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Enhanced thermoelectric properties in phosphorene nanorings
Using the tight-binding approach, we calculate the thermoelectric properties of phosphorene nanorings in the absence and presence of a perpendicular magnetic field, and we investigate the effect of symmetrically and asymmetrically positioned leads. Our findings indicate that the symmetry/asymmetry of our designed nanostructures, the geometrical characteristics of the ring, and the magnetic flux are three important factors in controlling their thermoelectric properties. Our results show that when zigzag phosphorene nanoribbons (ZPNRs) are coupled symmetrically/asymmetrically to rectangular rings, a large band gap is induced in the electronic conductance due to the suppression of the contribution of edge states. This gives rise to a remarkable increase in the thermopower response compared to the case of pristine ZPNRs. More intriguingly, we realized that the significantly smaller electronic thermal conductance and the reduced phonon thermal conductance of these phosphorene-based nanostructures result in a remarkable improvement in the figure of merit. Moreover, for asymmetric connection configurations with armchair-edged leads, we found that although the thermopower is almost intact, a remarkable reduction of the electronic and phononic thermal conductance leads to a notable improvement in the figure of merit. Also, our numerical calculations showed that by changing the magnetic flux through the nanoring, a drastic increase in the thermopower is observed near an antiresonance point. We demonstrate the tunability of the thermopower and the possibility to switch on and off the thermoelectric response with magnetic flux. Our results suggest phosphorene nanorings as promising candidate nanostructures for thermoelectric applications.