Internet in the palm of your hands; augmented reality to connect loved ones holographically; trucks without an engine. What’s next? A nano-camera? You guessed it! There are many reasons to collect light. We can’t touch and grab a distant galaxy to take a closer look inside its blindingly bright and ludicrously bright core, nor can we see the labyrinthine nature of the microcosm with our naked eyes. We require the cooperation and manipulation of captured light to do great things. One exciting prospect of this requirement is what makes up the recently published paper in the journal Applied Physics Letters. The first author is SBASSE’s own Shahzad Akhtar Ali, a student of Dr. Ata Ul Haq from the Department of Physics.

Nature speaks in mystifyingly ways. Shine a light on a crystal, carefully observe the light coming out the other end, deduce how photons toss and turn, spin and swivel as a result. Such berserk response from light can reveal plenty about the nature of the crystal. In other words, the way you react to situations tells a lot about who you are and what your nature could be like - an eerie similarity! Shahzad Akhtar Ali and his team of researchers studied the characteristics of crystals of molybdenum trioxide (MoO₃), also called alpha-molybdenum trioxide. Not just that, they studied layered crystals, which host a combination of hexaboron nitride together with MoO₃.

Their work, as intricate and complex as the materials they were working with, has to do with observing the twisting, turning, spinning, and swiveling (helicity) of photons as they came out the other end of these layered crystals called 2D materials. In this beautiful piece of work, it was revealed that alpha-molybdenum trioxide demonstrated very strong in-plane hyperbolicity, making it a strong candidate for possible nanophotonic applications, especially those requiring polarization control of photons. A prime method used in this study was Raman spectroscopy, which is an analysis technique that provides detailed information about chemical structure, phase and polymorphy, crystallinity and molecular interactions. On top of revealing so much about a compound, it is a non-destructive technique, making it the technique of choice when it comes to dealing with fragile samples.

Helicity is a thing of beauty. Almost complete helicity switching under Raman scattering points to strong phonon chirality around the high symmetry points in the Brillouin zone of the MoO₃ crystal, mentions the paper. The hyperbolic nature of flakes of α-MoO₃ makes them ideal candidates for nano-photonics applications apart from the highly rich physics of in-plane anisotropic phonon polariton. The chiral nature of the highly anisotropic phonons in this material system can play a crucial role in proposals, which combine this hyperbolicity with spin–orbit coupling resulting in novel surface plasmon modes. Thus, this makes it possible to fabricate nanometer-scale compact photonic devices! Consequently, these materials exhibit very high photon density of states, which enables the use of Purcell enhancement, which is at the heart of many schemes for interfacing quantum states of light and matter.

We congratulate Shahzad Akhtar Ali and his team who got their paper published in such a well reputed journal. We would also like to point out that all of the work by the first author was done using Dr. Ata Ul Haq’s lab, in the School. We wish them all the best for all their future work!

Reference: Shahzad Akhtar Ali, Abdullah Irfan, Aishani Mazumder, Sivacarendran Balendhran, Taimur Ahmed, Sumeet Walia, and Ata Ulhaq 

"Helicity-selective Raman scattering from in-plane anisotropic α-MoO₃", Appl. Phys. Lett. 119, 193104 (2021) https://doi.org/10.1063/5.0064464