Classical spiral spin liquids as a possible route to quantum spin liquids.

Quantum spin liquids are long-range entangled phases whose magnetic correlations are determined by strong quantum fluctuations. While an overarching principle specifying the precise microscopic coupling scenarios for which quantum spin-liquid behavior arises is unknown, it is well-established that they are preferably found in spin systems where the corresponding classical limit of spin magnitudes [Formula: see text] exhibits a macroscopic ground state degeneracy, so-called classical spin liquids. Spiral spin liquids represent a special family of classical spin liquids where degenerate manifolds of spin spirals form closed contours or surfaces in momentum space.

Quantum Spin Liquids in Frustrated Spin-1 Diamond Antiferromagnets.

Motivated by the recent synthesis of the spin-1 A-site spinel NiRh_{2}O_{4}, we investigate the classical to quantum crossover of a frustrated J_{1}-J_{2} Heisenberg model on the diamond lattice upon varying the spin length S. Applying a recently developed pseudospin functional renormalization group approach for arbitrary spin-S magnets, we find that systems with S≥3/2 reside in the classical regime, where the low-temperature physics is dominated by the formation of coplanar spirals and a thermal (order-by-disorder) transition. For smaller local moments S=1 or S=1/2, we find that the system evades a thermal ordering transition and forms a quantum spiral spin liquid where the fluctuations are restricted to characteristic momentum-space surfaces.