尋找可以實現拓撲超導的材料是當前研究的熱點。過去科學家們發現可通過超導體和拓撲材料的界面來實現拓撲超導。然而大多數拓撲材料需要加壓摻雜等方式來誘導或增強超導性，導致實驗上很難基於這類材料來實現拓撲超導。這樣尋找一個高質量的單晶樣品同時具有較高的超導轉變溫度和拓撲性質成為當下一個迫切的任務。本研究基於第一性原理計算和實驗測量發現HfRuP家族這類材料不僅具有很高的超導轉變溫度，同時具有拓撲性：HfRuP屬於第二類外爾半金屬相，而ZrRuAs，ZrRuP和HfRuAs屬於拓撲晶體絕緣體相。
來自中國科學院物理研究所的翁紅明和王志俊研究員領導的理論計算團隊，通過第一性原理計算，發現了HfRuP家族具有拓撲非平庸電子結構。根據他們的理論發現，物理研究所的實驗團隊對這類材料進行了進一步地物性研究。其中石友國研究員領導的材料生長團隊成功製備了高質量的HfRuP和ZrRuAs單晶樣品，並研究了其磁化率和電阻隨溫度變化的規律，發現其在超導轉變溫度後表現出邁斯納效應和零電阻特點，證明了這類材料確實具有超導電性。錢天和丁洪研究員領導的角分辨光電子譜團隊測量了他們的能帶結構，其結果與理論計算的電子結構吻合的相當好。利用這些獨特的電子結構，三維拓撲超導可能通過將超導體和外爾半金屬相結合的HfRuP來實現。此外，拓撲晶體絕緣體ZrRuAs、ZrRuP或HfRuAs也可能用來實現拓撲鏡面超導。與過去預言的需要壓力/摻雜來誘發/增強超導電性的拓撲超導材料相比，HfRuP家族的單晶樣品是具有較高超導轉變溫度的本徵超導體，為拓撲超導的研究提供了一個非常好的實驗平臺。
該文近期發表於npj Computational Materials 5: 121 (2019)，英文標題與摘要如下，點擊https://www.nature.com/articles/s41524-019-0260-6可以自由獲取論文PDF。
Topological electronic states in HfRuP family superconductors
Yuting Qian, Simin Nie, Changjiang Yi, Lingyuan Kong, Chen Fang, Tian Qian, Hong Ding, Youguo Shi,Zhijun Wang, Hongming Weng & Zhong Fang
Based on the first-principles calculations and experimental measurements, we report that the hexagonal phase of ternary transition metal pnictides TT’X (T=Zr, Hf; T’=Ru; X=P, As), which are well-known noncentrosymmetric superconductors with relatively high transition temperatures, host nontrivial bulk topology. Before the superconducting phase transition, we find that HfRuP belongs to a Weyl semimetal phase with 12 pairs of type-II Weyl points, while ZrRuAs, ZrRuP and HfRuAs belong to a topological crystalline insulating phase with trivial Fu-Kane Z2 indices but nontrivial mirror Chern numbers. High-quality single crystal samples of the noncentrosymmetric superconductors with these two different topological states have been obtained and the superconductivity is verified experimentally. The wide-range band structures of ZrRuAs have been identified by ARPES and reproduced by theoretical calculations. Combined with intrinsic superconductivity, the nontrivial topology of the normal state may generate unconventional superconductivity in both bulk and surfaces. Our findings could largely inspire the experimental searching for possible topological superconductivity in these compounds.
閱讀更多 知社學術圈 的文章
