  The quantum antiferromagnet on the pyrochlore lattice offers an archetypal
frustrated system, which potentially realizes a quantum spin liquid
characterized by the absence of standard spontaneous symmetry breaking even at
zero temperature, unusually as an isotropic 3D system. Despite tremendous
progress in the literature, however, the nature of the ground state of the
fully quantum-mechanical spin Hamiltonian on the pyrochlore lattice still
remains elusive. Here, we show that an unconventional type of quantum spin
liquid is born out from the pyrochlore system after the self-organized
dimensional reduction leading to confined states in 2D layers. This conclusion
is obtained from state-of-the-art variational Monte Carlo (VMC) simulations at
zero temperature. Quantum spin liquids triggered by the emergent dimensional
reduction is an unexplored route of the spin-liquid formation. The dimensional
reduction from 3D to 2D is a consequence of a conventional spontaneous symmetry
breaking, while the resultant decoupling of layers enables the emergence of a
2D quantum spin liquid that is adiabatically disconnected from trivial product
states and exhibits strong quantum entanglement. The stabilized quantum spin
liquid exhibits an algebraic decay of correlations and vanishing excitation gap
in the thermodynamic limit. The wave-function structure supports the
fractionalization of the spin into spinons. This spin-liquid ground state
persists in the presence of spin-orbit interactions, which expands the
possibilities of realizing quantum spin liquids in real pyrochlore-structured
materials.
