海歸學者發起的公益學術平臺
分享資訊，整合資源
交流學術，偶爾風月
Kagome晶格是由兩個共享頂角的三角形構成的，電子結構展示出平帶、範霍夫奇點以及Dirac點，因而具有十分豐富的物性。2019年，AV3Sb5體系成功被合成，並發現具有電荷密度波、非平庸拓撲性質、獨特的壓力依賴的超導相圖激起了人們對於以AV3Sb5為原型的材料探索熱潮。以AV3Sb5為原型的Kagome金屬材料因其具有電荷密度波、超導電性、非平庸的電子態以及拓撲超導電性成為了凝聚態物理學探索新奇物性的理想平臺。為了減少實驗的盲目性，理論預測新型可能被合成的AV3Sb5系列材料與物性顯得十分重要。
來自中國科學院物理研究所/松山湖材料實驗室的孟勝研究員、劉淼研究員與徐紀玉副研究員領導的團隊透過第一性原理計算的方式提出了一類具有熱力學、動力學穩定的Kagome金屬ANb3Bi5(A = K, Rb, Cs)，併發發現體系同時具有超導電性與非平庸電子性質。
他們透過系統的理論計算，探索了體系的穩定性、超導電性以及拓撲性質。研究結果表明：(1) 考慮單質、二元化合物等形成能計算均為負，聲子譜並無虛頻，表明體系具有良好的熱力學及動力學穩定性；(2) 基於Allen-Dynes修正的McMillan公式，計算發現KNb3Bi5,
RbNb3Bi5和CsNb3Bi5分別具有2.11, 2.15 和2.21 K的超導轉變溫度；(3) 透過能帶宇稱性計算了體系的Z2指數，結合費米能級附近具有明顯的表面態可以將體系歸結為Z2金屬。這些結果為實驗探索新型Kagme材料提供了有益指引。該研究為探索超導電性、非平庸電子性質與拓撲超導之間關聯性提供了新的研究平臺。
RbNb3Bi5和CsNb3Bi5分別具有2.11, 2.15 和2.21 K的超導轉變溫度；(3) 透過能帶宇稱性計算了體系的Z2指數，結合費米能級附近具有明顯的表面態可以將體系歸結為Z2金屬。這些結果為實驗探索新型Kagme材料提供了有益指引。該研究為探索超導電性、非平庸電子性質與拓撲超導之間關聯性提供了新的研究平臺。
該文近期發表於npj Computational Materials 10：96 (2024)，英文標題與摘要如下，點選左下角“閱讀原文”可以自由獲取論文PDF。
Fig.1 Crystal structure of ANb3Bi5(A = K, Rb, Cs).
ANb3Bi5(A = K, Rb, Cs) 晶體結構的(a)側檢視與(b)俯檢視。
Fig.2 Phonon dispersions of ANb3Bi5(A = K, Rb, Cs) weighted by different atomic vibrational modes and the
magnitude of the phonon linewidth.
magnitude of the phonon linewidth.
(a)-(c) 原子振動模式分辨的聲子譜及聲子態密度。(d)-(f) 聲子線寬權重的聲子譜，Eliashberg譜函式及積分電聲耦合強度。
Fig.3 Band structures without SOC for ANb3Bi5(A = K, Rb, Cs).
ANb3Bi5(A = K, Rb, Cs)體系不考慮自選軌道耦效應的原子軌道分辨的能帶結構及態密度。
Fig.4 Band structures with SOC for ANb3Bi5(A = K, Rb, Cs).
ANb3Bi5(A = K, Rb, Cs)體系考慮自選軌道耦合效應的能帶結構。陰影部分為連續能隙。
Fig.5 Surface states of KNb3Bi5.
(a)-(b) KNb3Bi5體系表面態。(c)-(d)表面態對應的等能面示意圖。
Coexistence of
superconductivity and topological phase in kagome metals ANb3Bi5(A = K, Rb, Cs) (Kagome金屬ANb3Bi5
superconductivity and topological phase in kagome metals ANb3Bi5(A = K, Rb, Cs) (Kagome金屬ANb3Bi5
Jianguo Si, Lanting Shi, Bozhu Chen, Huanhuan Yang, Jiyu Xu, Miao Liu & Sheng Meng
TheAV3Sb5 prototype kagome materials have been
demonstrated as a versatile platform for exploring exotic properties in
condensed matter physics, including charge density waves, superconductivity,
non-trivial electron topology, as well as topological superconductivity. Here
we identify that ANb3Bi5 (A = K, Rb, Cs)
exhibit non-trivial coexisting superconductivity and topological properties via
first-principles calculations. The negative formation energy and the absence of
imaginary phonon dispersion demonstrate both thermodynamics and dynamics
stabilities of ANb3Bi5 (A = K, Rb, Cs)
under ambient conditions. By analytically solving the Allen-Dynes-modified
McMillan formula, the superconducting transition temperatures are predicted to
be 2.11, 2.15 and 2.21 K for KNb3Bi5, RbNb3Bi5,
and CsNb3Bi5, respectively. More importantly, the kagome
materials proposed here can be classified into Z2 topological metals
due to the non-trivial topological index and the obvious surface states around
the Fermi level. Such coexistence of superconductivity and non-trivial band
characters in ANb3Bi5 (A = K, Rb, Cs) offer
us more insights to study the relationship between superconductivity and
topological properties, and to design innate topological superconductors.
demonstrated as a versatile platform for exploring exotic properties in
condensed matter physics, including charge density waves, superconductivity,
non-trivial electron topology, as well as topological superconductivity. Here
we identify that ANb3Bi5 (A = K, Rb, Cs)
exhibit non-trivial coexisting superconductivity and topological properties via
first-principles calculations. The negative formation energy and the absence of
imaginary phonon dispersion demonstrate both thermodynamics and dynamics
stabilities of ANb3Bi5 (A = K, Rb, Cs)
under ambient conditions. By analytically solving the Allen-Dynes-modified
McMillan formula, the superconducting transition temperatures are predicted to
be 2.11, 2.15 and 2.21 K for KNb3Bi5, RbNb3Bi5,
and CsNb3Bi5, respectively. More importantly, the kagome
materials proposed here can be classified into Z2 topological metals
due to the non-trivial topological index and the obvious surface states around
the Fermi level. Such coexistence of superconductivity and non-trivial band
characters in ANb3Bi5 (A = K, Rb, Cs) offer
us more insights to study the relationship between superconductivity and
topological properties, and to design innate topological superconductors.
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