshold of superconductivity

Igor A. Zaliznyak·Andrei T. Savici·Mark Lumsden·Alexei M. Tsvelik·Rongwei Hu·Cedomir Petrovic
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Abstract

We report neutron scattering measurements, which reveal spin-liquid polymorphism in a '11' iron chalcogenide superconductor, a poorly-metallic magnetic FeTe tuned towards superconductivity by substitution of a small amount of Tellurium with iso-electronic Sulphur. We observe liquid-like magnetic dynamics, which is described by a competition of two phases with different local structure, whose relative abundance depends on temperature. One is the ferromagnetic (FM) plaquette phase observed in the non-superconducting FeTe, which preserves the C$_4$ symmetry of the underlying square lattice and is favored at high temperatures. The other is the antiferromagnetic plaquette phase with broken C$_4$ symmetry, which emerges with doping and is predominant at low temperatures. These findings suggest a first-order liquid-liquid phase transition in the electronic spin system of FeTe$_{1-x}$(S,Se)$_x$. We thus discover remarkable new physics of competing spin liquid polymorphs in a correlated electron system approaching superconductivity. Our results facilitate an understanding of large swaths of recent experimental data in unconventional superconductors.

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Igor A. Zaliznyak, Andrei T. Savici, Mark Lumsden, Alexei M. Tsvelik, Rongwei Hu, Cedomir Petrovic. 2015-02-21. Spin liquid polymorphism in a correlated electron system on the threshold of superconductivity. https://doi.org/10.1073/pnas.1503559112

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