We report neutron scattering experiments which reveal two different spin-liquid phases in an “11” iron chalcogenide superconductor FeTe1-xSx. We observe a liquid-like magnetic response, which is described by the coexistence of two distinct disordered magnetic phases with different local structures whose relative abundance depends on temperature [1]. One is the ferromagnetic (FM) plaquette phase observed in undoped, nonsuperconducting FeTe [2,3], which preserves the C4 symmetry of the underlying square lattice and is favored at high temperatures, whereas the other is the antiferromagnetic plaquette phase with broken C4 symmetry, which emerges with doping and is predominant at low temperatures. We propose a simple plaquette model, which adequately describes variety of the existing neutron data in iron chalcogenides. These findings suggest the coexistence of and competition between two distinct spin-liquid states, and a liquid–liquid phase transformation between these states, in the electronic spin system of FeTe1-x(S,Se)x. This remarkable competition of two different electronic spin-liquid polymorphs in a chalcogenide material on the threshold of unconventional superconductivity suggests new understanding of electronic nematicity and non–Fermi-liquid behavior.
References:
[1] I. Zaliznyak, A. T. Savici, M. Lumsden, A. Tsvelik, R. Hu, C. Petrovic.``Spin-liquid polymorphism in a correlated electron system on the threshold of superconductivity'', Proc Natl Acad Sci USA,www.pnas.org/cgi/doi/10.1073/pnas.1503559112 (2015)
[2] D. Fobes, I. A. Zaliznyak, Z. Xu, R. Zhong, G. Gu, J. M. Tranquada, L. Harriger, D. Singh, V. O. Garlea, M. Lumsden, B. Winn, ``Ferro-orbital ordering transition in iron telluride Fe$_{1+y}$Te'', Phys. Rev. Lett. 112, 187202 (2014).
[3] I. A. Zaliznyak, Z. Xu, J. M. Tranquada, G. Gu, A. M. Tsvelik, M. B. Stone, ``Unconventional temperature enhanced magnetism in iron telluride'', Phys. Rev. Lett. 107, 216403 (2011).