M. Glazov - Academia.edu (original) (raw)
Papers by M. Glazov
Nature Communications
Energy relaxation of photo-excited charge carriers is of significant fundamental interest and cru... more Energy relaxation of photo-excited charge carriers is of significant fundamental interest and crucial for the performance of monolayer transition metal dichalcogenides in optoelectronics. The primary stages of carrier relaxation affect a plethora of subsequent physical mechanisms. Here we measure light scattering and emission in tungsten diselenide monolayers close to the laser excitation energy (down to ~0.6 meV). We reveal a series of periodic maxima in the hot photoluminescence intensity, stemming from energy states higher than the A-exciton state. We find a period ~15 meV for 7 peaks below (Stokes) and 5 peaks above (anti-Stokes) the laser excitation energy, with a strong temperature dependence. These are assigned to phonon cascades, whereby carriers undergo phonon-induced transitions between real states above the free-carrier gap with a probability of radiative recombination at each step. We infer that intermediate states in the conduction band at the Λ-valley of the Brillouin ...
Physical Review B
Two-dimensional stacking fault defects embedded in a bulk crystal can provide a homogeneous trapp... more Two-dimensional stacking fault defects embedded in a bulk crystal can provide a homogeneous trapping potential for carriers and excitons. Here we utilize state-of-the-art structural imaging coupled with density functional and effective-mass theory to build a microscopic model of the stackingfault exciton. The diamagnetic shift and exciton dipole moment at different magnetic fields are calculated and compared with the experimental photoluminescence of excitons bound to a single stacking fault in GaAs. The model is used to further provide insight into the properties of excitons bound to the double-well potential formed by stacking fault pairs. This microscopic exciton model can be used as an input into models which include exciton-exciton interactions to determine the excitonic phases accessible in this system.
Nature Communications
Monolayer transition metal dichalcogenides integrated in optical microcavities host excitonpolari... more Monolayer transition metal dichalcogenides integrated in optical microcavities host excitonpolaritons as a hallmark of the strong light-matter coupling regime. Analogous concepts for hybrid light-matter systems employing spatially indirect excitons with a permanent electric dipole moment in heterobilayer crystals promise realizations of exciton-polariton gases and condensates with inherent dipolar interactions. Here, we implement cavity-control of interlayer excitons in vertical MoSe 2-WSe 2 heterostructures. Our experiments demonstrate the Purcell effect for heterobilayer emission in cavity-modified photonic environments, and quantify the light-matter coupling strength of interlayer excitons. The results will facilitate further developments of dipolar exciton-polariton gases and condensates in hybrid cavityvan der Waals heterostructure systems.
physica status solidi (b)
We address the problem of free carrier screening of exciton states in two-dimensional monolayer s... more We address the problem of free carrier screening of exciton states in two-dimensional monolayer semiconductors. Basic theoretical considerations are presented concerning the applicability of the commonly used static approximation of the screening effect and the implications are discussed. We show that the low-frequency models lead to a major overestimation of the free carrier response and are inadequate to describe the screening of strongly bound excitons in monolayer materials. The presented arguments are consistent with existing high-level many-body theories and transparently illustrate the underlying physics.
Physical Review B
We study theoretically the electron spin noise in quantum dots under non-equilibrium conditions c... more We study theoretically the electron spin noise in quantum dots under non-equilibrium conditions caused by the pumping by a train of circularly polarized optical pulses. In such a situation, the nuclear spins are known to adjust in such a way, that the electron spin precession frequencies become multiples of the pump pulse repetition frequency. This so called phase synchronization effect was uncovered in [Science 317, 1896 (2007)] and termed nuclei-induced frequency focusing of electron spin coherence. Using the classical approach to the central spin model we evaluate the nuclear spin distribution function and the electron spin noise spectrum. We show that the electron spin noise spectrum consists of sharp peaks corresponding to the phase synchronization conditions and directly reveal the distribution of the nuclear spins. We discuss the effects of nuclear spin relaxation after the pumping is over and analyze the corresponding evolution of nuclear spin distributions and electron spin noise spectra.
Nature Communications
The original version of this Article contained an error in Fig. 2c, in which the numbers on the y... more The original version of this Article contained an error in Fig. 2c, in which the numbers on the y-axis were given in the wrong order: '800' at the bottom through to '0' at the top. This has been corrected in both the PDF and HTML versions of the Article. Also, the Source Data file initially published online was corrupted and was replaced.
Reviews of Modern Physics
Atomically thin materials such as graphene and monolayer transition metal dichalcogenides (TMDs) ... more Atomically thin materials such as graphene and monolayer transition metal dichalcogenides (TMDs) exhibit remarkable physical properties resulting from their reduced dimensionality and crystal symmetry. The family of semiconducting transition metal dichalcogenides is an especially promising platform for fundamental studies of two-dimensional (2D) systems, with potential applications in optoelectronics and valleytronics due to their direct band gap in the monolayer limit and highly efficient light-matter coupling. A crystal lattice with broken inversion symmetry combined with strong spin-orbit interactions leads to a unique combination of the spin and valley degrees of freedom. In addition, the 2D character of the monolayers and weak dielectric screening from the environment yield a significant enhancement of the Coulomb interaction. The resulting formation of bound electron-hole pairs, or excitons, dominates the optical and spin properties of the material. Here we review recent progress in our understanding of the excitonic properties in monolayer TMDs and lay out future challenges. We focus on the consequences of the strong direct and exchange Coulomb interaction, discuss exciton-light interaction and effects of other carriers and excitons on electron-hole pairs in TMDs. Finally, the impact on valley polarization is described and the tuning of the energies and polarization observed in applied electric and magnetic fields is summarized.
Physical review letters, Jan 3, 2018
Atomically thin semiconductors provide an ideal testbed to investigate the physics of Coulomb-bou... more Atomically thin semiconductors provide an ideal testbed to investigate the physics of Coulomb-bound many-body states. We shed light on the intricate structure of such complexes by studying the magnetic-field-induced splitting of biexcitons in monolayer WS_{2} using polarization-resolved photoluminescence spectroscopy in out-of-plane magnetic fields up to 30 T. The observed g factor of the biexciton amounts to about -3.9, closely matching the g factor of the neutral exciton. The biexciton emission shows an inverted circular field-induced polarization upon linearly polarized excitation; i.e., it exhibits preferential emission from the high-energy peak in a magnetic field. This phenomenon is explained by taking into account the hybrid configuration of the biexciton constituents in momentum space and their respective energetic behavior in magnetic fields. Our findings reveal the critical role of dark excitons in the composition of this many-body state.
Physical review letters, Jan 18, 2018
We directly monitor exciton propagation in freestanding and SiO_{2}-supported WS_{2} monolayers t... more We directly monitor exciton propagation in freestanding and SiO_{2}-supported WS_{2} monolayers through spatially and time-resolved microphotoluminescence under ambient conditions. We find a highly nonlinear behavior with characteristic, qualitative changes in the spatial profiles of the exciton emission and an effective diffusion coefficient increasing from 0.3 to more than 30 cm^{2}/s, depending on the injected exciton density. Solving the diffusion equation while accounting for Auger recombination allows us to identify and quantitatively understand the main origin of the increase in the observed diffusion coefficient. At elevated excitation densities, the initial Gaussian distribution of the excitons evolves into long-lived halo shapes with μm-scale diameter, indicating additional memory effects in the exciton dynamics.
AIP Conference Proceedings
ABSTRACT
Solid State Communications
Theory of magneto-oscillation phenomena has been developed for two-dimensional electron systems w... more Theory of magneto-oscillation phenomena has been developed for two-dimensional electron systems with linear-ink spin splitting. Both Dresselhaus and Rashba contributions are taken into account. It has been shown that the pattern of the magneto-oscillations depends drastically on the ratio between the above terms. The presence of only one type of the k-linear terms gives rise to the beats, i.e. two close harmonics corresponding to the spin-split subbands. However, if the strengths of both contributions are comparable, the third (central) harmonics appears in the spectrum of the magneto-oscillations. For equal strengths of the contributions, only the central harmonic survives, and the oscillations occur at a single frequency, although the k-linear terms remain in the Hamiltonian. Such suppression of the spin beats is studied in detail by the example of the Shubnikov-de Haas effect.
Physical Review B
We show theoretically that a weakly interacting gas of spin-polarized exciton-polaritons in a sem... more We show theoretically that a weakly interacting gas of spin-polarized exciton-polaritons in a semiconductor microcavity supports propagation of spin waves. The spin waves are characterised by a parabolic dispersion at small wavevectors which is governed by the polariton-polariton interaction constant. Due to spin-anisotropy of polariton-polariton interactions the dispersion of spin waves depends on the orientation of the total polariton spin. For the same reason, the frequency of homogeneous spin precession/polariton spin resonance depends on their polarization degree.
Acta Physica Polonica A
We analyse the recently observed effect of an in-plane electric current through a Si quantum well... more We analyse the recently observed effect of an in-plane electric current through a Si quantum well on the conduction electron spin resonance. We find that the ratio of resonance shift and current density is independent of temperature and dissipation processes, but the channel current is reduced due to a parallel electric channel in heavily modulation doped samples. The inhomogeneous current distribution results in some broadening of the ESR line width. In high mobility Si/SiGe layers the current induced increase in the electron temperature is considerably larger than the increase in the lattice temperature. The signal amplitude scales with the square of electron mobility.
Physica E: Low-dimensional Systems and Nanostructures
ABSTRACT
![Research paper thumbnail of Charge tuning in [111] grown GaAs droplet quantum dots](https://attachments.academia-assets.com/71974635/thumbnails/1.jpg)
](Applied Physics Letters, 2014
We demonstrate charge tuning in strain free GaAs/AlGaAs quantum dots (QDs) grown by droplet epita... more We demonstrate charge tuning in strain free GaAs/AlGaAs quantum dots (QDs) grown by droplet epitaxy on a GaAs(111)A substrate. Application of a bias voltage allows the controlled charging of the QDs from −3|e| to +2|e|. The resulting changes in QD emission energy and exciton fine-structure are recorded in micro-photoluminescence experiments at T = 4 K. We uncover the existence of excited valence and conduction states, in addition to the s-shell-like ground state. We record a second series of emission lines about 25 meV above the charged exciton emission coming from excited charged excitons. For these excited interband transitions a negative diamagnetic shift of large amplitude is uncovered in longitudinal magnetic fields.
Scientific reports, Jan 17, 2016
Rapid development of spin noise spectroscopy of the last decade has led to a number of remarkable... more Rapid development of spin noise spectroscopy of the last decade has led to a number of remarkable achievements in the fields of both magnetic resonance and optical spectroscopy. In this report, we demonstrate a new - magnetometric - potential of the spin noise spectroscopy and use it to study magnetic fields acting upon electron spin-system of an n-GaAs layer in a high-Q microcavity probed by elliptically polarized light. Along with the external magnetic field, applied to the sample, the spin noise spectrum revealed the Overhauser field created by optically oriented nuclei and an additional, previously unobserved, field arising in the presence of circularly polarized light. This "optical field" is directed along the light propagation axis, with its sign determined by sign of the light helicity. We show that this field results from the optical Stark effect in the field of the elliptically polarized light. This conclusion is supported by theoretical estimates.
Nature Communications
Energy relaxation of photo-excited charge carriers is of significant fundamental interest and cru... more Energy relaxation of photo-excited charge carriers is of significant fundamental interest and crucial for the performance of monolayer transition metal dichalcogenides in optoelectronics. The primary stages of carrier relaxation affect a plethora of subsequent physical mechanisms. Here we measure light scattering and emission in tungsten diselenide monolayers close to the laser excitation energy (down to ~0.6 meV). We reveal a series of periodic maxima in the hot photoluminescence intensity, stemming from energy states higher than the A-exciton state. We find a period ~15 meV for 7 peaks below (Stokes) and 5 peaks above (anti-Stokes) the laser excitation energy, with a strong temperature dependence. These are assigned to phonon cascades, whereby carriers undergo phonon-induced transitions between real states above the free-carrier gap with a probability of radiative recombination at each step. We infer that intermediate states in the conduction band at the Λ-valley of the Brillouin ...
Physical Review B
Two-dimensional stacking fault defects embedded in a bulk crystal can provide a homogeneous trapp... more Two-dimensional stacking fault defects embedded in a bulk crystal can provide a homogeneous trapping potential for carriers and excitons. Here we utilize state-of-the-art structural imaging coupled with density functional and effective-mass theory to build a microscopic model of the stackingfault exciton. The diamagnetic shift and exciton dipole moment at different magnetic fields are calculated and compared with the experimental photoluminescence of excitons bound to a single stacking fault in GaAs. The model is used to further provide insight into the properties of excitons bound to the double-well potential formed by stacking fault pairs. This microscopic exciton model can be used as an input into models which include exciton-exciton interactions to determine the excitonic phases accessible in this system.
Nature Communications
Monolayer transition metal dichalcogenides integrated in optical microcavities host excitonpolari... more Monolayer transition metal dichalcogenides integrated in optical microcavities host excitonpolaritons as a hallmark of the strong light-matter coupling regime. Analogous concepts for hybrid light-matter systems employing spatially indirect excitons with a permanent electric dipole moment in heterobilayer crystals promise realizations of exciton-polariton gases and condensates with inherent dipolar interactions. Here, we implement cavity-control of interlayer excitons in vertical MoSe 2-WSe 2 heterostructures. Our experiments demonstrate the Purcell effect for heterobilayer emission in cavity-modified photonic environments, and quantify the light-matter coupling strength of interlayer excitons. The results will facilitate further developments of dipolar exciton-polariton gases and condensates in hybrid cavityvan der Waals heterostructure systems.
physica status solidi (b)
We address the problem of free carrier screening of exciton states in two-dimensional monolayer s... more We address the problem of free carrier screening of exciton states in two-dimensional monolayer semiconductors. Basic theoretical considerations are presented concerning the applicability of the commonly used static approximation of the screening effect and the implications are discussed. We show that the low-frequency models lead to a major overestimation of the free carrier response and are inadequate to describe the screening of strongly bound excitons in monolayer materials. The presented arguments are consistent with existing high-level many-body theories and transparently illustrate the underlying physics.
Physical Review B
We study theoretically the electron spin noise in quantum dots under non-equilibrium conditions c... more We study theoretically the electron spin noise in quantum dots under non-equilibrium conditions caused by the pumping by a train of circularly polarized optical pulses. In such a situation, the nuclear spins are known to adjust in such a way, that the electron spin precession frequencies become multiples of the pump pulse repetition frequency. This so called phase synchronization effect was uncovered in [Science 317, 1896 (2007)] and termed nuclei-induced frequency focusing of electron spin coherence. Using the classical approach to the central spin model we evaluate the nuclear spin distribution function and the electron spin noise spectrum. We show that the electron spin noise spectrum consists of sharp peaks corresponding to the phase synchronization conditions and directly reveal the distribution of the nuclear spins. We discuss the effects of nuclear spin relaxation after the pumping is over and analyze the corresponding evolution of nuclear spin distributions and electron spin noise spectra.
Nature Communications
The original version of this Article contained an error in Fig. 2c, in which the numbers on the y... more The original version of this Article contained an error in Fig. 2c, in which the numbers on the y-axis were given in the wrong order: '800' at the bottom through to '0' at the top. This has been corrected in both the PDF and HTML versions of the Article. Also, the Source Data file initially published online was corrupted and was replaced.
Reviews of Modern Physics
Atomically thin materials such as graphene and monolayer transition metal dichalcogenides (TMDs) ... more Atomically thin materials such as graphene and monolayer transition metal dichalcogenides (TMDs) exhibit remarkable physical properties resulting from their reduced dimensionality and crystal symmetry. The family of semiconducting transition metal dichalcogenides is an especially promising platform for fundamental studies of two-dimensional (2D) systems, with potential applications in optoelectronics and valleytronics due to their direct band gap in the monolayer limit and highly efficient light-matter coupling. A crystal lattice with broken inversion symmetry combined with strong spin-orbit interactions leads to a unique combination of the spin and valley degrees of freedom. In addition, the 2D character of the monolayers and weak dielectric screening from the environment yield a significant enhancement of the Coulomb interaction. The resulting formation of bound electron-hole pairs, or excitons, dominates the optical and spin properties of the material. Here we review recent progress in our understanding of the excitonic properties in monolayer TMDs and lay out future challenges. We focus on the consequences of the strong direct and exchange Coulomb interaction, discuss exciton-light interaction and effects of other carriers and excitons on electron-hole pairs in TMDs. Finally, the impact on valley polarization is described and the tuning of the energies and polarization observed in applied electric and magnetic fields is summarized.
Physical review letters, Jan 3, 2018
Atomically thin semiconductors provide an ideal testbed to investigate the physics of Coulomb-bou... more Atomically thin semiconductors provide an ideal testbed to investigate the physics of Coulomb-bound many-body states. We shed light on the intricate structure of such complexes by studying the magnetic-field-induced splitting of biexcitons in monolayer WS_{2} using polarization-resolved photoluminescence spectroscopy in out-of-plane magnetic fields up to 30 T. The observed g factor of the biexciton amounts to about -3.9, closely matching the g factor of the neutral exciton. The biexciton emission shows an inverted circular field-induced polarization upon linearly polarized excitation; i.e., it exhibits preferential emission from the high-energy peak in a magnetic field. This phenomenon is explained by taking into account the hybrid configuration of the biexciton constituents in momentum space and their respective energetic behavior in magnetic fields. Our findings reveal the critical role of dark excitons in the composition of this many-body state.
Physical review letters, Jan 18, 2018
We directly monitor exciton propagation in freestanding and SiO_{2}-supported WS_{2} monolayers t... more We directly monitor exciton propagation in freestanding and SiO_{2}-supported WS_{2} monolayers through spatially and time-resolved microphotoluminescence under ambient conditions. We find a highly nonlinear behavior with characteristic, qualitative changes in the spatial profiles of the exciton emission and an effective diffusion coefficient increasing from 0.3 to more than 30 cm^{2}/s, depending on the injected exciton density. Solving the diffusion equation while accounting for Auger recombination allows us to identify and quantitatively understand the main origin of the increase in the observed diffusion coefficient. At elevated excitation densities, the initial Gaussian distribution of the excitons evolves into long-lived halo shapes with μm-scale diameter, indicating additional memory effects in the exciton dynamics.
AIP Conference Proceedings
ABSTRACT
Solid State Communications
Theory of magneto-oscillation phenomena has been developed for two-dimensional electron systems w... more Theory of magneto-oscillation phenomena has been developed for two-dimensional electron systems with linear-ink spin splitting. Both Dresselhaus and Rashba contributions are taken into account. It has been shown that the pattern of the magneto-oscillations depends drastically on the ratio between the above terms. The presence of only one type of the k-linear terms gives rise to the beats, i.e. two close harmonics corresponding to the spin-split subbands. However, if the strengths of both contributions are comparable, the third (central) harmonics appears in the spectrum of the magneto-oscillations. For equal strengths of the contributions, only the central harmonic survives, and the oscillations occur at a single frequency, although the k-linear terms remain in the Hamiltonian. Such suppression of the spin beats is studied in detail by the example of the Shubnikov-de Haas effect.
Physical Review B
We show theoretically that a weakly interacting gas of spin-polarized exciton-polaritons in a sem... more We show theoretically that a weakly interacting gas of spin-polarized exciton-polaritons in a semiconductor microcavity supports propagation of spin waves. The spin waves are characterised by a parabolic dispersion at small wavevectors which is governed by the polariton-polariton interaction constant. Due to spin-anisotropy of polariton-polariton interactions the dispersion of spin waves depends on the orientation of the total polariton spin. For the same reason, the frequency of homogeneous spin precession/polariton spin resonance depends on their polarization degree.
Acta Physica Polonica A
We analyse the recently observed effect of an in-plane electric current through a Si quantum well... more We analyse the recently observed effect of an in-plane electric current through a Si quantum well on the conduction electron spin resonance. We find that the ratio of resonance shift and current density is independent of temperature and dissipation processes, but the channel current is reduced due to a parallel electric channel in heavily modulation doped samples. The inhomogeneous current distribution results in some broadening of the ESR line width. In high mobility Si/SiGe layers the current induced increase in the electron temperature is considerably larger than the increase in the lattice temperature. The signal amplitude scales with the square of electron mobility.
Physica E: Low-dimensional Systems and Nanostructures
ABSTRACT
Applied Physics Letters, 2014
We demonstrate charge tuning in strain free GaAs/AlGaAs quantum dots (QDs) grown by droplet epita... more We demonstrate charge tuning in strain free GaAs/AlGaAs quantum dots (QDs) grown by droplet epitaxy on a GaAs(111)A substrate. Application of a bias voltage allows the controlled charging of the QDs from −3|e| to +2|e|. The resulting changes in QD emission energy and exciton fine-structure are recorded in micro-photoluminescence experiments at T = 4 K. We uncover the existence of excited valence and conduction states, in addition to the s-shell-like ground state. We record a second series of emission lines about 25 meV above the charged exciton emission coming from excited charged excitons. For these excited interband transitions a negative diamagnetic shift of large amplitude is uncovered in longitudinal magnetic fields.
Scientific reports, Jan 17, 2016
Rapid development of spin noise spectroscopy of the last decade has led to a number of remarkable... more Rapid development of spin noise spectroscopy of the last decade has led to a number of remarkable achievements in the fields of both magnetic resonance and optical spectroscopy. In this report, we demonstrate a new - magnetometric - potential of the spin noise spectroscopy and use it to study magnetic fields acting upon electron spin-system of an n-GaAs layer in a high-Q microcavity probed by elliptically polarized light. Along with the external magnetic field, applied to the sample, the spin noise spectrum revealed the Overhauser field created by optically oriented nuclei and an additional, previously unobserved, field arising in the presence of circularly polarized light. This "optical field" is directed along the light propagation axis, with its sign determined by sign of the light helicity. We show that this field results from the optical Stark effect in the field of the elliptically polarized light. This conclusion is supported by theoretical estimates.