Çakır, Özgür
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Cakir, Ozgur
Cakir, O.
Cakir, O
Çakır, Ö
Çakır, Ö.
Cakir, O.
Cakir, O
Çakır, Ö
Çakır, Ö.
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ozgurcakir@iyte.edu.tr
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04.05. Department of Pyhsics
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Current Staff
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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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8DECENT WORK AND ECONOMIC GROWTH
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9INDUSTRY, INNOVATION AND INFRASTRUCTURE
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10REDUCED INEQUALITIES
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Documents
22
Citations
118
h-index
5
This researcher does not have a WoS ID.
Scholarly Output
22
Articles
4
Views / Downloads
27409/7095
Supervised MSc Theses
15
Supervised PhD Theses
1
WoS Citation Count
16
Scopus Citation Count
15
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0
Projects
3
WoS Citations per Publication
0.73
Scopus Citations per Publication
0.68
Open Access Source
14
Supervised Theses
16
| Journal | Count |
|---|---|
| Physical Review B | 2 |
| ACS Photonics | 1 |
| Journal of Physics B: Atomic, Molecular and Optical Physics | 1 |
| Optics InfoBase Conference Papers | 1 |
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22 results
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Now showing 1 - 10 of 22
Article Citation - WoS: 5Citation - Scopus: 4Electromagnetically Induced Transparency and Absorption Cross-Over With a Four-Level Rydberg System(IOP Publishing, 2022) Oyun, Yağız; Çakır, Özgür; Sevinçli, SevilayElectromagnetically induced transparency (EIT) and absorption (EIA) are quantum coherence phenomena which result from the interference of excitation pathways. Combining these with Rydberg atoms have opened up many possibilities for various applications. We introduce a theoretical model to study Rydberg-EIT and Rydberg-EIA effects in cold Cs and Rb atomic ensembles in a four-level ladder type scheme taking into account van der Waals type interactions between the atoms. The proposed many-body method for analysis of such systems involves a self-consistent mean field approach and it produces results which display a very good agreement with recent experiments. Our calculations also successfully demonstrate experimentally observed EIT-EIA cross-over in the Rb case. Being able to simulate the interaction effects in such systems has significant importance, especially for controlling the optical response of these.Master Thesis Emission Characteristics of Two and Three Level Systems(Izmir Institute of Technology, 2022) Yılmaz, Teyfik; Çakır, Özgür; Çakır, ÖzgürIn this thesis, we mainly focus on the two subjects. Firstly, we investigate the spontaneous emission from a V-type three-level atom. We mainly study the influence of quantum interference between the decay processes from the two upper levels to a lower level to which the upper levels are coupled by the same vacuum modes. The effects of quantum interference on the spontaneous emission spectrum are studied. These effects are shown to induce spectral narrowing and a dark line in the spectrum. The influence of the interference on the upper level populations is also examined. It is seen that the upper level populations are not simple exponential decays. In the second part of this study, the fluorescence spectrum of a driven two-level atom is evaluated. Both the resonance and the off-resonance cases, and the weak and the strong coupling regimes are investigated.Conference Object Influence of Electron-Phonon Interactions on the Spectral Properties of Defects in Hexagonal Boron Nitride(OSA - The Optical Society, 2019) Arı, Ozan; Fırat, Volkan; Polat, Nihat; Çakır, Özgür.; Ateş, SerkanWe present temperature-dependent micro-PL studies on a single defect in hexagonal boron nitride. A zero-phonon line emission accompanied by Stokes and anti-Stokes phonon sidebands (˜ 6.5 meV) with a Debye-Waller factor of 0.59 is observed. © OSA 2019 © 2019 The Author(s)Article Citation - WoS: 4Citation - Scopus: 4Indirect Exchange Interaction in Two-Dimensional Materials With Quartic Dispersion(American Physical Society, 2022) Canbolat, Ahmet Utku; Sevinçli, Haldun; Çakır, ÖzgürWe investigate the indirect magnetic exchange interaction between two magnetic moments in a two-dimensional semiconductor with quartic dispersion, featuring a singularity at the band edge. We obtain the Green's functions analytically to calculate the magnetic exchange interaction at zero temperature. We show that the singularity in the density of states (DOS) for quartic dispersion gives rise to an enhancement in the amplitude of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction as the Fermi energy is swept toward the band edge. Furthermore, a region of finite exchange interaction arises, with a range increasing as the Fermi energy approaches the band edge. The results lay the possibility of an electrical/chemical control over the exchange interactions.Master Thesis Three-Photon Electromagnetically Induced Transparency in Rydberg Atoms(Izmir Institute of Technology, 2019) Oyun, Yağız; Sevinçli, Sevilay; Çakır, ÖzgürElectromagnetically Induced Transparency (EIT) is a quantum coherence phe- nomenon, in which an atomic medium is rendered transperent via destructive interference of excitation pathways. EIT was first observed in a three-level lambda scheme where a modified optical response is achieved by the interference of light field induced atomic state coherences at the resonance of transition. An EIT system also produces important optical effects including giant Kerr non-linearity and slow light. Rydberg-EIT media have been used to study optical properties of atomic media, non-linear optical effects and to gain better understanding on interacting many-body systems due to the controllable in- teractions of Rydberg atoms. Recently EIT in a four-level ladder scheme was realized experimentally in a dressed-state manner with Cs atomic vapor, in which a strong dress- ing field allows for a transparency window to be opened for probe field. Rydberg EIT has potential applications in terahertz regime, electrometry, metrology and quantum in- formation science, but extensive studies on four-level Rydberg EIT schemes are scarce. In this thesis; three-photon EIT in a cold atomic ensemble that has a ladder type excita- tion scheme, in which the highest energy state is a Rydberg state is investigated. Atom- light interactions of a four-level ladder system is developed for non-interacting case, then extended to many-body case. Starting with the steady-state solutions without atomic in- teractions, Rydberg EIT system is analyzed using mean-field and rate equation methods, though due to inadequate computing power and lack of time we could not finalize the rate equation method. To understand effects of Rydberg-Rydberg interactions on these systems in detail, two-body case is investigated with mean-field method. Afterwards, to achieve more realistic results, a self-consistent mean-field method for larger systems is developed. It is observed that as the van der Waals interaction energy increases, Rydberg blockade becomes more prominent. Therefore induced transparency weakens, broadens and shifts away from the resonance as expected. This means that, controllable interac- tions in a Rydberg EIT medium enables to control and modify the optical response of the atomic medium.Master Thesis Quantum transport in nanostructured materials(Izmir Institute of Technology, 2017) Kurt, Gizem; Sevinçli, Haldun; Çakır, ÖzgürDue to the advances in the measurement and fabrication techniques at the nanoscale it is now possible to measure thermal transport across single molecule junctions[1], which makes it possible to consider nano-scale thermal devices. One of the building blocks for such thermal devices should be thermal switches. The aim of this study is to design a thermal switch, which is based on a single molecule junction and photoisomerism. We propose reversible photoisomerism as a key ingredient to build reversible thermal switches based on single molecule junctions. In this thesis, the thermal conductances of molecular junctions built by azobenzene and its derivatives are computed using density functional theory based tight binding method combined with atomistic Green’s functions. These molecules show photoisomeric behaviour by switching their three-dimensional structure when exposed to radiation. We investigate the effects of different linker groups as well as the details of the reservoirs. Carbon nanotubes are used as reservoirs, while generic reservoirs are also investigated to illuminate the effects of the reservoir details. We show that thermal conductance can be altered by switching the molecule from trans to cis configuration. The effect is robust under the change of the linkers that bind the molecules to the reservoirs and under the change of the particular molecular species.Master Thesis Radiative and Topological Properties of One-Dimensional Atomic Chains(01. Izmir Institute of Technology, 2024) İyican, Arda Deniz; Çakır, ÖzgürBu tezde, bir boyutlu, her birim hücresinde iki özdeş iki seviyeli atom bulunan bir diatomik zincirin topolojik ve vakum aracılı kolektif özellikleri incelenmiştir. Zincir üzerinde sabit sayıda uyarılmanın olduğu altuzayda, sistem, dissipatif etkileri dikkate alan non-Hermityen bir efektif Hamiltonyen ile tanımlanmaktadır. Zincirde tek bir uyarım varlığında, sonsuz bir zincir için kolektif radyatif davranış, öz durumları Bloch tipi durumlar olan etkin Hamiltoniyene karşılık gelen karmaşık enerji bantlarından ortaya çıkarılmıştır.Tek bir uyarıma sahip sonlu bir zincir için radyatif özellikler, sistemin etkin Hamiltonyeninin tam diyagonalizasyonuyla ortaya çıkarılmıştır. Altışınımlı durumların varlık koşulları belirlenmiştir. Ele alınan model, uzun menzilli etkileşimler ve dissipasyon nedeniyle genişletilmiş, non-Hermityen bir SSH modelidir. Bu sistem için topolojik özellikleri ortaya çıkarmak amacıyla kompleks Berry fazı hesaplanmış ve ardından topolojik olarak trivial olmayan durumlar için kenar durumları belirlenmiştir. Ayrıca, ışınımlı, altışınımlı ve topolojik kenar durumlarından gelen radyasyon desenleri, radyasyon bölgesindeki Poynting vektörünün hesaplanmasıyla gösterilmiştir.Master Thesis Investigation of Anharmonic Effects in Phonon Transport(Izmir Institute of Technology, 2018) Çınar, Mustafa Neşet; Sevinçli, Haldun; Çakır, ÖzgürPhonons are quantum mechanical particles corresponding to ionic vibrations. They are similar to electrons in a way that they interact with other particles and defects, and they are responsible for thermal conduction in insulators like electrons are responsible for electrical conduction in conductors. Most of the physical properties due to ionic vibrations can be determined by using harmonic approximation which consider phonons as independent quantum mechanical harmonic oscillators having quadratic potentials depending on the displacements of atoms in their equilbirium positions. However, there are some physical processes such as finite thermal conductivity and thermal expansion which cannot be explained with only harmonic phonons. To investigate these physical processes anharmonicity needs to be taken into account. Anharmonicity is related to the higher order terms in the interatomic potential and corresponds to phonon-phonon interactions. The strength of these interactions depends on the temperature which is related to the available thermal energy, or, the number of phonons given by the Bose-Einstein distribution. In this thesis, the effects of anharmonicity on quantum thermal transport are studied in nanoscale systems by using Green functions. Non-Equilibrium Green Functions (NEGF) method is a perturbative approach to study transport properties of both electronic and phononic systems. Anharmonic terms in interatomic potential are incorporated into NEGF method in the form of a self-energy which can be computed self-consistently. This approach provides high accuracy with high computational cost. As an alternative, mean field technique is computationally more feasible which allows to do calculations for larger systems. In this study, we investigate anharmonic transport properties of one-dimensional chains using NEGF method. Our calculations involve self-energies of third and fourth order anharmonic terms. In addition, mean field calculation for fourth order anharmonicity is performed for comparison.Master Thesis Electronic Transport in a Boundary-Driven One-Dimensional Chain With Bulk Dephasing(01. Izmir Institute of Technology, 2024) Yeler, Hakan; Çakır, ÖzgürBu tezde, etkileşimli ve etkilemşimsiz fermiyonların bir boyutlu zincir üzerinde denge dışı durağan durumdaki taşınım özellikleri, çevre etkilerini de hesaba katarak incelenmiştir. Sistem dinamiği Lindblad master denklemi kullanılarak hesaplanmıştır. Taşınımı karakterize eden akım operatörü tanımlanmıştır. Hilbert uzayının eksponansiyel artış göstermesi sebebiyle, çok parçacıklı sistemlerin çözümünü hesaplamak zordur. Bu sebeple farklı çözüm metodları incelenmiştir. Hesaplama avantajlarından dolayı, etkileşimsiz sistemlerin çözümü için kovaryans matris methodu tanıtılmıştır. Etkileşimli sistemler için ortalama alan ve korelasyon fonksiyonların hiyerarşisi gibi yaklaşık metodlar tanıtılıp, birbirleriyle kıyaslanmıştır. Taşınımın davranışı kesin çözüm yöntemi yardımıyla incelenmiştir. Lindblad denklemi vektörize edilerek doğrusal denklem sistemi elde edilmiştir. Elde edilen doğrusal denklem sistemi, Python programlama dili kullanılarak çözülmüştür. Denge dışı durağan durum yoğunluk matrisi ve akım, farklı çevre parametrelerine göre hesaplanmıştır.Master Thesis Quantum Dynamics of Noise Assisted Excitation Transport(Izmir Institute of Technology, 2018) Özkan, Hazan; Çakır, ÖzgürIn this thesis, different types of systems are studied to investigate the effects of the environmental factors on diffusion and transfer time. Each system consists of different energy levels and excitation transfers between them. The mismatch between the energy levels leads to the Anderson localization. Localization has a negative effect on transport. It is shown that Anderson localization is suppressed due to interaction with the environment. To describe the dynamical evolution of the open quantum system Lindblad master equation is used. The transition times of the system from the pure state to the completely mixed state are examined with the help of the density matrix. In consequence of our study, because of the interaction between the system and environment the change in the wavefunction, the loss in the interference terms and an irreversible information flow in the total system are observed. Destructive effects of the environmental noise on localization are observed for different scenarios and diffusion enhanced. However, when the interaction with the environment becomes larger than a critical value, the system exhibits Zeno effect. In the Zeno regime, the time evolution of the quantum state of the system as well as the diffusion is suppressed.
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