No abstract

No abstract

Intersubband (ISB) plasmons in remotely doped wide quantum wells acquire a linewidth even at zero temperature and in-plane wave vector q k 0 by a combination of intrinsic (electron-electron interaction) and extrinsic effects (impurities and interface roughness). We present a quantitatively accurate theory of the linewidth that treats both effects on equal footing and from first principles by a combination of time-dependent density-functional theory with the memory function formalism. Comparison with recent optical absorption experiments shows that the ISB plasmon linewidth has a significant contribution from electron-electron interaction, and is only weakly related to the mobility. DOI: 10.1103/PhysRevLett.87.037402 PACS numbers: 78.67.De, 71.15.Mb, 71.45.Gm, 73.21.Fg In semiconductor quantum wells, the conduction band splits up into several subbands, and electrons (supplied, e.g., by remote doping) can perform collective transitions between them. These so-called intersubband (ISB) plasmons are currently of great experimental and theoretical interest [1], and they are the basis of a variety of new devices operating in the terahertz regime, such as detectors [2] and quantum cascade lasers [3]. In designing these devices, the emphasis usually lies in covering a particular frequency range. However, often it is desirable that the transitions also have a narrow linewidth, to achieve better frequency resolution and larger peak absorption in detectors, and higher gain in lasers. The linewidth arises from a complicated interplay of a variety of scattering mechanisms, intrinsic (electron-electron and electron-phonon) as well as extrinsic ones (impurity, alloy disorder, and interface roughness). Many aspects of this interplay are still not well understood, in particular the relative importance of the individual mechanisms [4].To disentangle the various contributions to the ISB linewidth, it is helpful to consider a situation where some of them are not effective. In a recent experiment, Williams et al.[5] studied collective ISB transitions in an n-type 40-nm-wide single GaAs͞Al 0.3 Ga 0.7 As quantum well, with Si doping centers 100 nm away from the well. Sharp transitions were found well below the LO phonon frequency of GaAs (35.6 meV), at a temperature of 2.3 K. Thus, neither remote impurity nor phonon scattering play any significant role (nor is alloy-disorder scattering, as shown in [6]). The linewidth is therefore expected to be dominated by bulk impurity and interface roughness scattering, while electronic many-body effects have traditionally been neglected. However, for high-quality samples this is no longer justified.In this Letter, we present a theory that treats both damping mechanisms on equal footing, by combining time-dependent density-functional theory [7] (which includes purely electronic damping [8-10] but neglects disorder) with the memory function formalism [11][12][13] (which describes disorder scattering, but ignores electronic damping).In the experiment [5], two parameters were controlled independen...

In this paper, the history, present status, and future of density-functional theory (DFT) is informally reviewed and discussed by 70 workers in the field, including molecular scientists, materials scientists, method...

The Bethe-Salpeter equation (BSE) is the standard computational method for optical excitations in solids, including excitonic effects. In this paper we explore ways to reduce the computational cost of the BSE by simplifying the dielectrically screened Coulomb interaction: Instead of calculating the dielectric function from first principles, we replace it by a momentum-dependent model dielectric function or just by a single parameter. Combined with a semilocal exchange-correlation kernel, this defines an alternative class of hybrid functionals for solids within generalized time-dependent density-functional theory. We perform a systematic assessment of these simplified approaches and find that they yield optical absorption spectra and exciton binding energies of semiconductors and wide-gap insulators in close agreement with the standard BSE and with experiment. We also present applications to the perovskite material CsPbBr 3 as an example of a more complex system.

No abstract

We review recent theoretical and computational developments in time-dependent density-functional theory (TDDFT) for periodic insulators and semiconductors. To capture excitonic effects within a linear-response TDDFT framework requires using exchange-correlation (xc) kernels with a proper long-range behavior, which can be efficiently modeled with a class of so-called long-range corrected xc kernels. While attractive from a computational standpoint, these xc kernels have their limitations and require judicious use. We review the pros and cons of various xc kernels in the literature, and discuss an empirical scaling approach to obtain accurate exciton binding energies with TDDFT. We also discuss generalized TDDFT approaches for excitons using hybrid functionals.

No abstract