Four-Electron Quantum Ring in a Magnetic Field

We study a quantum ring (QR) with four electrons in a perpendicular external magnetic field B by exact diagonalization. The low-lying spectra of the QR as a function of B are obtained. A phase diagram is presented indicating that the angular momentum and the spin of the ground state of the QR may jump when B and/or the radius of the QR vary, and a corresponding analysis is performed. By plotting the density functions of the QR, the ground-state configuration is found to be a regular quadrangle. Furthermore, the features of the ground-state persistent current are revealed.