Metallic and Insulating behaviour in p-SiGe at nu = 3/2

TL;DR

This paper investigates the insulating and metallic behaviors in p-SiGe at filling factor 3/2, revealing the role of exchange interactions in quantum Hall transitions and phase behavior.

Contribution

It provides new insights into the exchange interaction effects on Landau level crossing and the metal-insulator transition at fractional quantum Hall states in p-SiGe.

Findings

Identification of fixed points for quantum Hall transitions.

Hall resistivity approaches zero in the insulating phase.

Exchange interactions influence Landau level behavior.

Abstract

Shubnikov-de Haas data is presented for a p-SiGe sample exhibiting strongly insulating behaviour at nu = 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 nu = 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 uparrow and 1 downarrow Landau levels to cross and be well separated but at non-integer values of nu 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.