Spin gapless semiconductor

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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]

Contents

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]

A convergence of topology and magnetism known as Chern magnetism makes SGSs ideal candidate materials for realizing room-temperature quantum anomalous Hall effect (QAHE). [6]

SGSs are topologically non-trivial. [3]

Prediction and discovery

The spin gapless semiconductor was first proposed as a new spintronics concept and a new class of candidate spintronic materials in 2008 in a paper by Xiaolin Wang of the University of Wollongong in Australia. [7] [8] [9]

Properties and applications

The dependence of bandgap on spin direction leads to high carrier-spin-polarization, and offers promising spin-controlled electronic and magnetic properties for spintronics applications. [10]

The spin gapless semiconductor is a promising candidate material for spintronics because its charged particles can be fully spin-polarised, so that spin can be controlled via only a small applied external energy. [2]

Related Research Articles

A semiconductor is a material that has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity generally falls as its temperature rises; metals behave in the opposite way. In many cases their conducting properties may be altered in useful ways by introducing impurities ("doping") into the crystal structure. When two differently doped regions exist in the same crystal, a semiconductor junction is created. The behavior of charge carriers, which include electrons, ions, and electron holes, at these junctions is the basis of diodes, transistors, and most modern electronics. Some examples of semiconductors are silicon, germanium, gallium arsenide, and elements near the so-called "metalloid staircase" on the periodic table. After silicon, gallium arsenide is the second-most common semiconductor and is used in laser diodes, solar cells, microwave-frequency integrated circuits, and others. Silicon is a critical element for fabricating most electronic circuits.

Spintronics, also known as spin electronics, is the study of the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge, in solid-state devices. The field of spintronics concerns spin-charge coupling in metallic systems; the analogous effects in insulators fall into the field of multiferroics.

<span class="mw-page-title-main">Band gap</span> Energy range in a solid where no electron states exist

In solid-state physics and solid-state chemistry, a band gap, also called a bandgap or energy gap, is an energy range in a solid where no electronic states exist. In graphs of the electronic band structure of solids, the band gap refers to the energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. It is the energy required to promote an electron from the valence band to the conduction band. The resulting conduction-band electron are free to move within the crystal lattice and serve as charge carriers to conduct electric current. It is closely related to the HOMO/LUMO gap in chemistry. If the valence band is completely full and the conduction band is completely empty, then electrons cannot move within the solid because there are no available states. If the electrons are not free to move within the crystal lattice, then there is no generated current due to no net charge carrier mobility. However, if some electrons transfer from the valence band to the conduction band, then current can flow. Therefore, the band gap is a major factor determining the electrical conductivity of a solid. Substances having large band gaps are generally insulators, those with small band gaps are semiconductor, and conductors either have very small band gaps or none, because the valence and conduction bands overlap to form a continuous band.

<span class="mw-page-title-main">Semimetal</span> Metal with a small negative indirect band-gap

A semimetal is a material with a small energy overlap between the bottom of the conduction band and the top of the valence band, but they do not overlap in momentum space. According to electronic band theory, solids can be classified as insulators, semiconductors, semimetals, or metals. In insulators and semiconductors the filled valence band is separated from an empty conduction band by a band gap. For insulators, the magnitude of the band gap is larger than that of a semiconductor. Because of the slight overlap between the conduction and valence bands, semimetals have no band gap and a small density of states at the Fermi level. A metal, by contrast, has an appreciable density of states at the Fermi level because the conduction band is partially filled.

<span class="mw-page-title-main">Mesoscopic physics</span> Subdiscipline of condensed matter physics that deals with materials of an intermediate size

Mesoscopic physics is a subdiscipline of condensed matter physics that deals with materials of an intermediate size. These materials range in size between the nanoscale for a quantity of atoms and of materials measuring micrometres. The lower limit can also be defined as being the size of individual atoms. At the microscopic scale are bulk materials. Both mesoscopic and macroscopic objects contain many atoms. Whereas average properties derived from constituent materials describe macroscopic objects, as they usually obey the laws of classical mechanics, a mesoscopic object, by contrast, is affected by thermal fluctuations around the average, and its electronic behavior may require modeling at the level of quantum mechanics.

The quantum spin Hall state is a state of matter proposed to exist in special, two-dimensional semiconductors that have a quantized spin-Hall conductance and a vanishing charge-Hall conductance. The quantum spin Hall state of matter is the cousin of the integer quantum Hall state, and that does not require the application of a large magnetic field. The quantum spin Hall state does not break charge conservation symmetry and spin- conservation symmetry.

<span class="mw-page-title-main">Topological insulator</span> State of matter with insulating bulk but conductive boundary

A topological insulator is a material whose interior behaves as an electrical insulator while its surface behaves as an electrical conductor, meaning that electrons can only move along the surface of the material.

Electrically detected magnetic resonance (EDMR) is a materials characterisation technique that improves upon electron spin resonance. It involves measuring the change in electrical resistance of a sample when exposed to certain microwave frequencies. It can be used to identify very small numbers of impurities in semiconductors.

<span class="mw-page-title-main">Field effect (semiconductor)</span>

In physics, the field effect refers to the modulation of the electrical conductivity of a material by the application of an external electric field.

Valleytronics is an experimental area in semiconductors that exploits local extrema ("valleys") in the electronic band structure. Certain semiconductors have multiple "valleys" in the electronic band structure of the first Brillouin zone, and are known as multivalley semiconductors. Valleytronics is the technology of control over the valley degree of freedom, a local maximum/minimum on the valence/conduction band, of such multivalley semiconductors.

Weyl semimetals are semimetals or metals whose quasiparticle excitation is the Weyl fermion, a particle that played a crucial role in quantum field theory but has not been observed as a fundamental particle in vacuum. In these materials, electrons have a linear dispersion relation, making them a solid-state analogue of relativistic massless particles.

Bismuth antimonides, Bismuth-antimonys, or Bismuth-antimony alloys, (Bi1−xSbx) are binary alloys of bismuth and antimony in various ratios.

<span class="mw-page-title-main">Dirac cone</span> Quantum effect in some non-metals

In physics, Dirac cones are features that occur in some electronic band structures that describe unusual electron transport properties of materials like graphene and topological insulators. In these materials, at energies near the Fermi level, the valence band and conduction band take the shape of the upper and lower halves of a conical surface, meeting at what are called Dirac points.

<span class="mw-page-title-main">Electronic properties of graphene</span>

Graphene is a semimetal whose conduction and valence bands meet at the Dirac points, which are six locations in momentum space, the vertices of its hexagonal Brillouin zone, divided into two non-equivalent sets of three points. The two sets are labeled K and K′. The sets give graphene a valley degeneracy of gv = 2. By contrast, for traditional semiconductors the primary point of interest is generally Γ, where momentum is zero. Four electronic properties separate it from other condensed matter systems.

The term Dirac matter refers to a class of condensed matter systems which can be effectively described by the Dirac equation. Even though the Dirac equation itself was formulated for fermions, the quasi-particles present within Dirac matter can be of any statistics. As a consequence, Dirac matter can be distinguished in fermionic, bosonic or anyonic Dirac matter. Prominent examples of Dirac matter are graphene and other Dirac semimetals, topological insulators, Weyl semimetals, various high-temperature superconductors with -wave pairing and liquid helium-3. The effective theory of such systems is classified by a specific choice of the Dirac mass, the Dirac velocity, the gamma matrices and the space-time curvature. The universal treatment of the class of Dirac matter in terms of an effective theory leads to a common features with respect to the density of states, the heat capacity and impurity scattering.

Xiaolin Wang is a Chinese-Australian scientist recognised for his work in advanced materials synthesis and characterisation and spintronics. He is director of the Institute for Superconducting and Electronic Materials, University of Wollongong. Wang is a University of Wollongong senior professor, and an Australian Research Council future fellow.

Professor Lan Wang is a Chinese-Australian material scientist known for expertise in materials synthesis and advanced materials characterisation.

<span class="mw-page-title-main">Bipolar magnetic semiconductor</span>

Bipolar magnetic semiconductors (BMSs) are a special class of magnetic semiconductors characterized by a unique electronic structure, where valence band maximum (VBM) and conduction band minimum (CBM) are fully spin polarized in the opposite spin direction. BMSs can be described by three energy gaps, the spin-flip gap Δ2 in valence band (VB), band gap Δ1 and spin-flip gap Δ3 in conduction band (CB). Up to now, bipolar magnetic semiconductors, together with half-metal and spin gapless semiconductor, have been viewed as three important classes of spintronic materials.

<span class="mw-page-title-main">Rashba–Edelstein effect</span>

The Rashba–Edelstein effect (REE) is a spintronics-related effect, consisting in the conversion of a bidimensional charge current into a spin accumulation. This effect is an intrinsic charge-to-spin conversion mechanism and it was predicted in 1990 by the scientist V.M. Edelstein. It has been demonstrated in 2013 and confirmed by several experimental evidences in the following years.

References

  1. Skaftouros, S.; Özdoğan, K.; Şaşıoğlu, E.; Galanakis, I. (2013-01-14). "Search for spin gapless semiconductors: The case of inverse Heusler compounds". Applied Physics Letters. 102 (2): 022402. arXiv: 1210.5355 . Bibcode:2013ApPhL.102b2402S. doi:10.1063/1.4775599. ISSN   0003-6951. S2CID   311785.
  2. 1 2 3 "Spin gapless semiconductors: Promising materials for novel spintronics and dissipationless current flow | ARC Centre of Excellence in Future Low-Energy Electronics Technologies". 4 July 2017.
  3. 1 2 Wang, Xiaotian; Li, Tingzhou; Cheng, Zhenxiang; Wang, Xiao-Lin; Chen, Hong (2018). "Recent advances in Dirac spin-gapless semiconductors". Applied Physics Reviews. 5 (4): 041103. Bibcode:2018ApPRv...5d1103W. doi:10.1063/1.5042604. S2CID   125280965.
  4. Wang, Xiaotian (2018). "Search for a new member of parabolic-like spin-gapless semiconductors: The case of diamond-like quaternary compound CuMn2InSe4". Applied Physics Reviews. 10: 301. Bibcode:2018ResPh..10..301H. doi: 10.1016/j.rinp.2018.06.031 .
  5. Wang, Xiao-Lin (2016). "Dirac spin-gapless semiconductors: Promising platforms for massless and dissipationless spintronics and new (quantum) anomalous spin Hall effects". National Science Review. 4 (2): 252–257. arXiv: 1607.06057 . doi:10.1093/nsr/nww069.
  6. Wang, Xiaolin (21 June 2024). "Spin Gapless Quantum Materials and Devices". Advanced Materials. 36 (33): e2402503. Bibcode:2024AdM....3602503N. doi: 10.1002/adma.202402503 . PMID   38962884.
  7. Wang, Xiaolin (18 April 2008). "Proposal for a New Class of Materials: Spin Gapless Semiconductors". Physical Review Letters . 100 (15): 156404. Bibcode:2008PhRvL.100o6404W. doi:10.1103/physrevlett.100.156404. PMID   18518135. S2CID   22372621.
  8. "Media Centre | University of Wollongong".
  9. "Gapless oxide semiconductors: Designer spin". NPG Asia Materials: 1. 2008. doi: 10.1038/asiamat.2008.78 .
  10. "Half-Metals and Spin-Gapless Semiconductors".{{cite journal}}: Cite journal requires |journal= (help)