Emergence of exceptional points and their spectroscopic signature in Dirac semimetal-dirty Superconductor heterojunction

Abstract: We theoretically investigate the emergence of non-hermitian physics at the heterojunction of a type-II Dirac semi-metal (DSM) and a dirty superconductor (DSC). The non-hermiticity is introduced in the DSM through the self-energy term incorporated via the dirtiness of the superconducting material. This causes the spectra of the effective Hamiltonian to become complex, which gives rise to the appearance of the exceptional points (EPs). This complex self energy, apart from having a frequency dependence, also acquires spatial dependence as well, which is unique and can provide interesting effects related to non-hermitian physics in spectral function analysis. At an appropriate distance from the normal metal-superconductor junction of the DSC, non-hermitian degeneracies appear and a single Dirac point splits into two EPs. In the spectral function analysis, apart from the EPs, a Fermi-arc like structure also emerges, which connects the two degeneracies (EPs). The results discussed here are distinctive and possibly can be realized in spectroscopy measurements.