arXiv subjects

D. N. Krizhanovskii

Publications and source records attributed to D. N. Krizhanovskii.

At least 19 recordsLinked to original sources

arXiv2024

Planar Bragg microcavities with monolayer WS$_2$ for strong exciton-photon coupling

We propose and numerically investigate a novel compact planar microcavity design based on a high-index dielectric slab waveguide with embedded monolayer semiconductor. In comparison to more traditional vertical Bragg microcavities, our design relies on the transmission of guided optical modes and achieves strong exciton-photon coupling in a chip-compatible and compact geometry with sub-100 nm thickness. We show that Rabi splitting values of more than 70 meV can be obtained in planar microcavities with the total length below 5 um. Further, we reveal the dependence of Rabi splitting on the dimensions of the structure and explain it with a simple theoretical model. Our results contribute towards the development of novel compact 2D semiconductor-based components for integrated photonic circuits.

cond-mat.mes-hall↗

arXiv2023

Exciton-polaritons in GaAsbased slab waveguide photonic crystals

We report the observation of band gaps for low loss exciton-polaritons propagating outside the light cone in GaAs-based planar waveguides patterned into two-dimensional photonic crystals. By etching square lattice arrays of shallow holes into the uppermost layer of our structure, we open gaps on the order of 10 meV in the photonic mode dispersion, whose size and light-matter composition can be tuned by proximity to the strongly coupled exciton resonance. We demonstrate gaps ranging from almost fully photonic to highly excitonic. Opening a gap in the exciton-dominated part of the polariton spectrum is a promising first step towards the realization of quantum-Hall-like states arising from topologically nontrivial hybridization of excitons and photons.

physics.optics↗

arXiv2022

Polaron-enhanced polariton nonlinearity in lead halide perovskites

Exciton-polaritons offer a versatile platform for realization of all-optical integrated logic gates due to the strong effective optical nonlinearity resulting from the exciton-exciton interactions. In most of the current excitonic materials there exists a direct connection between the exciton robustness to thermal fluctuations and the strength of exciton-exciton interaction, making materials with highest levels of exciton nonlinearity applicable at cryogenic temperatures only. Here, we show that strong polaronic effects, characteristic for perovskite materials, allow to overcome this limitation. Namely, we demonstrate the record-high value of the nonlinear optical response in nanostructured organic-inorganic halide perovskite MAPbI$_3$, experimentally detected as 19.7 meV blueshift of the polariton branch under femtosecond laser irradiation. This is substantially higher than characteristic values for the samples based on conventional semiconductors and monolayers of transition metal dichalcogenides. The observed strong polaron-enhanced nonlinearity exists for both tetragonal and orthorombic phases of MAPbI$_3$, and remains stable at elevated temperatures.

cond-mat.mes-hall↗

arXiv2022

Nonlinear self-action of ultrashort guided exciton-polariton pulses in dielectric slab coupled to 2D semiconductor

Recently reported large values of exciton-polariton nonlinearity of transition metal dichalcogenide (TMD) monolayers coupled to optically resonant structures approach the values characteristic for GaAs-based systems in the regime of strong light-matter coupling. Contrary to the latter, TMD-based polaritonic devices remain operational at ambient conditions and therefore have greater potential for practical nanophotonic applications. Here we present the study of the nonlinear properties of Ta$_2$O$_5$ slab waveguide coupled to a WSe$_2$ monolayer. We first confirm that the hybridization between waveguide photon mode and a 2D semiconductor exciton resonance gives rise to the formation of exciton-polaritons with Rabi splitting of 36 meV. By measuring transmission of ultrashort optical pulses through this TMD-based polaritonic waveguide, we demonstrate for the first time the strong nonlinear dependence of the output spectrum on the input pulse energy. Our theoretical model provides semi-quantitative agreement with experiment and gives insights into the dominating microscopic processes which determine the nonlinear pulse self-action: Coulomb inter-particle interaction and scattering to incoherent excitonic reservoir. We also confirm that at intermediate pump energies the system supports quasi-stationary solitonic regime of pulse propagation. Our results are essential for the development of nonlinear on-chip polaritonic devices based of 2D semiconductors.

cond-mat.mes-hall↗

arXiv2021

Valley polarization of trions in monolayer MoSe$_2$ interfaced with bismuth iron garnet

Interfacing atomically thin van der Waals semiconductors with magnetic substrates enables additional control on their intrinsic valley degree of freedom and provides a promising platform for the development of novel valleytronic devices for information processing and storage. Here we study circularly polarized photoluminescence in heterostructures of monolayer MoSe$_2$ and thin films of ferrimagnetic bismuth iron garnet. We observe strong emission from charged excitons with negative valley polarization, which switches sign with increasing temperature, and demonstrate contrasting response to left and right circularly polarized excitation, associated with finite out-of-plane magnetization in the substrate. We propose a theoretical model accounting for magnetization-induced imbalance of charge carriers in the two valleys of MoSe$_2$, as well as for valley-switching scattering from B to A excitons and fast formation of trions with extended valley relaxation times, which shows excellent agreement with the experimental data. Our results provide new insights into valley physics in 2D semiconductors interfaced with magnetic substrates.

cond-mat.mes-hall↗

arXiv2020

Optical analogue of Dresselhaus spin-orbit interaction in photonic graphene

The concept of gauge fields plays a significant role in many areas of physics from particle physics and cosmology to condensed matter systems, where gauge potentials are a natural consequence of electromagnetic fields acting on charged particles and are of central importance in topological states of matter. Here, we report on the experimental realization of a synthetic non-Abelian gauge field for photons in a honeycomb microcavity lattice. We show that the effective magnetic field associated with TE-TM splitting has the symmetry of Dresselhaus spin-orbit interaction around Dirac points in the dispersion, and can be regarded as an SU(2) gauge field. The symmetry of the field is revealed in the optical spin Hall effect (OSHE), where under resonant excitation of the Dirac points precession of the photon pseudospin around the field direction leads to the formation of two spin domains. Furthermore, we observe that the Dresselhaus field changes its sign in the same Dirac valley on switching from s to p bands in good agreement with the tight binding modelling. Our work demonstrating a non-Abelian gauge field for light on the microscale paves the way towards manipulation of photons via spin on a chip.

cond-mat.mes-hall↗

arXiv2020

Spin-valley dynamics in alloy-based transition metal dichalcogenide heterobilayers

Van der Waals heterobilayers based on 2D transition metal dichalcogenides have been recently shown to support robust and long-lived valley polarization for potential valleytronic applications. However, the role of the band structure and alignment of the constituent layers in the underlying dynamics remains largely unexplored. Here we study spin--valley relaxation dynamics in heterobilayers with different band structures engineered via the use of alloyed monolayer semiconductors. Through a combination of time-resolved Kerr rotation spectroscopic measurements and theoretical modelling for Mo$_{1-x}$W$_{x}$Se$_2$/WSe$_2$ samples with different chemical compositions and stacking angles, we uncover the roles of interlayer exciton recombination and charge carrier spin depolarization in the overall valley dynamics. Our results provide insights into the microscopic spin--valley polarization mechanisms in van der Waals heterostructures for the development of future 2D valleytronic devices.

cond-mat.mes-hall↗

arXiv2020

Electrically pumped WSe$_2$-based light-emitting van der Waals heterostructures embedded in monolithic dielectric microcavities

Vertical stacking of atomically thin layered materials opens new possibilities for the fabrication of heterostructures with favorable optoelectronic properties. The combination of graphene, hexagonal boron nitride and semiconducting transition metal dichalcogenides allows fabrication of electroluminescence (EL) devices, compatible with a wide range of substrates. Here, we demonstrate a full integration of an electroluminescent van der Waals heterostructure in a monolithic optical microcavity made of two high reflectivity dielectric distributed Bragg reflectors (DBRs). Owing to the presence of graphene and hexagonal boron nitride protecting the WSe$_2$ during the top mirror deposition, we fully preserve the optoelectronic behaviour of the device. Two bright cavity modes appear in the EL spectrum featuring Q-factors of 250 and 580 respectively: the first is attributed directly to the monolayer area, while the second is ascribed to the portion of emission guided outside the WSe$_2$ island. By embedding the EL device inside the microcavity structure, a significant modification of the directionality of the emitted light is achieved, with the peak intensity increasing by nearly two orders of magnitude at the angle of the maximum emission compared with the same EL device without the top DBR. Furthermore, the coupling of the WSe$_2$ EL to the cavity mode with a dispersion allows a tuning of the peak emission wavelength exceeding 35 nm (80 meV) by varying the angle at which the EL is observed from the microcavity. This work provides a route for the development of compact vertical-cavity surface-emitting devices based on van der Waals heterostructures.

physics.optics↗

arXiv2019

Nonlinear quantum optics with trion-polaritons in 2D monolayers: conventional and unconventional photon blockade

We study a 2D system of trion-polaritons at the quantum level and demonstrate that for monolayer semiconductors they can exhibit a strongly nonlinear optical response. The effect is due to the composite nature of trion-based excitations resulting in their nontrivial quantum statistical properties, and enhanced phase space filling effects. We present the full quantum theory to describe the statistics of trion-polaritons, and demonstrate that the associated nonlinearity persists at the level of few quanta, where two qualitatively different regimes of photon antibunching are present for weak and strong single photon-trion coupling. We find that single photon emission from trion-polaritons becomes experimentally feasible in state-of-the-art transition metal dichalcogenide (TMD) setups. This can foster the development of quantum polaritonics using 2D monolayers as a material platform.

quant-ph↗

arXiv2019

Highly nonlinear trion-polaritons in a monolayer semiconductor

Highly nonlinear optical materials with strong effective photon-photon interactions (Kerr-like nonlinearity) are required in the development of novel quantum sources of light as well as for ultrafast and quantum optical signal processing circuitry. Here we report very large Kerr-like nonlinearities by employing strong optical transitions of charged excitons (trions) observed in semiconducting transition metal dichalcogenides (TMDCs). By hybridising trions in monolayer MoSe$_2$ at low electron densities with a microcavity mode, we realise trion-polaritons exhibiting significant energy shifts at very small photon fluxes due to phase space filling. Most notably, the strong trion-polariton nonlinearity is found to be 10 to 1000 larger than in other polariton systems, including neutral exciton-polaritons in TMDCs. Furthermore it exceeds by factors of $\sim 10^3-10^5$ the magnitude of Kerr nonlinearity in bare TMDCs, graphene and other widely used optical materials (e.g. Si, AlGaAs etc) in weak light-matter coupling regimes. The results are in good agreement with a theory which accounts for the composite nature of excitons and trions and deviation of their statistics from that of ideal bosons and fermions. This work opens a new highly nonlinear system for quantum optics applications enabling in principle scalability and control through nano-engineering of van der Waals heterostructures.

cond-mat.mes-hall↗

arXiv2019

Nonlinear polaritons in monolayer semiconductor coupled to optical bound states in the continuum

Optical bound states in the continuum (BICs) provide a way to engineer very narrow resonances in photonic crystals. The extended interaction time in such systems is particularly promising for enhancement of nonlinear optical processes and development of the next generation of active optical devices. However, the achievable interaction strength is limited by the purely photonic character of optical BICs. Here, we mix optical BIC in a photonic crystal slab with excitons in atomically thin semiconductor MoSe$_2$ to form nonlinear exciton-polaritons with a Rabi splitting of 27~meV, exhibiting large interaction-induced spectral blueshifts. The asymptotic BIC-like suppression of polariton radiation into far-field towards the BIC wavevector, in combination with effective reduction of excitonic disorder through motional narrowing, results in small polariton linewidths below 3~meV. Together with strongly wavevector-dependent Q-factor, this provides for enhancement and control of polariton--polariton interactions and resulting nonlinear optical effects, paving the way towards tunable BIC-based polaritonic devices for sensing, lasing, and nonlinear optics.

cond-mat.mes-hall↗

arXiv2019

Measurement of local optomechanical properties of a direct bandgap 2D semiconductor

Strain engineering is a powerful tool for tuning physical properties of 2D materials, including monolayer transition metal dichalcogenides (TMD) -- direct bandgap semiconductors with strong excitonic response. Here, we demonstrate an approach for local characterization of strain-induced modification of excitonic photoluminescence in TMD-based materials. We reversibly stress a monolayer of MoSe$_2$ with an AFM tip and perform spatio-spectral mapping of the excitonic photoluminescence in the vicinity of the indentation point. To fully reproduce the experimental data, we introduce the linear dependence of the exciton energy and corresponding photoluminescence intensity on the induced strain. Careful account for the optical resolution allows extracting these quantities with good agreement with the previous measurements, which involved macroscopic sample deformation. Our approach is a powerful tool for the study of local optomechanical properties of 2D direct bandgap semiconductors with strong excitonic response.

cond-mat.mes-hall↗

arXiv2018

Effect of photonic spin-orbit coupling on the topological edge modes of a Su-Schrieffer-Heeger chain

We study the effect of photonic spin-orbit coupling (SOC) in micropillar lattices on the topological edge states of a one-dimensional chain with a zigzag geometry, corresponding to the Su-Schrieffer-Heeger model equipped with an additional internal degree of freedom. The system combines the strong hopping anisotropy of the $p$-type pillar modes with the large TE-TM splitting in Bragg microcavities. By resolving the photoluminescence emission in energy and polarization we probe the effects of the resulting SOC on the spatial and spectral properties of the edge modes. We find that the edge modes feature a fine structure of states that penetrate by different amounts into the bulk of the chain, depending on the strength of the SOC terms present, thereby opening a route to manipulation of the topological states in the system.

physics.optics↗

arXiv2018

Spin domains in one-dimensional conservative polariton solitons

We report stable orthogonally polarised domains in high-density polariton solitons propagating in a semiconductor microcavity wire. This effect arises from spin dependent polariton-polariton interactions and pump-induced imbalance of polariton spin populations. The interactions result in an effective magnetic field acting on polariton spin across the soliton profile, leading to the formation of polarisation domains. Our experimental findings are in excellent agreement with theoretical modelling taking into account these effects.

cond-mat.mes-hall↗

arXiv2018

Exciton Polaritons in a Two-Dimensional Lieb Lattice with Spin-Orbit Coupling

We study exciton-polaritons in a two-dimensional Lieb lattice of micropillars. The energy spectrum of the system features two flat bands formed from $S$ and $P_{x,y}$ photonic orbitals, into which we trigger bosonic condensation under high power excitation. The symmetry of the orbital wave functions combined with photonic spin-orbit coupling gives rise to emission patterns with pseudospin texture in the flat band condensates. Our work shows the potential of polariton lattices for emulating flat band Hamiltonians with spin-orbit coupling, orbital degrees of freedom and interactions.

cond-mat.mes-hall↗

arXiv2018

Valley coherent exciton-polaritons in a monolayer semiconductor

Two-dimensional transition metal dichalcogenide (TMD) semiconductors provide a unique possibility to access the electronic valley degree of freedom using polarized light, opening the way to valley information transfer between distant systems. Excitons with a well-defined valley index (or valley pseudospin) as well as superpositions of the exciton valley states can be created with light having circular and linear polarization, respectively. However, the generated excitons have short lifetimes (ps) and are also subject to the electron-hole exchange interaction leading to fast relaxation of the valley pseudospin and coherence. Here we show that control of these processes can be gained by embedding a monolayer of WSe$_2$ in an optical microcavity, where part-light-part-matter exciton-polaritons are formed in the strong light-matter coupling regime. We demonstrate the optical initialization of the valley coherent polariton populations, exhibiting luminescence with a linear polarization degree up to 3 times higher than that of the excitons. We further control the evolution of the polariton valley coherence using a Faraday magnetic field to rotate the valley pseudospin by an angle defined by the exciton-cavity-mode detuning, which exceeds the rotation angle in the bare exciton. This work provides unique insight into the decoherence mechanisms in TMDs and demonstrates the potential for engineering the valley pseudospin dynamics in monolayer semiconductors embedded in photonic structures.

cond-mat.mes-hall↗

arXiv2018

Transition from propagating polariton solitons to a standing wave condensate induced by interactions

We explore nonlinear transitions of polariton wavepackets, first, to a soliton and then to a standing wave polariton condensate in a multi-mode microwire system. At low polariton density we observe ballistic propagation of the multi-mode polariton wavepackets arising from the interference between different transverse modes. With increasing polariton density, the wavepackets transform into single mode bright solitons due to effects of both inter-modal and intra-modal polariton-polariton scattering. Further increase of the excitation density increases thermalisation speed leading to relaxation of the polariton density distribution in momentum space with the resultant formation of a non-equilibrium condensate manifested by a standing wave pattern across the whole sample.

cond-mat.mes-hall↗

arXiv2017

Polariton pattern formation and photon statistics of the associated emission

We report on the formation of a diverse family of transverse spatial polygon patterns in a microcavity polariton fluid under coherent driving by a blue-detuned pump. Patterns emerge spontaneously as a result of energy-degenerate polariton-polariton scattering from the pump state to interfering high order vortex and antivortex modes, breaking azimuthal symmetry. The interplay between a multimode parametric instability and intrinsic optical bistability leads to a sharp spike in the value of second order coherence $g^{(2)}(0)$ of the emitted light, which we attribute to the strongly superlinear kinetics of the underlying scattering processes driving the formation of patterns. We show numerically by means of a linear stability analysis how the growth of parametric instabilities in our system can lead to spontaneous symmetry breaking, predicting the formation and competition of different pattern states in good agreement with experimental observations.

cond-mat.mes-hall↗