Lagrange spectrum of a circle over the Eisensteinian field

Abstract

We study an intrinsic Lagrange spectrum of the unit circle $|z|=1$ in the complex plane with respect to the Eisensteinian field $\mathbb{Q}(\sqrt{-3})$. We prove that the minimum of the Lagrange spectrum is $2$ and that its smallest accumulation point is $4/\sqrt{3}$. In addition, we characterize the set of all values in the spectrum between $2$ and $4/\sqrt3$.