Local minimality of $\mathbb{R}^N$-valued and $\mathbb{S}^N$-valued Ginzburg–Landau vortex solutions in the unit ball $B^N$

Abstract

We study the existence, uniqueness and minimality of critical points of the form $m_{\varepsilon,\eta}(x) = (f_{\varepsilon,\eta}(|x|)\smash{\frac{x}{|x|}}, g_{\varepsilon,\eta}(|x|))$ of the functional $E_{\varepsilon,\eta}[m] = \int_{B^N} [\frac{1}{2} |\nabla m|^2 + \smash{\frac{1}{4\varepsilon^2}} (1 - |m|^2)^2 + \frac{1}{2\eta^2} m_{N+1}^2]\,dx$ for $m=(m_1, \dots, m_N, m_{N+1}) \in H^1(B^N,\mathbb{R}^{N+1})$ with $m(x) = (x,0)$ on $\partial B^N$. We establish a necessary and sufficient condition on the dimension $N$ and the parameters $\varepsilon$ and $\eta$ for the existence of an escaping vortex solution $(f_{\varepsilon,\eta}, g_{\varepsilon,\eta})$ with $g_{\varepsilon,\eta}> 0$. We also establish its uniqueness and local minimality. In particular, when $\eta = 0$, we prove the local minimality of the degree-one vortex solution for the Ginzburg–Landau (GL) energy for every $\varepsilon > 0$ and $N \geq 2$. Similarly, when $\varepsilon = 0$, we prove the local minimality of the degree-one escaping vortex solution to an $\mathbb{S}^N$-valued GL model in micromagnetics for all $\eta > 0$ and $2 \leq N \leq 6$.