Thinner (a) BISMUTH Smoother Pb 4.36A Disordered 00.050.10.150.20.250.3 BKT 1/d(A) Transition (b) R N S R q (anti)Vortex 7427A unbinding Bi. LLl 121620 T(K) (k9) A.M. Goldman et al PRL622180(1989) PRB475931(1993)A.M. Goldman et al. PRL 62 2180 (1989) PRB 47 5931 (1993) Smoother Thinner Disordered Transition 𝑅𝑁 > 𝑅𝑞 BKT (anti)Vortex unbinding