Light from ripples
Light from ripples
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DOI：
10.1038/nphys2447
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发表时间：
2012-10
期刊：
影响因子：
19.6
通讯作者：
I. Georgescu
中科院分区：
文献类型：
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作者：
I. Georgescu
冷凝物;由半导体微腔中的二维激子极化激元形成（图1a）。激子极化激元是具有光子和电子激发（激子）的混合特性的准粒子。它们具有整数自旋和非常小的有效质量，这导致在相对较高的温度下有效冷凝。极化激元的寿命只有大约10 ps，但有人认为这足以形成准热化稳态。极化激元的动量、能量和自旋状态可以通过它们在衰变时发射的光子的分布和偏振在直接空间中成像。极化激元凝聚体的波函数可以用自旋的有效场与可控的有效磁场相互作用来描述。Hivet等人安排了他们的实验，以创建横向于极化激元流方向的一维有效自旋场。流动路径中的结构缺陷产生稳定的“半孤子”纹理，其对应于有效自旋场中的单极子。在真实的时间内观察到这些磁单极子响应于有效磁场的漂移和加速。“极化子单极子”服从一维库仑定律（因此它们是受限的），但由于它们的有效质量是负的，同性电荷相互吸引，异性电荷相互排斥。这种维度和力定律意味着它们不太像电荷或自旋冰单极子。也许它们更类似于铁磁纳米线中的横向畴壁，其中磁化场是远离壁的单极。这种磁性纹理被认为是未来逻辑器件的元素，暗示着极化子单极子的遥远应用。在这方面，极化子单极子至少有一个巨大的优势：由于它们的光子成分，它们的速度非常快，接近光速。相比之下，自旋冰9中的磁性，甚至畴壁10的运动都慢得令人痛苦（图1b）。的结果反映了最近在人工自旋冰阵列上的工作，该工作显示了纳米技术如何成为在有效自旋系统中构建拓扑缺陷的强大工具。然而，这个绰号可能被过度使用了。狄拉克磁单极子在数学上是美丽的物体，而真实的自旋冰中的磁单极子几乎是电荷的原始类比，而在极化激元的情况下，就像在人造自旋冰中一样，类比就不那么严格了。
condensate; formed by two-dimensional exciton polaritons in a semiconductor microcavity (Fig. 1a). Exciton polaritons are quasiparticles with the mixed characteristics of a photon and an electronic excitation (an exciton). They have integer spin and a very small effective mass, which leads to effective condensation at a relatively high temperature7. The polariton lifetime is only about 10 ps, but it has been argued that this is long enough for a quasi-thermalized steady state to form. The momentum, energy and spin state of the polaritons can be imaged in direct space via the distribution and polarization of the photons they emit on decay. The wavefunction of the polariton condensate can be described by an effective field of spins interacting with a controllable effective magnetic field. Hivet et al. have arranged their experiment to create a onedimensional effective spin field transverse to the direction of polariton flow. Structural defects in the path of the flow create stable ‘half-soliton’textures, which correspond to monopoles in the effective spin field. The drift and acceleration of these monopoles in response to the effective magnetic field have been observed in real time. The ‘polariton monopoles’ obey the one-dimensional Coulomb law (hence they are confined), but as their effective mass is negative, like charges attract and unlike ones repel. This dimensionality and force law means they are not very much like electric charges or spin-ice monopoles. Perhaps they more closely resemble transverse domain walls in ferromagnetic nanowires, where the magnetization field is monopolar far from the wall. Such magnetic textures have been considered as elements for future logic devices8, hinting at a far-off application for polariton monopoles. In this regard polariton monopoles have at least one huge advantage over their rivals: owing to their photonic component they are extremely fast, with velocities approaching the speed of light. The magnetricity in spin ice9 and even the motion of domain walls10 is painfully slow in comparison (Fig. 1b).Hivet et al.’s result mirrors recent work on artificial spin-ice arrays11 that shows how nanotechnology can be a powerful tool with which to construct topological defects12 in effective spin systems. However the monopole epithet may be over-used. Dirac monopoles are mathematically beautiful objects, and the monopoles in real spin ice are almost pristine analogues of electric charges, whereas in the case of polaritons, as in artificial spin ice, the analogy is looser.