# Low-Temperature Dielectric Anomalies at the Mott Insulator-Metal Transition

## TL;DR

This study explores the dielectric response of a Mott insulator during the insulator-metal transition, revealing anomalies and regimes that deepen understanding of the microscopic transition mechanisms.

## Contribution

It provides the first detailed experimental and theoretical analysis of dielectric anomalies across the Mott transition in a quantum spin liquid material.

## Key findings

- Enhanced dielectric constant near the transition point
- Identification of multiple dynamical regimes around the Mott transition
- Theoretical modeling aligns with experimental dielectric behavior

## Abstract

The correlation-driven Mott transition is commonly characterized by a drop in resistivity across the insulator-metal phase boundary; yet, the complex permittivity provides a deeper insight into the microscopic nature. We investigate the frequency- and temperature-dependent dielectric response of the Mott insulator $\kappa$-(BEDT-TTF)$_{2}$-Cu$_2$(CN)$_3$ when tuning from a quantum spin liquid into the Fermi-liquid state by applying external pressure and chemical substitution of the donor molecules. At low temperatures the coexistence region at the first-order transition leads to a strong enhancement of the quasi-static dielectric constant $\epsilon_1$ when the effective correlations are tuned through the critical value. Several dynamical regimes are identified around the Mott point and vividly mapped through pronounced permittivity crossovers. All experimental trends are captured by dynamical mean-field theory of the single-band Hubbard model supplemented by percolation theory.