Thin-Film Realization of an Improper Ferroelectric Quantum Spin Liquid Candidate

Magnetically frustrated materials offer a playground for realizing exotic magnetic ground states such as quantum spin ices and spin liquids that have been proposed as building blocks in quantum computing and as potential hosts for unconventional superconductivity. The ability to synthesize such materials in thin-film form is necessary for their integration into the proposed device architectures and also allows further tuning of the magnetic ground state with dimensionality and epitaxial strain. However, thin-film realizations of quantum spin liquid candidate materials remain scarce. Here, we use reactive oxide molecular beam epitaxy to synthesize the first thin films of hexagonal TbInO₃, a magnetically frustrated rare-earth system that was recently proposed as a spin liquid candidate. In bulk, TbInO₃ exhibits geometrically driven improper ferroelectricity similar to the multiferroic hexagonal manganites, and displays the same topologically protected vortex domain pattern. The underlying lattice distortion causing this domain pattern imposes a stuffed honeycomb geometry on the quasi-two-dimensional Tb³⁺ sublattice which harbors the magnetic frustration in TbInO₃. Here, we investigate the ferroelectric distortion in our epitaxial TbInO₃ thin films using in-situ RHEED and post-deposition HAADF-STEM. We furthermore use SQUID magnetometry and X-ray spectroscopy to investigate the low-temperature magnetic behavior. Our work constitutes one of the few thin-film realizations of a quantum spin liquid candidate, and opens up for the use of epitaxy to further manipulate the unusual coexistence of ferroelectricity and spin liquid physics in this thin-film system.