將兩種不同狀態(tài)的物質結合起來的新方法

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.

紐約市立學院的一個研究小組發(fā)現(xiàn)了一種將兩種不同狀態(tài)的物質結合起來的新方法。首次將拓撲光子與晶格振動(也稱為聲子)結合，以一種穩(wěn)健可控的方式控制它們的傳播。

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.

這項研究利用了拓撲光子學，這是光子學的一個新興方向，它利用了數(shù)學拓撲領域中關于守恒量的基本思想——拓撲不變量——在連續(xù)變形下改變幾何物體的部分時保持不變。這種不變量的一個最簡單的例子是洞的數(shù)量，例如，從拓撲的角度來看，這使得甜甜圈和馬克杯等價。拓撲性質賦予光子螺旋性，當光子在傳播時自旋，導致獨特和意外的特性，如對缺陷的堅固性和沿拓撲截然不同的材料界面單向傳播。由于與晶體振動的相互作用，這些螺旋光子可以利用振動引導紅外光。

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."

這項工作的意義是廣泛的，特別是允許研究人員推進拉曼光譜，這是用來確定分子的振動模式。這項研究也為振動光譜學——也被稱為紅外光譜學——帶來了希望。振動光譜學通過吸收、發(fā)射或反射來測量紅外輻射與物質的相互作用。這可以用來研究、鑒定和表征化學物質。

“我們將螺旋光子與六方氮化硼的晶格振動耦合在一起，創(chuàng)造了一種新的混合物質，稱為聲子-極化子，”該研究的主要作者、CCNY格羅夫工程學院的物理學家亞歷山大·哈尼卡耶夫說。“它一半是輕，一半是振動。由于紅外光和晶格振動與熱有關，我們創(chuàng)造了光和熱一起傳播的新通道。通常，晶格振動很難控制，引導它們繞過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.

這種新方法還可以實現(xiàn)定向輻射傳熱，這是一種通過電磁波散熱的能量傳遞形式。

"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教授團隊的博士后研究員、該手稿的第一作者Sriram Guddala博士補充說:“我們可以為這種混合光和物質激發(fā)形式創(chuàng)建任意形狀的通道，在我們創(chuàng)建的二維材料中引導它們。”“這種方法也允許我們改變振動沿這些通道的傳播方向，向前或向后，僅僅通過改變入射激光束的偏振方向。有趣的是，當聲子極化子傳播時，振動也隨著電場旋轉。這是一種全新的引導和旋轉晶格振動的方法，也使得晶格振動呈螺旋狀。”