Interaction effects on persistent current of ballistic cylindrical nanostructures

We consider clean cylindrical nanostructures with an applied longitudinal static magnetic field. Without Coulomb interaction, the field induces, for particular values, points of degeneracy where a change of ground state takes place due to Aharonov-Bohm effect. The Coulomb potential introduces interaction between the electronic configurations. As a consequence, when there is degeneracy, the ground state of the system becomes a many body state unable to be described by a mean-field theory and a gap is opened. To study this problem, we propose a variational multireference wave function which goes beyond the Hartree-Fock approximation. Using this ansatz, in addition to the avoided crossing formation, two other effects of the electron-electron interaction are pointed out: (i) the long-range part of the Coulomb potential tends to shift the position in magnetic field of the (avoided) crossing points and, (ii) at the points of (near) degeneracy, the interaction can drive the system from a singlet to a triplet state inducing new real crossing points in the ground state energy curve as function of the field. Such crossings should appear in various experiments as sudden changes in the response of the system (magnetoconductance, magnetopolarisability,...) when the magnetic field is tuned.