Organic Mott-FET
FET (Field-Effect-Transistor) can change the number of carriers at the interface, or the band filling, by applying a gate electric field. We have been trying to realize a filling-controlled Mott-transition by using such a FET structure with κ-type BEDT-TTF salt. This idea was originally proposed by IBM research group in 1990's and has been tried by several groups, but none of them was successful in observing clear Mott-transition. We have focused on formation of a thin single crystal of κ-type BEDT-TTF salt with clean surface to be incorporated into a Mott-FET (Figure 3A-C). As a result, we have succeeded in obtaining an efficient Mott-FET device to observe clear Mott-transition induced by a gate electric-field (Figure 4A-C).
Figure 3 A: Cross-section for Mott-FET. B: Microscope image for an organic Mott-FET. Scale bar is 100μｍ. C: AFM image for κ-Br single crystal surface. Steps at the surface are 1.7 nm-height, corresponding to one BEDT-TTF molecular layer
Figure 4 A: Temperature dependence of relative resistivity measured for κ-Br on top of subsrates. Black, blue, and red curves show bulk, on silicon, and on polystyrene measurement results, respectively. B: Transfer characteristics for κ-Br based Mott-FET. Red, log-scale and black, linear-scale. C: Carrier concentration at the Mott-FET interface as a function of gate-voltage, determined by Hall effect measurement (20 K).
［References］
- Y. Kawasugi, H. M. Yamamoto, M. Hosoda, N. Tajima, T. Fukunaga, K. Tsukagoshi, and R. Kato
Strain-Induced Superconductor/Insulator Transition and Field Effect in a Thin Single Crystal of Molecular Conductor
Appl. Phys. Lett., 92, 243508/1-243508/3 (2008). - Y. Kawasugi, H. M. Yamamoto, N. Tajima, T. Fukunaga, K. Tsukagoshi, and R. Kato
Field-Induced Carrier Delocalization in the Strain-Induced Mott Insulating State of an Organic Superconductor
Phys. Rev. Lett., 103(11), 116801/1-116801/4 (2009). - Y. Kawasugi, H. M. Yamamoto, N. Tajima, T. Fukunaga, K. Tsukagoshi, and R. Kato
Electric-Field-Induced Mott Transition in an Organic Molecular Crystal
Phys. Rev. B, 84, 125129/1-125129/9 (2011).
