Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Quantum Monte Carlo Study of Artificial Triangular Graphene Quantum Dots(Amer Physical Soc, 2025) Kul, E. Bulut; Habibzadeh, Alireza; Cinar, M. N.; Guclu, A. D.We investigate the magnetic phases of semiconductor-based artificial triangular graphene quantum dots (TGQDs) with zigzag edges using variational and diffusion Monte Carlo methods. These systems serve as quantum simulators for bipartite lattices with broken sublattice symmetry, providing a platform to study the extended Hubbard model's emergent magnetic phenomena, including Lieb's magnetism at half filling, edge depolarization upon single-electron addition, and Nagaoka ferromagnetism. Our nonperturbative quantum Monte Carlo simulations, performed for finite-sized TGQDs modeled as nanopatterned GaAs quantum wells, with system sizes up to Ns = 61 lattice sites, reveal a transition from metallic to insulating regimes as a function of the quantum well radius rho, while preserving edge-polarized ground states at half filling. Notably, edge depolarization occurs upon single-electron doping in both metallic and insulating phases, in contrast to the Nagaoka ferromagnetism observed in hexagonal armchair geometries.Article Observable-Enriched Entanglement(Amer Physical Soc, 2025) Winter, Joe H.; Ay, Reyhan; Braunecker, Bernd; Cook, A. M.We introduce methods of characterizing entanglement on the example of the quantum skyrmion Hall effect, in which entanglement measures are enriched by the matrix representations of operators for observables. These observable operator matrix representations can enrich the partial trace over subsets of a system's degrees of freedom, yielding reduced density matrices useful in computing various measures of entanglement, which also preserve the observable expectation value. We focus here on applying these methods to compute observableenriched entanglement spectra, unveiling bulk-boundary correspondences of canonical four-band models for topological skyrmion phases and their connection to simpler forms of bulk-boundary correspondence. Given the fundamental roles entanglement signatures and observables play in the study of quantum systems and the fundamental generalization of the interpretation and treatment of spin within the framework of the quantum skyrmion Hall effect, concepts of observable-enriched entanglement introduced here are broadly applicable to myriad problems of quantum systems.Article Citation - WoS: 4Citation - Scopus: 4Type-Ii Topological Phase Transitions of Topological Skyrmion Phases(Amer Physical Soc, 2025) Ay, Reyhan; Winter, Joe H.; Cook, A. M.We present minimal toy models for topological skyrmion phases of matter, which generically realize type-II topological phase transitions in effectively noninteracting systems, those which occur without closing of the minimum direct bulk energy gap. We study the bulk-boundary correspondence in detail to show that a nontrivial skyrmion number yields a rich bulk-boundary correspondence. We observe gapless edge states, which are robust against disorder, due to nontrivial skyrmion number. Edge states corresponds to bands, which do not traverse the bulk gap, instead yielding gaplessness due to their overlap in energy and exponential localization on opposite edges of the system. These gapless boundary modes can occur for total Chern number zero, and furthermore correspond to rich real-space spin textures with strong polarization of spin along the real-space edge. By introducing toy models generically exhibiting type-II topological phase transitions and characterizing the bulk-boundary correspondence due to nontrivial skyrmion number in these models, we lay the groundwork for understanding consequences of the quantum skyrmion Hall effect.Article Citation - Scopus: 1Magnetism in Twisted Triangular Bilayer Graphene Quantum Dots(Amer Physical Soc, 2025) Mirzakhani, Mohammad; Cetin, Zebih; Yagmurcukardes, Mehmet; Park, Hee Chul; Peeters, Francois M.; da Costa, Diego R.Using a tight-binding model along with the mean-field Hubbard method, we investigate the effect of twisting angle on the magnetic properties of twisted bilayer graphene (tBLG) quantum dots (QDs) with triangular shape and zigzag edges. We consider such QDs in two configurations: when their initial untwisted structure is a perfect AA- or AB-stacked BLG, referred to as AA- or AB-like dots. We find that AA-like dots exhibit an antiferromagnetic spin polarization for small twist angles, which transits to a ferromagnetic spin polarization beyond a critical twisting angle theta c. Our analysis shows that theta c decreases as the dot size increases, obeying a criterion, according to which once the maximum energy difference between electron and hole edge states (in the single-particle picture) is less than (U/gamma 0) t0, the spin-polarized energy levels are aligned ferromagnetically [U is the Hubbard parameter and gamma 0 (t0) the graphene intralayer (interlayer) hopping]. Unlike AA-like dots, AB-like dots exhibit finite magnetization for any twist angle. Furthermore, in the ferromagnetic polarization state, the ground net spin for both dot configurations agrees with the prediction from Lieb's theorem.Article Citation - WoS: 10Citation - Scopus: 10Structural, Electronic, Vibrational, and Thermoelectric Properties of Janus Ge 2 P<i> X</I> (<i> X</I> = N, As, Sb, and Bi) Monolayers(Amer Physical Soc, 2024) Ozbey, Dogukan Hazar; Varjovi, Mirali Jahangirzadeh; Sargin, Gozde Ozbal; Sevincli, Haldun; Durgun, EnginTwo-dimensional (2D) Janus systems have garnered significant scientific interest owing to their novel properties and potential applications. The growing interest in these materials is driven by the idea that their structural asymmetry offers unprecedented opportunities for enhancing thermoelectric performance and unlocking groundbreaking advancements in energy conversion and waste heat utilization. In this context, we present a comprehensive study on the structural, vibrational, electronic, thermal, and thermoelectric properties of Janus Ge2PX(X = N, As, Sb, and Bi) monolayers, using first-principles calculations combined with the Landauer formalism. The suggested configurations exhibit dynamical stability and retain structural integrity even at elevated temperatures. Electronic structure calculations employing hybrid functionals (HSE06) with spin-orbit coupling reveal that Ge2PAs and Ge2PSb monolayers exhibit anisotropic characteristics as indirect semiconductors, while Ge2PN and Ge2PBi exhibit metallic behavior. We also compare the thermal, electronic, and thermoelectric transport properties of these proposed monolayers to binary 2D GeP in the ballistic limit. Notably, both Ge2PAs and Ge2PSb exhibit n-type figure of merit (ZT ) values exceeding 1 at 800 K, with their n-type ZT values surpassing that of GeP at room temperature. Our analysis underscores the distinctive structural and electronic properties of Ge2PAs and Ge2PSb monolayers, accompanied by their highly promising thermoelectric performance. These findings position them as strong candidates for energy harvesting and conversion applications.Article Citation - WoS: 13Citation - Scopus: 15Electronic and Magnetic Properties of Single-Layer Fecl2 With Defects(Amer Physical Soc, 2021) Ceyhan, Eray; Yağmurcukardeş, Mehmet; Peeters, François M.; Şahin, HasanThe formation of lattice defects and their effect on the electronic properties of single-layer FeCl2 are investigated by means of first-principles calculations. Among the vacancy defects, namely mono-, di-, and three-Cl vacancies and mono-Fe vacancy, the formation of mono-Cl vacancy is the most preferable. Comparison of two different antisite defects reveals that the formation of the Fe-antisite defect is energetically preferable to the Cl-antisite defect. While a single Cl vacancy leads to a 1 mu(B) decrease in the total magnetic moment of the host lattice, each Fe vacant site reduces the magnetic moment by 4 mu(B). However, adsorption of an excess Cl atom on the surface changes the electronic structure to a ferromagnetic metal or to a ferromagnetic semiconductor depending on the adsorption site without changing the ferromagnetic state of the host lattice. Both Cl-antisite and Fe-antisite defected domains change the magnetic moment of the host lattice by -1 mu(B) and +3 mu(B), respectively. The electronic ground state of defected structures reveals that (i) single-layer FeCl2 exhibits half-metallicity under the formation of vacancy and Cl-antisite defects; (ii) ferromagnetic metallicity is obtained when a single Cl atom is adsorbed on upper-Cl and Fe sites, respectively; and (iii) ferromagnetic semiconducting behavior is found when a Cl atom is adsorbed on a lower-Cl site or a Fe-antisite defect is formed. Simulated scanning electron microscope images show that atomic-scale identification of defect types is possible from their electronic charge density. Further investigation of the periodically Fe-defected structures reveals that the formation of the single-layer FeCl3 phase, which is a dynamically stable antiferromagnetic semiconductor, is possible. Our comprehensive analysis on defects in single-layer FeCl2 will complement forthcoming experimental observations.