Evolution of elastocaloric signature across x of cantidate bulk excitonic insulator Ta_2Ni(Se_(1-x)Sx)_5

The near zero-gap semiconductor Ta2NiSe5 is a quasi 1-d van der Waals layered material that undergoes a structural transition at Tc~328K, which lowers the crystal symmetry from orthorhombic to monoclinic. It has been argued that this structural transition is driven by an excitonic instability, which binds the electrons and holes whose wavefunctions can only be hybridized in the monoclinic phase. Sulfur doping on the Se site is expected to increase the gap, which also suppresses the lattice instability, leading to a reduction of Tc. In this work, we report the study of elastocalroic effect of Sulfer doped Ta2NiSe5, which probes the excitonic susceptibility via the change of temperature induced by strain in the adiabatic condition. This work is intended to disentangle the lattice and electronic contributions to the symmetry breaking phase transition in this system.