Triple points and novel phase transitions of dyonic AdS black holes with quasitopological electromagnetism

Abstract

Quasitopological electromagnetism has an important influence on the strong gravity of dyonic black holes. For example, three photon spheres, with one being stable, are found, and we wish to test them with the observed black hole shadow. We are primarily concerned with the thermodynamics and phase transition for a dyonic anti--de Sitter (AdS) black hole when quasitopological electromagnetism is included. Unlike in a black hole solution without quasitopological electromagnetism, we observe a triple point phase structure by varying the coupling parameters. Of particular interest, for certain parameter values, two separate coexistence curves are present, which is an additional novel phase structure that is absent in a black hole solution without quasitopological electromagnetism. The critical exponents share the same values as mean field theory. These results uncover the intriguing properties of dyonic AdS black holes with quasitopological electromagnetism from a thermodynamic point of view.