On May 29^th, Prof. Li Wei and his research team’s paper entitled as An Unusual Phase Transition Driven by Vibrational Entropy Changes in a Hybrid Organic-Inorganic Perovskite was published on the website of Angewandte Chemie International Edition. This is a new research achievement of the Ultrafast Optical Laboratory, which is led by Prof. Lu Peixiang of School of Physics. And Ph. D student Wei Wenjuan at School of Physics of Huazhong University of Science and Technology (HUST) is the first author, with the corresponding authors Prof. Li Wei and Lu Peixiang, Dr. Keith T. Butler from Rutherford Appleton Laboratory and Prof. Michael A. Carpenter of University of Cambridge.

Recent years, hybrid organic-inorganic perovskites solar cells have attracted  extensive attention due to their rapidly increasing conversion efficiency, excellent device performance and unique optoelectronic properties. Similar to traditional oxide perovskites, hybrid perovskites exhibit abundant phase transitions under external stimuli. Generally speaking, phase transitions of materials play an important role in their optical, electrical and magnetic properties. In this regard, it's significant to understand their mechanisms from a microscale. Hitherto, the driving forces for their phase transitions have been limited to the octahedral tilting, order-disorder and displacements, while other factors have attracted little attention.

Based on structural characterizations and ab initio lattice dynamics calculations, Prof. Li Wei and co-authors explored a complex first-order phase transitions in a HOIP, [CH₃NH₃][Mn(N₃)₃], which is driven by the atomic vibrations of the whole lattice, along with concurrent molecular displacements and an unusual octahedral tilting. From a new perspective, this work has shown a new phase transition mechanism mainly caused by entropy differences, explored some important differences between this phase transition and the traditional phase transitions at the atomic scale, and proposed a possible way to drive the phase transitions of perovskites by controlling the collective modes.

On June 1^st, another research achievement of Ultrafast Optical Laboratory was published on the website of Physics Review Letters. The first author of the paper entitled as Scaling Law of High Harmonic Generation in the Framework of Photon Channels is Li Liang, 2012 undergraduate and 2016 directly Ph. D at School of Physics. Prof. Lu Peixiang and Lan Pengfei, associate professor Zhu Xiaosong and Prof. Chen Jing of Peking University are the corresponding authors.

Prof. Lu Peixiang and his team members used a quantized laser field to establish a theoretical model for high harmonic generation (HHG) by interaction and radiation of strong lasers and atoms, and quantitatively proposed new physical images generated by HHG based on photon channels. The image intuitively and simply explains the particle characteristics of the HHG, simplifies the quantitative analysis of the high harmonic spectrum, and provides a new idea for understanding the quantum image of the high-field and atoms' interaction. This research result has an important theoretical value for understanding the generation processing of HHG in complex light fields (double-circular polarized light, vortex light, etc.) and generating elliptical adjustable atomic-second light pulsed sources. After publishing on arxiv.org, the paper quickly attracted the attention of peers. A research team in the US has used the model to explain their experimental results and published them on the PRL.

In the last six months, the Ultrafast Optical Laboratory has produced and published many high-level papers, including one on Nature Communications, three on Physics Review Letters, one on Nano Letters, one on Angewandte Chemie International Edition and one on Advanced Functional Materials.