Pure nematic quantum critical point accompanied by a superconducting dome

When a symmetry-breaking phase of matter is suppressed to a quantum critical point (QCP) at absolute zero, quantum-mechanical fluctuations proliferate. Such fluctuations can lead to unconventional superconductivity, as evidenced by the superconducting domes often found near magnetic QCPs in correlated materials. Experimentally, however, it remains much less clear whether the superconductivity can be promoted around QCPs of the electronic nematic phase, characterized by rotational symmetry breaking. Here, we demonstrate from systematic elastoresistivity measurements that nonmagnetic FeSe [Formula: see text] Te(x) exhibits an electronic nematic QCP showing diverging nematic susceptibility. This finding establishes two nematic QCPs in FeSe-based superconductors with contrasting accompanying phase diagrams. In FeSe [Formula: see text] Te(x), a superconducting dome is centered at the QCP, whereas FeSe [Formula: see text] S(x) shows no QCP-associated enhancement of superconductivity. We find that this difference is related to the relative strength of nematic and spin fluctuations. Our results in FeSe [Formula: see text] Te(x) present the unprecedented case in support of the superconducting dome being associated with the QCP of pure electronic nematic order, which does not intertwine with any other long-range orders.