I would like to know what is the difference between a Half metal (HM) and a Spin Gapless Semiconductor (SGS) in terms of definition and DOS/Bandstructure appearance.
The concept of spin gapless semiconductors (SGS) was proposed in this paper: PRL 100, 156404 (2008).
- In quantum solid-state band theory, materials in nature are generally classified as insulators, semiconductors, metals, semimetals, and half-metals based on the electronic band structures (density of states or band structure), as shown below.
(b): Semiconductor or Insulator by the gap value
(c): Semimetal (The valence band and conduction band are touching slightly.)
Energy band diagrams for spin gapless semiconductors with linear dispersion between energy and momentum.
- Energy band diagrams for spin gapless semiconductors with parabolic dispersion between energy and momentum.
Compared to the band structure of half metal, one spin channel of SGS is touching slightly (gapless).
Take a careful look at the cited paper and then you will figure out the difference!