Observation of paramagnetic spin-degeneracy lifting in EuZn2Sb2

TL;DR

This study demonstrates that EuZn2Sb2 exhibits spin degeneracy lifting in its electronic band structure due to ferromagnetic fluctuations, even without long-range magnetic order, revealing potential Weyl physics.

Contribution

It provides the first experimental evidence of paramagnetic spin degeneracy lifting in EuZn2Sb2 using ARPES and supports the theoretical prediction of Weyl nodes in this material.

Findings

Spin degeneracy is lifted in the paramagnetic phase.

Good agreement between ARPES data and ferromagnetic calculations.

Prediction of Weyl nodes arising from spin-polarized bands.

Abstract

Taken together, time-reversal and spatial inversion symmetries impose a two-fold spin degeneracy of the electronic states in crystals. In centrosymmetric materials, this degeneracy can be lifted by introducing magnetism, either via an externally applied field or through internal magnetization. However, a correlated alignment of spins, even in the paramagnetic phase, can lift the spin degeneracy of electronic states. Here, we report an in-depth study of the electronic band structure of the Eu-ternary pnictide EuZn2Sb2 through a combination of high-resolution angle-resolved photoemission spectroscopy measurements and first principles calculations. An analysis of the photoemission lineshapes over a range of incident photon energies and sample temperatures is shown to reveal the presence of band spin degeneracy-lifting in the paramagnetic phase. Our ARPES results are in good agreement with theoretical ferromagnetic-phase calculations, which indicates the importance of ferromagnetic fluctuations in the system. Through our calculations, we predict that spin-polarized bands in EuZn2Sb2 generate a single pair of Weyl nodes. Our observation of band-splitting in EuZn2Sb2 provides a key step toward realizing time-reversal symmetry breaking physics in the absence of long-range magnetic order.