Spatial mapping of electronic states in κ-(BEDT-TTF)₂X using infrared reflectivity

Abstract

We review our recent work on spatial inhomogeneity of the electronic states in the strongly correlated molecular conductors κ-(BEDT-TTF) 2 X. Spatial mapping of infrared spectra (SMIS) is used for imaging the distribution of the local electronic states. In molecular materials, the infrared response of the specific molecular vibration mode with a strong electron-molecular vibration coupling can reflect the electronic states via the change in the vibration frequency. By spatially mapping the frequency shift of the molecular vibration mode, an electronic phase separation has been visualized near the first-order Mott transition in the bandwidth-controlled organic conductor κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br. In addition to reviewing SMIS of the phase separation, we briefly mention the electronic and optical properties of κ-(BEDT-TTF) 2 X.

Magnetic Properties of X-ray Irradiated Organic Mott Insulator κ-(BEDT-TTF)2Cu[N(CN)2]Cl

“…Furthermore, if the volume fraction of 15% is distributed to each extra carrier (0.04%) in the 2D donor layer, one can roughly evaluate the domain size of $(20 nm) 2 , which is randomly distributed with a mean distance of approximately 50 nm. In contrast to the phase separation 11) related to the Mott transition in -(BEDT-TTF) 2 Cu[N(CN) 2 ]Br, we have found no macroscopic inhomogeneity in the local infrared spectroscopy of -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl after X-ray irradiation. 25) The spatial inhomogeneity is thus on a scale much smaller than the resolution of the spectroscopy, $10 mm.…”

Charge localization in strongly correlated $κ$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]I due to inherent disorder

“…It appears as a broad resonance between 1250 and 1350 cm −1 for E||c, and between 1100 and 1250 cm −1 for E a. Vibrations of the ethylene endgroups result in four ν 5 (a g ) peaks observed at the lower edge of the main resonance for E a, and antiresonant dips in the E c spectra [26,27]. Here the ν 3 mode is shifted to lower frequency compare to κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br in agreement with higher correlation strength in the former one [56]. In addition, the other strong modes in Fig.…”

A strained organic field-effect transistor with a gate-tunable superconducting channel

“…1b by orange and red arrows. Device 1 showed insulating behaviour at low temperature, whereas device 2 showed a small resistance drop at 12 K, followed by a re-entrant percolation transition around 9 K. This behaviour of device 2 indicates that the system is in the partially SC phase where separation between SC and MI phases occurs and the SC fraction is maximized around 9 K. Such a situation has already been investigated in detail for a bulk material by infrared spectroscopy mapping 16 , nuclear magnetic resonance 17 , noise measurement 18 and so on. In our devices, magnetization measurement for another sample (device 3) also showed partial superconductivity and maximization of SC fraction at medium temperature range, which will be described later.…”