Samarium hexaboride

Samarium hexaboride
Identifiers
12008-30-9
Properties
B6Sm
Molar mass 215.22 g·mol−1
Melting point 2400 °C ±100[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Samarium hexaboride (SmB6) is an intermediate-valence compound where samarium is present both as Sm2+ and Sm3+ ions at the ratio 3:7.[2] It belongs to a class of Kondo insulators.

At temperatures above 50 K its properties are typical of a Kondo metal, with metallic electrical conductivity characterized by strong electron scattering, whereas at low temperatures, it behaves as a non-magnetic insulator with a narrow band gap of about 4–14 meV.[3]

The cooling-induced metal-insulator transition in SmB6 is accompanied by a sharp increase in thermal conductivity, peaking at about 15 K. The reason for this increase is that electrons do not contribute to thermal conductivity at low temperatures, which is instead dominated by phonons. The decrease in electron concentration reduced the rate of electron-phonon scattering.[4]

New research seems to show that it may be a topological insulator.[5][6][7]

Its electrical resistance indicates that the material behaves as an insulator; however, its Fermi surface (an abstract boundary used to reliably predict the properties of materials) contradicts this, indicating that the material actually behaves as a good metal. At temperatures approaching absolute zero, the quantum oscillations of the material grow as the temperature declines, a behavior that contradicts both the Fermi analysis and the rules that govern conventional metals.[8]

See also

References

  1. ↑ Plenum Press Handbooks of High-Temperature Materials: No. 1 Materials Index p42
  2. ↑ Nickerson, J.; White, R.; Lee, K.; Bachmann, R.; Geballe, T.; Hull, G. (1971). "Physical Properties of SmB6". Physical Review B 3 (6): 2030. Bibcode:1971PhRvB...3.2030N. doi:10.1103/PhysRevB.3.2030.
  3. ↑ Nyhus, P.; Cooper, S.; Fisk, Z.; Sarrao, J. (1995). "Light scattering from gap excitations and bound states in SmB6". Physical Review B 52 (20): R14308. Bibcode:1995PhRvB..5214308N. doi:10.1103/PhysRevB.52.R14308.
  4. ↑ Sera, M.; Kobayashi, S.; Hiroi, M.; Kobayashi, N.; Kunii, S. (1996). "Thermal conductivity of RB6 (R=Ce, Pr, Nd, Sm, Gd) single crystals". Physical Review B 54 (8): R5207. Bibcode:1996PhRvB..54.5207S. doi:10.1103/PhysRevB.54.R5207.
  5. ↑ Botimer, J.; Kim; Thomas; Grant; Fisk; Jing Xia (2012). "Robust Surface Hall Effect and Nonlocal Transport in SmB6: Indication for an Ideal Topological Insulator". arXiv:1211.6769 [cond-mat.str-el].
  6. ↑ Xiaohang Zhang; N. P. Butch; P. Syers; S. Ziemak; Richard L. Greene; Johnpierre Paglione (2012). "Hybridization, Inter-Ion Correlation, and Surface States in the Kondo Insulator SmB6". Phys. Rev. X (APS) 3 (1): 011011. arXiv:1211.5532 [cond-mat.str-el]. doi:10.1103/PhysRevX.3.011011.
  7. ↑ Wolgast; Cagliyan Kurdak; Kai Sun; Allen; Dae-Jeong Kim; Zachary Fisk (2012). "Discovery of the First Topological Kondo Insulator: Samarium Hexaboride". arXiv:1211.5104 [cond-mat.str-el].
  8. ↑ Borghino, Dario (July 7, 2015). "Puzzling material acts as conductor and insulator at the same time". www.gizmag.com. Retrieved 2015-07-08.
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