CURRENT FLUCTUATION IN THE BOHM-AHARONOV EFFECT

We calculate the current fluctuation of a mesoscopic ring in the ballistic-quantum-transport regime and in the presence of a magnetic field as a function of the Fermi energy, the applied external magnetic field, and the frequency. The system is represented by a tight-binding Hamiltonian, and nonequilibrium Green functions are obtained by the Keldysh formalism. The behavior of the shot noise as a function of the magnetic flux is very sensitive to the value of the Fermi energy and frequency. We find that for zero frequency and Fermi level such that the transmission is maximum the shot noise has oscillations with period hc/2e and vanishes when the current is maximum. This behavior holds for frequencies up to 1091010 Hz, for a ring of length of about 1500 and Fermi energy of 5 meV. On the other hand, for a Fermi level corresponding to a minimum in the transmission the period of the oscillations is hc/e, as for the current. © 1994 The American Physical Society.