Electron-induced nuclear magnetic ordering in n-type semiconductors

TL;DR

This paper predicts two types of nuclear magnetic ordering in n-doped semiconductors induced by electrons at ultra-low temperatures, including nuclear spin polarons and a long-range ferromagnetic state involving electrons and nuclei.

Contribution

It introduces a theoretical framework for electron-induced nuclear magnetic ordering, including novel predictions of nuclear spin polarons and a dynamically induced nuclear ferromagnet in n-doped semiconductors.

Findings

Nuclear spin polarons form at positive nuclear spin temperature.

A long-range nuclear ferromagnet can emerge at negative nuclear spin temperature.

Ferromagnetic order may be achievable at experimentally accessible conditions.

Abstract

Nuclear magnetism in n-doped semiconductors with positive hyperfine constant is revisited. Two kinds of nuclear magnetic ordering can be induced by resident electrons in a deeply cooled nuclear spin system. At positive nuclear spin temperature below a critical value, randomly oriented nuclear spin polarons similar to that predicted by I. Merkulov [I. Merkulov, Physics of the Solid State 40, 930 (1998)] should emerge. These polarons are oriented randomly and within each polaron nuclear and electron spins are aligned antiferromagnetically. At negative nuclear spin temperature below a critical value we predict another type of magnetic ordering - dynamically induced nuclear ferromagnet. This is a long-range ferromagnetically ordered state involving both electrons and nuclei. It can form if electron spin relaxation is dominated by the hyperfine coupling, rather than by the spin-orbit interaction. Application of the theory to the n-doped GaAs suggests that the ferromagnetic order may be reached at experimentally achievable nuclear spin temperature $\Theta_N \approx 0.5$ $\mu$K and lattice temperature $T_L \approx 5$ K.