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.

Valley Zeeman effect and spin-valley polarized conductance in monolayer MoS 2 in a perpendicular magnetic field

Abstract: We study the effect of a perpendicular magnetic field on the electronic structure and charge transport of a monolayer ${\text{MoS}}_{2}$ nanoribbon at zero temperature. We particularly explore the induced valley Zeeman effect through the coupling between the magnetic field $B$ and the orbital magnetic moment. We show that the effective two-band Hamiltonian provides a mismatch between the valley Zeeman coupling in the conduction and valence bands due to the effective mass asymmetry and it is proportional to ${B}^{2}$ similar to the diamagnetic shift of exciton binding energies. However, the dominant term which evolves with $B$ linearly, originates from the multiorbital and multiband structures of the system. Besides, we investigate the transport properties of the system by calculating the spin-valley resolved conductance and show that, in a low-hole doped case, the transport channels at the edges are chiral for one of the spin components. This leads to a localization of the nonchiral spin component in the presence of disorder and thus provides a spin-valley polarized transport induced by disorder.

Complete Fermi surface in BaFe2As2 observed via Shubnikov-de Haas oscillation measurements on detwinned single crystals.

Abstract: We show that the Fermi surface (FS) in the antiferromagnetic phase of BaFe(2)As(2) is composed of one hole and two electron pockets, all of which are three dimensional and closed, in sharp contrast to the FS observed by angle-resolved photoemission spectroscopy. Considerations on the carrier compensation and Sommerfeld coefficient rule out existence of unobserved FS pockets of significant sizes. A standard band structure calculation reasonably accounts for the observed FS, despite the overestimated ordered moment. The mass enhancement, the ratio of the effective mass to the band mass, is 2-3.

Temperature and angular dependences of upper critical fields for the layer structure superconductor 2H-NbSe 2

Abstract: The temperature and angular dependences of upper critical fieldsH c2 have been measured for several 2H-NbSe2 single crystals by use of an electrical conduction method in magnetic fields up to 150 kOe. As the temperature approaches the transition temperatureT c , the value ofH c2‖ (parallel to the layer planes) decreases with a positive curvature, while the value ofH c2⊥ (perpendicular to the layer planes) decreases almost linearly. The ratio ofH c2‖ toH c2⊥ increases monotonically from 2.4 nearT c with decreasing temperature and reaches the constant value of 3.2 at the lowest temperature. It becomes clear that the simple effective mass model based on the anisotropic Ginzburg-Landau theory does not explain our experimental results. The anisotropic behavior ofH c2 can be accounted for by the Takanaka theory, which includes anisotropies of both the Fermi velocity and the energy gap and the effect of nonlocality. Agreement between experimental results and the theoretical prediction is obtained by the use of values of 0.16≲e ≲0.25 and −0.6≲e 2 ≲−0.3, where e 1 is the mass anisotropy parameter and e 2 the gap anisotropy parameter. The coupling strength between layers is too strong to be explained by the Josephson phase coupling model proposed for quasi-two-dimensional layer superconductors.

Assessment of Electron Mobility in Ultrathin-Body InGaAs-on-Insulator MOSFETs Using Physics-Based Modeling

Abstract: We have investigated the electron mobility in ultrathin-body InGaAs-on-insulator devices using physics-based modeling that self-consistently accounts for quantum confinement and covers band-structure effects in ultrathin III-V layers. Scattering by nonpolar and polar acoustic and optical phonons, surface roughness, and thickness fluctuations, Coulomb and alloy disorder have been included in the calculations. The modeling, calibrated and verified on experimental data from the literature, has revealed a strong influence of thickness fluctuations caused by the light effective mass of Γ valley electrons. Our results indicate that InGaAs-on-insulator MOSFETs are more influenced by interface properties compared with silicon-on-insulator devices and outperform them only above certain body thickness that depends on interface quality.

Landau quantization in graphene monolayer, Bernal bilayer, and Bernal trilayer on graphite surface

Abstract: Electronic properties of surface areas decoupled from graphite are studied using scanning tunneling microscopy and spectroscopy. We show that it is possible to identify the decoupled graphene monolayer, the Bernal bilayer, and the Bernal trilayer on a graphite substrate according to their tunneling spectra in a high magnetic field. The decoupled monolayer and bilayer exhibit Landau quantization of massless and massive Dirac fermions, respectively. The substrate generates a sizable band gap $\ensuremath{\sim}35\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$ in the Bernal bilayer, therefore, the eightfold degenerate Landau level at the charge neutrality point is split into two valley-polarized quartets polarized on each layer. In the decoupled Bernal trilayer, we find that both massless and massive Dirac fermions coexist and its low-energy band structure can be described quite well by taking into account only the nearest-neighbor intra- and interlayer hopping parameters. A strong correlation between the Fermi velocity of the massless Dirac fermions and the effective mass of the massive Dirac fermions is observed in the graphene trilayer. Our result demonstrates that the surface of graphite provides a natural ideal platform to probe the electronic spectra of graphene layers.