Classification of gradient Einstein-type K\"ahler manifolds with $\alpha=0$

Thanks to the ambitious project initiated by Catino, Mastrolia, Monticelli and Rigoli, which aims to provide a unified viewpoint for various geometric solitons, many classes, including Ricci solitons, Yamabe solitons, $k$-Yamabe solitons, quasi-Yamabe solitons, and conformal solitons, can now be studied under a unified framework known as Einstein-type manifolds. Einstein-type manifolds are characterized by four constants, denoted by $\alpha, \beta, \mu$ and $\rho$. In this paper, we completely classify all non-trivial, complete gradient Einstein-type K"ahler manifolds with $\alpha = 0$. As a corollary, rotational symmetry for many classes is obtained. In particular, we show that any non-trivial complete gradient quasi-Yamabe soliton on K"ahler manifolds is rotationally symmetric.