Browsing by Subject "Macromolecular conducting rings"

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Open Access
Spontaneous and persistent currents in mesoscopic Aharonov-Bohm loops: Static properties and coherent dynamic behavior in crossed electric and magnetic fields
(M A I K Nauka - Interperiodica, 2005) Kulik, I. O.
Mesoscopic or macromolecular conducting rings with a fixed number of electrons are shown to support persistent currents due to the Aharonov-Bohm flux, and the "spontaneous" persistent currents without the flux when structural transformation in the ring is blocked by strong coupling to the externally azimuthal-symmetric environment. In the free-standing macromolecular ring, symmetry breaking removes the azimuthal periodicity, which is further restored at the increasing field, however. The dynamics of the Aharonov-Bohm loop in crossed electric and magnetic fields is investigated within the tight-binding approximation; we show that transitions between discrete quantum states occur when static voltage pulses of prescribed duration are applied to the loop. In particular, the three-site ring with one or three electrons is an interesting quantum system that can serve as a qubit (quantum bit of information) and a qugate (quantum logical gate) because in the presence of an externally applied static electric field perpendicular to a magnetic field, the macromolecular ring switches between degenerate ground states mimicking the NOT and Hadamard gates of quantum computers.
Open Access
Spontaneous and persistent currents in superconductive and mesoscopic structures
(American Institute of Physics, 2004) Kulik, I. O.
We briefly review aspects of superconductive persistent currents in Josephson junctions of the S/I/S, S/O/S and S/N/S types, focusing on the origin of jumps in the current versus phase dependences, and discuss in more detail the persistent as well as «spontaneous» currents in the Aharonov-Bohm mesoscopic and nanoscopic (macromolecular) structures. A fixed-number-of- electrons mesoscopic or macromolecular conducting ring is shown to be unstable against structural transformation removing spatial symmetry (in particular, azimuthal periodicity) of its electron-lattice Hamiltonian. In case when the transformation is blocked by strong coupling to an external azimuthally symmetric environment, the system becomes bistable in its electronic configuration at certain number of electrons. At such a condition, the persistent current has a nonzero value even at the (almost) zero applied Aharonov-Bohm flux, and results in very high magnetic susceptibility dM/dH at small nonzero fields, followed by an oscillatory dependence at larger fields. We tentatively assume that previously observed oscillatory magnetization in cyclic metallo-organic molecules by Gatteschi et al. can be attributed to persistent currents. If this proves correct, it may open an opportunity (and, more generally, macromolecular cyclic structures may suggest the possibility) of engineering quantum computational tools based on the Aharonov-Bohm effect in ballistic nanostructures and macromolecular cyclic aggregates.