Higgs transition from a magnetic Coulomb liquid to a ferromagnet in Yb2Ti2O7
Lieh-Jeng Chang , Shigeki Onoda, Yixi Su, Ying-Jer Kao , Ku-Ding Tsuei , Yukio Yasui, Kazuhisa Kakurai & Martin Richard Lees
Nature Communications, 3, 992 (2012), (DOI: 10.1038/ncomms1989)
Magnetic monopoles can be regarded as the magnetic version of a charged particle like electrons and protons. They carry an isolated magnetic pole, either the North or the South poles. Normally magnets come in the form of dipoles, with both North and South poles appearing in pairs. In a class of magnetic materials called spin ice, four electron spins reside at the four corners of a tetrahedron will be compromised to the spin configuration of 2-in and 2-out toward to the center of the tetrahedron, i.e. obeying the ice rule. When a spin is excited and reverse its direction, there will creat emergent magnetic monopoles, which interact through the magnetic Coulomb law. However, when the spins can rotate away from the “in” and “out” spin configuration because of the quantum-mechanical interactions between the spins, the system is called quantum spin ice. Magnetic monopoles can condense to form a ferromagnet, which can be regarded as the “superconducting” state of monopoles, and is formed through a Higgs mechanism.
磁單極可被視為磁性版本的帶電粒子，就像是電子和質子，它們只帶有一個磁極，北極或是南極。在一般的磁鐵中，磁矩以偶極子的形式，也就是南北兩極成對出現。在一類被稱為自旋冰(spin ice)的磁性材料中，在四面體上的四個電子自旋(spin)會排列成向四面體中心「二進二出」的組態，也就是符合了「冰組態的規則」。當其中一個自旋被翻轉，會產生激發的磁單極，而這些磁單極之間透過磁性的庫侖定律交互作用。當這些自旋因為量子力學的交互作用，而不再被限制在只能夠指進或出的時候，這個系統被稱作「量子自旋冰」。磁單極可以凝聚形成一個鐵磁態，而這個態可以視為磁單極通過一個希格斯機制(Higgs mechanism)所產生的超導態。