Uniaxial strain method for soft crystals: Application to the control of the electronic properties of organic conductors

Abstract

We developed the uniaxial strain method to compress a crystalline sample along any direction without involving Poisson’s effect. The uniaxial strain is realized by inserting a composite of either the sample embedded in epoxy or the sample in frozen oil into a cylinder much harder than the sample composite followed by the application of external forces to a piston put on the sample composite. We verified, by using a strain gauge embedded in the epoxy or the frozen oil, that the strain thus created has the uniaxial nature. Resistance measurements on two kinds of organic conductors, α-(BEDT–TTF)2KHg(SCN)4 and α-(BEDT–TTF)2I3 under the uniaxial strain showed novel electric properties that have never been found under hydrostatic pressures. Their properties were found to be largely dominated by the direction of the uniaxial strain even when it is applied along directions in the conducting plane having a two-dimensional nature.