In this paper, we consider nonlinear sub-elliptic systems with Dini continuous coefficients for the case 1<m<2 in Carnot groups. Based on a generalization of the technique of A-harmonic approximation introduced by Duzaar–Grotowski–Kronz, and a Sobolev–Poincaré type inequality established in Carnot groups, a C1-partial regularity result for weak solutions of sub-elliptic systems with natural growth terms is established. In particular, our result is optimal in the sense that in the case of Hölder continuous coefficients it yields directly the optimal Hölder exponent for horizontal gradients of weak solutions on its regular set.
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