In condensed matter physics, experimental control over material properties reflects a deep understanding of the underlying physics. In recent years, meaningful progress has been made towards a description of the physics of correlated electron systems, but examples of control of these systems remain rare. In this work, we confirm a phase diagram theoretically proposed for organic Mott insulators. We use $\kappa \text{−}{\left(\mathrm{BEDT}\text{−}\mathrm{TTF}\right)}_2\mathrm{Hg}{\left(\mathrm{SCN}\right)}_{2}X$ ($X$ = Br, Cl) [BEDT-TTF = bis(ethylenedithio)tetrathiafuvalene] materials as experimental realization of the proposed model and demonstrate the ability to tune them both ways across a phase border between a Mott insulator with a uniformly distributed charge and a charge-ordered state through the application of uniaxial strain. We induce charge order at 33 K in the quantum dipole liquid material $\kappa \text{−}{\left(\mathrm{BEDT}\text{−}\mathrm{TTF}\right)}_2\mathrm{Hg}{\left(\mathrm{SCN}\right)}_2\mathrm{Br}$ through the application of tensile strain of 0.4% along the $c$ axis. We suppress charge order down to 10 K in $\kappa \text{−}{\left(\mathrm{BEDT}\text{−}\mathrm{TTF}\right)}_2\mathrm{Hg}{\left(\mathrm{SCN}\right)}_2\mathrm{Cl}$ by applying a tensile strain of 1.6% along the $b$ axis. We use Raman scattering spectroscopy to probe the charge state through analysis of charge-sensitive molecular vibrations and a low-frequency mode of collective dipole fluctuations close to the phase border.

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• Elastic deformation
• Ferroelectricity
• Phase transitions
• Mott insulators
• Multiferroics
• Strongly correlated systems
• Triangular lattice
• Hubbard model
• Ising model
• Metropolis algorithm
• Raman spectroscopy
• Strain engineering