Interplay of charge and spin degrees of freedom in Mo3O13 cluster Mott insulators*

A promising approach to understanding the complexities of experimental quantum spin liquid candidates is to search for a way to tune the microscopic Hamiltonian and study changes in the resulting magnetic phases. In this talk I will present recent developments in a new class of highly tunable Mo₃O₁₃ cluster Mott insulators. This family of materials can be viewed as a breathing kagome lattice (BKL) of Mo ions, where the corner-sharing up and down triangles have two different sizes. In the compounds Li₂In_1-xSc_xMo₃O₈ the breathing parameter (λ) changes non-monotonically with Sc concentration (x), tuning the system from an antiferromagnetic Mott insulator for large λ, to a quantum spin liquid for small λ [1]. For large breathing parameter electrons become confined on the small triangles forming spin-1/2 Mo₃ clusters on a triangular lattice with antiferromagnetic exchange coupling between them, leading to long range antiferromagnetic order. On the other hand, for small breathing parameter electrons are no longer confined to individual Mo₃ clusters but can tunnel between adjacent clusters, leading to a novel long range plaquette charge order (PCO) [2]. Our thermodynamic and muon spin rotation (μSR) measurements, suggest that the PCO coincides with a high degree of spin frustration and leads to a quantum spin liquid ground state, with gapless spinon excitations. The tunability of these materials can be extended to lower and higher breathing parameter in several related Mo-oxide materials, revealing additional quantum spin liquids and even ferromagnetism.

[1] A. Akbari-Sharbaf et al., Phys. Rev. Lett. 120, 227201 (2018).
[2] G. Chen et al., Phys. Rev. B 93, 245134 (2016).