Superconductivity in ternary yttrium-zirconium hydride under high pressure

Compared to binary hydrides, ternary polyhydrides increase the configurational degrees of freedom and offer a richer variety of candidate structures. This significantly expands the search space for high-temperature superconductivity. According to theoretical predictions, P4/mmm-YZrH_8 is a promising superconductor that will exhibit a superconducting transition temperature (T_\rm c) of approximately 60-70 K at 200 GPa. In this work, we successfully synthesized P4/mmm-YZrH_8 under pressures remarkably lower than those used in theoretical calculations. P4/mmm-YZrH_8 shows a T_\rm c ranging from 64 K to 87 K within 167-190 GPa. Besides, the T_\rm c of P4/mmm-YZrH_8 increases at a rate of approximately 1.01 K/GPa, as pressure decreases from 190 GPa. The maximum T_\rm c observed is 87 K at 167 GPa. The upper critical field (\mu_0H_\rm c2(0)) at 183 GPa is determined to be 19.3 T (WHH) and 15.7 T (GL), respectively. Moreover, the existence of d-electrons in Zr suppresses the hydrogen-dominated superconductivity of hydrides, thereby leading to a lower T_\rm c. Zr is not an ideal element in ternary yttrium hydrides. Nevertheless, our research provides valuable insights for the future exploration of ternary hydride systems.