Direct imaging of a Berry curvature nematic state in a spin-compensated magnet

TL;DR

This paper reports the discovery of a Berry curvature density wave in a noncollinear antiferromagnet, revealing a nematic state with tunable properties driven by magnetic fields and doping.

Contribution

It introduces a new class of collective order in spin-compensated magnets mediated by the geometric phase of the wavefunction.

Findings

Observed micrometer-scale spatial modulations of Kerr signal in Mn3NiN

Identified a magnetic-field-induced Berry curvature density wave

Demonstrated control of wavelength via doping and amplitude via magnetic field

Abstract

Density waves conventionally describe the periodic modulation of charge or spin, yet the spatial modulation of electronic geometry has remained elusive. Here, we report subtle micrometer-scale spatial modulations of the magneto-optical Kerr signal in the noncollinear antiferromagnet Mn3NiN with compensated spins, consistent with a magnetic-field-induced Berry curvature density wave . These Berry curvature modulations exhibit orientations unpinned from the crystal lattice, forming a nematic state that spontaneously breaks rotational symmetry. We attribute this spatial instability to field-induced spatial variations of the spin texture driven by competing magnetic interactions. This discovery unveils a new class of collective order in spin-compensated magnets mediated by the geometric phase of the wavefunction itself. Its wavelength is controlled by chemical doping and its amplitude by magnetic field, providing concrete tuning knobs for antiferromagnetic and altermagnetic spintronics.