Pressure dependence of shear elastic mode near structural transition in the band Jahn-teller model

The temperature dependence of the pressure derivative of the shear elastic constant $\text{dC}{}_{\mathrm{<mtext>S</mtext>}}\text{dp}$ for degenerate electronic system is worked out in the band Jahn Teller model and is shown to follow C_S linearly as the temperature decreases and approaches the transition temperature T_M. The constant of proportionality gives useful informations on the characteristics of the band Jahn-Teller transition. This analysis can explain well the recently observed experimental results on Nb₃Sn.