Iron-based superconductors are believed to host a quantum critical point (QCP), a zero-temperature phase transition, beneath the “dome” delineating the superconducting phase. Elucidating the nature of this QCP is, however, tricky. Worasaran et al. set out to do just that in a prototypical iron-based superconductor, barium iron arsenide. By applying strain to their samples, the researchers found power-law behaviors that are characteristic of nematic quantum criticality. The associated quantum fluctuations were present over a large portion of the phase diagram. This method may be useful in studying quantum criticality in other material systems.
Science, abb9280, this issue p. 973
Quantum criticality may be essential to understanding a wide range of exotic electronic behavior; however, 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 nonthermal tuning parameter close to the quantum critical point (QCP). Here, we observed 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 iron-based superconductors, providing direct evidence of quantum critical nematic fluctuations in this material. These quantum critical fluctuations are not confined within a narrow regime around the QCP but rather extend over a wide range of temperatures and compositions.