Effective mass (solid-state physics)

About: Effective mass (solid-state physics) is a research topic. Over the lifetime, 12539 publications have been published within this topic receiving 295485 citations.

A theory of incoherent scattering of radio waves by a plasma: 4. The effect of unequal ion and electron temperatures

Abstract: The theory is extended to include the effects of unequal ion and electron temperatures and a magnetic field. Two approximate formulas for the total scattered power are derived, which, with certain restrictions, are applicable (1) when Te/Ti ≲ 1, (2) when Te/Ti » 1. For moderately large values of the temperature ratio, a full numerical calculation is necessary. In contrast to the equilibrium case, the total scattered power is not independent of the magnetic field when Te/Ti is not unity. In the interesting case in which the ion cyclotron radius is large compared to wavelengths of interest, but the electron cyclotron radius is small, the mass ratio me/mi is replaced by an effective ratio (me/mi) sec2 α, where α is the angle between the propagation vector k and the magnetic field. As α approaches 90°, the effective mass ratio ceases to be small, and the scattering is significantly altered. The general behavior of the scattering has a simple physical explanation. The scattering can be considered to be from acoustic waves that are in equilibrium with the particles that contribute most to their Landau damping.

Quantitative analysis of nonadiabatic effects in dense H$_3$S and PH$_3$ superconductors

Abstract: The comparison study of high pressure superconducting state of recently synthesized H$_3$S and PH$_3$ compounds are conducted within the framework of the strong-coupling theory. By generalization of the standard Eliashberg equations to include the lowest-order vertex correction, we have investigated the influence of the nonadiabatic effects on the Coulomb pseudopotential, electron effective mass, energy gap function and on the $2\Delta(0)/T_C$ ratio. We found that, for a fixed value of critical temperature ($178$ K for H$_3$S and $81$ K for PH$_3$), the nonadiabatic corrections reduce the Coulomb pseudopotential for H$_3$S from $0.204$ to $0.185$ and for PH$_3$ from $0.088$ to $0.083$, however, the electron effective mass and ratio $2\Delta(0)/T_C$ remain unaffected. Independently of the assumed method of analysis, the thermodynamic parameters of superconducting H$_3$S and PH$_3$ strongly deviate from the prediction of BCS theory due to the strong-coupling and retardation effects.

Computational prediction of high thermoelectric performance in p-type half-Heusler compounds with low band effective mass

Abstract: Half-Heusler (HH) compounds are important high temperature thermoelectric (TE) materials and have gained ever-increasing popularity. In recent years, p-type FeNbSb-based heavy-band HH compounds have attracted considerable attention with the record-high zT value of 1.5. Here, we use first-principles based methods to predict a very high zT value of 1.54 at 1200 K in p-type RuTaSb alloys. The high band degeneracy and low band effective mass contribute to a high power factor. Although the electrical thermal conductivity is high due to the high carrier mobility and hence electrical conductivity, the total thermal conductivity is moderate because of the low lattice thermal conductivity. The predicted high zT demonstrates that the p-type RuTaSb HH alloys are promising as TE materials for high temperature power generation.

Strain and electric field induced electronic properties of two-dimensional hybrid bilayers of transition-metal dichalcogenides

Abstract: Tunability of the electronic properties of two-dimensional bilayer hetero structures of transition-metal dichalcogenides (i.e., MX2-M′X′2 with (M, M′ = Mo, W; X, X′ = S, Se) is investigated. Application of both strain and electric field is found to modify the band gap and carrier effective mass in the hybrid bilayers considered. The calculated results based on density functional theory suggest that the tensile strain considerably changes the band gap of semiconducting bilayers; it makes the band gap to be indirect, and later initiates the semiconductor-to-metal transition. Application of the external electric fields, on the other hand, shows asymmetric variation in the band gap leading to the closure of the gap at about 0.5–1.0 V/A. Tuning of the band gap and carrier effective mass in such a controlled manner makes the hybrid bilayers of transition metal dichalcogenides to be promising candidates for application in electronic devices at nanoscale.