Observation of hidden altermagnetism in Cs$_{1-\delta}$V$_2$Te$_2$O

TL;DR

This study experimentally demonstrates hidden altermagnetism in Cs$_{1- ext{delta}}$V$_2$Te$_2$O, revealing a spatially modulated magnetic state with potential for exploring new magnetic phenomena.

Contribution

It provides the first experimental evidence of hidden altermagnetism with real-space modulation, combining multiple techniques and theoretical analysis.

Findings

Cs$_{1- ext{delta}}$V$_2$Te$_2$O exhibits spatially modulated altermagnetism.

Spin-resolved ARPES confirms local spin polarizations.

The state arises from G-type antiferromagnetism and 2D electronic states.

Abstract

Altermagnets are characterized by anisotropic band/spin splittings in momentum space, dictated by their spin-space group symmetries. However, the real-space modulations of altermagnetism are often neglected and have not been explored experimentally. Here we combine neutron diffraction, angle-resolved photoemission spectroscopy (ARPES), spin-resolved ARPES and density functional theory to demonstrate that Cs$_{1-\delta}$V$_2$Te$_2$O realizes a spatially modulated form of altermagnetism, i.e., hidden altermagnetism. Such a state in Cs$_{1-\delta}$V$_2$Te$_2$O results from its G-type antiferromagnetism and two-dimensional electronic states, allowing for the development of spatially alternating altermagnetic layers, whose local spin polarizations are directly verified by spin-resolved ARPES measurements. Our experimental discovery of hidden altermagnetism broadens the scope of unconventional magnetism and opens routes to exploring emergent phenomena from real-space modulations of altermagnetic order.