Güçlü, Alev Devrim
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Guclu, Alev Devrim
Güçlü, A. Devrim
Guclu, A. Devrim
Güçlü, AD
Güçlü, A. D.
Guclu, AD
Guclu, A. D.
Güçlü, A. Devrim
Guclu, A. Devrim
Güçlü, AD
Güçlü, A. D.
Guclu, AD
Guclu, A. D.
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Email Address
devrimguclu@iyte.edu.tr
Main Affiliation
04.05. Department of Pyhsics
Status
Current Staff
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WoS Researcher ID
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1NO POVERTY
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2ZERO HUNGER
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3GOOD HEALTH AND WELL-BEING
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4QUALITY EDUCATION
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5GENDER EQUALITY
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6CLEAN WATER AND SANITATION
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7AFFORDABLE AND CLEAN ENERGY
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8DECENT WORK AND ECONOMIC GROWTH
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9INDUSTRY, INNOVATION AND INFRASTRUCTURE
1
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10REDUCED INEQUALITIES
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11SUSTAINABLE CITIES AND COMMUNITIES
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12RESPONSIBLE CONSUMPTION AND PRODUCTION
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13CLIMATE ACTION
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14LIFE BELOW WATER
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15LIFE ON LAND
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16PEACE, JUSTICE AND STRONG INSTITUTIONS
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17PARTNERSHIPS FOR THE GOALS
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Documents
47
Citations
1481
h-index
23
Documents
41
Citations
1321
Scholarly Output
37
Articles
21
Views / Downloads
42555/13462
Supervised MSc Theses
7
Supervised PhD Theses
6
WoS Citation Count
366
Scopus Citation Count
290
Patents
0
Projects
6
WoS Citations per Publication
9.89
Scopus Citations per Publication
7.84
Open Access Source
31
Supervised Theses
13
| Journal | Count |
|---|---|
| Physical Review B | 9 |
| Physical Review B - Condensed Matter and Materials Physics | 4 |
| Solid State Communications | 3 |
| Physica Status Solidi - Rapid Research Letters | 2 |
| New Journal of Physics | 1 |
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37 results
Scholarly Output Search Results
Now showing 1 - 10 of 37
Article Citation - WoS: 8Citation - Scopus: 8Effects of Long-Range Disorder and Electronic Interactions on the Optical Properties of Graphene Quantum Dots(American Physical Society, 2017) Altıntaş, Abdulmenaf; Çakmak, K. E.; Güçlü, Alev DevrimWe theoretically investigate the effects of long-range disorder and electron-electron interactions on the optical properties of hexagonal armchair graphene quantum dots consisting of up to 10 806 atoms. The numerical calculations are performed using a combination of tight-binding, mean-field Hubbard, and configuration interaction methods. Imperfections in the graphene quantum dots are modeled as a long-range random potential landscape, giving rise to electron-hole puddles. We show that, when the electron-hole puddles are present, the tight-binding method gives a poor description of the low-energy absorption spectra compared to mean-field and configuration interaction calculation results. As the size of the graphene quantum dot is increased, the universal optical conductivity limit can be observed in the absorption spectrum. When disorder is present, the calculated absorption spectrum approaches the experimental results for isolated monolayers of graphene sheets.Article Citation - WoS: 4Citation - Scopus: 3Quantum Monte Carlo Study of Semiconductor Artificial Graphene Nanostructures(AMER PHYSICAL SOC, 2023) Öztarhan, Gökhan; Güçlü, Alev Devrim; Kul, E. Bulut; Okçu, Emre; Guclu, A. D.Semiconductor artificial graphene nanostructures where the Hubbard model parameter U/t can be of the order of 100, provide a highly controllable platform to study strongly correlated quantum many-particle phases. We use accurate variational and diffusion Monte Carlo methods to demonstrate a transition from antiferromagnetic to metallic phases for an experimentally accessible lattice constant a = 50 nm in terms of lattice site radius rho, for finite-sized artificial honeycomb structures nanopatterned on GaAs quantum wells containing up to 114 electrons. By analyzing spin-spin correlation functions for hexagonal flakes with armchair edges and triangular flakes with zigzag edges, we show that edge type, geometry, and charge nonuniformity affect the steepness and the crossover rho value of the phase transition. For triangular structures, the metal-insulator transition is accompanied with a smoother edge polarization transition.Book Part Citation - Scopus: 8Graphene-Based Integrated Electronic, Photonic and Spintronic Circuit(wiley, 2013) Güçlü,A.D.; Potasz,P.; Hawrylak,P.A special class of nanoscale graphene triangular quantum dots (GTQDs) with zigzag edges fulfills all three functions needed for information processing: (i) size quantization turns graphene, a semimetal, into a semiconductor like silicon, with a bandgap tunable from THz to UV, enabling a GTQD-based single electron transistor for information processing; (ii) unlike silicon, GTQDs are equivalent to direct-gap semiconductors that absorb and emit light, and hence can be used for communication; and (iii) GTQDs exhibit a voltage-tunable magnetic moment that can be used for information storage. Therefore, graphene quantum dots might potentially be used as elements of graphene-based integrated electronic, photonic and spintronic circuit. This chapter describes progress toward the understanding of the electronic, optical and magnetic properties of graphene quantum dots. Controlled Vocabulary Terms electronic circuits; graphene; information management; integrated optoelectronics; magnetoelectronics; optical properties; photonics; semiconductor quantum dots © 2013 John Wiley. © 2013 John Wiley & Sons, Inc. Published 2013 by John Wiley & Sons, Inc.Master Thesis Electronic Properties of Artificial Graphene Nanostructure(01. Izmir Institute of Technology, 2021) Okcu, Emre; Güçlü, Alev DevrimArtificial graphene is an artificial honeycomb structure which mimics the interesting properties of graphene. Such as Dirac cone in energy dispersion, zero band gap etc. Wide range of production type makes artificial graphene valuable material. It can be engineered by lasers, molecules and semiconductors. Semiconductor based artificial graphene can be produced by dot lattice with honeycomb patterned attractive potential or by antidot lattice with triangular patterned repulsive potential. In the following calculations, semiconductor (GaAs) based artificial graphene was used to compute electronic properties. Like in graphene, artificial graphene has Dirac cones in energy dispersion. However, graphene has 1.42 angstrom carbon to carbon atom distance. This distance can not be changed but artificial graphene offers us tunability. Different parameters yield tons of band structure. It offers not only Dirac cone but also gaped bands in energy dispersion. This graphene-like feature and tunability make artificial graphene an important and researchable subject. Besides, we added another tunable parameter stiffness to control the shape of potential. Stiffness became another important parameter in our calculations. We observed that stiffness dramatically changes the band structure of the material. As a first step, artificial graphene band structures are calculated from the single-electron approximation. Some parameters are compared with other works and the same results are found. Dirac cones are achieved in band structures. Hopping and Hubbard U values are computed. Those parameters are essential for computing finite structures. Mean-field Hubbard can be solved, and wave functions can be used as input for input required methods such as quantum Monte Carlo. As a second step, we used the density functional theory method to investigate electron-electron interactions. Local density approximation was chosen to solve the Kohn-Sham equation. Hopping parameters obtained from DFT are much realistic than the single-electron approximation. Stiffness plays a big role in DFT energy dispersioArticle Citation - WoS: 4Citation - Scopus: 4Atomic Collapse in Graphene Quantum Dots in a Magnetic Field(Elsevier, 2022) Eren, İsmail; Güçlü, Alev DevrimWe investigate finite size and external magnetic field effects on the atomic collapse due to a Coulomb impurity placed at the center of a hexagonal graphene quantum dot within tight binding and mean-field Hubbard approaches. For large quantum dots, the atomic collapse effect persists when the magnetic field is present, characterized by a series of Landau level crossings and anticrossings, in agreement with previous bulk graphene results. However, we show that a new regime arises if the size of the quantum dot is comparable to or smaller than the magnetic length: While the lowest bound states cross the Fermi level at a lower value of coupling constant β<0.5, a size independent critical coupling constant βc∗>0.5 emerges in the local density of states spectrum, which increases with the applied magnetic field. These effects are found to be persistent in the presence of electron–electron interactions within mean-field Hubbard approximation.Doctoral Thesis Electronic, Magnetic and Transport Properties of Graphene Quantum Dots With Charged Impurities(Izmir Institute of Technology, 2020) Polat, Mustafa; Güçlü, Alev DevrimIn this thesis, electronic, magnetic, and transport properties of armchair edged hexagonal and zigzag edged triangular graphene quantum dots (GQDs) are investigated in the presence of charged impurities. In this manner, a special attention has been paid to the Coulomb impurity problem in these structures. The collapse of the wave functions starting from the 1S$_{1/2}$ state is studied in the presence of not only the Coulomb impurity but also in the presence of a Coulomb charged vacancy with the help of tight-binding and extended mean-field Hubbard (MFH) models. Here, we report an interaction induced renormalization of the critical coupling constant ($\beta_{c}$). In addition, our results suggest that the induced charge for the interacting fermions is smaller than that of the non-interacting fermions. Furthermore, the transport coefficients reveal two different characteristics of the subcritical ($\beta$ $<$ $\beta_{c}$) and supercritical ($\beta$ $>$ $\beta_{c}$) regimes. As for the charged vacancy, the bare carbon vacancy induces a local magnetic moment in the hexagonal GQDs, but it is suppressed when the vacancy is charged with the subcritical Coulomb potential. Except the pristine cases of the GQDs, we numerically study a Coulomb impurity problem for the interacting fermions restricted in disordered hexagonal GQDs. In the presence of randomly distributed lattice defects and spatial potential fluctuations induced by Gaussian impurities, the response of $\beta_{c}$ for atomic collapse is mainly investigated by local density of states (LDOS) calculations within the MFH model. We find that both types of disorder cause an amplification of the critical threshold. As for the zigzag edged triangular GQDs, in the presence of the bare vacancy, we exactly obtain the spin splitting with the help of LDOS calculations in the energy spectrums, which are dominated by the edge states around the Fermi level. Similar to the hexagonal GQDs, if the vacancy is charged, the local magnetic moment disappears in these GQDs.Article Citation - WoS: 26Citation - Scopus: 26Theory of Optical Properties of Graphene Quantum Dots(John Wiley and Sons Inc., 2016) Özfidan, Işıl; Güçlü, Alev Devrim; Korkusinski, Marek; Hawrylak, PawelWe present here a theory of the optical properties of graphene quantum dots (GQDs) with tunable band gaps by lateral size confinement, from UV to THz. Starting from the Hartree-Fock ground state, we construct the correlated many-body ground and excited states of GQDs as a linear combination of a finite number of electron-hole pair excitations. We discuss the evolution of the band gap with size and its renormalization by self-energy and excitonic effects. We calculate and analyze the dipole moments of graphene quantum dots that possess a degenerate valence and conduction band edge, and construct a characteristic exciton and biexciton spectrum. We find an exciton band consisting of a pair of robust, spin singlet bright exciton states and a band of dark, spin singlet and spin triplet, exciton states at lower energies. We predict a characteristic band of biexciton levels at the band edge, discuss the Auger processes and identify a biexciton-exciton cascade. Our theoretical results are compared with experimental linear absorption and non-linear transient absorption spectra of colloidal GQDs. We next discuss the optical properties of triangular GQDs with zigzag edges whose magnetic moment can be controlled by gates. The control over the magnetic moment through carrier density manipulation results in optical spin blockade and gate tunable optical properties over a wide range of photon energies.Master Thesis Travel Time in Quantum Theory and Ionization Times of Noble Gases(01. Izmir Institute of Technology, 2020) Paçal, Serkan; Güçlü, Alev DevrimTime in Quantum mechanics, stands as an unresolved problem from the first time the theory was established to the present day. The present thesis consists of three main studies, in the first part, some time formulas that have been proposed in the past are included. In the second part, time is formulated by using David Bohm's "the guiding equation". In the third part, time formula has been applied to atomic potentials (He, Ar and Kr noble gases) for which time measurements done. It has been shown that the ionization time of the noble gases we have calculated gives results very compatible with the experiments.Article Citation - WoS: 7Citation - Scopus: 7Effects of Interedge Scattering on the Wigner Crystallization in Graphene Nanoribbons(American Physical Society, 2017) Modarresi, Mohsen; Güçlü, Alev DevrimWe investigate the effects of coupling between the two zigzag edges of graphene nanoribbons on the Wigner crystallization of electrons and holes using a combination of tight-binding, mean-field Hubbard and many-body configuration interaction methods. We show that the thickness of the nanoribbon plays a crucial role in the formation of Wigner crystal. For ribbon widths smaller than 16 Å, increased kinetic energy overcomes the long-range Coulomb repulsion and suppresses the Wigner crystallization. For wider ribbons up to 38 Å wide, strong Wigner localization is observed for an even number of electrons, revealing an even-odd effect also found in the Coulomb-blockade addition spectrum. Interedge correlations are found to be strong enough to allow simultaneous crystallization on both edges, although an applied electric field can decouple the two edges. Finally, we show that Wigner crystallization can also occur for holes, albeit weaker than for electrons.Master Thesis Electronic, Magnetic and Optical Properties of Graphene Nanoribbons(Izmir Institute of Technology, 2016) Özdemir, Hakan Ulaş; Güçlü, Alev DevrimIn this thesis, electronic, magnetic and optical properties of graphene nanoribbons are investigated within mean-field Hubbard model with two different disorder type; long and short range in finite and cyclic topology. First we investigated combined effect of electron-electron interaction effects and long range potential fluctuations. In both of the geometries, electron-electron interaction effects make edge states robust against disorders. Furthermore, surprisingly, strong enough disorder causes system to experience a phase transition from antiferromagnetically coupled edge states to ferromagnetic coupling in agreement with recent theoretical and experimental studies. Then, the stability of optical conductance under impurity effects, correlation between optical characteristic and magnetic phase of ZGNR is investigated, respectively. Similar to edge state density profile recovery, electronic interaction effects reduce the impurity induced peak around Fermi level. More importantly, we found distinct optical transitions due to edge-bulk mixed states around Fermi level that can be used to detect whether ZGNR is in antiferromagnetic or ferromagnetic phase. Finally, we investigated the disorder induced metalinsulator transition. Since, long range impurities protect the sublattice symmetry and leads to phenomena known as ”absence of backscattering”, there exist minimum conductivity for graphene. On the other hand, in order to model hydrogenation effects, we used short range impurity potential which breaks the sublattice symmetry. Using a time dependent tight binding model, we observed Anderson localization induced metal to insulator transition with a nanometer scale localization length for 2% hydrogen coverage. We found that, Anderson localization is stronger at high energy valence states since those states are more vulnerable to hydrogenation.