Accessing the entire overdoped regime in pristine ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6+x}$ by application of pressure

We uncover the previously inaccessible overdoped regime to attain the complete superconducting dome in a pristine high temperature cuprate superconductor, by applying pressures up to 280 kbar to single crystals near stoichiometric ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$. The obtained superconducting phase boundary as a function of hole doping closely follows the form of the superconducting dome in ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$. Measurements are now enabled to trace the evolution of various entangled phases and the Fermi surface from the underdoped to overdoped regime in a single high purity cuprate superconducting family of materials.

Figure 1

Progression of ac susceptibility curves for single crystal ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6.98}$ with increasing applied pressure. Measurements were taken over multiple runs, by increasing pressure in the same setup or by remounting the sample at a higher pressure in a new setup. The inset shows the YBCO unit cell.

Figure 2

Determination of $T_{\mathrm{c}}$ from ac susceptibility curves shows the decrease of transition temperature with increasing pressure for both single crystal and polycrystalline YBCO. Each point has a horizontal error of $\pm 2$ kbar or $\pm 3\%$, the greater of which indicates uncertainty in the determination of pressure inside the sample space as described above. The vertical error bar corresponds to uncertainty in $T_{\mathrm{c}}$, which is related to the width of the transition.

Figure 3

$T_{\mathrm{c}}$-doping phase diagram for single crystal YBCO, with translated pressure-tuned data from Fig. 2 (squares), previous calcium-doped data (hollow circles) [45], and previous zero-pressure data (filled circles) [18]. Translation from pressure to doping $n_{\mathrm{h}}$ was done using relations (1) and (2) while considering constraints in accordance with previous data on ${\mathrm{Y}}_{1-x}{\mathrm{Ca}}_x{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6.96}$ [45], for which $n_{\mathrm{h}}$ was estimated using a combination of copper and oxygen bond valence sums (BVS). The effects of the different constraints are reflected in the horizontal error bars. The dashed curve indicates the LSCO superconducting dome [2, 45], $1-T_{\mathrm{c}}/T_{\mathrm{c},\max }=82.6{(n_{\mathrm{h}}-0.16)}^2$, with $T_{\mathrm{c},\max }$ set to 94.3 K for YBCO single crystals [18].