Spontaneous Hall effect induced by strain in Pr$_2$Ir$_2$O$_7$ epitaxial thin films

TL;DR

This study demonstrates that strain in epitaxial Pr$_2$Ir$_2$O$_7$ thin films induces a spontaneous Hall effect and suggests the emergence of a Weyl semimetal state driven by lattice strain and time reversal symmetry breaking.

Contribution

First demonstration of strain-induced spontaneous Hall effect in Pr$_2$Ir$_2$O$_7$ thin films, indicating a possible Weyl semimetal phase without spontaneous magnetization.

Findings

Strained films exhibit a spontaneous Hall effect up to 50 K.

No spontaneous magnetization detected within experimental accuracy.

Results consistent with a Weyl semimetal state induced by strain and TRS breaking.

Abstract

Strongly correlated iridate pyrochlores with geometrically frustrated spins have been recognized as a potentially interesting group of oxide materials where novel topological phases may appear. A particularly attractive system is the metallic Pr$_2$Ir$_2$O$_7$, as it is known as a Fermi node semimetal characterized by quadratic band touching at the Brillouin zone center, suggesting that the topology of its electronic states can be tuned by moderate lattice strain. In this work we report the growth of epitaxial Pr$_2$Ir$_2$O$_7$ thin films grown by solid-state epitaxy. We show that the strained parts of the films give rise to a spontaneous Hall effect that persists up to 50 K without having spontaneous magnetization within our experimental accuracy. This indicates that a macroscopic time reversal symmetry (TRS) breaking appears at a temperature scale that is too high for the magnetism to be due to Pr 4$f$ moments, and must thus be related to magnetic order of the iridium 5$d$ electrons. The magnetotransport and Hall analysis results are consistent with the formation of a Weyl semimetal state that is induced by a combination of TRS breaking and cubic symmetry breaking due to lattice strain.