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近年来，高压下的富氢化合物被认为是室温超导体的最佳候选体系之一，如何降低富氢化合物稳定所需压力并保持其优异超导电性是目前该领域重要的科学问题.研究中利用第一性原理计算方法探索了电子及空穴掺杂对三元氢化物Pm-3m（CaYH12）动力学稳定性和超导电性的调控作用.结果表明，空穴掺杂可在晶格中产生“化学预压缩”效应，消除其在较低压力下的虚频声子，使其在较低压力下保持动力学稳定.当空穴掺杂浓度达到1.1 e/cell时，Pm-3m（CaYH12）的动力学稳定压力由180 GPa降低至70 GPa，且同时可以保持约194 K的超导转变温度.由此可见，空穴掺杂是一种实现Pm-3m（CaYH12）超导电性优化（低稳定压力、高温超导）的有效策略.本工作为三元氢化物在较低压力下实现高温超导提供了新途径，并为相关实验研究提供了理论支撑.Over the past decades, realizing room-temperature superconductivity has become the tireless pursuit of scientists. Guided by the ‘chemical precompression’ theory, hydrogen-rich compounds have emerged as prime candidates for high-temperature superconductors, positioning them at the forefront of superconducting materials research. Extensive computational studies have identified numerous binary hydrides with predicted superconducting transition temperatures (Tc) exceeding 200 K, such as CaH6, H3S, MgH6, YH6, YH9, YH10, and LaH10 et al. Significantly, the high-Tc of H3S, LaH10, CaH6, YH6, YH9 has been experimentally confirmed. Compared to binary hydrides, ternary hydrides offer more diverse chemical compositions and structures, potentially leading to enhanced properties. Zhang et al. theoretically designed a series of AXH8-type (A = Sc, Ca, Y, Sr, La, Ba; X = Be, B, Al) ternary hydrides with “fluorite-type” backbone, which were predicted to exhibit high-Tc under moderate pressure. Among them, LaBeH8 has been experimentally confirmed to achieve a Tc of 110 K at 80 GPa. The Tcs of ternary clathrate hydrides of Li2MgH16 and Li2NaH17 have been predicted to be significantly surpassing the room temperature, while the required stabilization pressures all exceed 200 GPa. Xie et al. and Liang et al. independently predicted CaYH12 compounds with Pm-3m and Fd-3m space groups, both of which exhibit high-Tc above 200 K at about 200 GPa. Other ternary hydrides, such as La-B-H, K-B-H, La-Ce-H, and Y-Ce-H, have also been extensively investigated. At current stage, a major focus of superconducting hydrides is to achieve high-temperature superconductivity at lower pressures. In this study, taking Pm-3m (CaYH12) as a representative, we systematically investigated the effects of electron and hole doping on the dynamical stability and superconductivity in ternary hydride by first-principal calculations. The Pm-3m (CaYH12) exhibits a Tc of 218 K at 200 GPa, which is consistent with previous report. When decompressing to below 180 GPa, imaginary phonons emerge. The analysis of doping simulations demonstrated that the electron doping exacerbates the softening of the imaginary phonons, whereas hole doping eliminates the imaginary frequencies. At the pressures of 130 GPa, 100 GPa and 70 GPa, the Pm-3m (CaYH12) phase can be stabilized by hole doping at the concentration of 0.9e/cell, 0.8 e/cell, and 1.1 e/cell, respectively. Further electron-phonon coupling calculations show that the Tcs of Pm-3m (CaYH12) at 130 GPa, 100 GPa and 70 GPa are 194 K, 209 K, and 194 K at the corresponding doping level, which are only 10-20 K less than the Tc at 200 GPa. At the pressure of 70 GPa, Tc slightly decreases to 189 K at a doping level of 1.2 e/cell, primarily due to the reduced ωlog compared to the case of 1.1e/cell. And the enhanced λ at 1.2 e/cell is mainly contributed by the average electron-phonon coupling matrix element $\left\langle I^2\right\rangle$ and average phonon frequency $\left\langle\omega^2\right\rangle^{1 / 2}$, rather than the electronic density of states at the Fermi level N(εF). These results indicated that hole doping represents a promising and effective strategy for optimizing the superconductivity of Pm-3m (CaYH12) by maintaining high-Tc at low pressures. Our study has paved an avenue for realizing high-temperature superconductors at low pressure.
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Keywords:
- superconducting ternary hydride /
- first-principles calculations /
- hole doping /
- stabilization pressure regulation
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