Experimental observation of light refraction going from negative to positive in the visible region at the pure air/Au interface

Abstract

We report wavelength-dependent refraction going from negative to positive in the visible region for the pure air/Au interface by fabricating a series of prismlike Au film samples. Results qualitatively agree with dispersion of the group refractive index ${n}_{g}$, in which the spectral properties of the phase refractive index ${n}_{p}$, play a significant role to make both the magnitude and sign of ${n}_{g}$ change in the energy region where interband transitions occur. The net refraction observed for the simplest air and metal interface will stimulate further exploration of the physical origin of slow or fast light characterized by the law of refraction in nature.