Pulsar Sparking: What if mountains on the surface?

A numerical framework to calculate the height and potential of the vacuum inner gap of pulsars is presented here. % The results demonstrate that small mountains on a pulsar's polar cap tend to significantly influence the properties of the inner vacuum gap, making it easier for sparks to form. % In this scenario, the magnetospheric activity observed from the pulsars PSR J0250$+$5854 and PSR J2144$-$3933 which lie below the traditional pulsar death line, and some single-pulse modulation phenomena could also then be understood. % Furthermore, the presence of small mountains should depend on the puzzling state of supranuclear matter inside pulsars. % In order to sustain stable mountains on the surface, pulsars might be made of solid strangeon matter, which is favoured by both the charge neutrality and the flavour symmetry of quarks.