Spin-split Energy Bands Research Articles

Plasmon spectrum of two-dimensional electron systems with Rashba spin-orbit interaction

The dielectric function and plasmon modes of a two-dimensional electron gas (2DEG) are studied in single- and double-quantum-well structures with Rashba spin-orbit interaction (RSOI) in the framework of the random-phase approximation. The RSOI splits each parabolic energy subband of a 2DEG into two nonparabolic spin branches and affects the electronic many-body correlation and dielectric properties of the 2DEG. The influence of the RSOI on the 2DEG plasmon spectrum in single quantum wells appear mainly in three ways: 1) an overall frequency lowering due to the energy band deformation; 2) a weak frequency oscillation stemming from the spin-split energy band; and 3)an enhancement of the Landau damping as a result of the emerging of the inter-branch single-particle-excitation spectrum. In double quantum wells, the above effects are enhanced for the optic plasmon mode but diminished for the acoustic one.

Spin-splitting in GaAs two-dimensional holes

We present quantitative measurements and calculations of the spin-orbit-induced zero-magnetic-field spin splitting in two-dimensional (2D) hole systems in modulation-doped GaAs (3 1 1) A quantum wells. The results show that the splitting is large and tunable. In particular, via a combination of back- and front-gate biases, we can tune the splitting while keeping the 2D hole density constant. The data also reveal a surprising result regarding the magnetoresistance (Shubnikov–de Haas) oscillations in a 2D system with spin-split energy bands: the frequencies of the oscillations are not simply related to the population of the spin-subbands. Next we concentrate on the metallic-like behavior observed in these 2D holes and its relation to spin-splitting. The data indicate that the metallic behavior is more pronounced when two spin-subbands with unequal populations are occupied. Our measurements of the magnetoresistance of these 2D hole systems with an in-plane magnetic field corroborate this conclusion: while the system is metallic at zero magnetic field, it turns insulating when one of the spin subbands is depopulated at high magnetic field.

The effect of the electron-phonon interaction on the spin splitting of electron energy bands in an itinerant electron ferromagnet

We report our discovery that the exchange splitting of the electron energy bands in the ferromagnetic state of a metal can be affected by the effect of the electron-phonon interaction and that, whereas the sign and magnitude of such a phonon effect depend sensitively on the electronic structure around the Fermi surface of the metal, the magnitude can be comparable with that of the ordinary Stoner exchange splitting. This conclusion was obtained by examining how the phonon frequencies, and therefore the phonon free energy, change with the spin splitting of the energy bands of the screening electrons in an itinerant electron ferromagnet. By carrying out a numerical calculation with a model electronic density of states, we demonstrate the importance of considering this effect in accounting for the observed magnetization and its temperature dependence in a ferromagnetic metal.

Absorption and elastic and inelastic reflection of spin-polarized low-energy electrons from Fe(110).

The spin dependence of low-energy electron absorption and reflection from ferromagnetic Fe(110) is investigated using the normalized difference between the absorption (or reflection) of electrons polarized parallel and antiparallel to sample magnetization. The resulting absorption and reflection spin asymmetries are found to be reciprocal to each other, with their magnitudes related in a simple manner. Structure in the spin asymmetries is identified with features in the spin-split bulk band structure and is thus found to be related to the spin-polarization fine structure of secondary electrons emitted from the same surface. The general structure of the spin asymmetry as a function of incident energy is dominated by elastic-scattering events, although inelastic scattering is found to play a major role in determining the sign and magnitude of the absorbed and total (energy-integrated) reflected asymmetries. Furthermore, the existence of nonzero elastic-reflection asymmetries indicates the existence of spin-split unoccupied energy bands up to 50 eV above the vacuum level. Inelastic-scattering spin asymmetries show a 2-eV energy-loss feature that is identified as due to the creation of Stoner excitations in the ferromagnet. This feature is determined to be surprisingly insensitive to the incident electron energy (from 0 to 50 eV) and angle (from 0\ifmmode^\circ\else\textdegree\fi{} to 65\ifmmode^\circ\else\textdegree\fi{} from the normal) in contrast to predictions of a recent theory of spin-polarized electron scattering in ferromagnets.

Abstract: Electronic and magnetic properties of nickel as described using experimental spin-split energy band dispersions

Angle-resolved photoemission studies of Ni (111) and Ni (100) crystals, used to determine energy-vs-momentum s- and d-band dispersions, show that ferromagnetic nickel can be described by a spin-split itinerant band model with an exchange splitting. An experimental one-electron energy band model for Ni gives a consistent description of various electronic and magnetic properties including Fermi surface radii, spin-polarized field emission and photoemission data, Bohr magneton number and optical properties. (AIP)

Inhomogeneous Electron Gas

This work is a generalization of the Hohenberg---Kohn---Sham theory of the inhomogeneous electron gas, with emphasis on spin effects. An argument based on quantum electrodynamics is used to express the ground-state energy of a system of interacting electrons as a functional of the current density. Expressions are derived for coefficients appearing in an expansion of the correlation functional in terms of the linear-response functions of the homogeneous system, for a gas of almost constant four-current density. The current density contains a spin-dependent term which leads, in the nonrelativistic limit, to a local potential which is also spin dependent. This potential is applied to the problems of spin splitting of energy bands in ferromagnets and spin-density-wave antiferromagnets. The relations between the present approach, that of Slater, and the collective electron theory of ferromagnetism of Stoner are described.

Spin Splitting and the Ultraviolet Absorption of Ge

The spin-split energy bands of germanium are computed throughout the entire Brillouin zone. A combined orthogonalized-plane-wave and pseudopotential approach is employed. A parametrization for the spin is given which we believe to be accurate to about 10% for both the valence and the conduction band, and which includes most of the $2p\ensuremath{-}3p$ core interference effects. A highly refined zone sampling is used to get the fine details of the optical spectrum. The resulting line shape is excellent for the 2.1-2.3-eV doublet. The structure near 5.0 eV is much improved over the spin-free results. In addition, a new, but quite weak, multiplet is found near 3 eV and is associated with the ${\ensuremath{\Gamma}}_{{25}^{\ensuremath{'}}}\ensuremath{\rightarrow}{\ensuremath{\Gamma}}_{15}$ transitions.