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AuthorSchwingenschlögl, Udo (65)Manchon, Aurelien (57)Zhang, Xixiang (18)Thoroddsen, Sigurdur T (17)Cheng, Yingchun (14)View MoreDepartmentPhysical Sciences and Engineering (PSE) Division (194)Materials Science and Engineering Program (145)Computational Physics and Materials Science (CPMS) (40)Computer, Electrical and Mathematical Sciences and Engineering (CEMSE) Division (36)Mechanical Engineering Program (29)View MoreJournalPhysical Review B (128)Physical Review Letters (35)Physical Review E (24)Physical Review A (14)Physical Review Applied (8)View MoreKAUST Acknowledged Support UnitOffice of Sponsored Research (OSR) (5)Cray XC40 (1)KAUST Office of Sponsored Research (1)KAUST Supercomputing Centre (1)Kaust supercomputing laboratory (1)View MoreKAUST Grant NumberOSR-2015-CRG4-2626 (3)OSR-CRG URF/1/1693-01 (3)CRG-2953 (2)FCC/1/1975 (2)Grant No. OSR-2015-CRG4-2626 (2)View MorePublisher

American Physical Society (APS) (224)

SubjectAnalytical predictions (1)Anomalous Hall effect (1)Atomic and molecular physics (1)Atomic physics (1)Bottom electrodes (1)View MoreTypeArticle (224)Year (Issue Date)2019 (22)2018 (22)2017 (24)2016 (32)2015 (18)View MoreItem Availability
Open Access (224)

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Rashba effect and enriched spin-valley coupling in
GaX
/
MX2
(
M
= Mo, W;
X
= S, Se, Te) heterostructures

Zhang, Qingyun; Schwingenschlögl, Udo (Physical Review B, American Physical Society (APS), 2018-04-16) [Article]

Using first-principles calculations, we investigate the electronic properties of the two-dimensional GaX/MX2 (M = Mo, W; X = S, Se, Te) heterostructures. Orbital hybridization between GaX and MX2 is found to result in Rashba splitting at the valence-band edge around the Γ point, which grows for increasing strength of the spin-orbit coupling in the p orbitals of the chalcogenide atoms. The location of the valence-band maximum in the Brillouin zone can be tuned by strain and application of an out-of-plane electric field. The coexistence of Rashba splitting (in-plane spin direction) and band splitting at the K and K′ valleys (out-of-plane spin direction) makes GaX/MX2 heterostructures interesting for spintronics and valleytronics. They are promising candidates for two-dimensional spin-field-effect transistors and spin-valley Hall effect devices. Our findings shed light on the spin-valley coupling in van der Waals heterostructures.

Pore-scale simulation of fluid flow and solute dispersion in three-dimensional porous media

Icardi, Matteo; Boccardo, Gianluca; Marchisio, Daniele L.; Tosco, Tiziana; Sethi, Rajandrea (Physical Review E, American Physical Society (APS), 2014-07-31) [Article]

In the present work fluid flow and solute transport through porous media are described by solving the governing equations at the pore scale with finite-volume discretization. Instead of solving the simplified Stokes equation (very often employed in this context) the full Navier-Stokes equation is used here. The realistic three-dimensional porous medium is created in this work by packing together, with standard ballistic physics, irregular and polydisperse objects. Emphasis is placed on numerical issues related to mesh generation and spatial discretization, which play an important role in determining the final accuracy of the finite-volume scheme and are often overlooked. The simulations performed are then analyzed in terms of velocity distributions and dispersion rates in a wider range of operating conditions, when compared with other works carried out by solving the Stokes equation. Results show that dispersion within the analyzed porous medium is adequately described by classical power laws obtained by analytic homogenization. Eventually the validity of Fickian diffusion to treat dispersion in porous media is also assessed. © 2014 American Physical Society.

Simple models of the hydrofracture process

Marder, M.; Chen, Chih-Hung; Patzek, Tadeusz (Physical Review E, American Physical Society (APS), 2015-12-29) [Article]

Hydrofracturing to recover natural gas and oil relies on the creation of a fracture network with pressurized water. We analyze the creation of the network in two ways. First, we assemble a collection of analytical estimates for pressure-driven crack motion in simple geometries, including crack speed as a function of length, energy dissipated by fluid viscosity and used to break rock, and the conditions under which a second crack will initiate while a first is running. We develop a pseudo-three-dimensional numerical model that couples fluid motion with solid mechanics and can generate branching crack structures not specified in advance. One of our main conclusions is that the typical spacing between fractures must be on the order of a meter, and this conclusion arises in two separate ways. First, it arises from analysis of gas production rates, given the diffusion constants for gas in the rock. Second, it arises from the number of fractures that should be generated given the scale of the affected region and the amounts of water pumped into the rock.

Hyperfine interaction in the Autler-Townes effect: The formation of bright, dark, and chameleon states

Kirova, T.; Cinins, A.; Efimov, D. K.; Bruvelis, M.; Miculis, K.; Bezuglov, N. N.; Auzinsh, M.; Ryabtsev, I. I.; Ekers, Aigars (Physical Review A, American Physical Society (APS), 2017-10-26) [Article]

This paper is devoted to clarifying the implications of hyperfine (HF) interaction in the formation of adiabatic (i.e.,

Collective excitations in liquid and glassy 3-methylpentane

Benassi, Paola; Nardone, Michele; Giugni, Andrea; Baldi, Giacomo; Fontana, Aldo (Physical Review B, American Physical Society (APS), 2015-09-28) [Article]

We present a detailed investigation of the terahertz vibrational dynamics of 3-methylpentane performed by means of high-resolution inelastic x-ray scattering (IXS). We probe the dynamics in a large temperature range, which includes the glass, the supercooled liquid, and the liquid phases. The characteristic frequency of the excitations follows a well-defined dispersion curve extending beyond 8nm−1 at all the investigated temperatures, indicating the persistence of a solidlike behavior also in the liquid phase. This implies the existence of a pseudo-Brillouin zone whose size compares surprisingly well with the periodicity inferred from the first sharp diffraction peak in the static structure factor. We show that, in the investigated temperature range, both sizes undergo a variation of about 15%–20%, comparable to that of the average intermolecular distance. We finally show that the IXS sound velocity coincides with the infinite frequency sound velocity previously inferred from visible and ultraviolet Brillouin spectroscopy data. This analysis confirms the role of the shear relaxation processes in determining the variation with frequency of the apparent sound velocity.

Nonlinear effects in optical pumping of a cold and slow atomic beam

Porfido, N.; Bezuglov, N. N.; Bruvelis, M.; Shayeganrad, G.; Birindelli, S.; Tantussi, F.; Guerri, I.; Viteau, M.; Fioretti, A.; Ciampini, D.; Allegrini, M.; Comparat, D.; Arimondo, E.; Ekers, Aigars; Fuso, F. (Physical Review A, American Physical Society (APS), 2015-10-12) [Article]

By photoionizing hyperfine (HF) levels of the Cs state 62P3/2 in a slow and cold atom beam, we find how their population depends on the excitation laser power. The long time (around 180μs) spent by the slow atoms inside the resonant laser beam is large enough to enable exploration of a unique atom-light interaction regime heavily affected by time-dependent optical pumping. We demonstrate that, under such conditions, the onset of nonlinear effects in the population dynamics and optical pumping occurs at excitation laser intensities much smaller than the conventional respective saturation values. The evolution of population within the HF structure is calculated by numerical integration of the multilevel optical Bloch equations. The agreement between numerical results and experiment outcomes is excellent. All main features in the experimental findings are explained by the occurrence of “dark” and “bright” resonances leading to power-dependent branching coefficients.

Spin-orbit torque in a three-dimensional topological insulator–ferromagnet heterostructure: Crossover between bulk and surface transport

Ghosh, Sumit; Manchon, Aurelien (Physical Review B, American Physical Society (APS), 2018-04-02) [Article]

Current-driven spin-orbit torques are investigated in a heterostructure composed of a ferromagnet deposited on top of a three-dimensional topological insulator using the linear response formalism. We develop a tight-binding model of the heterostructure adopting a minimal interfacial hybridization scheme that promotes induced magnetic exchange on the topological surface states, as well as induced Rashba-like spin-orbit coupling in the ferromagnet. Therefore our model accounts for the spin Hall effect from bulk states together with inverse spin galvanic and magnetoelectric effects at the interface on equal footing. By varying the transport energy across the band structure, we uncover a crossover from surface-dominated to bulk-dominated transport regimes. We show that the spin density profile and the nature of the spin-orbit torques differ substantially in both regimes. Our results, which compare favorably with experimental observations, demonstrate that the large dampinglike torque reported recently is more likely attributed to the Berry curvature of interfacial states, while spin Hall torque remains small even in the bulk-dominated regime.

Acoustic Purcell Effect for Enhanced Emission

Landi, Maryam; Zhao, Jiajun; Prather, Wayne E.; Wu, Ying; Zhang, Likun (Physical Review Letters, American Physical Society (APS), 2018-03-13) [Article]

We observe that our experimentally measured emission power enhancement of a speaker inside a previously proposed metacavity agrees with our numerically calculated enhancement of the density of states (DOS) of the source-cavity system. We interpret the agreement by formulating a relation between the emitted sound power and the acoustic DOS. The formulation is an analog to Fermi’s golden rule in quantum emission. The formulation complements the radiation impedance theory in traditional acoustics for describing sound emission. Our study bridges the gap between acoustic DOS and the acoustic Purcell effect for sound emission enhancement.

Hydromagnetic thin film flow: Linear stability

Amaouche, Mustapha; Ait Abderrahmane, Hamid; Bourdache, Lamia (Physical Review E, American Physical Society (APS), 2013-08-30) [Article]

This paper deals with the long wave instability of an electroconductor fluid film, flowing down an inclined plane at small to moderate Reynolds numbers, under the action of electromagnetic fields. A coherent second order long wave model and two simplified versions of it, referred to as first and second reduced models (FRM and SRM), are proposed to describe the nonlinear behavior of the flow. The modeling procedure consists of a combination of the lubrication theory and the weighted residual approach using an appropriate projection basis. A suitable choice of weighting functions allows a significant reduction of the dimension of the problem. The full model is naturally unique, i.e., independent of the particular form of the trial functions. The linear stability of the problem is investigated, and the influence of electromagnetic field on the flow stability is analyzed. Two cases are considered: the applied magnetic field is either normal or parallel to the fluid flow direction, while the electric field is transversal. The numerical solution of the Orr-Sommerfeld (OS) eigenvalue problem and those of the depth averaging model are used to assess the accuracy of the reduced models. It is found that the current models have the advantage of the Benney-like model, which is known to asymptote the exact solution near criticality. Moreover, far from the instability threshold, the current reduced models continue to follow the OS solution up to moderate Reynolds numbers, while the averaging model diverges rapidly. The model SRM gives better results than FRM beyond sufficiently high Reynolds numbers.

Rotating solitary wave at the wall of a cylindrical container

Amaouche, Mustapha; Ait Abderrahmane, Hamid; Vatistas, Georgios H. (Physical Review E, American Physical Society (APS), 2013-04-30) [Article]

This paper deals with the theoretical modeling of a rotating solitary surface wave that was observed during water drainage from a cylindrical reservoir, when shallow water conditions were reached. It represents an improvement of our previous study, where the radial flow perturbation was neglected. This assumption led to the classical planar Korteweg–de Vries equation for the wall wave profile, which did not account for the rotational character of the base flow. The present formulation is based on a less restricting condition and consequently corrects the last shortcoming. Now the influence of the background flow appears in the wave characteristics. The theory provides a better physical depiction of the unique experiment by predicting fairly well the wave profile at least in the first half of its lifetime and estimating the speed of the observed wave with good accuracy.

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