近日，英国爱丁堡大学的Davide Marenduzzo及其研究团队取得一项新进展。经过不懈努力，他们揭示三维活动向列中的马约拉纳准粒子和拓扑相。相关研究成果已于2024年12月19日在国际知名学术期刊
该研究团队提出一种在活性向列相中通过三维向错线实现马约拉纳费米子的纯经典方法。其基本原理在于，在三维空间中，+1/2局部缺陷构型与作为其反粒子的-1/2构型是等价的。这种映射还需要证明缺陷构型以旋量的形式变换，并且需要活性来克服与这些激发态相关的弹性成本，从而使它们能在稳态中自发出现。
研究人员结合拓扑学考虑和数值模拟，证明了受限条件下的活性向列相在其内部会自发产生带有拓扑电荷的向错线和环，类似于具有有限动量的马约拉纳准粒子。在一个长通道内，研究人员观察到的现象类似于基塔耶夫链，即马约拉纳态出现在边界附近，而一种非局域的拓扑激发则以手性向错线的形式出现。
三维向列相缺陷与拓扑准粒子之间的类比进一步表明，活性湍流可以被视为一种拓扑相，其中缺陷渗透形成类似于通道中观察到的非局域拓扑准粒子。研究人员提出，三维活性向错线可用于探究马约拉纳旋量的物理特性，其尺度远大于最初引入时的尺度，从而可能促进其实验研究。
据悉，准粒子是凝聚态物理中重要的低能激发态。一个有趣的例子是马约拉纳准粒子，它们与其反粒子等价。尽管马约拉纳准粒子与中微子振荡和拓扑超导性有关，但其在实验中的实现仍然非常罕见。
附：英文原文
Title: Majorana quasiparticles and topological phases in 3D active nematics
Author: Head, Louise C., Negro, Giuseppe, Carenza, Livio N., Johnson, Nathan, Keogh, Ryan R., Gonnella, Giuseppe, Morozov, Alexander, Orlandini, Enzo, Shendruk, Tyler N., Tiribocchi, Adriano, Marenduzzo, Davide
Issue&Volume: 2024-12-19
Abstract: Quasiparticles are low-energy excitations with important roles in condensed matter physics. An intriguing example is provided by Majorana quasiparticles, which are equivalent to their antiparticles. Despite being implicated in neutrino oscillations and topological superconductivity, their experimental realizations remain very rare. Here, we propose a purely classical realization of Majorana fermions in terms of three-dimensional disclination lines in active nematics. The underlying reason is the well-known equivalence, in 3D, between a +1/2 local defect profile and a -1/2 profile, which acts as its antiparticle. The mapping also requires proving that defect profiles transform as spinors, and activity is needed to overcome the elastic cost associated with these excitations, so they spontaneously appear in steady state. We combine topological considerations and numerics to show that active nematics under confinement spontaneously create in their interior topologically charged disclination lines and loops, akin to Majorana quasiparticles with finite momentum. Within a long channel, the phenomenology we observe resembles that of the Kitaev chain, as Majorana-like states appear near the boundaries, while a delocalized topological excitation arises in the form of a chiral disclination line. The analogy between 3D nematic defects and topological quasiparticles further suggests that active turbulence can be viewed as a topological phase, where defects percolate to form delocalized topological quasiparticles similar to those observed in the channel. We propose that three-dimensional active disclinations can be used to probe the physics of Majorana spinors at much larger scale than that for which they were originally introduced, potentially facilitating their experimental study.
DOI: 10.1073/pnas.2405304121
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2405304121