Emergence of charge degrees of freedom under high pressure in an organic dimer-Mott insulator ${\beta }^{\prime }$-(BEDT-TTF)${}_2$ICl${}_2$

Abstract

To elucidate the pressure evolution of the electronic structure in an antiferromagnetic dimer-Mott (DM) insulator ${\beta }^{\prime }$-(BEDT-TTF)${}_2$ICl${}_2$, which exhibits superconductivity at 14.2 K under 8 GPa, we measured the polarized infrared (IR) optical spectra under high pressure. At ambient pressure, two characteristic bands due to intra- and interdimer charge transfers have been observed in the IR spectra, supporting that this salt is a typical half-filled DM insulator at ambient pressure. With increasing pressure, however, the intradimer charge transfer excitation shifts to much lower energies, indicating that the effective electronic state changes from half-filled to 3/4-filled as a result of weakening of dimerization. This implies that the system approaches a charge-ordered state under high pressure, in which charge degrees of freedom emerge as an important factor. The present results suggest that charge fluctuation inside of dimers plays an important role in the high-temperature superconductivity.

7 pages, 4 figures, accepted for publication in Physical Review B

References in corpus (5)

• Bandwidth-controlled Mott transition in $\kappa -(BEDT-TTF{)}_{2}Cu[N(CN{)}_2]B{r}_{x}C{l}_{1-x}$ I. Optical studies of localized charge excitations
• Bandwidth-controlled Mott transition in kappa-(BEDT-TTF)2Cu[N(CN)2]Br{x}Cl{1-x}: Optical studies of correlated carriers
• Electronic properties of Fabre charge-transfer salts under various temperature and pressure conditions
• Polar Charge Fluctuation and Superconductivity in Organic Conductor
• Collective excitation of a short-range charge ordering in $\theta$-$\mbox{(BEDT-TTF)}_2\mbox{CsZn(SCN)}_4$

Cited by in corpus (10)

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• From charge- and spin-ordering to superconductivity in the organic charge-transfer solids
• Coulomb Enhanced Superconducting Pair Correlations in the Frustrated Quarter-Filled Band
• Antiferromagnetic State in $\kappa$-type Molecular Conductors: Spin Splitting and Mott Gap
• The metal-insulator transition in the organic conductor ${\beta }^{\prime \prime }$-(BEDT-TTF)${}_2$Hg(SCN)${}_2$Cl
• Electronic State and Optical Response in a Hydrogen-Bonded Molecular Conductor
• Charge imbalance in $\lambda$-(BETS)${}_2$GaCl${}_4$ and their interplay with superconductivity
• Dimer-Mott and charge-ordered insulating states in the quasi-one-dimensional organic conductors ${\delta }_P^{\prime }$- and ${\delta }_C^{\prime }$-(BPDT-TTF)${}_2$ICl${}_2$
• Thermoelectric transport properties of the quasi-one-dimensional dimer-Mott insulator ${\beta }^{\prime }$-(BEDT-TTF)${}_2$ICl${}_2$
• Stability of correlated insulating states in molecular conductors from first-principles calculation