Kaibing Wen^1,2, Yuting Zhang^1,2, Zefeng Lin¹, Qihong Chen^1,2,*, and Kui Jin^1,2,*

¹ Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China

² School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China

Nematicity is ubiquitous in iron-based superconductors, yet its role in achieving high superconducting transition temperature (T_c) remains a central issue. FeSe_1-xTe_x (FST) is an ideal system due to its unique phase diagram with separated nematic and antiferromagnetic orders. Here, we grow composition-spread FST epitaxial films (x = 0-1) on CaF₂ substrates by combinatorial laser molecular beam epitaxy, enabling continuous tuning of composition within a single high-quality film. Compositional and structural uniformity are confirmed by wavelength-dispersive spectroscopy (WDS) and X-ray diffraction reciprocal space mapping (RSM), revealing a smooth compositional gradient and systematic lattice evolution without phase separation. Systematic transport measurements, including resistivity, Hall effect, and angular magnetoresistance (AMR), show that the nematic transition is progressively suppressed with increasing Te content and vanishes at a nematic quantum critical point (QCP). Compared to bulk FST, the nematic QCP in thin films shifts toward lower Te content, accompanied by a corresponding shift of the maximum Tc, which consistently occurs at the QCP in both systems. This correlation demonstrates that superconductivity is enhanced near the nematic QCP. Our results provide clear evidence that nematic fluctuations play a key role in enhancing superconductivity in FST, highlighting the importance of nematicity in iron-based superconductors.