Strain Controlled Charge Density Wave Transition in 1T-TaS2 Films*

We study the influence of strain on the phase transition between the Near Commensurate and the Commensurate Charge Density Wave states in thin films of 1T-TaS2. CDWs emerge due to the enhanced coupling between the conducting electrons and the crystal lattice when they are almost commensurate with each other. As a result, the formation of CDWs is sensitive to changes in the structure induced by external perturbations such as strain. To introduce strain in a controllable fashion we employed two methods. The first consisted of depositing thin 1T-TaS2 films onto arrays of micron size Au pillars and utilized the capillary force to introduce the strain. The pillars were supported on a highly doped Si substrate capped by 300nm of SiO2. The amount of strain was controlled by varying the pillars spacing. In any given sample the pillar spacing was varied in order to achieve an in-situ comparison of the different strain magnitudes. In the second method we introduced strain in suspended thin 1T-TaS2 films over trenches etched into SiO2 by utilizing gate induced electrostatic force. Our results show that the CDW transition temperature increases with the amount of strain, and offer direct evidence that strain provides a mechanism to stabilize the CCDW phase.