Pressure-dependent optical investigations of Fabre salts in the charge-ordered state

Abstract

In a comprehensive infrared study, the molecular vibrational features of (TMTTF)SbF, (TMTTF)AsF and (TMTTF)PF single crystals have been measured down to temperatures as low as 7 K by applying hydrostatic pressure up to 11 kbar. We follow the charge disproportionation below the critical temperatures T as pressure increases, and determine the critical pressure values p at which the charge-ordered phase is suppressed. The coexistence of the spin-Peierls phase with charge order is explored at low temperatures, and the competition of these two phases is observed. Based on our measurements we construct a generic phase diagram of the Fabre salts with centrosymmetric anions. The pressure-dependent anion and methyl-group dynamics in these quasi-one-dimensional charge transfer compounds yields information about the interplay of the organic molecules in the stacks and the anions, and how this interaction varies upon the transition to the charge-ordered state.

Structural and Electronic Properties of (TMTTF)2X Salts with Tetrahedral Anions

“…Our pressure-dependent DC-transport measurements yield valuable information on the influence of the lattice on the ordering phenomena in the quasi one-dimensional charge-transfer salts (TMTTF) 2 X with tetrahedral anions X = BF 4 , ClO 4 and ReO 4 . We observe a decrease of the charge ordering temperature T CO upon pressure for (TMTTF) 2 BF 4 and (TMTTF) 2 ReO 4 ; similar to the observation reported for salts with octahedral anions [104]. In contrast to CO, the pressure dependence of AO differs for each salt such that the construction of a generic phase diagram of (TMTTF) 2 X salts with tetrahedral anions is not possible.…”

Light-Induced Current Oscillations in the Charge-Ordered State of (TMTTF)2SbF6

“…This allows us to assign T CO more precisely compared to optical methods [7,8] and to deduce the contact resistances in this particular case. In Figure 5 the logarithm of the resistance of (TMTTF) 2 SbF 6 is illustrated for the a-direction in a temperature range from room temperature down to 125 K. When lowering the temperature, the resistance decreases down to a minimum at T = 215 K, which corresponds to the sign change of its slope (see inset).…”

“…During the last years several comprehensive investigations have been conducted on the optical [5][6][7][8][9] and transport properties [10], the lattice [11,12] and electronic structure [13][14][15] as well as on the magnetic properties [16][17][18][19][20][21]. However, not much is known about the non-linear properties at the charge-order transition taking place at T CO = 157 K and transient conduction phenomena.…”

Light-Induced Current Oscillations in the Charge-Ordered State of (TMTTF)2SbF6

“…This allows us to assign T CO more precisely compared to optical methods [7,8] and to deduce the contact resistances in this particular case. In Figure 6 the logarithm of the resistance of (TMTTF) 2 SbF 6 is illustrated for the a-direction in a temperature range from room temperature down to 125 K. When lowering the temperature, the resistance decreases down to a minimum at T = 215 K, which corresponds to the sign change of its slope (see inset).…”

“…In recent years, several comprehensive investigations have been conducted on the optical [5][6][7][8][9] and transport properties [10], the lattice [11,12] and electronic structure [13][14][15] as well as on the magnetic properties [16][17][18][19][20][21]. However, not much is known about the non-linear properties at the charge-order transition taking place at T CO = 157 K and transient conduction phenomena.…”