将两种不同状态的物质结合起来的新方法

New research by a City College of New York team has uncovered a novel way to combine two different states of matter. For one of the first times, topological photons—light—has been combined with lattice vibrations, also known as phonons, to manipulate their propagation in a robust and controllable way.

纽约市立学院的一个研究小组发现了一种将两种不同状态的物质结合起来的新方法。首次将拓扑光子与晶格振动(也称为声子)结合，以一种稳健可控的方式控制它们的传播。

The study utilized topological photonics, an emergent direction in photonics which leverages fundamental ideas of the mathematical field of topology about conserved quantities—topological invariants—that remain constant when altering parts of a geometric object under continuous deformations. One of the simplest examples of such invariants is number of holes, which, for instance, makes donut and mug equivalent from the topological point of view. The topological properties endow photons with helicity, when photons spin as they propagate, leading to unique and unexpected characteristics, such as robustness to defects and unidirectional propagation along interfaces between topologically distinct materials. Thanks to interactions with vibrations in crystals, these helical photons can then be used to channel infrared light along with vibrations.

这项研究利用了拓扑光子学，这是光子学的一个新兴方向，它利用了数学拓扑领域中关于守恒量的基本思想——拓扑不变量——在连续变形下改变几何物体的部分时保持不变。这种不变量的一个最简单的例子是洞的数量，例如，从拓扑的角度来看，这使得甜甜圈和马克杯等价。拓扑性质赋予光子螺旋性，当光子在传播时自旋，导致独特和意外的特性，如对缺陷的坚固性和沿拓扑截然不同的材料界面单向传播。由于与晶体振动的相互作用，这些螺旋光子可以利用振动引导红外光。

The implications of this work are broad, in particular allowing researchers to advance Raman spectroscopy, which is used to determine vibrational modes of molecules. The research also holds promise for vibrational spectroscopy—also known as infrared spectroscopy—which measures the interaction of infrared radiation with matter through absorption, emission, or reflection. This can then be utilized to study and identify and characterize chemical substances."We coupled helical photons with lattice vibrations in hexagonal boron nitride, creating a new hybrid matter referred to as phonon-polaritons," said Alexander Khanikaev, lead author and physicist with affiliation in CCNY's Grove School of Engineering. "It is half light and half vibrations. Since infrared light and lattice vibrations are associated with heat, we created new channels for propagation of light and heat together. Typically, lattice vibrations are very hard to control, and guiding them around defects and sharp corners was impossible before."

这项工作的意义是广泛的，特别是允许研究人员推进拉曼光谱，这是用来确定分子的振动模式。这项研究也为振动光谱学——也被称为红外光谱学——带来了希望。振动光谱学通过吸收、发射或反射来测量红外辐射与物质的相互作用。这可以用来研究、鉴定和表征化学物质。

“我们将螺旋光子与六方氮化硼的晶格振动耦合在一起，创造了一种新的混合物质，称为声子-极化子，”该研究的主要作者、CCNY格罗夫工程学院的物理学家亚历山大·哈尼卡耶夫说。“它一半是轻，一半是振动。由于红外光和晶格振动与热有关，我们创造了光和热一起传播的新通道。通常，晶格振动很难控制，引导它们绕过缺陷和尖角之前是不可能的。”

The new methodology can also implement directional radiative heat transfer, a form of energy transfer during which heat is dissipated through electromagnetic waves.

这种新方法还可以实现定向辐射传热，这是一种通过电磁波散热的能量传递形式。

"We can create channels of arbitrary shape for this form of hybrid light and matter excitations to be guided along within a two-dimensional material we created," added Dr. Sriram Guddala, postdoctoral researcher in Prof. Khanikaev's group and the first author of the manuscript. "This method also allows us to switch the direction of propagation of vibrations along these channels, forward or backward, simply by switching polarizations handedness of the incident laser beam. Interestingly, as the phonon-polaritons propagate, the vibrations also rotate along with the electric field. This is an entirely novel way of guiding and rotating lattice vibrations, which also makes them helical."

Khanikaev教授团队的博士后研究员、该手稿的第一作者Sriram Guddala博士补充说:“我们可以为这种混合光和物质激发形式创建任意形状的通道，在我们创建的二维材料中引导它们。”“这种方法也允许我们改变振动沿这些通道的传播方向，向前或向后，仅仅通过改变入射激光束的偏振方向。有趣的是，当声子极化子传播时，振动也随着电场旋转。这是一种全新的引导和旋转晶格振动的方法，也使得晶格振动呈螺旋状。”