FCMP: Phase Diagram and Spectroscopic Signatures of a Supersolid in the Quantum Ising Magnet K2Co(SeO3)2
Tong Chen
Johns Hopkins University
Time:
Tuesday, Aug./26/2025, 2:00 PM to 3:30 PM (Houston)
4:00 AM Wednesday (Tokyo)
3:00 AM Wednesday (Beijing)
Link:
https://riceuniversity.zoom.us/j/93872419348?pwd=A8ytB7lddenltpVmyTOLZl0XZUIcZ8.1
Abstract: A supersolid is a quantum-entangled state of matter exhibiting the dual characteristics of superfluidity and solidity. Theory predicts that hard-core bosons with repulsive interactions on a triangular lattice can form supersolid phases at half filling and near complete filling. Leveraging an exact mapping between bosons and spin-1/2 degrees of freedom, we investigate these phases in the spin-1/2 triangular-lattice antiferromagnet K2Co(SeO3)2 with exchange constants = 2.96(2) meV and meV. At zero field, neutron diffraction reveals the gradual development for K of quasi-two-dimensional magnetic order with Z3 translational symmetry breaking (solidity) albeit with 44(5)% reduced amplitude at K indicating strong quantum fluctuations. These are apparent in equidistant bands of continuum neutron scattering for, where the quasi-elastic Q-dependent continuum has a lower resonant edge and is gapless to within 0.7% at K, consistent with broken U(1) spin rotational symmetry (boson superfluidity). Competing instabilities are apparent in soft albeit finite-energy modes at M and at K. For c-axis-oriented magnetic fields that almost saturate the magnetization, corresponding to nearly filling the lattice with bosons, we find a new phase consistent with a second supersolid. These phases are separated by a pronounced 1/3 magnetization plateau that supports coherent spin waves, from which we determine the spin Hamiltonian.
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