Quantum spin liquids and the metal-insulator transition in doped semiconductors

TL;DR

This paper proposes a novel route to the metal-insulator transition in doped semiconductors via a quantum spin liquid state, predicting metallic thermal conductivity in the insulating phase and a discontinuous zero-temperature electrical conductivity jump.

Contribution

It introduces the concept of a quantum spin liquid as an intermediate phase in the metal-insulator transition of doped semiconductors, with testable experimental predictions.

Findings

Quantum spin liquid state can occur between metal and insulator phases.

Metallic thermal conductivity persists in the insulating phase near transition.

Electrical conductivity exhibits a discontinuous jump at zero temperature.

Abstract

We describe a new possible route to the metal-insulator transition in doped semiconductors such as Si:P or Si:B. We explore the possibility that the loss of metallic transport occurs through Mott localization of electrons into a quantum spin liquid state with diffusive charge neutral "spinon" excitations. Such a quantum spin liquid state can appear as an intermediate phase between the metal and the Anderson-Mott insulator. An immediate testable consequence is the presence of metallic thermal conductivity at low temperature in the electrical insulator near the metal-insulator transition. Further we show that though the transition is second order the zero temperature residual electrical conductivity will jump as the transition is approached from the metallic side. However the electrical conductivity will have a non-monotonic temperature dependence that may complicate the extrapolation to zero temperature. Signatures in other experiments and some comparisons with existing data are made.