Data for "Nematic quantum criticality in an Fe-based superconductor revealed by strain-tuning"

Quantum criticality has been invoked as being essential to the understanding of a wide range of exotic electronic behavior, including heavy Fermion and unconventional superconductivity, but conclusive evidence of quantum critical fluc- tuations has been elusive in many materials of current interest. An expected characteristic fea- ture of quantum criticality is power law behavior of thermodynamic quantities as a function of a non-thermal tuning parameter close to the quan- tum critical point (QCP). In the present work, we observe power law behavior of the critical temperature of the coupled nematic/structural phase transition as a function of uniaxial stress in a representative family of Fe-based supercon- ductors. Our measurements provide direct evi- dence of quantum critical nematic fluctuations in this material. Furthermore, these quantum criti- cal fluctuations are not confined within a narrow regime around the QCP, but extend over a wide range of temperatures and tuning parameters.