Metallic and insulating behaviour in p-SiGe at v =3/2

摘要

Shubnikov-de Haas data is presented for a p-SiGe sample exhibiting strongly insulating behaviour at v= 3/2. In addition to the fixed points defining a high field metal- insulator transition into this phase separate fixed points can also be identified for the v = 3→2 and 2→ 1 Integer quantum Hall transitions. Another feature of the data, that the Hall resistivity approaches zero in the insulating phase, indicates it is not a re-entrant Hall insulator. The behaviour is explained in terms of the strong exchange interactions. At integer filling factors these cause the 0 ↑ and 1 ↓, Landau levels to cross and are well separated but at non-integer values of v screening reduces exchange effects and causes the levels to stick together. It is suggested the insulating behaviour, and high field metal/insulator transition, is a consequence of the strong exchange interactions.