Topology of dyonic AdS black holes with quasitopological electromagnetism in Einstein-Gauss-Bonnet gravity

Abstract: In this study, we employ the thermodynamic topological method to classify critical points for the dyonic AdS black holes with quasitopological electromagnetism in the Einstein-Gauss-Bonnet background. To this end, we find a small/large black hole phase transition in all dimensions of space-time, the existence of a conventional critical point implies a total topological charge of $Q_t=-1$. The coupling constant $\alpha$ gives rise to a more intricate phase structure, with the emergence of a triple points requires $\alpha\geq0.5$ and $d=6$. Interestingly, the condition for the occurrence of small/intermediate/large phase transition is that the coupling constant a takes a special value ($\alpha=0.5$), the two conventional critical points $CP_{1},CP_{2}$ of the black hole are physical critical point, and the novel critical point $CP_{3}$ that lacks the capability to minimize the Gibbs free energy. The critical points $CP_{1}$ and $CP_{2}$ are observed to occur at the maximum extreme points of temperature in the isobaric curve, while the critical point $CP_{3}$, emerges at the minimum extreme points of temperature. Furthermore, the number of phases at the novel critical point exhibits an upward trend, followed by a subsequent decline at the conventional critical points. With the increase of the coupling constant ($\alpha = 1$), although the system has three critical points, only the conventional $CP_{1}$ is a (physical) critical point, and the conventional $CP_{2}$ serves as the phase annihilation point. This means that the coupling constant $\alpha$ has a non-negligible effect on the phase structure.