Temperature and Doping-Dependent Renormalization Effects of the Low Energy Electronic Structure of ${\mathrm{Ba}}_{1-x}{\mathbf{K}}_x{\mathrm{Fe}}_2{\mathrm{As}}_2$ Single Crystals

We investigate the low energy electronic structure of ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x{\mathrm{Fe}}_2{\mathrm{As}}_2$ ($x=0$; 0.3, $T_c=32\mathrm{K}$) single crystals by angle-resolved photoemission spectroscopy with a focus on the renormalization of the dispersion. A kink feature is detected at $E\approx 25\mathrm{meV}$ for the doped compound which vanishes at $T=200\mathrm{K}$ but stays virtually constant when $T_c$ is crossed. Our experimental findings rule out the magnetic resonance mode as the origin of the kink and render conventional electron-phonon coupling unlikely. They put stringent restrictions on the dominant source of the electronic interaction channel.

Figure 1

Low energy electronic structure of ${\mathrm{Ba}}_{0.7}{\mathrm{K}}_{0.3}{\mathrm{Fe}}_2{\mathrm{As}}_2$. (a) Fermi surface with Brillouin zone boundary (white dotted line). The blue lines indicate positions of the energy dependent measurements shown in (b) and (c). A slight bending of the dispersion at low energies ($\approx 25\mathrm{meV}$) is visible even in these false color representations.

Figure 2

(a) Dispersions for ${\mathrm{Ba}}_{0.7}{\mathrm{K}}_{0.3}{\mathrm{Fe}}_2{\mathrm{As}}_2$ as a function of temperature along $\Gamma M$. The two clusters of curves belong to the outer and inner $\Gamma$-barrels, respectively. The dispersions above 60 K are horizontally shifted for clarity. The green dotted lines are guides to the eye and parallel. (b) Example of a horizontal cut through the data in Fig. 1b and the fit with four Lorentzians plus linear background. (c) Dispersion along $\Gamma X$.

Figure 3

Low energy electronic structure of undoped ${\mathrm{BaFe}}_2{\mathrm{As}}_2$. (a) Fermi surface map. The dotted lines reflect the Brillouin zone boundaries. (b) Energy dependence of the photoemission intensity along the blue line in (a). (c) Extracted dispersion for $T=6\mathrm{K}$ and 35 K. The red dashed line is a guide to the eye.

Figure 4

(a) Resistance of ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x{\mathrm{Fe}}_2{\mathrm{As}}_2$. Black lines are guides to the eye. Inset: Fermi velocities extracted from data in Fig. 2a. (b) Temperature derivative of the resistance compared to functions of $v_F$.