  We report the first experimental evidence for the intimate connection between
superconductivity and antiferromagnetism in Rb0.8Fe2Se2-xTex single crystal
under negative chemical pressure by substituting Se with isovalent Te atoms.
Electrical resistance measurements in the temperature range from 4 K to 550 K
demonstrate that both superconducting transition temperature (Tc) and Neel
temperature (TN) were suppressed continuously with the lattice expansion. When
the Te concentration x in Rb0.8Fe2Se2-xTex approaches 0.3, the superconducting
transition temperature Tc is completely suppressed and the sample behaves like
a semiconductor, meanwhile the characteristic peak of antiferromagnetic
transition on resistance curve disappears. Our observation suggests that the
pressure-induced lattice expansion can be used to tune the correlativity of
superconductivity and antiferromagnetism.
