Resistive anisotropy of candidate excitonic insulator Ta₂NiSe₅under pressure

We have measured anisotropic electrical resistivity of quasi-one-dimensional Ta2NiSe5 single crystals under pressure. While the in-plane anisotropy is almost pressure independent, the inter-plane one greatly decreases at P c ∼ 3 GPa accompanied by a pressure-induced semiconductor-semimetal transition. Nevertheless, a similar anomaly in the temperature dependence of in-plane anisotropy has been observed in each phase. This anomaly in the low-pressure phase below P c is regarded as an excitonic transition, and thus both of these anomalies are suppressed with increasing pressure. These results suggest that the suppression of the excitonic binding energy with pressure is caused by the increase of free carrier densities and the inter-plane conductivity.