Closing the spin gap in the Kondo insulator Ce sub(3)Bi sub(4)Pt sub(3) at high magnetic fields

• Published in: Nature (London) 2000-05, Vol.405 (6783), p.160-163
• Main Authors: Jaime, Marcelo, Movshovich, Roman, Stewart, Gregory R, Beyermann, Ward P, Berisso, Mariano Gomez, Hundley, Michael F, Canfield, Paul C, Sarrao, John L
• Format: Article
• Language: English
• Subjects: Conduction band; Energy gap; External pressure; Fermi surfaces; Insulators; Intermetallic compounds; Magnetic fields; Mathematical models
• ISSN: 0028-0836
• DOI: 10.1038/35012027

Kondo insulator materials--such as CeRhAs, CeRhSb, YbB sub(12), Ce sub(3)Bi sub(4)Pt sub(3) and SmB sub(6)--are 3d, 4f and 5f intermetallic compounds that have attracted considerable interest in recent years. At high temperatures, they behave like metals. But as temperature is reduced, an energy gap opens in the conduction band at the Fermi energy and the materials become insulating. This contrasts with other f-electron compounds, which are metallic at all temperatures. The formation of the gap in Kondo insulators has been proposed to be a consequence of hybridization between the conduction band and the f-electron levels, giving a 'spin' gap. If this is indeed the case, metallic behaviour should be recovered when the gap is closed by changing external parameters, such as magnetic field or pressure. Some experimental evidence suggests that the gap can be closed in SmB sub(6) (refs 5, 8) and YbB sub(12) (ref. 9). Here we present specific-heat measurements of Ce sub(3)Bi sub(4)Pt sub(3) in d.c. and pulsed magnetic fields up to 60 tesla. Numerical results and theanalysis of our data using the Coqblin-Schrieffer model demonstrate unambiguously a field-induced insulator-to-metal transition.