Bi-stability in a two-level quantum dot with attracting e–e interaction

By considering a current carrying two-level quantum dot (QD) with e–e attraction, we obtain the current and electron populations as functions of applied bias voltage using a self-consistent Hartree–Fock (HF) approximation and show that the system could be bi-stable and there exist hysteresis loops. Investigating the permanent polarization, we also show that the permanent polarization changes sign and interpret this as a quantum phase transition, since our system is at zero temperature. - Highlights: • Our system could have zero, one or two steps in its I–V curve. • Depending on the strength of the e–e attraction, there could be hysteresis loops around each step. • The polarization of the system changes sign by changing the bias voltage and this is a quantum phase transition.