演講主題：RD-BZ Hamiltonian in quantum rings
Theoretically, a quantum ring of a circular curve has an
internal Zeeman field, which plays an important role in
spin transport, which manifests the interplay between
the Aharonov-Bohm and Aharonov-Casher topological phases.
We proporse a quantum ring Hamiltonian (RD-BZ Hamiltonian)
that could be used to experimentally detect the existence of the
internal Zeeman field, and thus enable us to change the strength
of the internal Zeeman field. Importantly, we show that the RD-BZ
Hamiltonian can be constructed from the topological insulator.
Similar to the topological insulator, the conductance can exhibit a
quasi plateau near the small spin-orbit coupling. Unlike the topological insulator,
the increase in the strength of the internal Zeeman field would result in a
wider quasi-plateau in conductance, which implies that the ring could remain insulating
state (or conducting state) regardless of the small change in the
spin-orbit coupling. The thermal average of spin and charge currents are
calculated at low temperatures without impurities. We find that the persistent
spin current could be nonzero even when the charge current vanishes at nonzero
magnetic flux. The result suggests a pure spin current in quantum rings, and
its direction can be reversed by changing the magnetic flux. Importantly,
the change in the internal Zeeman field would exhibit the plateau-like pure spin current.