# Pressure-tuning the quantum spin Hamiltonian of the triangular lattice antiferromagnet Cs$_2$CuCl$_4$

## TL;DR

This study demonstrates how applying hydrostatic pressure to Cs$_2$CuCl$_4$ can tune its quantum spin Hamiltonian, revealing new magnetic phases and providing a novel method to explore frustrated quantum magnets.

## Contribution

The paper introduces pressure as a tool to modify the spin Hamiltonian in a triangular-lattice antiferromagnet, enabling experimental exploration of its phase diagram without chemical substitution.

## Key findings

- Exchange coupling ratio increases from 0.3 to 0.42 at 1.8 GPa
- Emergent field-induced magnetic phases observed
- Pressure tuning allows precise control of magnetic parameters

## Abstract

Quantum triangular-lattice antiferromagnets are important prototype systems to investigate phenomena of the geometrical frustration in condensed matter. Apart from highly unusual magnetic properties, they possess a rich phase diagram (ranging from an unfrustrated square lattice to a quantum spin liquid), yet to be confirmed experimentally. One major obstacle in this area of research is the lack of materials with appropriate (ideally tuned) magnetic parameters. Using Cs$_2$CuCl$_4$ as a model system, we demonstrate an alternative approach, where, instead of the chemical composition, the spin Hamiltonian is altered by hydrostatic pressure. The approach combines high-pressure electron spin resonance and magnetization measurements, allowing us not only to quasi-continuously tune the exchange parameters, but also to accurately monitor them. Our experiments indicate a substantial increase of the exchange coupling ratio from 0.3 to 0.42 at a pressure of 1.8 GPa, revealing a number of emergent field-induced phases.