Electrically induced phase transition inα−(BEDT-TTF)2I3: Indications for Dirac-like hot charge carriers

Abstract

The two-dimensional organic conductor α-(BEDT-TTF)2I3 undergoes a metal-insulator transition at TCO = 135 K due to electronic charge ordering. We have conducted time-resolved investigations of its electronic properties in order to explore the field-and temperature-dependent dynamics. At a certain threshold field, the system switches from low-conducting to a high-conducting state, accompanied by a negative differential resistance. Our time-dependent infrared investigations indicate that close to TCO the strong electric field pushes the crystal into a metallic state with optical properties similar to the one for T > TCO. Well into the insulating state, however, at T = 80 K, the spectral response evidences a completely different electronically-induced high-conducting state. Applying a two-state model of hot electrons explains the observations by excitation of charge carriers with a high mobility. They resemble the Dirac-like charge-carriers with a linear dispersion of the electronic bands found in α-(BEDT-TTF)2I3 at high-pressure. Extensive numerical simulations quantitatively reproduce our experimental findings in all details.

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

“…In general a coherent sliding of the density wave is observed above a more or less well defined electric threshold field of a few mV/cm [46,75]; this is not the case for (TMTTF) 2 SbF 6 . Here we have to apply an electric field of several V/cm, much more than typically needed for classical CDW systems; but two orders of magnitude smaller than the threshold fields in the charge-ordered salt α-(BEDT-TTF) 2 I 3 [22,28]. The large difference can be explained by the fact that most of the typical CDW compounds develop an incommensurate charge modulation that is pinned to impurities.…”

“…Following the approach presented in Ref. [28,56], we calculated the temporal behavior of the sample temperature and correlate it with the temperature-dependent sample resistance depicted in Figure 5. The result of the simulation is visualized in Figure 10 for various temperatures T between 125 K and 154 K. We assume that the complete pulse energy is absorbed and transferred into Joule heat at the surface of the specimen as the penetration depth is only a few hundred nanometers.…”

“…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. This is surprising, since nonlinear behavior was observed in various inorganic as well as organic compounds in the vicinity of a metal-insulator transition, such as the charge-density wave transition in NbSe 3 , the metal insulator transition in VO 2 , or the charge-order transition in the two-dimensional α-(BEDT-TTF) 2 I 3 salt [22][23][24][25][26][27][28].…”

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

“…Note, this is just the temperature of the hot electrons and does not mean that the sample is heated up. The electron-electron interaction is much faster than the electron-phonon interaction [28]. These excited electrons or quasi-particles follow the heat balance equation:…”

“…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. This is surprising, since nonlinear behavior was observed in various inorganic as well as organic compounds in the vicinity of a metal-insulator transition, such as the charge-density wave transition in NbSe 3 , the metal insulator transition in VO 2 , or the charge-order transition in the two-dimensional α-(BEDT-TTF) 2 I 3 salt [22][23][24][25][26][27][28][29].…”