Research Group:  



Wed Nov 24, 2021 (1400/9/3)


Nov 24


Environmental fate of 2D materials in aquatic ecosystems: the case of graphene oxide 2D membranes

Abstract:An increasing number of 2D materials are being deployed for different applications across energy generation, conversion and storage sectors. Among these materials, however, graphene oxide and not graphite oxide, as the most technologically relevant 2D material of choice for energy-related applications, has gained a stronghold and is near the final stage of commercialization ready to enter the mass market. This calls for a thorough understanding of the behaviour of this intriguing atomically thin material and possibly other members of the mushrooming family of 2D materials in aquatic environment as their toxicity can easily pose a threat to aquatic life at global levels not seen before due to the huge surface area of 2D materials (~2000 m2/g). Although a great deal of research has been dedicated to this subject, a key misconception is the treatment of these materials as a sphere with an effective radius or that their flat surface would fold upon itself resulting in a much lower aspect ratio and consequently lower available surface area. This essentially implies a much higher critical concentration at which it is alleged that these 2D materials are toxic to the aqueous environment. Our findings presented here point out that this is not a valid assumption by showing that 2D materials in saline waters hold their flat morphology and therefore pose a greater challenge for the environment rather than their professed 3D conformed counterparts.
Lecturer(s): Seyed Hamed Aboutalebi
From : Condensed Matter National Laboratory, IPM
Research Group: Condensed Matter and Statistical Physics Group Weekly Seminar
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Wed Nov 10, 2021 (1400/8/19)


Nov 10


Floquet Engineering of Topological Insulators

Abstract:Recent technological progresses in mid-infrared lasers have established a new route for engineering of the electronic band structure. Indeed, an interplay between the periodicity of lattice and time originated from the oscillating field extends the Hilbert space by inducing the so-called Floquet-Bloch states and enables one to modify the band structure (opening the gaps) and to engineer phase transitions at will by using photon-assisted processes. Fortunately, such light-induced states have been experimentally observed on the surface of irradiated topological insulators, optical lattices, graphene etc. Many striking phenomena are predicted or observed in this field: light-induced Hall conductivity, light-induced QAHI on TI�??s, etc. However, experimental challenge would be huge heating rate when the system is irradiated by the laser. In this talk, I will present a short review on the Floquet theory including on- and off- resonant regimes, the gap opening and emergence of topological phases accompanied by anomalous edge states. Then I will focus on the special case of magnetically topological insulator thin film irradiated by circularly-polarized electromagnetic field in the off-resonant regime. Fascinating feature of distinct phases emerges in the phase diagram depending on the frequency and intensity of the light as well as the system parameters and also magnetic field. We also try to go through the on-resonant regime and calculate optical conductivity of this driven system.
Lecturer(s): Hosein Cheraghchi
From : Damghan University
Research Group: Condensed Matter and Statistical Physics Group Weekly Seminar
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Wed Oct 27, 2021 (1400/8/5)


Oct 27


An Amelioration for the Sign Problem: Adiabatic Quantum Monte Carlo

Abstract:In this talk, I will introduce the adiabatic quantum Monte Carlo (AQMC) method, where we gradually crank up the interaction strength, as an amelioration of the sign problem. It is motivated by the adiabatic theorem and will approach the true ground-state if the evolution time is long enough. I will demonstrate that the AQMC enhances the average sign exponentially such that low enough temperatures can be accessed and ground-state properties probed. It is a controlled approximation that satisfies the variational theorem and provides an upper bound for the ground-state energy. I will first benchmark the AQMC vis-à-vis the undoped Hubbard model on the square lattice which is known to be sign-problem-free within the conventional quantum Monte Carlo formalism. Next, I will test the AQMC against the density-matrix-renormalization-group approach for the doped four-leg ladder Hubbard model and demonstrate its remarkable accuracy. As a nontrivial example, I will apply our method to the Hubbard model at p=1/8 doping for a 16�?8 system and discuss its ground-state properties. I will finally utilize our method and demonstrate the emergence of U(1)2�?�SU(2)1 topological order in a strongly correlated Chern insulator.
Lecturer(s): Abolhassan Vaezi
From : Sharif University of Technology
Research Group: Condensed Matter and Statistical Physics Group Weekly Seminar
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Wed Oct 13, 2021 (1400/7/21)


Oct 13


Localization and delocalization in one-dimensional Anderson model with a general hopping matrix

Abstract:Much of our present understanding of wave-function localization in one spatial dimension is based on the original Anderson model on a one-dimensional lattice. The experimental simulation of this model using cold atoms, owing to the high degree of control over system parameters, has made possible the direct observation of localization of matter waves. In this talk, after giving an introduction to Anderson localization, I will present some new results on localization properties of this model with a general hopping matrix.
Lecturer(s): Reza Sepehrinia
From : University of Tehran
Research Group: Condensed Matter and Statistical Physics Group Weekly Seminar
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Wed Sep 29, 2021 (1400/7/7)


Sep 29


Evolutionary Dynamics on Complex Networks: A Mean Field Approach

Abstract:Mathematical models of evolution have attracted considerable attention in recent years. The main ingredients of such models are "selection", "reproduction", and "mutation". Furthermore, population structure plays an important role in evolution. "Evolutionary Graph Theory" is a powerful tool to study the interplay between population structure and evolutionary dynamics. In this talk, we try to give a brief review of this theory and then we mention to a number of recent results, among them is the effect of network topology on fixation time and fixation probability of mutants. Furthermore we propose a mean field approach to obtain the fixation time analytically for some network topologies.
Lecturer(s): Keivan Aghababaei Samani
From : Isfahan University of Technology
Research Group: Condensed Matter and Statistical Physics Group Weekly Seminar
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Wed Sep 15, 2021 (1400/6/24)


Sep 15


Resonant nonlinear Hall effect

Abstract:The classical Hall effect in its textbook form is nothing but the creation of transverse resistance in the presence of a magnetic field due to Lorentz force. However, after the discovery of new versions of the Hall effect with quantum natures, it has become a cornerstone in studying quantum condensed matter. Recently and motivated by theoretical predictions of the nonlinear Hall effect (NLHE) due to the Berry curvature dipole, an endeavor has been started to search for materials with time-reversal symmetry (TRS) but without inverse symmetry. In this talk, after a brief introduction to the NLHE in time-reversal-invariant systems, I will introduce a different yet simple model for engineering NLHE in the presence of a periodic magnetic profile. In this model which lacks TRS, the effect largely stems from boundary states associated with the real-space magnetic dipole. I will also talk about the parametric resonance feature of the effect, involving the cyclotron ratio and characteristic widths of the magnetic profile, which can greatly enhance the nonlinear Hall signal.
Lecturer(s): Ali Ghorbanzadeh Moghaddam
From : IASBS
Research Group: Condensed Matter and Statistical Physics Group Weekly Seminar
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Wed Aug 11, 2021 (1400/5/20)


Aug 11


Thermoelectricity of phosphorene and plasmonics of hBN-encapsulated-phosphorene

Abstract:Low-dimensional materials are different in symmetries in comparison with their bulk counterparts, and underlaying theories aiming to describe countless emerging phenomena within their realms are thus different. Transport and many-body properties are of these phenomena from which we focus on the thermoelectricity and plasmonics of phosphorene; the elemental puckered and anisotropic monolayer of black-phosphorus (BP). In the former study, after proposing a model Hamiltonian for phosphorene�??s energy bands respecting its time-reversal symmetry, the generalized semiclassical Boltzmann formalism is applied. The electric conductivity is shown to be highly anisotropic, while the Seebeck coefficient and its figure of merit are nearly isotropic; the figure of merit is about 1.2 at low temperature which is considerable among other monolayer competitors. In the latter study, the phosphorene charge-charge linear response function is initially calculated and then its dielectric function within random-phase-approximation (RPA) and consequently its plasmon dispersion are yielded. These calculations are done for phosphorene and phosphorene encapsulated between two thin layers hBN; a uniaxial hyperbolic material. This paves the way for the birth of the trifurcated anisotropic surface plasmon-phonon-polaritons (SPPP). They are phonon-like, more elongated and less energetic in the zigzag direction. Moreover, a semiclassical model (SC) is proposed for anisotropic 2D materials based on the Maxwell's classical theory of electrodynamics. RPA and SC results have a great overlap especially in the long-wavelength limit. Ultimately, our recent research about many-body localization of a 6-atom hexagonal ring is discussed which shows that even a weak disorder in each of the charge and spin channels triggers localization in both.
Lecturer(s): Farnood Ghamsari
From : School of Physics
Research Group: Condensed Matter and Statistical Physics Group Weekly Seminar
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Wed Jul 28, 2021 (1400/5/6)


Jul 28


Pressure and effective forces on external bodies immersed in active fluids

Abstract:Active matter is referred to a wide class of nonequilibrium systems, whose constituent particles use ambient free energy and convert it to self-propelled motion. Such active particles are commonplace in biology and include microswimmers such as bacteria, algae and spermatozoa that swim in fluid media. Active particles are also made artificially and serve numerous applications across the whole range of nano to micrometer scales, with the relevant examples furnished by self-propelled nano and micromachines. Due to its out-of-equilibrium nature and rich theoretical and experimental aspects, active matter has attracted a lot of attention from physicists in recent years. In our recent works, we have studied the active pressure and effective interactions experienced by external bodies (such as colloidal inclusions) immersed in an active fluid, consisting specifically of active Brownian disks or rods. We have thus uncovered salient effects due to permeability of the inclusions, spatial heterogeneity of the motility field experienced by the self-propelled particles, and shape of the self-propelled particles themselves.
Lecturer(s): Mahmoud Sebtosheikh
From : IPM, School of Physics
Research Group: Condensed Matter and Statistical Physics Group Weekly Seminar
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Wed Jul 07, 2021 (1400/4/16)


Jul 07


Thermometry of cold systems at the quantum regime

Abstract:Controlling and measuring the temperature in different devices and platforms that operate in the quantum regime is, without any doubt, essential for any potential application. The theory of quantum thermometry is built under a unifying framework at the crossroads of quantum metrology, open quantum systems, and quantum many-body physics. At a fundamental level, theoretical quantum thermometry is concerned with finding the ultimate bounds and scaling laws that limit the precision of temperature estimation for systems in and out of thermal equilibrium. At a more practical level, it provides the tools to formulate precise, yet feasible, thermometric protocols for relevant experimental architectures. Last but not least, the theory of quantum thermometry examines genuine quantum features, like entanglement and many-body criticality, for their exploitation in enhanced-resolution thermometry. In this talk, I will give an overview on the basics of estimating very low temperatures in quantum systems. Criticality of many-body systems as a resource for thermometry will be explained. Then (if there was enough time) I will focus on non-equilibrium thermometry of Bosonic environments, its usage in estimation of sub-nK temperatures of Bose Einstein condensates and the role of bath induced correlations in thermometry. Some related references 1. M. Mehboudi, A. Sanpera, L.A. Correa (2019) "Topical Review---Thermometry in the quantum regime: Recent theoretical progress�?�, J. Phys. A: Math. Theor. 52 303001. DOI: 10.1088/1751-8121/ab2828 2. Antonella De Pasquale, Thomas M. Stace, "Quantum Thermometry", Thermodynamics in the Quantum Regime pp 503-527 3. M. Mehboudi, A. Lampo, C. Charalambous, L.A. Correa, M.A.l García-March, M. Lewenstein, (2019) �??Using polarons for sub-nK quantum nondemolition thermometry in a Bose-Einstein condensate,'' Phys. Rev. Lett. 122, 030403. DOI: 10.1103/PhysRevLett.122.030403. 4. L.A. Correa, M. Perarnau-Llobet, K.V. Hovhannisyan, S. Hernández-Santana, M. Mehboudi, A. Sanpera (2017) �??Enhancement of low-temperature thermometry by strong coupling�?�, Phys. Rev. A 96, 062103. DOI: 10.1103/PhysRevA.96.062103 5. L.A. Correa, M. Mehboudi, G. Adesso, and A. Sanpera (2015) �??Individual Quantum Probes for Optimal Thermometry�?�, Phys. Rev. Lett. 114, 220405. DOI: 10.1103/PhysRevLett.114.220405 6. M Mehboudi, M Moreno-Cardoner, G De Chiara, A Sanpera "Thermometry precision in strongly correlated ultracold lattice gases", New Journal of Physics 17 (5), 055020
Lecturer(s): Mohammad Mehboudi
From : University of Geneva
Research Group: Condensed Matter and Statistical Physics Group Weekly Seminar
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Wed Jun 23, 2021 (1400/4/2)


Jun 23


Spin and charge order in doped spin-orbit coupled Mott insulators: Application to Sr2IrO4

Abstract: We study an antisymmetric spin-orbit coupling of a two-dimensional single-band Hubbard Hamiltonian. We propose that this is the most basic paradigm for understanding the electrical characteristics of locally noncentrosymmetric transition metal (TM) oxides like Sr2IrO4. Based on exact diagonalizations of small clusters and the random-phase approximation, we investigate the correlation effects on charge and magnetic order as a function of doping and of the TM-oxygen-TM bond angle. For small doping and small-angle, we find dominant commensurate in-plane antiferromagnetic fluctuations, while ferromagnetic fluctuations dominate for larger angles. Moderately strong nearest-neighbor Hubbard interactions can also stabilize a charge density wave order. Furthermore, we compare the dispersion of magnetic excitations for the hole-doped case to resonant inelastic x-ray scattering data and find good qualitative agreement.
Lecturer(s): Alireza Akbari
From : Max Planck Institute for the Chemical Physics of Solids
Research Group: Condensed Matter and Statistical Physics Group Weekly Seminar
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