Signatures of a gearwheel quantum spin liquid in a spin-$\frac{1}{2}$ pyrochlore molybdate Heisenberg antiferromagnet

Abstract

We theoretically investigate the low-temperature phase of the recently synthesized Lu${}_2$Mo${}_2$O${}_5$N${}_2$ material, an extraordinarily rare realization of a $S=1/2$ three-dimensional pyrochlore Heisenberg antiferromagnet in which Mo${}^{5+}$ are the $S=1/2$ magnetic species. Despite a Curie-Weiss temperature ($\hat{I}{˜}_{\mathrm{CW}}$) of $-121(1)$ K, experiments have found no signature of magnetic ordering $or$ spin freezing down to $T^{\ast }\approx 0.5$ K. Using density functional theory, we find that the compound is well described by a Heisenberg model with exchange parameters up to third nearest neighbors. The analysis of this model via the pseudofermion functional renormalization group method reveals paramagnetic behavior down to a temperature of at least $T=|\hat{I}{˜}_{\mathrm{CW}}|/100$, in agreement with the experimental findings hinting at a possible three-dimensional quantum spin liquid. The spin susceptibility profile in reciprocal space shows momentum-dependent features forming a "gearwheel" pattern, characterizing what may be viewed as a molten version of a chiral noncoplanar incommensurate spiral order under the action of quantum fluctuations. Our calculated reciprocal space susceptibility maps provide benchmarks for future neutron scattering experiments on single crystals of Lu${}_2$Mo${}_2$O${}_5$N${}_2$.

Published version. Main paper (6 pages, 3 figures) + Supplemental Material (4 pages, 3 figures, 1 table)