Figure 2. Ta₂NiSe₅ transport and specific heat.

(a) Temperature dependence of the in-plane resistivity of Ta₂NiSe₅ single crystal ρ_a (red) along the a axis parallel to the Ta and Ni chains, and ρ_c (blue) along the c axis perpendicular to the chains. An anomaly is observed at T_C=326 K (emphasized by black triangle). The inset shows the temperature dependence of the resistivity ratio, ρ_c/ρ_a as an indicator of the in-plane anisotropy. (b) The temperature dependence of the activation energy E_ρ of the resistivity data in a given by E_ρ=−k_BT²(‖lnρ/‖T). (c) Temperature dependence of heat capacity C of a Ta₂NiSe₅ single crystal. An anomaly in C at T_C is clearly visible. The phonon contribution (black dashed line) is roughly estimated from a Debye fit to the low-temperature data below T_C. The inset shows the excess specific heat ΔC/T around T_C obtained from the raw heat capacity by subtracting the lattice contribution.