We report a high-pressure study of superconductivity and structural evolution in the layered Zintl compound $6R-\mathrm{CaG}{\mathrm{e}}_2$. Upon compression, $\mathrm{CaG}{\mathrm{e}}_2$ undergoes two successive structural transitions, from $R\text{−}3m$ to $P\text{−}3m1$ at 7.5 GPa and then to $P$-1 at 30.4 GPa. Superconductivity emerges near 16 GPa in the $P\text{−}3m1$ phase with $T_{\mathrm{c}}\sim 3$ K; $T_{\mathrm{c}}$ then shows an initial increase followed by a nearly pressure-independent plateau. A second superconducting state appears near the onset of the $P$-1 phase, where $T_{\mathrm{c}}$ reaches $\sim 7$ K and is gradually suppressed upon further compression. Upon decompression, $T_{\mathrm{c}}$ in the $P$-1 phase increases as the Debye temperature decreases, highlighting the important role of lattice dynamics. First-principles calculations indicate that the contrasting $T_{\mathrm{c}}$ evolution in the two high-pressure phases arises from phase-dependent electron-phonon coupling. In $P\text{−}3m1$, superconductivity is mainly associated with the reorganization and softening of low-frequency acoustic modes, whereas in $P$-1, $T_{\mathrm{c}}$ suppression arises from phonon hardening and a reduced electronic density of states at the Fermi level. Our results show that pressure-driven structural evolution in $\mathrm{CaG}{\mathrm{e}}_2$ reshapes electronic states and lattice dynamics, leading to phase-dependent superconductivity and providing insight into pressure-tuned superconductivity in layered Zintl compounds.

Close

PrevNext

View figure in article

• Phase transitions
• Pressure effects
• Superconductivity