Field-induced Quantum Disorder in the Unconventional Diamond-lattice Magnet CaCo₂TeO₆

CaCo₂TeO₆ is rare among diamond-lattice Heisenberg antiferromagnets, as this system is driven out of long-range magnetic order by magnetic fields above 20 T and enters a quantum disordered state. Physical property and neutron diffraction measurements reveal a J_eff = 1/2 ground state with strong quantum fluctuations down to 0.06 K and a significant reduction in the static magnetic moment on both Co octahedral sites. This unique realization, which has not been observed in conventional diamond-lattice magnets with spinel structures, arises from strong competition between nearest-neighbor and next-nearest-neighbor Heisenberg exchange interactions at a similar energy scale. In contrast to the tetrahedral crystal field in spinels, the octahedral crystal field in CaCo₂TeO₆ enables new magnetic exchange pathways and shapes the many-body electronic energy landscape, favoring a robust J = ½ state that persists even in the presence of magnetic field perturbations. These results enable a new avenue for realizing quantum disorder in three-dimensional frustrated magnets.