  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
fluctuations has been elusive in many materials of current interest. An
expected characteristic feature of quantum criticality is power law behavior of
thermodynamic quantities as a function of a non-thermal tuning parameter close
to the quantum 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 superconductors. Our measurements provide direct evidence of quantum
critical nematic fluctuations in this material. Furthermore, these quantum
critical fluctuations are not confined within a narrow regime around the QCP,
but extend over a wide range of temperatures and tuning parameters.
