# Dynamical reduction of the dimensionality of exchange interactions and the "spin-liquid" phase of $\kappa$-(BEDT-TTF)$_2X$

## TL;DR

This paper demonstrates that the anisotropy in the effective spin model of $$-(BEDT-TTF)$_2X$ salts leads to a spin-liquid phase arising from coupled spin chains, reconciling experimental observations with theoretical models.

## Contribution

It reveals how intra-dimer quantum interference reduces the effective dimensionality, explaining the spin-liquid phase as a remnant of single-chain physics.

## Key findings

- Anisotropy of the effective spin model differs from the tight-binding model.
- Frustrated interchain interactions suppress long-range magnetic order.
- The spin-liquid phase is linked to Tomonaga-Luttinger physics of a single chain.

## Abstract

We show that the anisotropy of the effective spin model for the dimer Mott insulator phase of $\kappa$-(BEDT-TTF)$_2X$ salts is dramatically different from that of the underlying tight-binding model. Intra-dimer quantum interference results in a model of coupled spin chains, where frustrated interchain interactions suppress long-range magnetic order. Thus, we argue, the "spin liquid" phase observed in some of these materials is a remnant of the Tomonaga-Luttinger physics of a single chain. This is consistent with previous experiments and resolves some outstanding puzzles. An erratum [Phys. Rev. Lett. 120, 199901 (2018).] is added as an appendix.