On the Size of Minimal Surfaces in $\mathbb{R}^4$

The Gauss map $g$ of a surface $\Sigma$ in $\mathbb{R}^4$ takes its values in the Grassmannian of oriented 2-planes of $\mathbb{R}^4$: $G^+(2,4)$. We give geometric criteria of stability for minimal surfaces in $\mathbb{R}^4$ in terms of $g$. We show in particular that if the spherical area of the Gauss map $|g(\Sigma)|$ of a minimal surface is smaller than $2\pi$ then the surface is stable by deformations which fix the boundary of the surface.This answers a question of Barbosa and Do Carmo in $\mathbb{R}^4$.