Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userWannier interpolation of the electron-phonon matrix elements in polar semiconductors: Polar-optical coupling in GaAs
111
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We generalize the Wannier interpolation of the electron-phonon matrix elements to the case of polar-optical coupling in polar semiconductors. We verify our methodological developments against experiments, by calculating the widths of the electronic bands due to electron-phonon scattering in GaAs, the prototype polar semiconductor. The calculated widths are then used to estimate the broadenings of excitons at critical points in GaAs and the electron-phonon relaxation times of hot electrons. Our findings are in good agreement with available experimental data. Finally, we demonstrate that while the Frohlich interaction is the dominant scattering process for electrons/holes close to the valley minima, in agreement with low-field transport results, at higher energies, the intervalley scattering dominates the relaxation dynamics of hot electrons or holes. The capability of interpolating the polar-optical coupling opens new perspectives in the calculation of optical absorption and transport properties in semiconductors and thermoelectrics.
rate research
Read More
In this paper, we present a collection of results focussing on the transport properties of doped direct-gap inverted-band highly polar III-nitride semiconductors (GaN, AlN, InN) and GaAs in the transient and steady state, calculated by using nonlinear quantum kinetic theory based on a non-equilibrium statistical ensemble formalism (NESEF). In the present paper, these results are compared with calculations usingMonteCarlo modelling simulations and experimental measurements. Both n-type and p-type materials, in the presence of intermediate to high electric fields, are considered for several temperatures and carrier concentrations.The agreement between the results obtained using nonlinear quantum kinetic theory, with those ofMonte Carlo calculations and experimental data is remarkably good, thus satisfactorily validating the NESEF.
The zone-center $E_{2g}$ modes play a crucial role in MgB$_2$, controlling the scattering mechanisms in the normal state as well the superconducting pairing. Here, we demonstrate via first-principles quantum-field theory calculations that, due to the anisotropic electron-phonon interaction, a $hot$-$phonon$ regime where the $E_{2g}$ phonons can achieve significantly larger effective populations than other modes, is triggered in MgB$_2$ by the interaction with an ultra-short laser pulse. Spectral signatures of this scenario in ultrafast pump-probe Raman spectroscopy are discussed in detail, revealing also a fundamental role of nonadiabatic processes in the optical features of the $E_{2g}$ mode.
We propose a mechanism of energy relaxation for carriers confined in a non-polar quantum dot surrounded by an amorphous polar environment. The carrier transitions are due to their interaction with the oscillating electric field induced by the local vibrations in the surrounding amorphous medium. We demonstrate that this mechanism controls energy relaxation for electrons in Si nanocrystals embedded in a SiO$_2$ matrix, where conventional mechanisms of electron-phonon interaction are not efficient.
Polarized infrared reflectivity spectra of a (110)-oriented TbScO3 single crystal plate were measured down to 10 K. The number of observed polar phonons active along the crystallographic c axis at low temperatures is much higher than predicted by factor-group analysis for the orthorhombic Pbnm space group. Moreover, the lowest frequency phonons active in E||c as well as in E||[1-10] polarized spectra exhibit dramatic softening tending to a lattice instability at low temperatures. The dielectric permittivity at microwave frequencies does not show any ferroelectric-like anomaly, but the dielectric loss exhibits a maximum at 100 K. The origin of the discrepancy between the number of predicted and observed polar phonons as well as the tendency toward lattice instability are discussed. Magnetic measurements reveal an antiferromagnetic phase transition near 3 K.
We use first-principles methods to study doped strong ferroelectrics (taking BaTiO$_3$ as a prototype). Here we find a strong coupling between itinerant electrons and soft polar phonons in doped BaTiO$_3$, contrary to Anderson/Blounts weakly coupled electron mechanism for ferroelectric-like metals. As a consequence, across a polar-to-centrosymmetric phase transition in doped BaTiO$_3$, the total electron-phonon coupling is increased to about 0.6 around the critical concentration, which is sufficient to induce phonon-mediated superconductivity of about 2 K. Lowering the crystal symmetry of doped BaTiO$_3$ by imposing epitaxial strain can further increase the superconducting temperature via a sizable coupling between itinerant electrons and acoustic phonons. Our work demonstrates a viable approach to modulating electron-phonon coupling and inducing phonon-mediated superconductivity in doped strong ferroelectrics and potentially in polar metals. Our results also show that the weakly coupled electron mechanism for ferroelectric-like metals is not necessarily present in doped strong ferroelectrics.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
