In the strongly correlated materials such as cuprate high-temperature superconductors, superconductivity can be controlled either by changing the number of electrons or by changing the kinetic energy, or transfer energy, of electrons in the system.Although a large number of strongly correlated materials have been examined with different parameters to understand the mechanism of superconductivity, the range of parameter control is always limited. A versatile experimental method to achieve simultaneous control of the number and the transfer energy of the electrons has been long desired.
A flexible electric-double-layer transistor (EDLT), or “correlated” transistor, composed of an organic strongly correlated material was constructed (Fig. 1) by researchers at RIKEN, Institute for Molecular Science (IMS), Nagoya University and Toho University. The number of electrons can be controlled by gate voltages of the EDLT, and the transfer energy of electrons can be controlled by bending the EDLT substrate. They found that the system changed from an insulator to a superconductor in both cases of increasing and decreasing electron numbers. Conditions for these superconducting states in the above two cases, however, were found to be fundamentally different. In addition, another superconducting state emerged when the substrate was bent. The present result was published online on Science Advances on May 10, 2019.