Closing in on a Magnetic Analog of Liquid Crystals

In 1888, the Austrian chemist Friedrich Reinitzer was trying to measure the melting point of cholesteryl benzoate crystals [1] when, much to his surprise, he observed not one but two phase transitions. Reinitzer had inadvertently discovered liquid crystals. In this cloudy-looking phase, intermittent between a solid and a liquid, the molecules are at random positions but nonetheless break rotational symmetry. The essence of this type of order escaped the physics community until the 1960s, when Pierre-Gilles De Gennes realized that the order parameter describing it could not be expressed as a number (like the density of a gas) or a vector (like the direction of a solid’s magnetization), but only by a more complex mathematical entity: a tensor [2]. Soon after, theorists predicted that a quantum version of a common type of order found in liquid crystals, known as nematic order, might be possible in a lattice of spins [3]. Yet besides being observed in condensates of cold atoms [4], spin-nematic order has remained elusive. Among solids, the most promising spin-nematic candidate today is the copper oxide LiCuVO4 [5]. Thanks to nuclear magnetic resonance (NMR) measurements performed at high magnetic fields, Anna Orlova of France’s National Laboratory for Intense Magnetic Fields (LNCMI) and colleagues now provide the strongest evidence to date that LiCuVO4 indeed exhibits a spin-nematic phase [6].