First-Order Antiferromagnetic Transition and Novel Gapless Excitation in a 4f Zigzag Chain Compound YbCuS2

TL;DR

This study investigates the magnetic transition and low-temperature spin excitations in YbCuS2, revealing a first-order antiferromagnetic transition at 0.95 K and evidence of gapless spin excitations.

Contribution

It provides the first NQR evidence of a first-order AFM transition and uncovers novel gapless spin excitations in a 4f zigzag chain compound.

Findings

First-order AFM transition at 0.95 K confirmed by NQR signals.

Abrupt decrease in 1/T1 below transition temperature.

Presence of gapless spin excitations indicated by T-linear 1/T1 behavior.

Abstract

We report on the 63/65Cu-nuclear magnetic resonance and nuclear quadrupole resonance (NQR) studies of trivalent Yb zigzag chain compound YbCuS2. Sharp NQR signals were observed in the paramagnetic (PM) state. Below TO = 0.95 K, the multi peaks induced by the internal magnetic fields arising from the antferromagnetic (AFM) ordered moments appear and coexist with the PM signal down to 0.85 K, evidencing the first-order AFM phase transition at TO. In addition, the nuclear spin-lattice relaxation rate 1/T1 abruptly decreases below TO and shows the T-linear behavior below 0.5 K. The significant large 1/T1T value strongly suggests the presence of the novel gapless spin excitation in low temperature region.