Universal properties of many-body localization transitions in quasiperiodic systems

Precise nature of MBL transitions in both random and quasiperiodic (QP) systems remains elusive so far. In particular, whether MBL transitions in QP and random systems belong to the same universality class or two distinct ones has not been decisively resolved. Here we investigate MBL transitions in one-dimensional ($d\!=\!1$) QP systems as well as in random systems by state-of-the-art real-space renormalization group (RG) calculation. Our real-space RG shows that MBL transitions in 1D QP systems are characterized by the critical exponent $\nu\!\approx\!2.4$, which respects the Harris-Luck bound ($\nu\!>\!1/d$) for QP systems. Note that $\nu\!\approx\! 2.4$ for QP systems also satisfies the Harris-CCFS bound ($\nu\!>\!2/d$) for random systems, which implies that MBL transitions in 1D QP systems are stable against weak quenched disorder since randomness is Harris irrelevant at the transition. We shall briefly discuss experimental means to measure $\nu$ of QP-induced MBL transitions.