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.

Coupled Membranes with Doubly Negative Mass Density and Bulk Modulus

Abstract: We present a structurally and conceptually simple acoustic double negative metamaterial comprising two coupled membranes. Owing to its symmetry, the system can generate both monopolar and dipolar resonances that are separately tunable, thereby making broadband double negativity possible. A homogenization scheme is implemented that enables the exact characterization of our metamaterial by the effective mass density and bulk modulus even beyond the usual long-wavelength regime, with the measured displacement fields on the sample's surfaces as inputs. Double negativity is achieved in the frequency range of 520--830 Hz. Transmission and reflection predictions using effective parameters are shown to agree remarkably well with the experiment.

Towards efficient band structure and effective mass calculations for III-V direct band-gap semiconductors

Abstract: The band structures and effective masses of III-V semiconductors (InP, InAs, InSb, GaAs, and GaSb) are calculated using the $GW$ method, the Heyd, Scuseria, and Ernzerhof hybrid functional, and modified Becke-Johnson combined with the local-density approximation (MBJLDA)---a local potential optimized for the description of the fundamental band gaps [F. Tran and P. Blaha, Phys. Rev. Lett. 102, 226401 (2009)]. We find that MBJLDA yields an excellent description of the band gaps at high-symmetry points, on par with the hybrid functional and $GW$. However, the effective masses are generally overestimated by $20--30\text{ }\mathrm{%}$ using the MBJLDA local multiplicative potential. We believe this to be related to incorrect nearest-neighbor hopping elements, which are little affected by the choice of the local potential. Despite these shortcomings, the MBJLDA method might be a suitable approach for predicting or interpolating the full band dispersion, if only limited experimental data are available. Furthermore, the method is applicable to systems containing several thousand atoms where accurate quasiparticle methods are not applicable.

Bulk superconducting phase with a full energy gap in the doped topological insulator Cu(x)Bi₂Se₃.

Abstract: The superconductivity recently found in the doped topological insulator Cu(x)Bi₂Se₃ offers a great opportunity to search for a topological superconductor. We have successfully prepared a single-crystal sample with a large shielding fraction and measured the specific-heat anomaly associated with the superconductivity. The temperature dependence of the specific heat suggests a fully gapped, strong-coupling superconducting state, but the BCS theory is not in full agreement with the data, which hints at a possible unconventional pairing in Cu(x)Bi₂Se₃. Also, the evaluated effective mass of 2.6m(e) (m(e) is the free electron mass) points to a large mass enhancement in this material.

Intrinsic Electron Mobility Limits in beta-Ga2O3

Abstract: By systematically comparing experimental and theoretical transport properties, we identify the polar optical phonon scattering as the dominant mechanism limiting electron mobility in beta-Ga2O3 to lower than 200 cm2/Vs at 300 K for donor doping densities lower than 1018 cm-3. In spite of similar electron effective mass of beta-Ga2O3 to GaN, the electron mobility is 10x lower because of a massive Frohlich interaction, due to the low phonon energies stemming from the crystal structure and strong bond ionicity. Based on the theoretical and experimental analysis, we provide an empirical expression for electron mobility in beta-Ga2O3 that should help calibrate its potential in high performance device design and applications.

Reference Spectrum Method for Nuclear Matter

Abstract: A new method is presented for the calculation of the reaction matrix $G$ of the Brueckner-Goldstone theory. The spectrum of the intermediate states is replaced by a "reference spectrum" of the form $A+B{k}^{2}$ where the constants $A$ and $B$ are chosen so as to approximate, as closely as possible, the actual particle energies for $k$ between 3 and 6 ${\mathrm{F}}^{\ensuremath{-}1}$. The reason for this choice is explained. With the reference spectrum, the Brueckner integral equation reduces to a differential equation which is easily solved. The case of a repulsive core can be solved explicitly, and can be summed over angular momentum, taking into account the correct statistical weights. If an attractive potential is added to the repulsive core, a simple "modified Born approximation" can be developed. Noncentral forces, such as tensor forces, are considered.The actual $G$ matrix, ${G}^{N}$, is calculated from the reference matrix ${G}^{R}$. It is shown that this can be done to sufficient accuracy (0.1 to 0.2 MeV per nucleon) by a simple quadrature. The difference ${G}^{N}\ensuremath{-}{G}^{R}$ arises mainly from the Pauli principle which is not taken into account in ${G}^{R}$. A small correction, less than 1 MeV per nucleon, arises from the inaccuracy of the reference spectrum. This shows that the details of the particle energy spectrum are not important for the calculation of the nuclear binding energy.The particle energy spectrum is carefully investigated. In agreement with Brueckner and Goldman, the $G$ matrices determining the potential energy of states in the Fermi sea are calculated "on the energy shell," and a more detailed justification is given for this procedure. Those for states above the Fermi sea are calculated "off the energy shell." This, in combination with the repulsive core, has the consequence of making the potential energy very large and positive for large $k$, corresponding to an effective mass between 0.8 and 0.9 for highly excited states. In addition, there is an energy gap at the Fermi momentum, a feature which helps to justify the reference spectrum.A modified Moszkowski-Scott separation into short- and long-range potentials is developed and gives, in second order, results accurate to better than 0.1 MeV per particle. The wave functions of interacting particles are calculated in the reference spectrum approximation for central and tensor forces.