Harmonic Extraction in Graphene: Monte Carlo Analysis of the Substrate Influence

Graphene on different substrates, such as SiO2, h-BN and Al2O3, has been subjected to oscillatory electric fields to analyse the response of the carriers in order to explore the generation of terahertz radiation by means of high-order harmonic extraction. The properties of the ensemble Monte Carlo simulator employed for such study have allowed us to evaluate the high-order harmonic intensity and the spectral density of velocity fluctuations under different amplitudes of the periodic electric field, proving that strong field conditions are preferable for the established goal. Furthermore, by comparison of both harmonic intensity and noise level, the threshold bandwidth for harmonic extraction has been determined. The results have shown that graphene on h-BN presents the best featuring of the cases under analysis and that in comparison to III–V semiconductors, it is a very good option for high-order harmonic extraction under AC electric fields with large amplitudes.

Wigner ensemble Monte Carlo simulation without splitting error of a GaAs resonant tunneling diode

A Monte Carlo technique for the solution of the Wigner transport equation has been developed, based on the generation and annihilation of signed particles (Nedjalkov et al. in Phys Rev B 70:115319, 2004). A stochastic algorithm without time discretization error has been recently introduced (Muscato and Wagner in Kinet Relat Models 12(1):59–77, 2019). Its derivation is based on the theory of piecewise deterministic Markov processes. Numerical experiments are performed in the case of a GaAs resonant tunneling diode. Convergence of the time-splitting scheme to the no-splitting algorithm is demonstrated. The no-splitting algorithm is shown to be more efficient in terms of computational effort.

Wigner Ensemble Monte Carlo Simulation Without Discretization Error of a GaAs Resonant Tunneling Diode

A Monte Carlo technique for the solution of the Wigner transport equation has been developed during these years, based on the generation and annihilation of signed particles. A stochastic algorithm without time discretization error has been recently introduced. Its derivation is based on the theory of piecewise deterministic Markov processes.Numerical experiments are performed in the case of a GaAs Resonant Tunneling Diode. Convergence of the time-splitting scheme to the no-splitting algorithm is demonstrated. The no-splitting algorithm is shown to be more efficient in terms of computational effort.

On the feasibility of hearing electrons in a 1D device through emitted phonons

This work investigates the vibrational power that may potentially be delivered by electron-emitted phonons at the terminals of a device with a 1D material as the active channel. Electrons in a 1D material traversing a device excite phase-limited acoustic and optical phonon modes as they undergo streaming motion. At ultra-low temperature (4 K in this study, for example), in the near absence of background phonon activity, the emitted traveling phonons may potentially be collected at the terminals before they decay. Detecting those phonons is akin to hearing electrons within the device. Results here show that traveling acoustic phonons can deliver up to a fraction of a nW of vibrational power at the terminals, which is within the sensitivity range of modern instruments. The total vibrational power from traveling optical and acoustic phonons is found to be in order of nW. In this work, Ensemble Monte Carlo (EMC) simulations are used to model the behavior of a gate-all-around (GAA) field-effect transistor (FET), with a single-wall semiconducting carbon nanotube (SWCNT) as the active channel, and a free-hanging SWCNT between two contacts. Electronic band structure of the SWCNT is calculated within the framework of a tight-binding (TB) model. The principal scattering mechanisms are due to electron–phonon interactions using 1st order perturbation theory. A continuum model is used to determine the longitudinal acoustic (LA) and optical (LO) phonons, and a single lowest radial breathing mode (RBM) phonon is considered.

Gibbs-ensemble Monte Carlo simulations for binary mixtures

<p>We explore the performance of the Gibbs-ensemble Monte Carlo simulation method by calculating the miscibility gap of H<sub>2</sub>-He mixtures with analytical exponential-six potentials [1]. We calculate demixing curves for pressures up to <em>500</em> kbar and temperatures up to <em>1800</em> K. Our results are in good agreement with <em>ab initio </em>simulations in the non-dissociated region of the phase diagram. Next, we determine new parameters for the Stockmayer potential [2] to model the interactions in the H<sub>2</sub>O-H<sub>2</sub>O system for temperatures of <em>1000</em> K < <em>T</em> < <em>2000</em> K. The corresponding miscibility gap of H<sub>2</sub>-H<sub>2</sub>O mixtures was determined and we calculated demixing curves for pressures up to <em>150</em> kbar and temperatures up to <em>2000</em> K. Our results show reasonable agreement with previous experimental data of Bali <em>et al.</em> [3]. These results are important for interior and evolution models for ice giant planets [4].<br><br><strong>References</strong><br>[1] A. Bergermann, M. French, M. Schöttler and R. Redmer, Phys. Rev. E, 103 (2021)<br>[2] W. Stockmayer, The Journal of Chemical Physics 9, S. 398-402 (1941)<br>[3] E. Bali, A. Audétat and H. Keppler, Nature, 495, 7440 (2013)<br>[4] R. Helled, N. Nettelmann and T. Guillot, Space Science Reviews, 216 (2020)<br><br><br><br><br></p>

Ensemble Monte Carlo Simulation of Hole Transport in SiGe Alloys

This paper employs Ensemble Monte Carlo method to simulate transport of holes in SiGe alloys. A three-band model was employed to describe the valence band of these alloys. The nonparabolicity and the warping effect of the heavy-hole and light-hole bands were considered in their dispersion relation, while the split-off band was described as parabolic and spherical. We consider phonon and alloy disorder scattering in these calculations. The mobility of holes for a range of SiGe al-loys was calculated at 300K. The simulation mobility results agree with the experimental data, implying that the selected transport model for holes in SiGe alloys is adequate.

Voltage-driven mutual phase locking of planar nano-oscillators

Phase locking is a common phenomenon related to coupled oscillators that play an important role in various natural and artificial systems. In this study, we analyzed the possibility of dynamically controlling such a phenomenon between Gunn-effect-based planar nanooscillators via an ensemble Monte Carlo (EMC) method. We found that between two oscillators in parallel with each other, there are two coupling paths, which could be opened or closed via structure determined inner-field effect. One of the paths results in in-phase locking, and whereas the other gives rise to anti-phase locking. Furthermore, by combining the inner-field effect and a top-gate effect, one could dynamically control the phase locking via the top gate’s bias. EMC results showed that the transition time from in-phase to anti-phase locking can be less than 0.2 ns. Accompanied by this was a signal-frequency doubling, from approximately 0.33 THz to approximately 0.66 THz. Based on Adler’s theory, we confirmed the phase locking and concluded that the phase-locking transition could not be properly modeled unless electron-scattering noise was included. Moreover, we obtained the locking range and the frequency fluctuation due to electron-transport noise. The proposed method is convenient and may be applied to other electronic oscillators, thereby aiding in developing high-speed beam-steerable THz sources.