Strain as a tool to stabilize the isotropic triangular lattice in a geometrically frustrated organic quantum magnet

TL;DR

This study demonstrates that applying large, controlled anisotropic strains to a triangular-lattice quantum magnet can precisely tune geometric frustration, enabling exploration of different quantum states and providing a new method for engineering frustrated quantum materials.

Contribution

The paper introduces a novel approach of using strain to control frustration in a triangular-lattice quantum magnet, offering a new experimental pathway to study and realize exotic quantum states.

Findings

Strain effectively tunes the degree of geometric frustration.

Temperature-strain phase diagram maps ground states of the lattice.

Lattice engineering can realize perfectly frustrated quantum materials.

Abstract

Geometric frustration is a key ingredient in the emergence of exotic states of matter, such as the quantum spin liquid in Mott insulators. While there has been intense interest in experimentally tuning frustration in candidate materials, achieving precise and continuous control has remained a major hurdle -- particularly in accessing the properties of the ideally frustrated lattice. Here, we show that large, finely controlled anisotropic strains can effectively tune the degree of geometric frustration in the Mott insulating $\kappa$-(ET)$_2$Cu$_2$(CN)$_3$ -- a slightly anisotropic triangular-lattice quantum magnet. Using thermodynamic measurements of the elastocaloric effect, we experimentally map out a temperature-strain phase diagram that captures both the ground state of the isotropic lattice and the less frustrated parent state. Our results provide a new benchmark for calculations of the triangular-lattice Hubbard model as a function of frustration and highlight the power of lattice engineering as a route to realizing perfectly frustrated quantum materials.