Hosein Cheraghchi

Damghan University

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S. Sajad Dabiri

Shahid Beheshti University

Fatemeh Adinehvand

Damghan University

Mohsen Yarmohammadi

The University of Texas at Dallas

Keivan Esfarjani

Rutgers, The State University of New Jersey

S. M. Fazeli

Groupe de Recherches sur l'Energétique des Milieux Ionisés

Mahroo Shiranzaei

Uppsala University

Fariborz Parhizgar

Uppsala University

Reza Asgari

Institute for Research in Fundamental Sciences

Zahra Askarpour

Iran University of Science and Technology

Maliheh Azadparvar

Damghan University

Cooperative Institutions

Institute for Research in Fundamental Sciences

Damghan University

Sharif University of Technology

University of Tehran

Iran University of Science and Technology

Amirkabir University of Technology

Shahid Beheshti University

Institute for Advanced Studies in Basic Sciences

Uppsala University

National Institute for Materials Science

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Spin polarization and magnetoresistance through a ferromagnetic barrier in bilayer graphene

Journal of Physics Condensed Matter (2012)

Hosein Cheraghchi Fatemeh Adinehvand

We study spin dependent transport through a magnetic bilayer graphene nanojunction configured as two dimensional normal/ferromagnetic/normal structure where the gate-voltage is applied on the layers of ferromagnetic graphene.Based on the fourband Hamiltonian, conductance is calculated by using Landauer Butikker formula at zero temperature.For parallel configuration of the ferromagnetic layers of bilayer graphene, the energy band structure is metallic and spin polarization reaches to its maximum value close to the resonant states, while for antiparallel configuration, the nanojunction behaves as a semiconductor and there is no spin filtering.As a result, a huge magnetoresistance is achievable by altering the configurations of ferromagnetic graphene especially around the band gap.

Bilayer graphene

10.1088/0953-8984/24/4/045303

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Citations (10)

Light-induced switch based on edge modes in irradiated thin topological insulators

arXiv (Cornell University) (2022)

Zahra Askarpour Hosein Cheraghchi

We investigate transport properties through nano-ribbons of thin topological insulators irradiated by high frequency light with circular polarization. By using high frequency regime, a coherent and quantized transport through the nano-ribbon is guaranteed and then Lanadauer formalism is applicable. It is demonstrated that the pseudo-spin edge modes inside the band gap can host transmission through this nano-junction which their localization on the top and bottom edges depend strongly on the light polarization. These edge modes persist even if we apply a source-drain bias. Based on this edge selectivity for the current, one can design a light-induced switch with an appropriate on/off ratio of the current which is composed of two scattering regions with opposite light polarization. The local current on each bond shows how the current is passing through the edges and jumps into the opposite edge. Furthermore, some other nano-junctions are proposed as electronic switches which are designed based on the mass term engineering of the scattering region by means of perpendicular magnetization induced by magnetic doping and also structure inversion asymmetry applied on the scattering region.

Topological insulator

10.48550/arxiv.2210.06222

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Straintronics in graphene nanoribbons

arXiv (Cornell University) (2019)

Maliheh Azadparvar Hosein Cheraghchi

The interplay between uniaxial strain and charging effects in zigzag graphene nanoribbons (ZGNR) is investigated by using non-equilibrium Green's function formalism. The I-V characteristic curves and especially negative differential resistance (NDR) induced by some quantum selection rules are affected by the type, strength and also direction of the applied strain. For the oblique strain, the parity conservation fails while it conserves at the longitudinal and transverse strains. Therefore, in the oblique strain, on-off current ratio drastically decreases in compared to the un-strained case. For the tensile strain along the ribbon axis, $ I_{on}/I_{off} $ ratio increases while for the compressive strain, NDR will be gradually disappeared. This property can be useful for nano-electromechanical switch in which by changing the tensile to compressive strain, current switches between its on and off-current state. Furthermore, under influence of the oblique uniaxial strain, the geometry symmetry of charge accumulation as well as bond local currents will be broken across ZGNR giving rise to a transverse current between upper and lower edges of the nanoribbon. This transverse current would be enhanced by the strain strength where gradient of charge density would be maximum at the off-current state.

Zigzag

Ribbon

Lateral strain

Tensile strain

10.48550/arxiv.1912.02017

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Effective low-energy RKKY interaction in doped topological crystalline insulators

Physical review. B./Physical review. B (2020)

Mohsen Yarmohammadi Hosein Cheraghchi

We study the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between two magnetic impurities resided on the (001) plane of topological crystalline insulator (TCI) SnTe associated with four anisotropic Dirac cones protected by the mirror symmetry. The lattice Green's functions governing the correlation of both the sublattices and spins are deduced by developing a two-band effective model. We explore the RKKY Heisenberg interaction of the system established by the interference between four Dirac cones. Our key finding is that, independent of the position of magnetic impurities on the same sublattices or different ones, multiple wave vectors with different orders describe the RKKY coupling physics in TCIs. Further, both the undoped and doped spin susceptibility give rise to the same decay rates like graphene. Magnetic impurities on the same and different sublattices propose the ferromagnetic and antiferromagnetic base phase of the undoped system, respectively. Here we demonstrate that RKKY exchange in TCIs, undergoes a ferromagnetic-to-antiferromagnetic transition and vice versa in response to switching on/off the electron and hole doping. Analytic expressions of doped TCIs are obtained to draw the magnetic phase diagram of the distance between two magnetic impurities and the doping concentration, clarifying the contributions of short and long distances as well as low and high concentrations to the RKKY coupling. Our results may tailor the magnetic features of TCIs for further research and application.

RKKY interaction

Topological insulator

Exchange interaction

10.1103/physrevb.102.075411

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Metal–insulator transition in a ternary model with long range correlated disorder

Journal of Statistical Mechanics Theory and Experiment (2007)

Ayoub Esmailpour Hosein Cheraghchi Pedro Carpena M. Reza Rahimi Tabar

We study the metal–insulator transition of the one-dimensional diagonal Anderson ternary model with long range correlated disorder. The starting point of the model corresponds to a ternary alloy (i.e. with three possible on-site energies), and shows a metal–insulator transition when the random distribution of site energies is assumed to have a power spectrum . In this paper, we define a purity parameter for the ternary alloy which adjusts the occupancy probability of site potentials, and for any given α we calculate the critical purity parameter for which extended states are obtained. In this way, we show that the ternary alloy requires weaker correlations than the binary alloy to present a phase transition from localized to extended states. A phase diagram which separates the extended regime from the localized one for the ternary alloy is presented, obtained as the critical purity parameter in terms of the corresponding correlation exponent.

Critical point (mathematics)

Transition point

Exponent

10.1088/1742-5468/2007/09/p09014

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Anisotropic Ferroelectric Distortion Effects on the RKKY Interaction in Topological Crystalline Insulators

Research Square (Research Square) (2020)

Hosein Cheraghchi Mohsen Yarmohammadi

Abstract Manipulation of electronic and magnetic properties of topological materials is a topic of much interest in spintronic and valleytronic applications. Perturbation tuning of multiple Dirac cones on the (001) surface of topological crystalline insulators (TCIs) is also a related topic of growing interest. Here we show the numerical evidence for the ferroelectric structural distortion effects on the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between two magnetic impurity moments on the SnTe (001) and related alloys. The mirror symmetry breaking between Dirac cones induced by the ferroelectric distortion could be divided into various possible configurations including the isotropically gapped, coexistence of gapless and gapped, and anisotropically gapped phases. Based on the retarded perturbed Green’s functions of the generalized gapped Dirac model, we numerically find the RKKY response for each phase. The distortion-induced symmetry breaking constitutes complex and interesting magnetic responses between magnetic moments compared to the pristine TCIs. In the specific case of coexisted gapless and gapped phases, a nontrivial behavior of the RKKY interaction is observed, which has not been seen in other Dirac materials up until now. For two impurities resided on the same sublattices, depending on the distortion strength, magnetic orders above of a critical impurity separation exhibit irregular ferromagnetic $ antiferromagnetic phase transitions. However, independent ofthe impurity separation and distortion strength, no phase transition emerges for two impurities resided on different sublattices. This essential study sheds light on magnetic properties of Dirac materials with anisotropic mass terms and also makes TCIs applications relatively easy to understand.

Topological insulator

10.21203/rs.3.rs-121068/v1

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Superconducting electron and hole lenses

Physical review. B./Physical review. B (2016)

Hosein Cheraghchi Haniyeh Esmailzadeh Ali G. Moghaddam

We show how a superconducting region (S) sandwiched between two normal leads (N), in the presence of barriers, can act as a lens for propagating electron and hole waves by virtue of the so- called crossed Andreev reflection (CAR). The CAR process which is equivalent to the Cooper pair splitting into the two N electrodes provides a unique possibility of constructing entangled electrons in solid state systems. When electrons are locally injected from an N lead, due to the CAR and normal reflection of quasiparticles by the insulating barriers at the interfaces, sequences of electron and hole focuses are established inside another N electrode. This behavior originates from the change of momentum during electron-hole conversion beside the successive normal reflections of electrons and holes due to the barriers. The focusing phenomena studied here is fundamentally different from the electron focusing in other systems like graphene pn junctions. In particular due to the electron-hole symmetry of superconducting state, the focusing of electrons and holes are robust against thermal excitations. Furthermore the effect of superconducting layer width, the injection point position, and barriers strength is investigated on the focusing behavior of the junction. Very intriguingly, it is shown that by varying the barriers strength, one can separately control the density of electrons or holes at the focuses.

Cooper pair

Andreev reflection

10.1103/physrevb.93.214508

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Statistical properties of a localization–delocalization transition induced by correlated disorder

Journal of Statistical Mechanics Theory and Experiment (2006)

Hosein Cheraghchi S. M. Fazeli

The exact probability distributions of the resistance, the conductance and the transmission are calculated for the one-dimensional Anderson model with long-range correlated off-diagonal disorder at E=0. It is proved that despite of the Anderson transition in 3D, the functional form of the resistance (and its related variables) distribution function does not change when there exists a Metal-Insulator transition induced by correlation between disorders. Furthermore, we derive analytically all statistical moments of the resistance, the transmission and the Lyapunov Exponent. The growth rate of the average and typical resistance decreases when the Hurst exponent $H$ tends to its critical value ($H_{cr}=1/2$) from the insulating regime. In the metallic regime $H\geq1/2$, the distributions become independent of size. Therefore, the resistance and the transmission fluctuations do not diverge with system size in the thermodynamic limit.

Hurst exponent

Anderson impurity model

Exponent

Anderson Localization

10.1088/1742-5468/2006/11/p11004

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Topological properties and edge states in a driven modified dimerized chain

arXiv (Cornell University) (2017)

Fatemeh Askari Shahid Hosein Cheraghchi

We investigate topological phases induced by a driven electric field coupled to a dimer chain (a model for poly-acetylene) at high frequency regime. It is shown how the topological invariant of the system can be controlled by the field amplitude. Furthermore, in the presence of a time-periodic electric field, the effect of the next-nearest neighbor hopping amplitudes on topological properties is studied. Breaking of the inversion symmetry causes to remove the degeneracy of zero edge states. The fractional Zak phase which is now measurable by ultra-cold atoms in one dimensional optical lattice is also calculated. For calculating modified band structure, we also develop a general Floquet-Bloch approach for systems under application of a potential with lattice and time translation invariance.

Floquet theory

Point reflection

Bloch oscillations

Lattice (music)

Topological degeneracy

Source

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Engineering of topological phases in driven thin topological insulators: Structure inversion asymmetry effect

Physical review. B./Physical review. B (2021)

S. Sajad Dabiri Hosein Cheraghchi

We investigate the effect of a high frequency electromagnetic field with both of circularly and linearly polarization, on the emergence of quantum phases on thin topological insulators. Simultaneously, the influence of the system parameters (such as magnetic impurity, thickness engineering and structural inversion asymmetry of the potential) on emergence of topological phases is studied. We take our attention to the high frequency regime in which it is possible to consider an expansion for the Floquet Hamiltonian in terms of orders of 1/\Omega. The topological invariants are determined and it is demonstrated that some phase transitions between quantum anomalous Hall insulator, quantum pseudospin Hall insulator, quantum spin Hall insulator and normal insulator can be induced by altering the aforementioned parameters of the system. To avoid heating process, tuning of the system parameters gives us the opportunity to observe these phase transitions at small intensities of light.

Topological insulator

Hamiltonian (control theory)

Floquet theory

10.1103/physrevb.104.245121

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Citations (13)