Quantum Melting of Spin Ice: Emergent Cooperative Quadrupole and Chirality

Quantum melting of spin ice is proposed for pyrochlore-lattice magnets Pr2TM2O7 (TM = Ir, Zr, and Sn). The quantum superexchange Hamiltonian having a nontrivial magnetic anisotropy is derived on the basis of atomic non-Kramers magnetic doublets. The ground states exhibit a cooperative ferroquadrupole and pseudospin chirality, forming a magnetic analog of smectic liquid crystals. Our theory accounts for dynamic spin-ice behaviors experimentally observed in Pr2TM2O7.