Samarium hexaboride

Samarium hexaboride
Identifiers
CAS Number	12008-30-9;
3D model (JSmol)	Interactive image;
ChemSpider	58803190;
ECHA InfoCard	100.031.384
EC Number	234-536-3;
PubChem CID	133108844;
CompTox Dashboard (EPA)	DTXSID701315601 ;
	InChI InChI=1S/6B.Sm Key: IYKQPDWKORWUNW-UHFFFAOYSA-N;
	SMILES [B].[B].[B].[B].[B].[B].[Sm];
Properties
Chemical formula	B6Sm
Molar mass	215.22 g·mol−1
Melting point	2400 °C ±100
	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 is a Kondo insulator having a metallic surface state.^[3]

Early studies

It was first studied by soviet scientists in the early 1960s.^[4] Further studies were then undertaken at Bell Laboratories.^[4] By 1968 their researchers had noted changes in the electronic configuration at different temperatures.^[5] 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.^[6] 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.^[7]

Twenty first century research

By the twenty first century condensed matter physicists grew more interested in SmB₆ with claims that it may be a topological insulator.^[8]^[9]^[10] Other researchers found no evidence of topological surface states.^[11]

The increasing electrical resistance with a reduction in temperature indicates that the material behaves as an insulator; however, recent measurements reveal a Fermi surface (an abstract boundary of electrons in momentum space) characteristic of a good metal, indicating a more exotic dual metal-insulating ground state.^[12]^[13] The electrical resistivity at temperatures below 4K displays a distinct plateau,^[14] which is thought to be the coexistence of an insulating state (bulk) and a conducting state (surface). 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.^[12]^[15]^[13] While it has been argued that quantum oscillations on samples grown from aluminium flux^[16] may arise from aluminum inclusions,^[17] such an explanation is excluded for samples grown by the image furnace method^[12]^[14] rather than by the flux growth method.^[16]^[17]

References

^ Plenum Press Handbooks of High-Temperature Materials: No. 1 Materials Index p42
^ 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.
^ Li, Lu; Sun, Kai; Kurdak, Cagliyan; Allen, J. W. (2020). "Emergent mystery in the Kondo insulator samarium hexaboride". Nature Reviews Physics. 2 (9): 463–479. Bibcode:2020NatRP...2..463L. doi:10.1038/s42254-020-0210-8. ISSN 2522-5820. OSTI 1649780. S2CID 257113116.
^ ^a ^b Wolchover, Natalie (2015). "Paradoxical Crystal Baffles Physicists". Quanta Magazine. Retrieved 12 May 2023.
^ Menth, A.; Buehler, E.; Geballe, T. H. (17 February 1969). "Magnetic and Semiconducting Properties of Sm B 6". Physical Review Letters. 22 (7): 295–297. Bibcode:1969PhRvL..22..295M. doi:10.1103/PhysRevLett.22.295.
^ Nyhus, P.; Cooper, S.; Fisk, Z.; Sarrao, J. (1995). "Light scattering from gap excitations and bound states in SmB₆". Physical Review B. 52 (20): 14308–14311. Bibcode:1995PhRvB..5214308N. doi:10.1103/PhysRevB.52.R14308. PMID 9980746.
^ 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–R5210. Bibcode:1996PhRvB..54.5207S. doi:10.1103/PhysRevB.54.R5207. PMID 9986570.
^ Botimer, J.; Kim; Thomas; Grant; Fisk; Jing Xia (2013). "Robust Surface Hall Effect and Nonlocal Transport in SmB₆: Indication for an Ideal Topological Insulator". Scientific Reports. 3: 3150. arXiv:1211.6769. Bibcode:2013NatSR...3E3150K. doi:10.1038/srep03150. PMC 3818682. PMID 24193196.
^ Xiaohang Zhang; N. P. Butch; P. Syers; S. Ziemak; Richard L. Greene; Johnpierre Paglione (2013). "Hybridization, Inter-Ion Correlation, and Surface States in the Kondo Insulator SmB₆". Phys. Rev. X. 3 (1): 011011. arXiv:1211.5532. Bibcode:2013PhRvX...3a1011Z. doi:10.1103/PhysRevX.3.011011. S2CID 53638956.
^ Wolgast, Steven; Kurdak, Çağlıyan; Sun, Kai; Allen, J. W.; Kim, Dae-Jeong; Fisk, Zachary (2013). "Low-temperature surface conduction in the Kondo insulator SmB₆". Phys. Rev. B. 88 (18): 180405. arXiv:1211.5104. Bibcode:2013PhRvB..88r0405W. doi:10.1103/physrevb.88.180405. ISSN 1098-0121. S2CID 119242604.
^ Hlawenka; Siemensmeyer; Weschke; Varykhalov; Sánchez-Barriga; Shitsevalova; Dukhnenko; Filipov; Gabáni; Flachbart; Rader; Rienks (2018). "Samarium hexaboride is a trivial surface conductor". Nature Communications. 9 (1): 1–7. arXiv:1502.01542. Bibcode:2018NatCo...9..517H. doi:10.1038/s41467-018-02908-7. PMC 5802797. PMID 29410418.
^ ^a ^b ^c B. S. Tan; Y.-T. Hsu; B. Zeng; M. Ciomaga Hatnean; N. Harrison; Z. Zhu; M. Hartstein; M. Kiourlappou; A. Srivastava; M. D. Johannes; T. P. Murphy; J.-H. Park; L. Balicas; G. G. Lonzarich; G. Balakrishnan; Suchitra Sebastian (2015). "Unconventional Fermi surface in an insulating state". Science. 349 (6245): 287–290. arXiv:1507.01129. Bibcode:2015Sci...349..287T. doi:10.1126/science.aaa7974. PMID 26138105. S2CID 206635941.
^ ^a ^b Natalie Wolchover (2 July 2015). "Paradoxical Crystal Baffles Physicists". Quanta Magazine. Retrieved 2020-01-15.
^ ^a ^b M. Ciomaga Hatnean; M. R. Lees; D. Mck. Paul; G. Balakrishnan (2013). "Large, high quality single-crystals of the new Topological Kondo Insulator, SmB6". Nature. 3 (3071): 3071. Bibcode:2013NatSR...3E3071H. doi:10.1038/srep03071. PMC 3810659. PMID 24166216.
^ Borghino, Dario (July 7, 2015). "Puzzling material acts as conductor and insulator at the same time". www.gizmag.com. Retrieved 2015-07-08.
^ ^a ^b Li, G.; Xiang, Z.; Yu, F.; Asaba, T.; Lawson, B.; Cai, P.; Tinsman, C.; Berkley, A.; Wolgast, S. (2014-12-05). "Two-dimensional Fermi surfaces in Kondo insulator SmB6". Science. 346 (6214): 1208–1212. arXiv:1306.5221. Bibcode:2014Sci...346.1208L. doi:10.1126/science.1250366. ISSN 0036-8075. PMID 25477456. S2CID 39786801.
^ ^a ^b S. M. Thomas; Xiaxin Ding; F. Ronning; V. Zapf; J. D. Thompson; Z. Fisk; J. Xia; P. F. S. Rosa (2019). "Quantum oscillations in flux-grown SmB6 with embedded aluminum". Physical Review Letters. 122 (16): 166401. arXiv:1806.00117. Bibcode:2019PhRvL.122p6401T. doi:10.1103/PhysRevLett.122.166401. PMID 31075018. S2CID 59407039.