Weak phonon coupling to nematic quantum critical mode in BaFe 2 ( As 1 − x P x ) 2

Despite intense focus on quantum critical behavior, microscopic information on the evolution of spin and nematic correlations remains scarce. Using high-resolution inelastic scattering, the authors investigate here in-plane transverse acoustic phonons in BaFe₂(As_1-xPₓ)₂ near its nematic quantum critical point. The authors observe a weak coupling between the critical nematic fluctuations and the lattice near the critical regime. Together with theory, this result suggests the nature of nematicity evolves from spin-driven with strong lattice coupling in the underdoped regime to orbital-driven with weak coupling near the critical point.