PERSISTENT CURRENTS IN MESOSCOPIC RINGS AND CONFORMAL-INVARIANCE

The effect of point defects on persistent currents in mesoscopic rings is studied in a simple tight-binding model. Using an analogy with the treatment of the critical quantum Ising chain with defects, conformal invariance techniques are employed to relate the persistent current a mplitude to the Hamiltonian spectrum just above the Fermi energy. From this, the dependence of the current on the magnetic flux is found exa ctly for a ring with one or two point defects. The effect of an aperio dic modulation of the ring, generated through a binary substitution se quence, on the persistent current is also studied, The flux-dependence of the current is found to vary remarkably between the Fibonacci and the Thue-Morse sequences.