Simultaneous Control of Bandfilling and Bandwidth in Electric Double-Layer Transistor Based on Organic Mott Insulator κ-(BEDT-TTF)2Cu[N(CN)2]Cl

Abstract

The physics of quantum many-body systems have been studied using bulk correlated materials, and recently, moiré superlattices formed by atomic bilayers have appeared as a novel platform in which the carrier concentration and the band structures are highly tunable. In this brief review, we introduce an intermediate platform between those systems, namely, a band-filling- and bandwidth-tunable electric double-layer transistor based on a real organic Mott insulator κ-(BEDT-TTF)2Cu[N(CN)2]Cl. In the proximity of the bandwidth-control Mott transition at half filling, both electron and hole doping induced superconductivity (with almost identical transition temperatures) in the same sample. The normal state under electric double-layer doping exhibited non-Fermi liquid behaviors as in many correlated materials. The doping levels for the superconductivity and the non-Fermi liquid behaviors were highly doping-asymmetric. Model calculations based on the anisotropic triangular lattice explained many phenomena and the doping asymmetry, implying the importance of the noninteracting band structure (particularly the flat part of the band).

Chasing the spin gap through the phase diagram of a frustrated Mott insulator

“…As described in previous work 39,47,48 , cooling yields differential thermal expansion between sample and substrate: the length change is ≤1% between 0 K and 300 K for κ-(BEDT-TTF) 2 Cu 2 (CN) 3 19,49 compared to >>1% for PET. As a result, the sample is subject to biaxial compression of order 1-2 kbar, deduced from the transport results in Fig.…”

“…2a. Assuming that the bent substrate is an arc of a circle, the strain S is estimated as S = 4tx/(l 2 + 4x 2 ) 47,48 using the small angle approximation, where x is the displacement of the nanopositioner, t = 177 μm and l = 12 mm are the thickness and length of the substrate, respectively. The uniaxial tensile strain was applied at 100 K in descending order from 0% to 0.32%.…”

Chasing the spin gap through the phase diagram of a frustrated Mott insulator

“…As described in previous work, 31,36,37 cooling yields differential thermal expansion between sample and substrate: the length change is ≤ 1% between 0 K and 300 K for κ-(BEDT-TTF) 2 Cu 2 (CN) 3 25,38 compared to 1% for PET. As a result, the sample is subject to biaxial compression of order 1-2 kbar, deduced from the transport results in Fig.…”

New Spin on Metal-Insulator Transitions

“…While doping is the preferential tool in oxides, such as superconducting nickelates that are impacted by topotactic hydrogen [1], pressure tuning is the method of choice for organic charge-transfer salts. Kawasugi et al achieved simultaneous control of band filling and bandwidth via in situ strain and gate tuning on κ-(BEDT-TTF) 2 X crystals [2]. Another powerful tuning method is partial chemical substitution, as applied in κ-type systems [3] and quasi one-dimensional (TMTTF) 2 X [4].…”