“…In recent years, there has been extensive work on the electronic properties of mesoscopic rings in the framework of the ballistic model or waveguide theory. [16][17][18][19][20] Along this line, theoretical studies to date have concentrated largely on the isolated ring and open rings connected via leads to electron reservoirs, both of which are threaded by a magnetic flux. For the isolated ring, the persistent currents are the main subjects, in which an important and well-known conclusion is the ''period halfing, '' 22 i.e., the persistent current is periodic in magnetic flux ⌽ with a period ⌽ 0 /2, ⌽ 0 ϭhc/e being the elementary flux quantum.…”