  The ultimate limit on fiber loss is set by the intrinsic Rayleigh scattering
of silica glass material. Here, we challenge this limit in the visible region
by using a hollow-core fiber approach. Two visible-guiding hollow-core
conjoined-tube negative-curvature fibers are successfully fabricated and
exhibit the overall losses of 3.8 dB/km at 680 nm and 4.9 dB/km at 558 nm
respectively. The loss of the latter fiber surpasses the Rayleigh scattering
limit of silica glass fiber in the green spectral region by 2 dB. Numerical
simulation indicates that this loss level is still much higher than the
fundamental surface scattering loss limit of hollow-core fiber.
