Spin Order by Quantum Frustration in Triangular Lattice Mott Insulator NaCrO2 : A Neutron Scattering Study

TL;DR

This neutron scattering study reveals how quantum frustration in NaCrO2 leads to a dimensional crossover and the emergence of three-dimensional magnetic order below a certain temperature, highlighting the role of inter-layer frustration.

Contribution

The paper demonstrates the development of incommensuration and 3D magnetic order in NaCrO2 driven by quantum frustration, a novel insight into triangular lattice Mott insulators.

Findings

Incommensuration develops below 0.75T_c.

Three-dimensional magnetic order supports coherent spin waves.

Inter-layer frustration stabilizes the 2D correlated phase.

Abstract

We report high resolution neutron scattering measurements on the triangular lattice Mott insulator Na$_x$CrO$_2$ ($x$=1) which has recently been shown to exhibit an unusually broad fluctuating crossover regime extending far below the onset of spin freezing ($T_c\sim$41K). Our results show that below some crossover temperature ($T\sim0.75T_c$) a small incommensuration develops which helps resolve the spin frustration and drives three-dimensional magnetic order supporting coherent spin wave modes. This incommensuration assisted dimensional crossover suggests that inter-layer frustration is responsible for stabilizing the rare 2D correlated phase above 0.75$T_c$. In contrast to the host compound of 2D cobaltate superconductor such as Na$_x$CoO$_2$ ($\xi_c>50$\AA), no magnetic long-range order is observed down to 1.5K ($\xi_c<16$\AA).