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  • 1. Bhalla, Pankaj
    et al.
    Rostami, Habib
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). University of Bath, United Kingdom.
    Light-induced nonlinear spin Hall current in single-layer WTe22024In: New Journal of Physics, E-ISSN 1367-2630, Vol. 26, no 2, article id 023042Article in journal (Refereed)
    Abstract [en]

    In this theoretical investigation, we analyze light-induced nonlinear spin Hall currents in a gated single-layer 1T′-WTe2, flowing transversely to the incident laser polarization direction. Our study encompasses the exploration of the second and third-order rectified spin Hall currents using an effective low-energy Hamiltonian and employing the Kubo's formalism. We extend our analysis to a wide frequency range spanning both transparent and absorbing regimes, investigating the influence of light frequency below and above the optical band gap. Additionally, we investigate the influence of an out-of-plane gate potential on the system, disrupting inversion symmetry and effectively manipulating both the strength and sign of nonlinear spin Hall responses. We predict a pronounced third-order spin Hall current relative to its second-order counterpart. The predicted nonlinear spin currents show strong anisotropic dependence on the laser polarization angle. The outcomes of our study contribute to a generalized framework for nonlinear response theory within the spin channel will impact the development of emerging field of opto-spintronic.

  • 2.
    Bhalla, Pankaj
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Rostami, Habib
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Second harmonic helicity and Faraday rotation in gated single-layer 1T ' -WTe22022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, no 23, article id 235132Article in journal (Refereed)
    Abstract [en]

    A single layer of the 1T' phase of WTe2 provides a rich platform for exotic physical properties such as the nonlinear Hall effect and high-temperature quantum spin Hall transport. Utilizing a continuum model and the diagrammatic method, we calculate the second harmonic conductivity of monolayer 1T'-WTe2 modulated by an external vertical electric field and electron doping. We obtain a finite helicity and Faraday rotation for the second harmonic signal in response to linearly polarized incident light in the presence of time-reversal symmetry. The second harmonic signal's helicity is highly controllable by altering the bias potential and serves as an optical indicator of the nonlinear Hall current. Our study motivates future experimental investigation of the helicity spectroscopy of two-dimensional materials.

  • 3.
    Bhalla, Pankaj
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Vignale, Giovanni
    Rostami, Habib
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Pseudogauge field driven acoustoelectric current in two-dimensional hexagonal Dirac materials2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, no 12, article id 125407Article in journal (Refereed)
    Abstract [en]

    Using a diagrammatic scheme, we study the acoustoelectric effects in two-dimensional (2D) hexagonal Dirac materials due to the sound-induced pseudogauge field. We analyze both uniform and spatially dispersive currents in response to copropagating and counterpropagating sound waves, respectively. In addition to the longitudinal acoustoelectric current, we obtain an exotic transverse charge current flowing perpendicular to the sound propagation direction owing to the interplay of transverse and longitudinal gauge field components jTALAT. In contrast to the almost isotropic directional profile of the longitudinal uniform current, a highly anisotropic transverse component jT∼sin(6θ) is achieved that stems from the inherited threefold symmetry of the hexagonal lattice. However, both longitudinal and transverse parts of the dispersive current are predicted to be strongly anisotropic ∼sin2(3θ) or cos2(3θ). We quantitatively estimate the pseudogauge field contribution to the acoustoelectric current that can be probed in future experiments in graphene and other 2D hexagonal Dirac materials.

  • 4. Cappelluti, Emmanuele
    et al.
    Silva-Guillén, Jose Angel
    Rostami, Habib
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). University of Bath, United Kingdom.
    Guinea, Francisco
    Flat-band optical phonons in twisted bilayer graphene2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, no 12, article id 125401Article in journal (Refereed)
    Abstract [en]

    Twisting bilayer sheets of graphene have been proven to be an efficient way to manipulate the electronic Dirac-like properties, resulting in flat bands at magic angles. Inspired by the electronic model, we develop a continuum model for the lattice dynamics of twisted bilayer graphene and we show that a remarkable band flattening applies to almost all the high-frequency in-plane lattice vibration modes, including the valley Dirac phonon, valley optical phonon, and zone-center optical phonon bands. Utilizing an approximate approach, we estimate small but finite magic angles at which a vanishing phonon bandwidth is expected. In contrast to the electronic case, the existence of a restoring potential prohibits the emergence of a magic angle in a more accurate modeling. The predicted phonon band flattening is highly tunable by the twist angle and this strong dependence is directly accessible by spectroscopic tools.

  • 5. Girija, Aswathy V.
    et al.
    Basini, Martina
    Stockholm University, Faculty of Science, Department of Physics.
    Rostami, Habib
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). University of Bath, UK.
    Highlights from Faraday Discussion: From optical to THz control of materials, London, UK, May 20222023In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 59, no 27, p. 3939-3947Article in journal (Other academic)
    Abstract [en]

    The Faraday Discussion 'From optical to THz control of materials' was held in London, UK, and online on the 23rd, 24th, and 25th May 2022. The meeting brought together established and early-career scientists, postgraduate students, scientific editors, and industrial researchers in the field of spectroscopy and materials science from over ten different countries interested in exploring the physical properties of materials at ultrafast timescales driven by optical and THz excitations. This conference report provides highlights of this meeting and we give summaries of the presentations including the introductory lecture, all the papers discussed, and the concluding remarks.

  • 6. Principi, Alessandro
    et al.
    Bandurin, Denis
    Rostami, Habib
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Polini, Marco
    Pseudo-Euler equations from nonlinear optics: Plasmon-assisted photodetection beyond hydrodynamics2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 7, article id 075410Article in journal (Refereed)
    Abstract [en]

    A great deal of theoretical and experimental efforts have been devoted in the last decades to the study of long-wavelength photodetection mechanisms in field-effect transistors hosting two-dimensional (2D) electron systems. A particularly interesting subclass of these mechanisms is intrinsic and based on the conversion of the incoming electromagnetic radiation into plasmons, which resonantly enhance the photoresponse, and subsequent rectification via hydrodynamic nonlinearities. In this paper, we show that such a conversion and subsequent rectification occur well beyond the frequency regime in which hydrodynamic theory applies. We consider the nonlinear optical response of generic 2D electron systems and derive pseudo-Euler equations of motion for suitable collective variables. These are solved in one- and two-dimensional geometries for the case of graphene and the results are compared with those of hydrodynamic theory. Significant qualitative differences are found, which are amenable to experimental studies. Our theory expands the knowledge of the fundamental physics behind long-wavelength photodetection.

  • 7.
    Rostami, Habib
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). University of Bath, United Kingdom.
    Light-induced shear phonon splitting and instability in bilayer graphene2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 16, article id 165418Article in journal (Refereed)
    Abstract [en]

    Coherent engineering of landscape potential in crystalline materials is a rapidly evolving research field. Ultrafast optical pulses can manipulate low-frequency shear phonons in van der Waals layered materials through the dynamical dressing of electronic structure and photoexcited carrier density. In this work, we provide a diagrammatic formalism for nonlinear Raman force and implement it to shear phonon dynamics in bilayer graphene. We predict a controllable splitting of double degenerate shear phonon modes due to light-induced phonon mixing and renormalization according to a coherent nonlinear Raman force mechanism. Intriguingly, we obtain a light-induced shear phonon softening that facilitates structural instability at a critical field amplitude for which the shear phonon frequency vanishes. The phonon splitting and instability strongly depend on the laser intensity, frequency, chemical potential, and temperature of photoexcited electrons. This study motivates future experimental investigation of the optical fine tuning and regulation of shear phonons and layer stacking order in layered van der Waals materials.

  • 8.
    Rostami, Habib
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Theory for shear displacement by light-induced Raman force in bilayer graphene2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 106, no 15, article id 155405Article in journal (Refereed)
    Abstract [en]

    Coherent excitation of shear phonons in van der Waals layered materials is a nondestructive mechanism to fine-tune the lattice structure and the electronic state of the system. We develop a diagrammatic theory for the displacive Raman force and apply it to the shear phonon's dynamics. We obtain a noticeable light-induced Raman force of the order of F∼10–100 nN/nm2 leading to a large rectified shear displacement Q0 in bilayer graphene. In analogy to the photogalvanic effect, we decompose the Raman force to circular and linear components where the former vanishes due to the lattice symmetry in bilayer graphene. We show that the laser frequency and polarization can effectively tune Q0 in different electronic doping, temperature, and scattering rates. The finite rectified shear displacement induces a Dirac crossing pair in the low-energy dispersion that photoemission spectroscopy can probe. Our systematic formalism of Raman force can simulate the coherent manipulation of stacking order in the heterostructures of layered materials by laser irradiation.

  • 9.
    Rostami, Habib
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Cappelluti, Emmanuele
    Dominant role of two-photon vertex in nonlinear response in two-dimensional Dirac systems2021In: npj 2d materials and applications, ISSN 2397-7132, Vol. 5, no 1, article id 50Article in journal (Refereed)
    Abstract [en]

    We show that the standard concepts of nonlinear response to electromagnetic fields break down in two-dimensional Dirac systems, like graphene, in the quantum regime close to the Dirac point. We present a compelling many-body theory for nonlinear transport focusing on disorder scattering as a benchmark example. We show that, although the diamagnetic two-photon vertex is absent at the non-interacting level, disorder effects give rise to a self-generation of such two-photon vertex surviving even in the clean limit. We predict that the two-photon vertex self-generation is present only in two dimensions. The impact of such a striking scenario on the nonlinear quantum transport is discussed, predicting a huge enhancement of third-order dc conductivity comparing to the common models.

  • 10.
    Rostami, Habib
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Cappelluti, Emmanuele
    Many-body effects in third harmonic generation of graphene2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, no 12, article id 125415Article in journal (Refereed)
    Abstract [en]

    The low-energy (intraband) range of the third harmonic generation of graphene in the terahertz regime is governed by the damping terms induced by the interactions. A controlled many-body description of the scattering processes is thus a compelling and desirable requirement. In this paper, using a Kadanoff-Baym approach, we systematically investigate the impact of many-body interaction on the third harmonic generation of graphene, taking elastic impurity scattering as a benchmark example. We predict the onset in the mixed inter- and intraband regime of incoherent features driven by the interaction at four- and five-photon transition frequencies in the third harmonic optical conductivity with a spectral weight proportional to the scattering rate. We also show that in spite of the complex many-body physics, the purely intraband term governing the limit omega -> 0 resembles the constraints of the phenomenological model. We ascribe this agreement to the fulfilling of the conservation laws enforced by the conserving approach. However, the overlap with incoherent features and the impact of many-body-driven multiphoton vertex couplings severely limit the validity of phenomenological description.

  • 11.
    Rostami, Habib
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Cappelluti, Emmanuele
    Balatsky, Alexander
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Helical metals and insulators: Sheet singularity of the inflated Berry monopole2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 24, article id 245114Article in journal (Refereed)
    Abstract [en]

    We study phases of interacting Dirac matter that host Berry signatures. We predict a topological Lifshitz phase transition caused by the changes of a Dirac cone intersection from a semimetallic phase to helical insulating or metallic phases. These helical phases provide examples of a gapless topological phase where the spectral gap is not required for a topological protection. To realize nodal helical phases one would need to consider isotropic infinite-range interparticle. interaction. This interaction could emerge because of a momentum conserving scattering of electrons from a bosonic mode. For repulsive/attractive inter-particle interaction in density/pseudospin channel, the system undergoes a transition to the helical insulator phase. For an attractive density-density interaction, a metallic phase forms that hosts a nodal circle and a nodal sphere in two and three dimensions, respectively. A sheet singularity of Berry curvature is highlighted as a peculiar feature of the nodal sphere phase in three dimensions and represents the extension of the Berry monopole singularities into an inflated monopole. To illustrate the properties of these helical phases we investigate Landau levels in both metallic and insulating phases. Our study provides an extension of the paradigm in the interacting Dirac matter and makes an interesting connection to inflated topological singularities in cosmology.

  • 12.
    Rostami, Habib
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Guinea, Francisco
    Cappelluti, Emmanuele
    Strain-driven chiral phonons in two-dimensional hexagonal materials2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, no 19, article id 195431Article in journal (Refereed)
    Abstract [en]

    Hexagonal two-dimensional materials with broken inversion symmetry (as BN or transition metal dichalcogenides) are known to sustain chiral phonons with finite angular momentum, adding a further useful degree of freedom to the extraordinary entangled (electrical, optical, magnetic, and mechanical) properties of these compounds. However, because of lattice symmetry constraints, such chiral modes are constrained to the corners of the Brillouin zone, allowing little freedom for manipulating the chiral features. In this paper, we show how the application of uniaxial strain leads to the existence of unique chiral modes in the vicinity of the zone center. We also show that such strain-induced chiral modes, unlike the ones pinned at the K points, can be efficiently manipulated by modifying the strain itself, which determines the position of these modes in the Brillouin zone. The present paper results add a technique for the engineering of the quantum properties of two-dimensional lattices.

  • 13.
    Rostami, Habib
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Istituto Italiano di Tecnologia, Graphene Labs, Italia.
    Guinea, Francisco
    Polini, Marco
    Roldán, Rafael
    Piezoelectricity and valley chern number in inhomogeneous hexagonal 2D crystals2018In: Npj 2D Materials and Applications, ISSN 2397-7132, Vol. 2, p. 1-6, article id 15Article in journal (Refereed)
    Abstract [en]

    Conversion of mechanical forces to electric signal is possible in non-centrosymmetric materials due to linear piezoelectricity. The extraordinary mechanical properties of two-dimensional materials and their high crystallinity make them exceptional platforms to study and exploit the piezoelectric effect. Here, the piezoelectric response of non-centrosymmetric hexagonal two-dimensional crystals is studied using the modern theory of polarization and k-p model Hamiltonians. An analytical expression for the piezoelectric constant is obtained in terms of topological quantities, such as the valley Chern number. The theory is applied to semiconducting transition metal dichalcogenides and hexagonal Boron Nitride. We find good agreement with available experimental measurements for MoS2. We further generalize the theory to study the polarization of samples subjected to inhomogeneous strain (e.g., nanobubbles). We obtain a simple expression in terms of the strain tensor, and show that charge densities greater than or similar to 10(11)cm(-2) can be induced by realistic inhomogeneous strains, epsilon approximate to 0.01-0.03.

  • 14.
    Rostami, Habib
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Katsnelson, Mikhail
    Vignale, Giovanni
    Polini, Marco
    Gauge invariance and Ward identities in nonlinear response theory2021In: Annals of Physics, ISSN 0003-4916, E-ISSN 1096-035X, Vol. 431, article id 168523Article in journal (Refereed)
    Abstract [en]

    We present a formal analysis of nonlinear response functions in terms of correlation functions in real-and imaginary-time domains. In particular, we show that causal nonlinear response functions, expressed in terms of nested commutators in real time, can be obtained from the analytic continuation of time ordered response functions, which are more easily amenable to diagrammatic calculation. This generalizes the well-known result of linear response theory. We then use gauge invariance arguments to derive exact relations between second-order response functions in density and current channels. These identities, which are non-perturbative in the strength of inter-particle interactions, allow us to establish exact connections between nonlinear optics calculations done in different electromagnetic gauges.

  • 15.
    Rostami, Habib
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Volckaert, Klara
    Lanata, Nicola
    Mahatha, Sanjoy K.
    Sanders, Charlotte E.
    Bianchi, Marco
    Lizzit, Daniel
    Bignardi, Luca
    Lizzit, Silvano
    Miwa, Jill A.
    Balatsky, Alexander
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Hofmann, Philip
    Ulstrup, Søren
    Layer and orbital interference effects in photoemission from transition metal dichalcogenides2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 23, article id 235423Article in journal (Refereed)
    Abstract [en]

    In this work, we provide an effective model to evaluate the one-electron dipole matrix elements governing optical excitations and the photoemission process of single-layer (SL) and bilayer (BL) transition metal dichalcogenides. By utilizing a k . p Hamiltonian, we calculate the photoemission intensity as observed in angle-resolved photoemission from the valence bands around the (K) over bar valley of MoS2. In SL MoS2, we find a significant masking of intensity outside the first Brillouin zone, which originates from an in-plane interference effect between photoelectrons emitted from the Mo d orbitals. In BL MoS2, an additional interlayer interference effect leads to a distinctive modulation of intensity with photon energy. Finally, we use the semiconductor Bloch equations to model the optical excitation in a time- and angle-resolved pump-probe photoemission experiment. We find that the momentum dependence of an optically excited population in the conduction band leads to an observable dichroism in both SL and BL MoS2.

  • 16. Shahnazaryan, V.
    et al.
    Kyriienko, Oleksandr
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). ITMO University, Russia; University of Exeter, United Kingdom.
    Rostami, Habib
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Exciton routing in the heterostructure of a transition metal dichalcogenide monolayer on a paraelectric substrate2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 16, article id 165303Article in journal (Refereed)
    Abstract [en]

    We propose a scheme for the spatial exciton energy control and exciton routing in a transition-metal dichalcogenide (TMD) monolayer which lies on a quantum paraelectric substrate. It relies on the ultrasensitive response of the substrate dielectric permittivity to temperature changes, allowing for spatially inhomogeneous screening of Coulomb interaction in a monolayer. As an example, we consider the heterostructure of TMD and strontium titanate oxide SrTiO3, where large dielectric screening can be attained. We study the impact of substrate temperature on the characteristic electronic features of TMD monolayers such as the particle band gap and exciton binding energy, Bohr radius, and nonlinearity (an exciton-exciton interaction). The combination of particle band gap and exciton binding energy modulation results in the shift of the exciton resonance energy. Applying local heating, we create spatial patterns with varying exciton resonant energy and an exciton flow toward the energetically lower region of the sample.

  • 17. Shahnazaryan, Vanik
    et al.
    Rostami, Habib
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Nonlinear exciton drift in piezoelectric two-dimensional materials2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, no 8, article id 085405Article in journal (Refereed)
    Abstract [en]

    The noncentrosymmetric nature of single-layer (SL) transition-metal dichalcogenides (TMD) manifests itself in the finite piezoelectricity and valley-Zeeman coupling. We microscopically model nonlinear exciton transport in nanobubbles of SL TMDs. Thanks to the giant piezoelectric effect, we obtain an enormous internal electric field, E-piezo similar to 10(7) V/m, resulting in a built-in dipole moment of excitons. We demonstrate that the piezo-induced dipole-dipole interaction provides a novel channel for the nonlinear exciton transport distinct from the conventional isotropic funneling of excitons and leads to the formation of a hexagon-shaped exciton droplet on the top of circularly symmetric nanobubbles. Moreover, we found that the hexagonal distribution of exciton density is preserved even for strongly elliptic nanobubbles. The effect is tunable via the bubble-size dependence of the piezoelectric field E-piezo similar to h(max)(2)/R-3 with h(max) and R being the bubble height and radius, respectively.

  • 18.
    Sukhachov, Pavlo O.
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Rostami, Habib
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Acoustogalvanic Effect in Dirac and Weyl Semimetals2020In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 124, no 12, article id 126602Article in journal (Refereed)
    Abstract [en]

    The acoustogalvanic effect is proposed as a nonlinear mechanism to generate a direct electric current by passing acoustic waves in Dirac and Weyl semimetals. Unlike the standard acoustoelectric effect, which relies on the sound-induced deformation potential and the corresponding electric field, the acoustogalvanic one originates from the pseudoelectromagnetic fields, which are not subject to screening. The longitudinal acoustogalvanic current scales at least quadratically with the relaxation time, which is in contrast to the photogalvanic current where the scaling is linear. Because of the interplay of pseudoelectric and pseudomagnetic fields, the current could show a nontrivial dependence on the direction of sound wave propagation. Being within the experimental reach, the effect can be utilized to probe dynamical deformations and corresponding pseudoelectromagnetic fields, which are yet to be experimentally observed in Weyl and Dirac semimetals.

  • 19. Volckaert, Klara
    et al.
    Rostami, Habib
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Biswas, Deepnarayan
    Marković, Igor
    Andreatta, Federico
    Sanders, Charlotte E.
    Majchrzak, Paulina
    Cacho, Cephise
    Chapman, Richard T.
    Wyatt, Adam
    Springate, Emma
    Lizzit, Daniel
    Bignardi, Luca
    Lizzit, Silvano
    Mahatha, Sanjoy K.
    Bianchi, Marco
    Lanata, Nicola
    King, Phil D. C.
    Miwa, Jill A.
    Balatsky, Alexander
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Hofmann, Philip
    Ulstrup, Søren
    Momentum-resolved linear dichroism in bilayer MoS22019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 24, article id 241406Article in journal (Refereed)
    Abstract [en]

    In solid state photoemission experiments it is possible to extract information about the symmetry and orbital character of the electronic wave functions via the photoemission selection rules that shape the measured intensity. This approach can be expanded in a pump-probe experiment where the intensity contains additional information about interband excitations induced by an ultrafast laser pulse with tunable polarization. Here, we find an unexpected strong linear dichroism effect (up to 42.4%) in the conduction band of bilayer MoS2, when measuring energy- and momentum-resolved snapshots of excited electrons by time- and angle-resolved photoemission spectroscopy. We model the polarization-dependent photoemission intensity in the transiently populated conduction band using the semiconductor Bloch equations. Our theoretical analysis reveals a strongly anisotropic momentum dependence of the optical excitations due to intralayer single-particle hopping, which explains the observed linear dichroism.

  • 20. Wang, Yadong
    et al.
    Iyikanat, Fadil
    Rostami, Habib
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Bai, Xueyin
    Hu, Xuerong
    Das, Susobhan
    Dai, Yunyun
    Du, Luojun
    Zhang, Yi
    Li, Shisheng
    Lipsanen, Harri
    García de Abajo, F. Javier
    Sun, Zhipei
    Probing Electronic States in Monolayer Semiconductors through Static and Transient Third-Harmonic Spectroscopies2022In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 34, no 3, article id 2107104Article in journal (Refereed)
    Abstract [en]

    Electronic states and their dynamics are of critical importance for electronic and optoelectronic applications. Here, various relevant electronic states in monolayer MoS2, such as multiple excitonic Rydberg states and free-particle energy bands are probed with a high relative contrast of up to ≥200 via broadband (from ≈1.79 to 3.10 eV) static third-harmonic spectroscopy (THS), which is further supported by theoretical calculations. Moreover, transient THS is introduced to demonstrate that third-harmonic generation can be all-optically modulated with a modulation depth exceeding ≈94% at ≈2.18 eV, providing direct evidence of dominant carrier relaxation processes associated with carrier–exciton and carrier–phonon interactions. The results indicate that static and transient THS are not only promising techniques for the characterization of monolayer semiconductors and their heterostructures, but also a potential platform for disruptive photonic and optoelectronic applications, including all-optical modulation and imaging.

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