Significantly enhanced superconductivity in monolayer FeSe films on SrTiO3(001) via metallic δ-doping
Xiaotong Jiao, Wenfeng Dong, Mingxia Shi, Heng Wang, Cui Ding, Zhongxu Wei, Guanming Gong, Yanan Li, Yuanzhao Li, Binjie Zuo, Jian Wang, Ding Zhang, Minghu Pan, Lili Wang, Qi‐Kun Xue
Abstract
ABSTRACT Superconductivity transition temperature (Tc) marks the inception of a macroscopic quantum phase-coherent paired state in fermionic systems. For 2D superconductivity, the paired electrons condense into a coherent superfluid state at Tc, which is usually lower than the pairing temperature, between which intrinsic physics including Berezinskii–Kosterlitz–Thouless transition and pseudogap state are hotly debated. In the case of monolayer FeSe superconducting films on SrTiO3(001), although the pairing temperature (Tp) is revealed to be 65–83 K by using spectroscopy characterization, the measured zero-resistance temperature (${{T}}_{{\rm c}}^0$) is limited to 20 K. Here, we report significantly enhanced superconductivity in monolayer FeSe films by δ-doping of Eu or Al on SrTiO3(001) surface, in which ${{T}}_{{\rm c}}^0$ is enhanced by 12 K with a narrowed transition width ΔTc ∼ 8 K, compared with non-doped samples. Using scanning tunneling microscopy/spectroscopy measurements, we demonstrate lowered work function of the δ-doped SrTiO3(001) surface and enlarged superconducting gaps in the monolayer FeSe with improved morphology/electronic homogeneity. Our work provides a practical route to enhance 2D superconductivity by using interface engineering.