Orbital Magnetism in Honeycomb Ladder

We investigate the orbital magnetic susceptibility of the tight-binding model for the honeycomb ladder with the additional vertical hopping. Despite being one-dimensional, the magnetic flux penetrating the hexagonal rings affects the energetics of electrons, resulting in the finite orbital magnetic response. We find that the orbital magnetic susceptibility is sensitive to the parameters as well as the chemical potential. At half-filling, the response is diamagnetic when the system is close to the pure honeycomb ladder, whereas it turns to paramagnetic when it is close to the two-leg ladder. We also find several characteristic properties away from half-filling, such as the diamagnetic response at the band top and bottom, and the large paramagnetic response at the band gap sandwiched by the divergent density of states.