A5055271724- 2D Materials and Applications
- Graphene research and applications
- Topological Materials and Phenomena
- Mechanical and Optical Resonators
- Quantum and electron transport phenomena
- Photonic and Optical Devices
- Advanced Fiber Laser Technologies
- Perovskite Materials and Applications
- MXene and MAX Phase Materials
- Plasmonic and Surface Plasmon Research
- Diamond and Carbon-based Materials Research
- Quantum Information and Cryptography
- Molecular Junctions and Nanostructures
- Magnetic properties of thin films
- Terahertz technology and applications
- Strong Light-Matter Interactions
- Photorefractive and Nonlinear Optics
- Quantum, superfluid, helium dynamics
- Nonlinear Optical Materials Studies
- Spectroscopy and Laser Applications
- Speech and Audio Processing
- Quantum Mechanics and Non-Hermitian Physics
- Ga2O3 and related materials
- Underwater Acoustics Research
- Theoretical and Computational Physics
University of Bath
2023-2025
KTH Royal Institute of Technology
2018-2024
Stockholm University
2018-2024
Nordic Institute for Theoretical Physics
2018-2024
ITMO University
2021
Italian Institute of Technology
2016-2018
Institute for Research in Fundamental Sciences
2012-2016
Istituto Nanoscienze
2015
University of Tehran
2010
Abstract Nonlinear optical processes, such as harmonic generation, are of great interest for various applications, e.g., microscopy, therapy, and frequency conversion. However, high-order conversion is typically much less efficient than low-order, due to the weak intrinsic response higher-order nonlinear processes. Here we report ultra-strong nonlinearities in monolayer MoS 2 (1L-MoS ): third 30 times stronger second, fourth comparable second. The generation efficiency 1L-MoS approximately...
We propose an effective lattice Hamiltonian for monolayer MoS${}_{2}$ in order to describe the low-energy band structure and investigate effect of perpendicular electric magnetic fields on its electronic structure. derive a tight-binding model based hybridization $d$ orbitals molybdenum $p$ sulfur atoms then introduce modified two-band continuum by exploiting quasidegenerate partitioning method. Our theory proves that excitations system are no longer massive Dirac fermions. It reveals...
Strain engineering has emerged as a powerful tool to modify the optical and electronic properties of two-dimensional crystals. Here we perform systematic study strained semiconducting transition metal dichalcogenides. The effect strain is considered within full Slater-Koster tight-binding model, which provides us with band structure in whole Brillouin zone. From this, derive an effective low-energy model valid around K point BZ, includes terms up second order momentum strain. For generic...
We study the effect of a perpendicular magnetic field on electronic structure and charge transport monolayer ${\text{MoS}}_{2}$ nanoribbon at zero temperature. particularly explore induced valley Zeeman through coupling between $B$ orbital moment. show that effective two-band Hamiltonian provides mismatch in conduction valence bands due to mass asymmetry it is proportional ${B}^{2}$ similar diamagnetic shift exciton binding energies. However, dominant term which evolves with linearly,...
We study the second-order nonlinear optical response of a Weyl semimetal (WSM), i.e. three-dimensional metal with linear band touchings acting as point-like sources Berry curvature in momentum space, termed "Weyl-Berry monopoles". first show that anomalous photocurrent WSMs can be elegantly parametrized terms Weyl-Berry dipole and quadrupole moments. then calculate corresponding charge node conductivities either broken time-reversal invariance or inversion symmetry. In particular, we predict...
We explore the electronic structure, orbital character and topological aspect of a monolayer MoS2 nanoribbon using tight-binding (TB) low-energy () models. obtain mid-gap edge mode in zigzag ribbon MoS2, which can be traced back to properties bulk band structure. Monolayer considered as valley Hall insulator. The boundary conditions at armchair edges mix valleys on edges, gap is induced modes. spin–orbit coupling valence reduces hybridization states.
Interaction driven symmetry breaking in a metallic (doped) Dirac system can manifest the spontaneous gap generation at nodal point buried below Fermi level. Across this transition linear conductivity remains finite making its direct observation difficult transport. We propose nonlinear Hall effect as probe of when inversion is broken. Specifically, for two-dimensional material with tilted low-energy dispersion, we first predict transformation characteristic inter-band resonance peak into...
We develop a microscopic large-$N$ theory of electron-electron interaction corrections to multilegged Feynman diagrams describing second- and third-order non-linear-response functions. Our theory, which reduces the well-known random-phase approximation in linear-response limit, is completely general useful understand all nonlinear effects, including harmonic generation, wave mixing, photon drag. apply our theoretical framework case graphene, by carrying out calculations functions an...
We present a finite-temperature diagrammatic perturbation theory of third-harmonic generation in doped graphene. carry out calculations the third-order conductivity scalar potential gauge, highlighting subtle cancellation between Fermi surface contribution, which contains only power laws, and power-law contributions interband nature. Only logarithms survive final result. conclude by presenting quantitative results for upconversion efficiency at zero finite temperature. Our approach can be...
Abstract Understanding the bending behaviour of a crystal onto flexible platform is crucial for electronics. The Young’s modulus, measure how easily material deforms, plays critical role in coupled deformation on substrate, as well transfer strain from substrate layer. Here, we report gallium selenide (GaSe), van der Waals semiconductor with small modulus and strain-dependent electronic band structure. A controllable, reproducible uniaxial strain, ϵ , applied to nanometer-thick GaSe layers...
We study the Ruderman-Kittle-Kasuya-Yosida (RKKY) interaction in a monolayer MoS${}_{2}$. show that rotation of itinerant electron spin due to spin-orbit coupling causes twisted between two magnetic adatoms, which consists different RKKY terms: Heisenberg, Dzyaloshinsky-Moriya, and Ising interactions. find terms are very sensitive Fermi energy values change dramatically from doped undoped systems. A finite doping all parts oscillate with distance impurities $R$, behaves like...
Hot electrons dominate the ultrafast (∼fs–ps) optical and electronic properties of metals semiconductors, they are exploited in a variety applications including photovoltaics photodetection. We perform power-dependent third-harmonic generation measurements on gated single-layer graphene detect significant deviation from cubic power law expected for process. assign this to presence hot electrons. Our results indicate that performance nonlinear photonics devices based graphene, such as...
We present a formal analysis of nonlinear response functions in terms correlation real- and imaginary-time domains. In particular, we show that causal functions, expressed nested commutators real time, can be obtained from the analytic continuation time-ordered which are more easily amenable to diagrammatic calculation. This generalizes well-known result linear theory. then use gauge invariance arguments derive exact relations between second-order density current channels. These identities,...
We analytically calculate the intrinsic longitudinal and transverse optical conductivities of electronic systems which govern by a modified Dirac fermion model Hamiltonian for materials beyond graphene such as monolayer ${\text{MoS}}_{2}$ ultrathin film topological insulator. analyze effect term in on conductivity transmittance. show that response enhances nontrivial phase insulator Hall changes sign at transition from trivial to phases has significant consequences circular dichroism...
Conversion of mechanical forces to electric signal is possible in non-centrosymmetric materials due linear piezoelectricity. The extraordinary properties two-dimensional and their high crystallinity make them exceptional platforms study exploit the piezoelectric effect. Here, response hexagonal crystals studied using modern theory polarization ${\bm k} \cdot {\bm p}$ model Hamiltonians. An analytical expression for constant obtained terms topological quantities such as {\it valley Chern...
The acoustogalvanic effect is proposed as a nonlinear mechanism to generate direct electric current by passing acoustic waves in Dirac and Weyl semimetals. Unlike the standard acoustoelectric effect, which relies on sound-induced deformation potential corresponding field, one originates from pseudoelectromagnetic fields, are not subject screening. longitudinal scales at least quadratically with relaxation time, contrast photogalvanic where scaling linear. Because of interplay pseudoelectric...
Using a diagrammatic scheme, we study the acoustoelectric effects in two-dimensional (2D) hexagonal Dirac materials due to sound-induced pseudogauge field. We analyze both uniform and spatially dispersive currents response copropagating counterpropagating sound waves, respectively. In addition longitudinal current, obtain an exotic transverse charge current flowing perpendicular propagation direction owing interplay of gauge field components ${j}_{T}\ensuremath{\propto}{A}_{L}{A}_{T}^{*}$....
Andreev reflection in a monolayer molybdenum disulfide superconducting-normal (S/N) hybrid junction is investigated. We find, by using modified Dirac Hamiltonian and the scattering formalism, that perfect happens at normal incidence with $p$-doped S N regions. The probability of resulting conductance, this system, are demonstrated to be large comparison corresponding gapped graphene structure. further investigate effect topological term ($\ensuremath{\beta})$ show it results an enhancement...
Graphene is a unique platform for tunable opto-electronic applications thanks to its linear band dispersion, which allows electrical control of resonant light-matter interactions. Tuning the nonlinear optical response graphene possible both electrically and in an all-optical fashion, but each approach involves trade-off between speed modulation depth. Here, lattice temperature, electron doping, tuning third-harmonic generation are combined hexagonal boron nitride-encapsulated device...
We consider the effect of Coulomb interaction in strained graphene using tight-binding approximation together with Hartree-Fock interactions. The many-body energy dispersion relation, anisotropic Fermi velocity renormalization, and charge compressibility presence uniaxial strain are calculated. show that quasiparticle quantities sensitive to homogenous and, indeed, its sign. is enhanced by stretching suppressed compressing a sheet. find reduction renormalization along direction deformation,...
We study analytically and numerically the magnetotransport of strained graphene in a Corbino geometry gating presence an external perpendicular magnetic field. The conductance disc deformed with uniaxial inhomogeneous strain is calculated by using Landauer-B\"{u}ttiker method. show that oscillation period as function flux depends on sharply drops along direction stretching. amplitude, other hand, can be manipulated induced pseudomagnetic flux. A valley polarized regime, caused strain,...
A great deal of theoretical and experimental efforts have been devoted in the last decades to study long-wavelength photodetection mechanisms field-effect transistors hosting two-dimensional (2D) electron systems. particularly interesting subclass these is intrinsic based on conversion incoming electromagnetic radiation into plasmons, which resonantly enhance photoresponse, subsequent rectification via hydrodynamic nonlinearities. In this Article we show that such occur well beyond frequency...
We propose a scheme for the spatial exciton energy control and routing in transition metal dichalcogenide (TMD) monolayer which lies on quantum paraelectric substrate. It relies ultrasensitive response of substrate dielectric permittivity to temperature changes, allowing spatially inhomogeneous screening Coulomb interaction monolayer. As an example, we consider heterostructure TMD strontium titanate oxide SrTiO$_3$, where large can be attained. study impact characteristic electronic features...