  Berezinskii-Kosterlitz-Thouless transition of the classical XY model is
re-investigated, combining the Tensor Network Renormalization (TNR) and the
Level Spectroscopy method based on the finite-size scaling of the Conformal
Field Theory. By systematically analyzing the spectrum of the transfer matrix
of the systems of various moderate sizes which can be accurately handled with a
finite bond dimension, we determine the critical point removing the logarithmic
corrections. This improves the accuracy by an order of magnitude over previous
studies including those utilizing TNR. Our analysis also gives a visualization
of the celebrated Kosterlitz Renormalization Group flow based on the numerical
data.
