Changing Spin and Orbital Ground State Symmetries in Colloidal Nanoplatelets with Magnetic Fields

The symmetry of the electronic ground state is of paramount importance in determining the magnetic, optical, and electrical properties of semiconductor nanostructures. Here, it is shown theoretically that nontrivial spin and orbital symmetries can be induced in colloidal nanoplatelets (NPLs) by applying out-of-plane magnetic fields. Two scenarios are presented. The first one deals with two electrons confined inside a platelet. Here, the strong electron-electron exchange interaction reduces the interlevel energy spacing set by lateral quantum confinement. As a result, relatively weak magnetic fields suffice to induce a singlet-to-triplet spin transition. The second one deals with type-II core/crown NPLs. Here, the crown has doubly connected topology, akin to that of quantum rings. As a result, the energy levels of carriers within it undergo Aharonov-Bohm (AB) oscillations. This implies changes in the ground state orbital symmetry, which switch the exciton and trion optical activity from bright to dark.