Normalized ground states of nonlinear biharmonic Schrödinger equations with Sobolev critical growth and combined nonlinearities

This paper is devoted to studying the following nonlinear biharmonic Schrödinger equation with combined power-type nonlinearities \begin{equation*} \begin{aligned} Δ^{2}u-λu=μ|u|^{q-2}u+|u|^{4^-2}u\quad$\mathrm{i}\mathrm{n}$\ $\mathbb{R}$^{N}, \end{aligned} \end{equation} where $N\ge 5$, $\mu >0$, $2<q<2+\frac{8}{N}$, $4^{\ast }=\frac{2N}{N-4}$ is the $H^2$-critical Sobolev exponent, and $\lambda$ appears as a Lagrange multiplier. By analyzing the behavior of the ground state energy with respect to the prescribed mass, we establish the existence of normalized ground state solutions. Furthermore, all ground states are proved to be local minima of the associated energy functional.