Nematic quantum criticality in an Fe-based superconductor revealed by strain adjustment
Iron-based superconductors are believed to harbor a Quantum Critical Point (QCP), a phase transition at zero temperature, under the “dome” delimiting the superconducting phase. Elucidating the nature of this QCP is however delicate. Worasaran et al. set out to do just that in a prototypical iron-based superconductor, barium iron arsenide. By applying a constraint to their samples, the researchers found power law behaviors that are characteristic of nematic quantum criticality. The associated quantum fluctuations were present over much of the phase diagram. This method can be useful for studying quantum criticality in other hardware systems.
Science, abb9280, this issue p. 973
Quantum criticality can be essential for understanding a wide range of exotic electronic behaviors; however, conclusive evidence for critical quantum fluctuations has been elusive in many materials of current interest. An expected characteristic of quantum criticality is the power law behavior of thermodynamic quantities as a function of a non-thermal tuning parameter close to the quantum critical point (QCP). Here, we observed the behavior of the critical temperature power law of the coupled nematic / structural phase transition as a function of the uniaxial stress in a representative family of iron-based superconductors, providing direct evidence for critical nematic fluctuations. quantum in this material. These critical quantum fluctuations are not confined to a tight regime around the QCP but rather extend over a wide range of temperatures and compositions.