Electronic State and Optical Response in a Hydrogen-Bonded Molecular Conductor

Abstract

Motivated by recent experimental studies of hydrogen-bonded molecular conductors $\kappa$-$X_3$(Cat-EDT-TTF)${}_2$ [$X$=H, D], interplays of protons and correlated electrons, and their effects on magnetic, dielectric, and optical properties, are studied theoretically. We introduce a model Hamiltonian for $\kappa$-$X_3$(Cat-EDT-TTF)${}_2$, in which molecular dimers are connected by hydrogen bonds. Ground-state phase diagram and optical conductivity spectra are examined by using the mean-field approximation and the exact diagonalization method in finite-size cluster. Three types of the competing electronic and protonic phases, charge density wave phase, polar charge-ordered phase, and antiferromagnetic dimer-Mott insulating phase are found. Observed softening of the inter-dimer excitation due to the electron-proton coupling implies reduction of the effective electron-electron repulsion, i.e. "Hubbard $U$", due to the quantum proton motion. Contrastingly, the intra-dimer charge excitation is harden due to the proton-electron coupling. Implications of the theoretical calculations to the recent experimental results in $\kappa$-$X_3$(Cat-EDT-TTF)${}_2$ are discussed.

13 pages, 9 figures

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Cited by in corpus (3)

• Antiferromagnetic State in $\kappa$-type Molecular Conductors: Spin Splitting and Mott Gap
• First-principles study of the charge ordered phase in $\kappa$-D${}_3$(Cat-EDT-TTF/ST)${}_2$: Stability of $\pi$-electron deuterium coupled ordering in hydrogen-bonded molecular conductors
• Quantum valence bond ice theory for proton-driven quantum spin-dipole liquids