Research: Supersolidity in bond-frustrated MnCr2S4

Supersolidity in bond-frustrated MnCr₂S₄

Frustrated magnets provide a promising avenue for realizing exotic quantum states of matter, such as spin-liquid, spin-ice, and even supersolid states. A supersolid is an ordered solid which, due to quantum phenomena, has also superfluid properties and, under some conditions, can thus behave as a liquid without viscosity. This can be considered as an example of a Bose-Einstein condensate (BEC). Active search for the supersolidity has been performed in solid helium and, very recently, in ultracold trapped atoms. Researchers from the Center for Electronic Correlations and Magnetism at the University of Augsburg and the Dresden High Magnetic Field Laboratory have chosen another way by investigating the spin states in the frustrated magnet MnCr₂S₄.

In this material, prominent anomalies in the magnetization and sound velocity have been observed in high magnetic fields, which reveal two fascinating features: (i) an extremely robust magnetization plateau with an unusual spin structure stabilized by field-induced lattice distortions and (ii) two intermediate phases, indicating possible realizations of a supersolid state.

The measurements reveal that MnCr₂S₄ exhibits a manifold of competing spin states as a function of external magnetic field. Thereby, the chromium moments are always aligned parallel to the external field, but the manganese spins exhibit different types of transverse and longitudinal order, which, by analogy with bosonic systems, can be described as superliquid and supersolid phases.

Indeed, the comparison of the phase diagram with respect to the manganese spins with theoretical predictions from the quantum-lattice-gas model suggests the existence of extended supersolid phases, in addition to superfluid and crystalline phases. The work shows that magnetic systems under extreme conditions are prime candidates for the emergence of coherent quantum phenomena.

V. Tsurkan, S. Zherlitsyn, L. Prodan, V. Felea, P. T. Cong, Y. Skourski, Z. Wang, J. Deisenhofer, H.-A. Krug von Nidda, J. Wosnitza, and A. Loidl,
Ultra-robust high-field magnetization plateau and supersolidity in bond-frustrated MnCr₂S₄,
Sci. Adv. 3, e1601982 (2017).