Search for: excited-states
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    Geometric and electronic properties in a series of phosphorescent heteroleptic Cu(I) complexes: Crystallographic and computational studies

    , Article Polyhedron ; Volume 124 , 2017 , Pages 166-176 ; 02775387 (ISSN) Kubiček, K ; Thekku Veedu, S ; Storozhuk, D ; Kia, R ; Techert, S ; Sharif University of Technology
    Elsevier Ltd  2017
    We have investigated the electronic and geometric structures in the lowest excited states of six phosphorescent heteroleptic [CuI(NN)(DPEphos)]+ (DPEphos = bis[(2-diphenylphosphino)phenyl]ether) complexes with varying NN = diimine ligand structures using density functional theory. In comparison to the ground state, the results show a decrease of the dihedral angle between the N–Cu–N and P–Cu–P planes for these excited states with mixed ligand-to-ligand (DPEphos lone pair → π∗(NN)) and metal-to-ligand charge transfer (dπ(Cu) → π∗(NN)) character. Sterically less demanding ligands facilitate this process, which is accompanied by a geometric relaxation of the DPEphos ligand and contraction of... 

    Relative intensity noise study in two mode quantum dot laser

    , Article Optica Applicata ; Volume 41, Issue 4 , 2011 , Pages 961-970 ; 00785466 (ISSN) Horri, A ; Mirmoeini, S. Z ; Faez, R ; Sharif University of Technology
    In this paper, for the first time, we present a semiclassical noise model for InAs/GaAs quantum dot (QD) laser considering two photon modes, i.e., ground and first excited states lasing. This model is based on the five level rate equations. By using this model, the effect of temperature variations on relative intensity noise (RIN) of QD laser is investigated. We find that the RIN significantly degrades when excited state (ES) lasing emerges at high temperature. Furthermore, we investigate the influence of the quantum dot numbers on the RIN properties  

    How do adsorbent orientation and direction of external electric field affect the charge-transfer surface-enhanced raman spectra?

    , Article Journal of Physical Chemistry C ; Volume 125, Issue 24 , 2021 , Pages 13382-13390 ; 19327447 (ISSN) Ashtari Jafari, S ; Jamshidi, Z ; Sharif University of Technology
    American Chemical Society  2021
    Surface-enhanced Raman spectroscopy is a highly sensitive phenomenon and a powerful fingerprint detection tool that reflects the small changes in polarizability on the pattern and intensity of Raman signals. The SERS enhancement signals elucidate with the surface-selection rules. In this regard, molecular configuration and adsorption orientation on the surface, in addition to the direction of external electric field, can lead to different patterns of SERS spectra. To evaluate how the variation of these features influences the pattern and reproducibility of the spectra, the chemical charge-transfer SERS spectra for pyridine on silver clusters are calculated for different field directions,... 

    Effect of Correlation in SrRu03 Metal Sand LiF Insulators

    , Ph.D. Dissertation Sharif University of Technology Hadipour Siahmazgi, Hanif (Author) ; Akhavan, Mohammad (Supervisor)
    There is no satisfactory agreement between theory and experiment in the Hartree-Fock (HF) and density functional theory (DFT) calculation for metals, semiconductors and metals. It is clear that this discrepancy is attributed to the neglecting of correlation. For example, experimentally
    LiF have the largest band gap about 13.6 eV among the alkali halides and show an exciton peak at 12.6 eV . Brener have obtained a value of 22.9 eV for LiF band gap in the HF approximation. DFT has been very successful tool in calculating the ground-state properties of materials. As
    we expect, the band gap in LiF are underestimated in the local density approximation (LDA) calculation (about 8.3 eV) .... 

    3-D electrical model of a neuroprosthesis stimulator based on the concept of stimulus router system

    , Article 2013 20th Iranian Conference on Biomedical Engineering, ICBME 2013 ; 2013 , Pages 265-268 Ashiri, M ; Zahedi, E ; Sharif University of Technology
    IEEE Computer Society  2013
    Lost sensory or motor functions can be restored using electrical neural prostheses (NP), which include surface NPs, implanted or subcutaneous NPs and the more recent Stimulus Router System (SRS). The latter type of NP outperforms the other types in its selective excitation and least invasiveness. In each case, the achieved performance depends on a multitude of design factors among which the electrical excitation waveform shape, frequency, duration of pulses, configuration of electrodes, number of intervals, thermal conditions and electrode material. To investigate the effects of these parameters on the distribution of electric current inside biological tissues, numerical modeling can be... 

    Generation of quantum states by the dynamics of spin chains: Analytical solution

    , Article Physical Review A ; Volume 99, Issue 5 , 2019 ; 24699926 (ISSN) Moradi, M ; Karimipour, V ; Sharif University of Technology
    American Physical Society  2019
    We design a quasi-one-dimensional spin chain with engineered coupling strengths such that the natural dynamics of the spin chain evolves a single excitation localized at the left-hand site to any specified single-particle state on the whole chain. Our treatment is an exact solution to a problem which has already been addressed in approximate ways. As two important examples, we study the W states and Gaussian states of arbitrary width. © 2019 American Physical Society  

    Delocalization of phonons and energy spectrum in disordered nonlinear systems

    , Article Physical Review B ; Volume 101, Issue 22 , 2020 Akaberian, M ; Jafari, S ; Rahimi Tabar, M. R ; Esfarjani, K ; Sharif University of Technology
    American Physical Society  2020
    We study phonon delocalization in disordered media in the presence of nonlinearity. By considering the Fermi-Pasta-Ulam β-model, we show that regardless of whether the initial state of the linear system is localized or not, the final state will be an extended mode after turning on the nonlinear term. We report on the results of an extensive dynamical simulation of a disordered nonlinear system, which show that, independent of the initial mode frequency, in the final state the energy spectrum is excited according to the Kolmogorov spectrum E(ω)∼ω-5/3. Finally, we show that disorder will not cause delocalization of intrinsic localized modes. © 2020 American Physical Society  

    Effect of lattice relaxation on spin density of nitrogen-vacancy centers in diamond and oscillator strength calculations

    , Article European Physical Journal B ; Volume 84, Issue 1 , 2011 , Pages 1-9 ; 14346028 (ISSN) Babamoradi, M ; Heidari Saani, M ; Ranjbar, A ; Vesaghi, M. A ; Kawazoe, Y ; Sharif University of Technology
    Using a generalized Hubbard Hamiltonian, many-electron wavefunctions of negatively charged (NV -) and neutral nitrogen-vacancy (NV 0) centers in diamond were calculated. We report the effect of symmetric relaxation of surrounding atoms on the spin density, calculated from the many electron wavefunctions in the ground and excited states. We evaluated the error, that, arises in estimation of spin density when lattice relaxation effect is neglected in Electron Paramagnetic Resonance experiment and showed that the ground state spin density distribution is accessible in outward relaxations. The computed oscillator strengths give a higher efficiency for the 1.945 eV photoluminescence (PL) line of... 

    Synthesis, structure and photophysical properties of binuclear methylplatinum complexes containing cyclometalating 2-phenylpyridine or benzo{h}quinoline ligands: A comparison of intramolecular Pt-Pt and π-π Interactions

    , Article Dalton Transactions ; Volume 40, Issue 36 , 2011 , Pages 9123-9130 ; 14779226 (ISSN) Jamali, S ; Czerwieniec, R ; Kia, R ; Jamshidi, Z ; Zabel, M ; Sharif University of Technology
    The binuclear cyclometalated complexes [Pt2Me 2(ppy)2(μ-dppm)], 1a, and [Pt2Me 2(bhq)2(μ-dppm)], 1b, in which ppy = 2-phenylpyridyl, bhq = benzo{h}quinoline and dppm = bis(diphenylphosphino)methane, were synthesized by the reaction of [PtMe(SMe2)(ppy)] or [PtMe(SMe 2)(bhq)] with 1/2 equiv of dppm at room temperature, respectively. Complexes 1a and 1b were fully characterized by multinuclear (1H, 31P, 13C, and 195Pt) NMR spectroscopy and were further identified by single crystal X-ray structure determination. A comparison of the intramolecular Pt-Pt and π-π interactions in complexes 1a and 1b has been made on the basis of data on crystal structures and wave functions analysis. The binuclear... 

    A small signal circuit model of two mode InAs/GaAs quantum dot laser

    , Article IEICE Electronics Express ; Volume 8, Issue 4 , 2011 , Pages 245-251 ; 13492543 (ISSN) Horri, A ; Faez, R ; Hoseini, H. R ; Sharif University of Technology
    In this paper, for the first time, we present a small signal circuit model of quantum dot laser considering two photon modes, i.e., ground and first excited states lasing. By using the presented model, effect of temperature variations on modulation response of quantum dot laser is investigated. Simulation results of modulation response are in agreement with the numerical and experimental results reported by other researchers  

    Phase diagram of J1-J2 transverse field Ising model on the checkerboard lattice: a plaquette-operator approach

    , Article European Physical Journal B ; Volume 88, Issue 10 , October , 2015 ; 14346028 (ISSN) Sadrzadeh, M ; Langari, A ; Sharif University of Technology
    springer berlin  2015
    We study the effect of quantum fluctuations by means of a transverse magnetic field (Γ) on the antiferromagnetic J1-J2 Ising model on the checkerboard lattice, the two dimensional version of the pyrochlore lattice. The zero-temperature phase diagram of the model has been obtained by employing a plaquette operator approach (POA). The plaquette operator formalism bosonizes the model, in which a single boson is associated to each eigenstate of a plaquette and the inter-plaquette interactions define an effective Hamiltonian. The excitations of a plaquette would represent an-harmonic fluctuations of the model, which lead not only to lower the excitation energy compared with a single-spin flip but... 

    Excitation spectrum of one-dimensional extended ionic Hubbard model

    , Article European Physical Journal B ; Volume 78, Issue 3 , 2010 , Pages 323-333 ; 14346028 (ISSN) Hafez, M ; Jafari, S. A ; Sharif University of Technology
    We use perturbative continuous unitary transformations (PCUT) to study the one dimensional extended ionic Hubbard model (EIHM) at half-filling in the band insulator region. The extended ionic Hubbard model, in addition to the usual ionic Hubbard model, includes an inter-site nearest-neighbor (n.n.) repulsion, V. We consider the ionic potential as unperturbed part of the Hamiltonian, while the hopping and interaction (quartic) terms are treated as perturbation. We calculate total energy and ionicity in the ground state. Above the ground state, (i) we calculate the single particle excitation spectrum by adding an electron or a hole to the system; (ii) the coherence-length and spectrum of... 

    A novel approach for the steady-state analysis of a three-phase self excited induction generator including series compensation

    , Article ISIEA 2010 - 2010 IEEE Symposium on Industrial Electronics and Applications, 3 October 2010 through 5 October 2010, Penang ; 2010 , Pages 371-375 ; 9781424476473 (ISBN) Hashemnia, M. N ; Kashiha, A ; Ansari, K ; Sharif University of Technology
    A new method to evaluate the steady state performance of a three-phase self excited induction generator based on conductance minimization is proposed. It can be simply used to take series compensation into account. Among the priorities of this method are the absence of convergence problem and flexibility. Simple methods to find the frequency and magnetizing reactance have been proposed. Simulation results show the efficiency of this method  

    Thermal effects on coherence and excitation transfer

    , Article Physical Review A ; Volume 96, Issue 4 , 2017 ; 24699926 (ISSN) Memarzadeh, L ; Mani, A ; Sharif University of Technology
    To control and utilize quantum features in small scale for practical applications such as quantum transport, it is crucial to gain a deep understanding of the quantum characteristics of states such as coherence. Here by introducing a technique that simplifies solving the dynamical equation, we study the dynamics of coherence in a system of qubits interacting with each other through a common bath at nonzero temperature. Our results demonstrate that depending on the initial state, the environment temperature affects coherence and excitation transfer in different ways. We show that when the initial state is incoherent, as time goes on, coherence and the probability of excitation transfer... 

    Critical slowing down of multiatom entanglement by Rydberg blockade

    , Article Physical Review A ; Volume 98, Issue 2 , 2018 ; 24699926 (ISSN) Abad, T ; Mølmer, K ; Sharif University of Technology
    American Physical Society  2018
    Laser excitation pulses that lead to perfect adiabatic state transfer in an ensemble of three-level ladder atoms lead to highly entangled states of many atoms if their highest excited state is subject to Rydberg blockade. Solution of the Schrödinger equation shows that it is increasingly difficult to ensure the adiabatic evolution as the number of atoms increases. A diminishing energy gap, significant variations in collective observables, and increased work fluctuations link the critical slowing down of the adiabatic evolution with a quantum-phase-transition-like behavior of the system. © 2018 American Physical Society  

    Blue and red wavelength resolved impedance response of efficient perovskite solar cells

    , Article Sustainable Energy and Fuels ; Volume 2, Issue 11 , 2018 , Pages 2407-2411 ; 23984902 (ISSN) Prochowicz, D ; Tavakoli, M. M ; Turren Cruz, S. H ; Pandey, K ; Saliba, M ; Yadav, P ; Sharif University of Technology
    Royal Society of Chemistry  2018
    The identification of recombination centers in perovskite solar cells is highly challenging. Here, we demonstrate the red and blue excitation wavelength resolved impedance response in state-of-the-art perovskite solar cells (PSCs) providing insights into charge recombination and ion accumulation. To get insight into the interfacial electronic characteristics, we fabricated PSCs with a planar architecture containing state-of-the-art triple-cation perovskite materials as absorber layers. The capacitance-frequency response under various blue and red illumination conditions were used to investigate interfacial charge accumulations and found that under high energy photons irradiation maximum... 

    Fast multiqubit gates by adiabatic evolution in interacting excited-state manifolds of rydberg atoms and superconducting circuits

    , Article Physical Review X ; Volume 10, Issue 2 , June , 2020 Khazali, M ; Mølmer, K ; Sharif University of Technology
    American Physical Society  2020
    Quantum computing and quantum simulation can be implemented by concatenation of one- and two-qubit gates and interactions. For most physical implementations, however, it may be advantageous to explore state components and interactions that depart from this universal paradigm and offer faster or more robust access to more advanced operations on the system. In this article, we show that adiabatic passage along the dark eigenstate of excitation exchange interactions can be used to implement fast multiqubit Toffoli (Ck-NOT) and fan-out (C-NOTk) gates. This mechanism can be realized by simultaneous excitation of atoms to Rydberg levels, featuring resonant exchange interaction. Our theoretical... 

    Mechanical hydrolysis imparts self-destruction of water molecules under steric confinement

    , Article Physical Chemistry Chemical Physics ; Volume 23, Issue 10 , 2021 , Pages 5999-6008 ; 14639076 (ISSN) Hosseini, E ; Zakertabrizi, M ; Habibnejad Korayem, A ; Carbone, P ; Esfandiar, A ; Shahsavari, R ; Sharif University of Technology
    Royal Society of Chemistry  2021
    Decoding behavioral aspects associated with the water molecules in confined spaces such as an interlayer space of two-dimensional nanosheets is key for the fundamental understanding of water-matter interactions and identifying unexpected phenomena of water molecules in chemistry and physics. Although numerous studies have been conducted on the behavior of water molecules in confined spaces, their reach stops at the properties of the planar ice-like formation, where van der Waals interactions are the predominant interactions and many questions on the confined space such as the possibility of electron exchange and excitation state remain unsettled. We used density functional theory and... 

    Polar and low polar solvents media effect on dipole moments of some diazo Sudan dyes

    , Article Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy ; Vol. 127 , 2014 , Pages 340-348 ; ISSN: 13861425 Zakerhamidi, M. S ; Golghasemi Sorkhabi, Sh ; Shamkhali, A. N ; Sharif University of Technology
    Absorption and fluorescence spectra of three Sudan dyes (Sudan III, SudanIV and Sudan black B) were recorded in various solvents with different polarity in the range of 300-800 nm, at room temperature. The solvatochromic method was used to investigate dipole moments of these dyes in ground and excited states, in different media. The solvatochromic behavior of these substances and their solvent-solute interactions were analyzed via solvent polarity parameters. Obtained results express the effects of solvation on tautomerism and molecular configuration (geometry) of Sudan dyes in solvent media with different polarity. Furthermore, analyze of solvent-solute interactions and value of ground and... 

    Equations-of-motion method for triplet excitation operators in graphene

    , Article Journal of Physics Condensed Matter ; Volume 24, Issue 9 , February , 2012 ; 09538984 (ISSN) Jafari, S. A ; Baskaran, G ; Sharif University of Technology
    The particlehole continuum in the Dirac sea of graphene has a unique window underneath, which in principle leaves room for bound state formation in the triplet particlehole channel (Baskaran and Jafari 2002 Phys. Rev. Lett. 89 016402). In this work, we construct appropriate triplet particlehole operators and, using a repulsive Hubbard-type effective interaction, we employ equations of motion to derive approximate eigenvalue equations for such triplet operators. While the secular equation for the spin density fluctuations gives rise to an equation which is second order in the strength of the short range interaction, the explicit construction of the triplet operators obtained here shows that,...