Emergent spin-gapped magnetization plateaus in a spin-1/2 perfect kagome antiferromagnet

TL;DR

This study reports the experimental observation of emergent spin-gapped magnetization plateaus at 1/9 and 1/3 of saturation in a kagome quantum spin liquid candidate, revealing novel quantum states and spin gaps.

Contribution

First experimental detection of 1/9 and 1/3 magnetization plateaus in a kagome quantum spin liquid candidate, demonstrating emergent quantum states and spin gaps.

Findings

Observation of a 1/3 magnetization plateau above 50 T.

Detection of a 1/9 plateau around 20 T.

Estimated spin gap is approximately 10% of exchange interaction.

Abstract

The two-dimensional (2D) spin-1/2 kagome Heisenberg antiferromagnet is believed to host quantum spin liquid (QSL) states with no magnetic order, but its ground state remains largely elusive. An important outstanding question concerns the presence or absence of the 1/9 magnetization plateau, where exotic quantum states, including topological ones, are expected to emerge. Here we report the magnetization of a recently discovered kagome QSL candidate YCu$_3$(OH)$_{6.5}$Br$_{2.5}$ up to 57 T. Above 50 T, a clear magnetization plateau at 1/3 of the saturation moment of Cu$^{2+}$ ions is observed, supporting that this material provides an ideal platform for the kagome Heisenberg antiferromagnet. Remarkably, we found another magnetization plateau around 20 T, which is attributed to the 1/9 plateau. The temperature dependence of this plateau reveals the distinct spin gap, whose magnitude estimated by the plateau width is approximately 10% of the exchange interaction. The observation of 1/9 and 1/3 plateaus highlights the emergence of novel states in quantum spin systems.