Influence of spin fluctuations on the thermal conductivity in superconducting Ba(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$

The thermal conductivity of electron-doped Ba(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$ single crystals is investigated below 200 K, with an emphasis on the behavior near the magnetic and superconducting ($T_c$) transition temperatures. An enhancement of the in-plane thermal conductivity ${\kappa }_{ab}$ is observed below $T_c$ for all samples, with the greatest enhancement observed near optimal doping. The observed trends are consistent with the scattering of heat carriers by low-energy magnetic excitations. Upon entering the superconducting state, the formation of a spin gap leads to reduced scattering and an enhancement in $\kappa \left(T\right)$. Similarly, an enhancement of $\kappa$ is observed for polycrystalline BaFe${}_2$As${}_2$ below the magnetic transition, and qualitative differences in $\kappa \left(T\right)$ between single crystalline and polycrystalline BaFe${}_2$As${}_2$ are utilized to discuss anisotropic scattering. This study highlights how measuring $\kappa$ near $T_c$ in novel superconductors can be useful as a means to probe the potential role of spin fluctuations.

Figure 1

The in-plane (a) electrical resistivity, (b) Seebeck coefficient, and (c) thermal conductivity of Ba(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$ single crystals along with the estimated electronic contribution ${\kappa }_{\mathrm{ele}}$. The low temperature data are highlighted in Fig. 3.

Figure 2

A comparison of the thermal transport data for polycrystalline and single crystalline (${\kappa }_{ab}$) BaFe${}_2$As${}_2$, with the (a) total, (b) lattice, and (c) electronic components of the thermal conductivity shown.

Figure 3

The in-plane thermal conductivity and electrical resistivity of Ba(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$ single crystals at low temperatures highlighting the behavior around $T_c$.

Figure 4

(a) The thermal conductivity (${\kappa }_{ab}$) of Ba(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$ normalized to ${\kappa }_{ab}\left(T_{c,50\%}\right)$; (b) the in-plane $\kappa /T$ data are normalized to the values of this quantity at $T_{c,50\%}$.

Figure 5

The relative importance of the (in-plane) electronic contribution ${\kappa }_{\mathrm{ele}}$ in Ba(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$ at low $T$.