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Aharonov-Bohm oscillations beating and universal conductance fluctuations in a single-mode quantum interferometer
Published in Jong-Chun Woo, Yoon Soo Park, Compound Semiconductors 1995, 2020
A A Bykov, Z D Kvon, E B Ol'shanetskii
The lower curve in Fig. 1a is the result of numerical calculation using the expressions for G(B). Two parameters were varied to fit the calculated curve to the experimental data - the coefficient w0 which determines the potential across the conducting channels and the Fermi energy of electrons EF. The knowledge of these two parameters allows one to evaluate the width W of conducting channels. At first glance there is a good agreement between the calculated and experimental curves. However the parameters W = 73nm and EF= 0.8 meV determined from the fitting procedure differ significantly from those derived from an independent self-consistent calculation of the energy spectrum in the ring which yielded W = 40 nm and EF= 5 meV. Yet another estimate of W was made from the magnetic field value at which total separation of edge current states in the ring leads to suppression of Aharonov-Bohm oscillations (to our opinion this is a more direct estimate). It gives an even lower value for the width of conducting channels - W< 20 nm. Thus we come to the conclusion that the theory [7] provides only a qualitative description of experiment. That is not surprising since this theory is founded on a model of an isolated ring only weakly coupled to current probes while the experimental structures are basically open systems.
Free Radical Polymerization of Expandable Oxaspiro Monomers
Published in Rajender K. Sadhir, Russell M. Luck, Expanding Monomers, 2020
The ring-opened polymer 5 can be distinguished by the presence of a strong carbonate carbonyl absorption at approximately 1750 cm–1 in the IR and the disappearance of the intense tetraoxaspiro carbon-oxygen absorption at near 1200 cm–1 from the monomer. The 1H-NMR spectrum of the linear polymer 5 (Figure 3) is characterized by the downfield shift of the vinylidine protons compared with monomer, and separation of the methylene protons in the backbone into distinct signals. The 13 C-NMR spectrum of the ring- opened polymer is notable for the presence of the carbonate carbonyl signal (Figure 4). The mixed-mode polymerization of monomer 4, involving both ring-opening and 1,2-addition pathways, yields an IR spectrum with a moderate carbonyl absorption and a significant tetraoxaspiro linkage still present (Figure 5).
Physics and fabrication of Micro-Ring Resonator (MRR) structure devices
Published in Iraj Sadegh Amiri, Abdolkarim Afroozeh, Harith Ahmad, Integrated Micro-Ring Photonics, 2016
Iraj Sadegh Amiri, Abdolkarim Afroozeh, Harith Ahmad
The established use of Wavelength Division Multiplexed (WDM) for local area network systems has raised the demand for new filtering and switching functions (Park et al., 2004). In order to integrate these devices on a wafer scale, whispering gallery mode micro resonators represent the most compact and efficient solution. They consist of a bus waveguide evanescently coupled to a micrometer-size ring resonator; the characteristic size-dependent frequency spectrum of the ring allows only selected wavelength channels to be transmitted or shifted to another waveguide. Small radii allow a large free spectral range – i.e. large separation between the filtered channels but increase the propagation bending losses, which can compromise the quality factor (Melloni et al., 2001). To overcome this limitation, high refractive index contrast between the ring core and the surrounding materials is mandatory (Knight et al., 1998). A second, very important, requirement relates to the tenability. The possibility to electrically control the transmission spectrum, via electro-optic effect, would allow extremely compact and ultrafast modulation and switching (Scolari et al., 2005). By integrating arrays of micro-ring resonators on a single optical chip, the realization of complex functions would be feasible. Besides, large-Q resonators based on non centro-symmetric materials would exploit the high amount of stored energy for enhancing the efficiency of nonlinear optical phenomena (Brochu & Pei, 2010).
Geometry tailored magneto-optical absorption spectra of elliptically deformed double quantum rings
Published in Philosophical Magazine, 2022
When the single quantum ring is bounded by two ellipses, its energy spectrum splits in separated pairs of levels that cross repeatedly as B increases, as can be seen in Figure 5(b). Also, the entire spectrum is displaced towards lower energies as R1y decreases and/or R2y increases. These features were reported before by Planelles et al. [41] for the spectrum of a ring bounded by two ellipses with parallel largest semi-axes and by us [42,43] for the pseudo-elliptic rings. The first two levels are well separated from the upper ones and almost superposed. The separation between the pair of levels increases for the higher levels. The spectrum still presents Aharonov–Bohm-like oscillations with a period that augments only slightly with the ring deformation. The energy increases quadratic with the field, analogously to the diamagnetic shift seen in quantum dots and wells [44,45].