Pressure dependence of the charge-density-wave and superconducting states in ${\text{GdTe}}_3, {\text{TbTe}}_3$, and ${\text{DyTe}}_3$

We present electrical resistivity and ac-susceptibility measurements of ${\text{GdTe}}_3, {\text{TbTe}}_3$, and ${\text{DyTe}}_3$ performed under pressure. An upper charge-density-wave (CDW) is suppressed at a rate of $d{T}_{\mathrm{CDW},1}/dP\sim -85\mathrm{K}/\mathrm{GPa}$. For ${\text{TbTe}}_3$ and ${\text{DyTe}}_3$, a second CDW below $T_{\mathrm{CDW},2}$ increases with pressure until it reaches the $T_{\mathrm{CDW},1}$($P$) line. For ${\text{GdTe}}_3$, the lower CDW emerges as pressure is increased above $\sim 1\text{GPa}$. As these two CDW states are suppressed with pressure, superconductivity (SC) appears in the three compounds at lower temperatures. Ac-susceptibility experiments performed on ${\text{TbTe}}_3$ provide compelling evidence for bulk SC in the low-pressure region of the phase diagram. We provide measurements of superconducting critical fields and discuss the origin of a high-pressure superconducting phase occurring above 5 GPa.

Figure 1

In-plane electrical resistivity $\rho$ vs temperature $T$ of (a) ${\text{GdTe}}_3$ and (b) ${\text{DyTe}}_3$ at different pressures (hydrostatic cell). CDW ordering temperatures $T_{\mathrm{CDW},1}$ and $T_{\mathrm{CDW},2}$ were obtained from the derivatives of these curves (not shown). Insets display the superconducting and magnetic ordering features occurring at low temperatures. Superconducting transitions in ${\text{GdTe}}_3$ obtained from the Bridgman-anvil cell are shown in the inset of (a).

Figure 2

Determination of critical fields of ${\text{GdTe}}_3, {\text{TbTe}}_3$, and ${\text{DyTe}}_3$ at different pressures obtained in the hydrostatic cell experiments. Magnetic fields were applied perpendicular to the planes; i.e., $H\parallel b$ axis. (a)–(c) Electrical resistivity of ${\text{GdTe}}_3$. (d)–(f) Electrical resistivity of ${\text{DyTe}}_3$. (g) $H_{c2}\left(T\right)$ of ${\text{GdTe}}_3$ at 1.2, 1.8, and 2.5 GPa. (h) $H_{c2}\left(T\right)$ of ${\text{DyTe}}_3$ at 1.2, 1.8, and 2.5 GPa. The inset shows the evolution of the Fermi velocities $v_F$ obtained from the slopes near $T_c$. (i) $H_{c2}\left(T\right)$ of ${\text{GdTe}}_3, {\text{TbTe}}_3$, and ${\text{DyTe}}_3$ at similar pressures. For ${\text{TbTe}}_3$, data were obtained from the ac-susceptibility measurements displayed in the inset. The dashed lines plotted in (g)–(i) correspond to calculations of $H_{c2}\left(T\right)$ with the WHH model.

Figure 3

Superconducting $T_c$ (onset) vs pressure $P$ phase diagram of ${\text{GdTe}}_3, {\text{TbTe}}_3$ and ${\text{DyTe}}_3$. Data below 2.7 GPa were obtained in the hydrostatic clamped-cell experiments, while higher-pressure data were obtained from the Bridgman-anvil cell experiments. Data corresponding to tellurium is displayed for comparison (white triangles). The dashed line represents a dome-shaped region where the superconducting phase intrinsic to the $R{\text{Te}}_3$ possibly occurs.

Figure 4

(a) Electrical resistivity $\rho$ vs temperature $T$ of tellurium at 1.2 GPa. The sample of Te was measured in a hydrostatic-clamped cell together with a sample of ${\text{TbTe}}_3$. At 1.2 GPa, Te is nonmetallic down to 150 mK, while ${\text{TbTe}}_3$ superconducts below $T_c=0.7$ K (inset, $H\parallel b$). (b) Ac-susceptibility measurement of ${\text{TbTe}}_3$ at 1.75 GPa ($H\parallel b$). The cartoon illustrates the secondary coils used in the high-pressure experiments.

Figure 5

Temperature vs pressure phase diagram of ${\text{GdTe}}_3, {\text{TbTe}}_3$, and ${\text{DyTe}}_3$. $T_{\mathrm{CDW},1}$ is suppressed with pressure and merges with $T_{\mathrm{CDW},2}$, which can no longer be determined above 2.7 GPa. At lower temperatures, SC emerges above 1 GPa and below 1.5 K ($T_c$ from low-pressure region of Fig. 3, amplified by a factor of 20). Ambient pressure data taken from Refs. [15] and [45].