Physics of Quantum Rings

Abstract

This chapter is devoted to optical properties of so-called Aharonov-Bohm quantum rings (quantum rings pierced by a magnetic flux resulting in Aharonov-Bohm oscillations of their electronic spectra) in external electromagnetic fields. It studies two problems. The first problem deals with a single-electron Aharonov-Bohm quantum ring pierced by a magnetic flux and subjected to an in-plane (lateral) electric field. We predict magneto-oscillations of the ring electric dipole moment. These oscillations are accompanied by periodic changes in the selection rules for inter-level optical transitions in the ring allowing control of polarization properties of the associated terahertz radiation. The second problem treats a single-mode microcavity with an embedded Aharonov-Bohm quantum ring which is pierced by a magnetic flux and subjected to a lateral electric field. We show that external electric and magnetic fields provide additional means of control of the emission spectrum of the system. In particular, when the magnetic flux through the quantum ring is equal to a half-integer number of the magnetic flux quanta, a small change in the lateral electric field allows for tuning of the energy levels of the quantum ring into resonance with the microcavity mode, thus providing an efficient way to control the quantum ring-microcavity coupling strength. Emission spectra of the system are discussed for several combinations of the applied magnetic and electric fields.

Interplay between the quantum interference and current localization phenomena in superconductor non-ideal mesoscopic rings

“…Superconducting bridges, which are narrower than the effective magnetic penetration depth, experience enhancement of the first critical field that scales with the bridge width w as 32,33]. Since the onset of a vortex changes the sample's topology like the presence of a ring [5], we argue that phase dynamics of I s are similar to the probe ones from a phenomenological point of view. Indeed, standard I s dynamics are straightforwardly recognized by looking at the MR zoom reported in figure 2(b).…”

“…Within the frame of transport measurements, the pioneering experiments on LP effect in 60ies kept high interest [3,4] , because-on the one sideit represents the reference phenomenological expression of topological effects [5], while-on the other side-it provides the basic start-up experiment for the investigation and development of flux-based quantum devices [6].…”

“…Since long time, the LP effect has been conceived as a quantum phenomenon involving some sort of interference process [5,7], but to date a model providing a direct phenomenological connection between the measured differential voltage and screening currents dynamics has not been provided yet.…”

“…modulus[10]. It is straightforward to represent (see appendix C) equation(5) in terms of the phase j = / p F F 2 ' , 0 which is related to the gauge invariant momentum through functional…”

“…Representation of the phase of the order parameter as a functional of the supercurrent In the approximation valid for a thin wire or film[10], the order parameter can be considered as composed by a constant modulus | | Y = n s and a spatially varying phase Employing equation(5), supercurrent density can be expressed in terms of the phase gradient Integration of (C3) over a line of current (parametrized by a scalar l) from some initial point (l=0) to any arbitrary point (l=L) gives ( phase results to be a functional of the current ( ( ))J r l , https:/ /orcid.org/0000-0003-2368-0064…”