Physics - Journal Articles
http://hdl.handle.net/10468/225
Mon, 16 Sep 2019 10:27:45 GMT2019-09-16T10:27:45ZExcitable interplay between lasing quantum dot states
http://hdl.handle.net/10468/8520
Excitable interplay between lasing quantum dot states
Dillane, Michael; Dubinkin, I.; Fedorov, N.; Erneux, T.; Goulding, D.; Kelleher, Bryan; Viktorov, E. A.
The optically injected semiconductor laser system has proven to be an excellent source of experimental nonlinear dynamics, particularly regarding the generation of excitable pulses. Typically for low-injection strengths, these pulses are the result of a small above-threshold perturbation of a stable steady state, the underlying physics is well described by the Adler phase equation, and each laser intensity pulse is accompanied by a 2π phase rotation. In this article, we show how, with a dual-state quantum dot laser, a variation of type I excitability is possible that cannot be described by the Adler model. The laser is operated so that emission is from the excited state only. The ground state can be activated and phase locked to the master laser via optical injection while the excited state is completely suppressed. Close to the phase-locking boundary, a region of ground-state emission dropouts correlated to excited-state pulses can be observed. We show that the phase of the ground state undergoes bounded rotations due to interactions with the excited state. We analyze the system both experimentally and numerically and find excellent agreement. Particular attention is devoted to the bifurcation conditions needed for an excitable pulse as well as its time evolution.
Wed, 17 Jul 2019 00:00:00 GMThttp://hdl.handle.net/10468/85202019-07-17T00:00:00ZBroadband semiconductor light sources operating at 1060 nm based on InAs:Sb/GaAs submonolayer quantum dots
http://hdl.handle.net/10468/8393
Broadband semiconductor light sources operating at 1060 nm based on InAs:Sb/GaAs submonolayer quantum dots
Herzog, B.; Lingnau, Benjamin; Kolarczik, M.; Helmrich, S.; Achtstein, A. W.; Thommes, K.; Alhussein, F.; Quandt, D.; Strittmatter, A.; Pohl, U. W.; Brox, O.; Weyers, M.; Woggon, U.; Lüdge, Kathy; Owschimikow, N.
In this paper, we investigate the potential of submonolayer-grown InAs:Sb/GaAs quantum dots as active medium for opto-electronic devices emitting in the 1060 nm spectral range. Grown as multiple sheets of InAs in a GaAs matrix, submonolayer quantum dots yield light-emitting devices with large material gain and fast recovery dynamics. Alloying these structures with antimony enhances the carrier localization and red shifts the emission, whereas dramatically broadening the optical bandwidth. In a combined experimental and numerical study, we trace this effect to an Sb-induced bimodal distribution of localized and delocalized exciton states. While the former do not participate in the lasing process, they give rise to a bandwidth broadening at superluminescence operation and optical amplification. Above threshold laser properties like gain and slope efficiency are mainly determined by the delocalized fraction of carriers.
Wed, 29 May 2019 00:00:00 GMThttp://hdl.handle.net/10468/83932019-05-29T00:00:00ZTemperature effects on the electronic band structure of PbTe from first principles
http://hdl.handle.net/10468/8508
Temperature effects on the electronic band structure of PbTe from first principles
Querales-Flores, José D.; Cao, Jiang; Fahy, Stephen B.; Savić, Ivana
We report a fully ab initio calculation of the temperature dependence of the electronic band structure of PbTe. We address two main features relevant for the thermoelectric figure of merit: the temperature variations of the direct gap and the difference in energies of the two topmost valence band maxima located at L and Σ. We account for the energy shift of the electronic states due to thermal expansion, as well as electron-phonon interaction computed using the nonadiabatic Allen-Heine-Cardona formalism within density functional perturbation theory and the local density approximation. We capture the increase of the direct gap with temperature in very good agreement with experiment. We also predict that the valence band maxima at L and Σ become aligned at ∼600–700K. We find that both thermal expansion and electron-phonon interaction have a considerable effect on these temperature variations. The Fan-Migdal and Debye-Waller terms are of almost equal magnitude but have an opposite sign, and the delicate balance of these terms gives the correct band shifts. The electron-phonon induced renormalization of the direct gap is produced mostly by high-frequency optical phonons, while acoustic phonons are also responsible for the alignment of the valence band maxima at L and Σ.
Thu, 23 May 2019 00:00:00 GMThttp://hdl.handle.net/10468/85082019-05-23T00:00:00ZS-matrix pole symmetries for non-Hermitian scattering Hamiltonians
http://hdl.handle.net/10468/8371
S-matrix pole symmetries for non-Hermitian scattering Hamiltonians
Simon, M. A.; Buendia, A.; Kiely, Anthony; Mostafazadeh, Ali; Muga, J. G.
The complex eigenvalues of some non-Hermitian Hamiltonians, e.g., parity-time-symmetric Hamiltonians, come in complex-conjugate pairs. We show that for non-Hermitian scattering Hamiltonians (of a structureless particle in one dimension) possessing one of four certain symmetries, the poles of the S-matrix eigenvalues in the complex momentum plane are symmetric about the imaginary axis, i.e., they are complex-conjugate pairs on the complex-energy plane. This applies even to states which are not bounded eigenstates of the system, i.e., antibound or virtual states, resonances, and antiresonances. The four Hamiltonian symmetries are formulated as the commutation of the Hamiltonian with specific antilinear operators. Example potentials with such symmetries are constructed and their pole structures and scattering properties are calculated.
Mon, 13 May 2019 00:00:00 GMThttp://hdl.handle.net/10468/83712019-05-13T00:00:00Z