Quantum Dynamics in the Supersolid Phase of the Frustrated Triangular-Lattice XXZ Model

Geometric frustration is a key driver in the search for exotic states of matter. Since Wannier’s pioneering work over 75 years ago, the triangular-lattice Ising model has been known to host a macroscopically degenerate ground-state manifold, a consequence of its inability to minimize energy efficiently. Quantum fluctuations are expected to lift this degeneracy, stabilizing a highly entangled ground state with unconventional excitations.

For more than a decade, it has been established that the XXZ model in the Ising limit realizes a supersolid spin ground state. While its static properties are well studied, the excitation spectrum remains poorly understood. Recent discoveries of materials in this regime, combined with advances in neutron scattering, now allow direct experimental access to these quantum dynamics, which depart markedly from semi-classical expectations.

In this talk, we revisit key developments in the field and show how a controlled expansion scheme enables quantum Monte Carlo simulations that capture the excitation spectrum with striking agreement to experiment. These findings open new questions, which will be discussed in detail.