The electronic nematic phase—in which electronic degrees of freedom lower the crystal rotational symmetry—is commonly observed in high-temperature superconductors. However, understanding the role of nematicity and nematic fluctuations in Cooper pairing is often made more complicated by the coexistence of other orders, particularly long-range magnetic order. Here we report the enhancement of superconductivity in a model electronic nematic system that is not magnetic, and show that the enhancement is directly born out of strong nematic fluctuations associated with a quantum phase transition. We present measurements of the resistance as a function of strain in Ba1−xSrxNi2As2 to show that strontium substitution promotes an electronically driven nematic order in this system. In addition, the complete suppression of that order to absolute zero temperature leads to an enhancement of the pairing strength, as evidenced by a sixfold increase in the superconducting transition temperature. The direct relation between enhanced pairing and nematic fluctuations in this model system, as well as the interplay with a unidirectional charge-density-wave order comparable to that found in the cuprates, offers a means to investigate the role of nematicity in strengthening superconductivity.
Bibliographical noteFunding Information:
Research at the University of Maryland was supported by the AFOSR Grant No. FA9550-14-10332, the National Science Foundation Grant No. DMR1905891, and the Gordon and Betty Moore Foundation’s EPiQS Initiative through Grant No. GBMF4419. We also acknowledge support from the Maryland Quantum Materials Center as well as the Maryland Nanocenter and its FabLab. The identification of any commercial product or trade name does not imply endorsement or recommendation by the National Institute of Standards and Technology. Theory work (R.M.F. and M.H.C.) was supported by the US Department of Energy, Office of Science, Basic Energy Sciences under award number DE-SC0012336. X-ray experiments at UIUC were supported by DOE grant DE-FG02-06ER46285. P.A. acknowledges support from the Gordon and Betty Moore Foundation’s EPiQS initiative through grant GBMF4542.