Elastic properties of hidden order in URu₂Si₂ are reproduced by staggered nematic order

We develop a phenomenological mean field theory of the hidden order phase in URu₂Si₂ as a "staggered nematic" order. Several experimental features are reproduced when the order parameter is a nematic of the B_1g representation, staggered along the c-axis: the topology of the temperature–pressure phase diagram, the response of the elastic modulus (C₁₁ – C₁₂) / 2 above the hidden-order transition at zero pressure, and orthorhombic symmetry breaking in the high-pressure antiferromagnetic phase. In this scenario, hidden order is characterized by broken rotational symmetry that is modulated along the c-axis, the primary order of the high-pressure phase is an unmodulated nematic state, and the triple point joining those two phases with the high-temperature paramagnetic phase is a Lifshitz point.