Quantum rings with tunnel barriers in a threading magnetic field: Spectra, persistent current and ballistic conductance

The electronic states of isolated quantum rings with some tunnel barriers in a threading magnetic field are calculated. We show that the presence of obstacles analogously to smooth and tiny variations in the width may strongly affect the Aharonov–Bohm (AB) oscillations by producing a quenching of magnetic dependent oscillating behavior of the lower energy levels. This quenching reflects the localization of the quantum states and can be justified in terms of metallic-insulating transition induced by the barriers. We discuss how the behavior of the energy levels has effects both on the persistent charge currents in isolated ring and on the ballistic conductance of a conducting ring symmetrically coupled to two leads.