T(c)=21 K in epitaxial FeSe(0.5)Te(0.5) thin films with biaxial compressive strain

Epitaxial FeSe 0.5 Te 0.5 thin \ufb01lms with different thickness were grown by pulsed laser ablation deposition on different substrates. High purity phase and fully epitaxial growth were obtained. By varying the \ufb01lm thickness, superconducting transition temperatures up to 21 K were observed, signi\ufb01cantly larger than the bulk value 16.2 K. Structural analyses indicated that the c-axis is smaller than the bulk value but it is almost independent of the \ufb01lm thickness and the a-axis changes signi\ufb01cantly with the \ufb01lm thickness and is linearly related to the Tc . The latter result indicates the important role of the compressive strain in enhancing Tc . Tc is also related to both the Fe\u2013(Se,Te) bond length and angle, suggesting the possibility of further enhancement