狄拉克錐
狄拉克錐是一種特殊二維材料中的電子能帶結構,在此結構中,電子具有像光一樣的相對論性質。科研人員認為狄拉克錐可能是通向未來超級晶片、量子計算機、超導和桌面相對論技術的路徑。[1][2][3][4]
![](http://upload.wikimedia.org/wikipedia/commons/thumb/e/e7/MIT20120424.jpg/220px-MIT20120424.jpg)
典型的狄拉克錐材料包括石墨烯、拓撲絕緣體、鉍銻薄膜和其他新型納米材料。[1][5][6] 這些特殊二維材料中電子的能量和動量具有線性的色散關係,因此其費米能級附近的電子能帶結構呈現出上下兩個錐體,分別代表電子和空穴。兩個錐體的頂端剛好相連,形成「零帶隙」的半金屬相.
狄拉克錐的名字來源於狄拉克方程,由保羅·狄拉克 (Paul Dirac) 提出,用以統一描述物質的量子力學效應和相對論效應。狄拉克錐可以是各向同性,也可是各向異性的。石墨烯中存在各向同性的狄拉克錐,由飛利浦·華萊士 (P. R. Wallace) 於1947提出[7],並由諾貝爾物理學獎得主安德烈·海姆 (Andre Geim) 和康斯坦丁·諾沃肖洛夫 (Konstantin Novoselov) 於2005年首次在實驗中觀察到。[8] 麻省理工學院的唐爽和崔瑟豪斯夫人(Mildred Dresselhaus)於2012年在其唐-崔瑟豪斯理論 (Tang-Dresselhaus Theory) 中首次提出了系統性構建各向異性狄拉克錐的方法。[9][10][11]
描述
編輯在量子力學中,狄拉克錐描述 [12]價帶和導帶的能量在二維晶格k空間中,除了零維狄拉克點所在的位置外,其他任何動量的價帶和導帶能量都不相等。由於是錐型,電傳導可以用無質量費米子的電荷載流子來描述,在理論上這種情況可由相對論性的狄拉克方程來處理。 [13]無質量費米子可以導致各種奇異的量子霍爾效應、或是拓撲材料中的磁電效應和超高載流子遷移率。 [14] [15]在 2008-2009 年實驗上使用角分辨光電子能譜(ARPES) 對鉀-石墨插層化合物KC 8 [16]和幾種鉍基合金的狄拉克錐進行了觀察。[17] [18] [15]
狄拉克錐是二維材料 (像是單層石墨烯)或拓撲絕緣體的表面態的特徵。狄拉克錐在材料中是線性色散關係,由能量與晶體動量的兩個分量k x和k y來描述。然而,這個概念可以擴展到三維材料,其中狄拉克半金屬由能量與k x 、 k y和k z的線性色散關係來定義。在動量空間中,色散關係為超圓錐體,它具有雙重簡併能帶,也在狄拉克點相交。 [15]狄拉克半金屬同時包含時間反演對稱性和空間反演對稱性;當其中一個對稱性被破壞時,狄拉克點可以分裂成兩個外爾點,材料變成外爾半金屬。 [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] 在2014年,實驗上利用ARPES對狄拉克半金屬砷化鎘 的能帶結構進行了直接觀測。 [30] [31] [32]
模擬系統
編輯參看
編輯- 狄拉克物質
參考文獻
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