Spin gapless semiconductor

Condensed matter physics
Phases Phase transition QCP
States of matter Solid Liquid Gas Plasma Bose–Einstein condensate Bose gas Fermionic condensate Fermi gas Fermi liquid Supersolid Superfluidity Luttinger liquid Time crystal
Phase phenomena Order parameter Phase transition QCP
Electronic phases Electronic band structure Plasma Insulator Mott insulator Semiconductor Semimetal Conductor Superconductor Thermoelectric Piezoelectric Ferroelectric Topological insulator Spin gapless semiconductor
Electronic phenomena Quantum Hall effect Spin Hall effect Kondo effect
Magnetic phases Diamagnet Superdiamagnet Paramagnet Superparamagnet Ferromagnet Antiferromagnet Metamagnet Spin glass
Quasiparticles Phonon Exciton Plasmon Polariton Polaron Magnon Roton
Soft matter Amorphous solid Colloid Granular material Liquid crystal Polymer
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Spin gapless semiconductors are a novel class of materials with unique electrical band structure for different spin channels in such a way that there is no band gap (i.e., 'gapless') for one spin channel while there is a finite gap in another spin channel.^[1]

In a spin-gapless semiconductor, conduction and valence band edges touch, so that no threshold energy is required to move electrons from occupied (valence) states to empty (conduction) states. This gives spin-gapless semiconductors unique properties: namely that their band structures are extremely sensitive to external influences (e.g., pressure or magnetic field). ^[2]

Because very little energy is needed to excite electrons in an SGS, charge concentrations are very easily ‘tuneable’. For example, this can be done by introducing a new element (doping) or by application of a magnetic or electric field (gating).

A new type of SGS identified in 2017, known as Dirac-type linear spin-gapless semiconductors, has linear dispersion and is considered an ideal platform for massless and dissipationless spintronics because spin-orbital coupling opens a gap for the spin fully polarized conduction and valence band, and as a result, the interior of the sample becomes an insulator, however, an electrical current can flow without resistance at the sample edge. This effect, the quantum anomalous Hall effect has only previously been realised in magnetically doped topological insulators.^[2]

As well as Dirac/linear SGSs, the other major category of SGS are parabolic spin gapless semiconductors.^{[3] [4]}

Electron mobility in such materials is two to four orders of magnitude higher than in classical semiconductors.^[5]

SGSs are topologically non-trivial.^[3]