I will start with a small digression about sine-Gordon model in low dimensional systems and the Berezinskii-Kosterlitz-Thouless (BKT) phase diagram. Then I will move on to introduce the material, with its long history that spans over the last four decades. It belongs to a family of purple bronzes, whose other members were early on shown to be Peierls-CDW compounds, while the physics of this Li-compound has remained elusive. From the beginning of 21st century experimental evidence has been mounting, indicating that it may be a rare realization of Tomonaga-Luttinger liquid in a solid state material. However, its lowest energy physics does not obey the canonical picture and the origin of a mysterious upturn of resistivity was understood only few years ago [1].
Then I will present our most recent findings that directly probe the parent state of superconductivity [2]. We were able to show that the Li0.9Mo6O17 is in fact in the higher symmetry state, right on the edge of Mott insulating region in the BKT picture. I will explain how the specific properties of Li0.9Mo6O17 enabled us to measure directly the BKT renormalization group flow and what conclusions we were able to draw from that.
[1] J. Lu et al., Sci. Adv. 5, eaar8027 (2019).
[2] P. Chudzinski et al., Science 382, 792-796 (2023).
