Document Type : Research Paper
Department of Mathematics, South China Normal University, and Faculty of Applied Mathematics, Guangdong University of Technology
Department of Mathematics, South China Normal University, Guangzhou 510631, P. R. China
It is known that the directed cycle of order $n$ uniquely achieves the minimum spectral
radius among all strongly connected digraphs of order $n\ge 3$.
In this paper, among others, we determine the digraphs which achieve the second, the third
and the fourth minimum spectral radii respectively among strongly connected
digraphs of order $n\ge 4$.