Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 3Citation - Scopus: 3Spin-Orbit Coupling and Optical Detection of Spin Polarisation in Triangular Graphene Quantum Dots(Inderscience Enterprises Ltd., 2015) Potasz, P.; Güçlü, Alev Devrim; Özfidan, I.; Hawrylak, P.We present a theory of the effect of spin-orbit coupling on optical properties of triangular graphene quantum dots (TGQD). TGQDs with zigzag edges exhibit a degenerate band of states at the Fermi level. For the charge neutral TGQD, the shell is expected to be half-filled by spin polarised electrons leading to finite magnetisation. Using four-band tight-binding and effective Kane-Mele models, we show that, if the TGQD is spin polarised, the low energy optical absorption spectrum reveals two distinct peaks corresponding to left and right circularly polarised light while the unpolarised TGQD shows only one peak. This allows optical detection of spin polarisation, its direction and the strength of spin-orbit coupling in TGQDs.Conference Object Graphene-Based Integrated Electronic, Photonic and Spintronic Circuit(SPIE, 2013) Potasz, P.; Güçlü, Alev Devrim; Özfidan, Işıl; Korkusinski, Marek; Hawrylak, PawelTo create carbon-based nanoscale integrated electronic, photonic, and spintronic circuit one must demonstrate the three functionalities in a single material, graphene quantum dots (GQDs), by engineering lateral size, shape, edges, number of layers and carrier density. We show theoretically that spatial confinement in GQDs opens an energy gap tunable from UV to THz, making GQDs equivalent to semiconductor nanoparticles. When connected to leads, GQDs act as single-electron transistors. The energy gap and absorption spectrum can be tuned from UV to THz by size and edge engineering and by external electric and magnetic fields. The sublattice engineering in, e.g., triangular graphene quantum dots (TGQDs) with zigzag edges generates a finite magnetic moment. The magnetic moment can be controlled by charging, electrical field, and photons. Addition of a single electron to the charge-neutral system destroys the ferromagnetic order, which can be restored by absorption of a photon. This allows for an efficient spin-photon conversion. These results show that graphene quantum dots have potential to fulfill the three functionalities: electronic, photonic, and spintronic, realized with different materials in current integrated circuits, as well as offer new functionalities unique to graphene.Article Citation - WoS: 8Citation - Scopus: 9Sublattice Engineering and Voltage Control of Magnetism in Triangular Single and Bi-Layer Graphene Quantum Dots(John Wiley and Sons Inc., 2016) Güçlü, Alev Devrim; Potasz, P.; Hawrylak, PawelWhen a Dirac electron is confined to a triangular graphene quantum dot with zigzag edges, its low-energy spectrum collapses to a shell of degenerate states at the Fermi level leading to a magnetized edge. The shell degeneracy and the total magnetization are proportional to the edge size and can be made macroscopic. In this review, we start with a general discussion of magnetic properties of graphene structures and its relation to broken sublattice symmetry. Then, we discuss single electronic properties of single and bilayer triangular graphene quantum dots, focusing on the nature of edge states. Finally, we investigate the role of electronic correlations in determining the nature of ground state and excitation spectra of triangular graphene quantum dots as a function of dot size and filling fraction of the shell of zero-energy states. The interactions are treated by a combination of tight-binding, Hartree-Fock and configuration interaction methods. We show that the spin polarization of the triangular graphene quantum dots can be controlled through gating, i.e., by adding or removing electrons. In bilayer graphene dots, the relative filling of edge states in each layer and the magnetization can be tuned down to single localized spin using an external vertical electrical field.Article Citation - WoS: 38Citation - Scopus: 41Zero-Energy States of Graphene Triangular Quantum Dots in a Magnetic Field(American Physical Society, 2013) Güçlü, Alev Devrim; Potasz, P.; Hawrylak, P.We present a tight-binding theory of triangular graphene quantum dots (TGQD) with zigzag edge and broken sublattice symmetry in an external magnetic field. The lateral size quantization opens an energy gap, and broken sublattice symmetry results in a shell of degenerate states at the Fermi level. We derive a semianalytical form for zero-energy states in a magnetic field and show that the shell remains degenerate in a magnetic field, in analogy to the zeroth Landau level of bulk graphene. The magnetic field closes the energy gap and leads to the crossing of valence and conduction states with the zero-energy states, modulating the degeneracy of the shell. The closing of the gap with increasing magnetic field is present in all graphene quantum dot structures investigated irrespective of shape and edge termination.