Emergent symmetry in lithium molybdate (LMO)

Upon cooling, condensed matter systems typically transition into states of lower symmetry. While the converse, i.e. the emergence of higher symmetry at lower temperatures, has been hypothesized, it is extremely rare. Here, we show how an unusually isotropic 25 magnetoresistance in the highly anisotropic, one-dimensional conductor Li0.9Mo6O17 (LMO), and its temperature dependence, can be interpreted as a renormalization group (RG) flow towards a so-called separatrix. This approach is equivalent to an emergent symmetry in the system. The existence of two distinct ground states – Mott insulator and superconductor – can then be traced back to two opposing RG trajectories. By establishing a direct link between quantum field theory 30 and an experimentally measurable quantity, we uncover a path through which emergent symmetry might be identified in other candidate materials., Hall effect and magnetoresistance (MR) measurements were carried out using a standard ac lockin detection technique in three different magnet cryostat systems: an 8 T Cryogen Free Measurement System from CryogenicTM, a 16 T superconducting magnet from Oxford InstrumentsTM and a 35 T Bitter magnet from the High Field Magnet Laboratory at Radboud University, Nijmegen. For all measurements, field sweeps were performed in both polarities. For the thermal conductivity measurements, we used a zero-field set-up housed in a He-4 flow cryostat that covers the temperature range 10K < T < 300K. We employed a modified steady-state method in which a temperature gradient, measured using a differential thermocouple, is set up across the sample through a pair of calibrated heat-links attached to each end.
In the main manuscript, only Figures 3 and 4 contain data. Panels A/C/E of Fig. 3 contain zero-field resistivity data of LMO with the current applied along the chain. Panels B/D/F of Fig. 3 cont..., ,