Reentrant Lock-in Transition of the Charge-Density Wave in2H-TaSe2at High Pressure

High-pressure x-ray scattering studies of $2H$-Ta${\mathrm{Se}}_2$ reveal reentrant behavior of the charge-density-wave (CDW) lock-in transition. As pressure is increased the normal-to-incommensurate CDW transition changes less than 5 K; however, the lock-in transition, initially suppressed to $T\to 0$ K at ∼1.7 GPa, reappears at ∼2.5 GPa. At the highest pressures (4.4 GPa) the temperature dependence of the incommensurability approaches the universal curve given by Landau theory for a single-$\overrightarrow{\mathrm{q}}$ CDW.