Fig. 2: Transformation onto the imaginary time axis.
From: Quantum critical fluctuations in an Fe-based superconductor
Shown is \(\beta \tilde{{{\Lambda }}}(\beta /2)\), the imaginary time-ordered correlation function \(\tilde{{{\Lambda }}}(\tau )\) derived from the Raman spectra of Ba(Fe1−xCox)2As2 and evaluated at τ = β/2 multiplied by the inverse temperature β = 1/kBT, versus temperature T. The dashed lines correspond to \(\beta \tilde{{{\Lambda }}}(\beta /2,T)={{{{{{{\rm{const}}}}}}}}\), and the blue regions indicate the deviation from this constant behavior, which we use to define the crossover temperatures \({T}_{{{{{{{{\rm{UD}}}}}}}}}^{* }\) and \({T}_{{{{{{{{\rm{OD}}}}}}}}}^{* }\) for x < xc and x > xc, respectively. a At x = 0.052 doping a nematic transition occurs at Tnem ~ 50 K at which \(\beta \tilde{{{\Lambda }}}(\beta /2,T)\) develops a cusp and then decreases toward Tc. b At x = 0.057, \(\beta \tilde{{{\Lambda }}}(\beta /2,T)\) increases toward lower temperatures and develops a maximum above Tc. c Closer to the quantum critical point (QCP) \(\beta \tilde{{{\Lambda }}}(\beta /2,T)\) develops a hump between \({T}_{{{{{{{{\rm{UD}}}}}}}}}^{* }\) and Tc. d On the overdoped side at x = 0.073 the Ω/T scaling persists down to Tc. e Further away, the crossover temperature increases again. f The high crossover temperature at x = 14.6 coincides with a small superconducting transition temperature.
