ORCID Profile
0000-0002-2207-118X
Current Organisation
Australian National University
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Publisher: The Optical Society
Date: 29-09-2017
DOI: 10.1364/OE.25.024816
Publisher: AIP Publishing
Date: 29-05-2017
DOI: 10.1063/1.4984747
Abstract: The lateral carrier diffusion process is investigated in coupled InGaAs/GaAs quantum dot-quantum well (QD-QW) structures by means of spatially resolved photoluminescence spectroscopy at low temperature. Under non-resonant photo-excitation above the GaAs bandgap, the lateral carrier transport reflected in the distorted electron-hole pair emission profiles is found to be mainly governed by high energy carriers created within the 3D density of states of GaAs. In contrast, for the case of resonant excitation tuned to the QW-like ground state of the QD-QW system, the emission profiles remain unaffected by the excess kinetic energy of carriers and local phonon heating within the pump spot. The lateral diffusion lengths are determined and present certain dependency on the coupling strength between QW and QDs. While for a strongly coupled structure the diffusion length is found to be around 0.8 μm and monotonically increases up to 1.4 μm with the excitation power density, in weakly coupled structures, it is determined to ca. 1.6 μm and remained virtually independent of the pumping power density.
Publisher: IEEE
Date: 10-2012
Publisher: American Physical Society (APS)
Date: 05-08-2019
Publisher: Springer Science and Business Media LLC
Date: 06-05-2022
Publisher: American Physical Society (APS)
Date: 12-04-2018
Publisher: Institute of Physics, Polish Academy of Sciences
Date: 11-2013
Publisher: Springer Science and Business Media LLC
Date: 10-09-2021
DOI: 10.1038/S41467-021-25656-7
Abstract: Monolayer transition metal dichalcogenide crystals (TMDCs) hold great promise for semiconductor optoelectronics because their bound electron-hole pairs (excitons) are stable at room temperature and interact strongly with light. When TMDCs are embedded in an optical microcavity, excitons can hybridise with cavity photons to form exciton polaritons, which inherit useful properties from their constituents. The ability to manipulate and trap polaritons on a microchip is critical for applications. Here, we create a non-trivial potential landscape for polaritons in monolayer WS 2 , and demonstrate their trapping and ballistic propagation across tens of micrometers. We show that the effects of dielectric disorder, which restrict the diffusion of WS 2 excitons and broaden their spectral resonance, are dramatically reduced for polaritons, leading to motional narrowing and preserved partial coherence. Linewidth narrowing and coherence are further enhanced in the trap. Our results demonstrate the possibility of long-range dissipationless transport and efficient trapping of TMDC polaritons in ambient conditions.
Publisher: AIP Publishing
Date: 08-2020
DOI: 10.1063/5.0010633
Publisher: Elsevier BV
Date: 05-2016
Publisher: AIP Publishing
Date: 16-01-2012
DOI: 10.1063/1.3678031
Abstract: We demonstrate room temperature, continuous wave lasing of laser diodes based on AlGaAs whispering gallery mode (WGM) resonators (microcylinder and microring) embedding a quantum dot (QD) active layer. Using InGaAlAs QDs, high-Q (& 000) lasing modes are observed around 910 nm, up to 50 °C. Lasing with similar performance is obtained around 1230 nm, using InAs QDs. Furthermore, we show that the current injection in the active part of the device is improved in ring resonators, leading to threshold currents of approximately 4 mA for a device with 80 μm diameter. This geometry also suppresses WGMs with a high radial order, thus simplifying the lasing spectra. In these conditions, stable single-mode and two-color lasing can be obtained.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 05-11-2021
Abstract: A non-Hermitian topological invariant arising from exceptional points is directly probed in an exciton-polariton system.
Publisher: Springer Science and Business Media LLC
Date: 22-01-2020
DOI: 10.1038/S41467-019-14243-6
Abstract: Superfluidity, first discovered in liquid 4 He, is closely related to Bose–Einstein condensation (BEC) phenomenon. However, even at zero temperature, a fraction of the quantum liquid is excited out of the condensate into higher momentum states via interaction-induced fluctuations—the phenomenon of quantum depletion. Quantum depletion of atomic BECs in thermal equilibrium is well understood theoretically but is difficult to measure. This measurement is even more challenging in driven-dissipative exciton–polariton condensates, since their non-equilibrium nature is predicted to suppress quantum depletion. Here, we observe quantum depletion of a high-density exciton–polariton condensate by detecting the spectral branch of elementary excitations populated by this process. Analysis of this excitation branch shows that quantum depletion of exciton–polariton condensates can closely follow or strongly deviate from the equilibrium Bogoliubov theory, depending on the exciton fraction in an exciton polariton. Our results reveal beyond mean-field effects of exciton–polariton interactions and call for a deeper understanding of the relationship between equilibrium and non-equilibrium BECs.
Publisher: American Physical Society (APS)
Date: 28-10-2021
Publisher: American Physical Society (APS)
Date: 29-06-2022
Publisher: National Library of Serbia
Date: 2012
Abstract: The single agent extractions of major and trace metals from soil s le were conducted by means of rotary mixer and ultrasonic bath with sonication time of 10, 20, 30, 40 and 50 min. The sequential extraction according to the BCR scheme was undertaken. The obtained soil extracts were analyzed by ICP-OES and according to the results the rotary mixer assisted extraction was more efficient in the case of alkaline-earth elements. However, by the use of ultrasound several times higher amounts of matrix elements (Fe, Al and Mn) and heavy metals predominantly associated with Fe, Al and Mn oxyhydroxides were extracted. The increase of the sonication time failed to improve extraction yields. The changes of the conductivity, pH, oxidoreduction potential, particle size diameter and zeta potential of colloid particles, with the sonication time increase were measured. The extraction mechanism and expressed selectivity of ultrasound is discussed and explanation is suggested.
Publisher: Institute of Physics, Polish Academy of Sciences
Date: 08-2017
Publisher: Optica Publishing Group
Date: 11-08-2021
Abstract: Topological insulators are a class of electronic materials exhibiting robust edge states immune to perturbations and disorder. This concept has been successfully adapted in photonics, where topologically nontrivial waveguides and topological lasers were developed. However, the exploration of topological properties in a given photonic system is limited to a fabricated s le, without the flexibility to reconfigure the structure in situ . Here, we demonstrate an all-optical realization of the orbital Su–Schrieffer–Heeger model in a microcavity exciton-polariton system, whereby a cavity photon is hybridized with an exciton in a GaAs quantum well. We induce a zigzag potential for exciton polaritons all-optically by shaping the nonresonant laser excitation, and measure directly the eigenspectrum and topological edge states of a polariton lattice in a nonlinear regime of bosonic condensation. Furthermore, taking advantage of the tunability of the optically induced lattice, we modify the intersite tunneling to realize a topological phase transition to a trivial state. Our results open the way to study topological phase transitions on-demand in fully reconfigurable hybrid photonic systems that do not require sophisticated s le engineering.
Publisher: Springer Science and Business Media LLC
Date: 02-08-2017
DOI: 10.1038/S41598-017-07470-8
Abstract: Semiconductor microcavities are often influenced by structural imperfections, which can disturb the flow and dynamics of exciton-polariton condensates. Additionally, in exciton-polariton condensates there is a variety of dynamical scenarios and instabilities, owing to the properties of the incoherent excitonic reservoir. We investigate the dynamics of an exciton-polariton condensate which emerges in semiconductor microcavity subject to disorder, which determines its spatial and temporal behaviour. Our experimental data revealed complex burst-like time evolution under non-resonant optical pulsed excitation. The temporal patterns of the condensate emission result from the intrinsic disorder and are driven by properties of the excitonic reservoir, which decay in time much slower with respect to the polariton condensate lifetime. This feature entails a relaxation oscillation in polariton condensate formation, resulting in ultrafast emission pulses of coherent polariton field. The experimental data can be well reproduced by numerical simulations, where the condensate is coupled to the excitonic reservoir described by a set of rate equations. Theory suggests the existence of slow reservoir temporarily emptied by stimulated scattering to the condensate, generating ultrashort pulses of the condensate emission.
Publisher: IOP Publishing
Date: 10-2017
Publisher: Optica Publishing Group
Date: 03-05-2022
DOI: 10.1364/OE.452918
Abstract: Optical trapping has been proven to be an effective method of separating exciton-polariton condensates from the incoherent high-energy excitonic reservoir located at the pumping laser position. This technique has significantly improved the coherent properties of exciton-polariton condensates, when compared to a quasi-homogeneous spot excitation scheme. Here, we compare two experimental methods on a s le, where a single spot excitation experiment allowed us only to observe photonic lasing in the weak coupling regime. In contrast, the ring-shaped excitation resulted in the two-threshold behavior, where an exciton-polariton condensate manifests itself at the first and photon lasing at the second threshold. Both lasing regimes are trapped in an optical potential created by the pump. We interpret the origin of this confining potential in terms of repulsive interactions of polaritons with the reservoir at the first threshold and as a result of the excessive free-carrier induced refractive index change of the microcavity at the second threshold. This observation offers a way to achieve multiple phases of photonic condensates in s les, e.g., containing novel materials as an active layer, where two-threshold behavior is impossible to achieve with a single excitation spot.
Publisher: American Physical Society (APS)
Date: 26-11-2018
Publisher: Research Square Platform LLC
Date: 07-10-2020
DOI: 10.21203/RS.3.RS-85675/V1
Abstract: In monolayer WSe 2 , interactions between the lower-energy momentum- and spin-indirect “dark” excitons and the bright exciton (X) are likely to be significant in determining the optical properties of X at high power, and limit the ultimate exciton densities that can be achieved, yet little is known about them. Here, by employing time-resolved photoluminescence measurements, we demonstrate an efficient population of dark excitons via inter-state conversion between X and the spin-indirect intravalley excitons (D) through spin-flip, and between D and the momentum-indirect intervalley excitons (X K ) mediated by the exchange interaction (D+D ←→ X K +X K ). Moreover, we observe a persistent redshift of the X exciton on sub-ns timescales due to strong excitonic screening by the long-lived dense X K exciton. Our results provide a new insight into the many-body interactions between bright and dark excitons, and point to a possibility to employ dark excitons for investigating exciton condensation and valleytronics.
Publisher: Institute of Physics, Polish Academy of Sciences
Date: 11-2013
Publisher: Elsevier BV
Date: 08-2016
Publisher: Institute of Physics, Polish Academy of Sciences
Date: 2016
Publisher: American Physical Society (APS)
Date: 26-10-2015
Publisher: AIP Publishing
Date: 27-09-2021
DOI: 10.1063/5.0058267
Abstract: We investigate the effects of direct deposition of different dielectric materials (AlOx, SiOx, SiNx) onto atomically thin TMDC WS2 on its optical response using atomic layer deposition (ALD), electron beam evaporation (EBE), plasma-enhanced chemical vapor deposition (PECVD), and magnetron sputtering. The photoluminescence measurements reveal quenching of the excitonic emission after all deposition processes, which is linked to the increased level of charge doping and associated rise of the trion emission and/or the localized (bound) exciton emission. Furthermore, Raman spectroscopy allows us to clearly correlate the observed changes in excitonic emission with the increased levels of lattice disorder and defects. In particular, we show that the different doping levels in a monolayer WS2 capped by a dielectric material are strongly related to the defects in the WS2 crystal introduced by all capping methods, except for ALD. The strong charge doping in the ALD-capped s le seems to be caused by other factors, such as deviations in the dielectric layer stoichiometry or chemical reactions on the monolayer surface, which makes ALD distinct from all other techniques. Overall, the EBE process results in the lowest level of doping and defect densities and in the largest spectral weight of the exciton emission in the PL. Sputtering is revealed as the most aggressive dielectric capping method for WS2, fully quenching its optical response. Our results demonstrate and quantify the effects of direct deposition of dielectric materials onto monolayer WS2, which can provide valuable guidance for the efforts to integrate monolayer TMDCs into functional optoelectronic devices.
Publisher: American Physical Society (APS)
Date: 15-02-2021
Start Date: 2013
End Date: 2015
Funder: Ministry of Science and Higher Education
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