Quantum material

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Under quantum materials mean those materials whose macroscopic properties significantly by the quantum mechanical wave function of electrons be embossed. A distinction is made between properties that can be traced back to interactions between electrons (such as ferromagnetism , antiferromagnetism and superconductivity ) and phenomena that depend on the topological character of the wave function (such as topological insulators , Dirac semimetals, Weyl - Semimetal). A new branch of research deals with materials that combine both types of phenomena (such as spin fluids and topological superconductors ).

In addition, applications of quantum materials in spin-based electronics ( spintronics ), in photovoltaics and in quantum computers are explored.

Superconductor

Meißner-Ochsenfeld effect and perfect diamagnetism in the superconductor below the transition temperature T c .

The theory of Bardeen, Cooper and Schrieffer (BCS) according becomes a superconductor by a macroscopically the electron system coherent , from Cooper pairs composite wave function described. All known superconductors are described by a BCS wave function. A distinction is made between conventional superconductors, in which the Cooper pairs are formed by the electron - phonon interaction, and unconventional superconductors, in which the mechanism of the Cooper pair formation has not yet been finally clarified. Since the vanishing electrical resistance and perfect diamagnetism of superconductors are consequences of the macroscopic quantum coherence of the BCS wave function, superconductors are considered to be typical quantum materials.

Dirac semimetals

Band structure of graphene with Dirac dispersion . The energy axis is vertical and the pulse axes horizontal.

The valence electrons of graphene (i.e., individual monolayers of graphite ) are described by a Dirac equation. Due to the two-dimensional electronic structure and the very high electron mobility, the Hall resistance of graphene shows a quantization behavior even at room temperature. Since the quantum Hall effect is a consequence of the topological properties of the wave function of two-dimensional electron systems, graphene is also regarded as a typical quantum material. In addition, superconductivity was detected in two mutually twisted graphene layers in 2018. Other Dirac semimetals such as B. Na 3 Bi show an unusual magnetoresistance, which is also understood as a topological quantum phenomenon.

Individual evidence

  1. ^ Bernhard Keimer , JE Moore: The physics of quantum materials . In: Nature Physics . tape 13 , no. 11 , October 30, 2017, ISSN  1745-2473 , p. 1045-1055 , doi : 10.1038 / nphys4302 ( nature.com [accessed October 4, 2018]).
  2. ^ Yoshinori Tokura , Masashi Kawasaki, Naoto Nagaosa : Emergent functions of quantum materials . In: Nature Physics . tape 13 , no. 11 , September 25, 2017, ISSN  1745-2473 , p. 1056-1068 , doi : 10.1038 / nphys4274 ( nature.com [accessed October 4, 2018]).
  3. ↑ J. Bardeen, LN Cooper, JR Schrieffer: Theory of Superconductivity . In: Physical Review . tape 108 , no. 5 , December 1, 1957, ISSN  0031-899X , p. 1175–1204 , doi : 10.1103 / physrev.108.1175 ( aps.org [PDF; accessed October 7, 2018]).
  4. ↑ KS Novoselov, Z. Jiang, Y. Zhang, SV Morozov, HL Stormer: Room-Temperature Quantum Hall Effect in Graphene . In: Science . tape 315 , no. 5817 , March 9, 2007, ISSN  0036-8075 , p. 1379–1379 , doi : 10.1126 / science.1137201 , PMID 17303717 ( sciencemag.org [accessed October 7, 2018]).
  5. ^ The Nobel Prize in Physics 2016. Retrieved October 7, 2018 (American English).
  6. ↑ Yuan Cao, Valla Fatemi, Shiang Fang, Kenji Watanabe, Takashi Taniguchi: Unconventional superconductivity in magic-angle graphene superlattices . In: Nature . tape 556 , no. 7699 , March 5, 2018, ISSN  0028-0836 , p. 43–50 , doi : 10.1038 / nature26160 ( nature.com [accessed October 7, 2018]).
  7. ↑ Jun Xiong, Satya K. Kushwaha, Tian Liang, Jason W. Krizan, Max Hirschberger: Evidence for the chiral anomaly in the Dirac semimetal Na3Bi . In: Science . tape 350 , no. 6259 , October 23, 2015, ISSN  0036-8075 , p. 413-416 , doi : 10.1126 / science.aac6089 , PMID 26338798 ( sciencemag.org [accessed October 7, 2018]).