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Lee Osheroff Richardson Prize Winner 2023 Q&A

Lee Osheroff Richardson Prize Winner 2023 Q&A

We spoke with Xiaomeng Liu, winner of the Lee Osheroff Richardson Prize 2023, which supports young scientists working with low temperatures, high magnetic fields or surface science research in North and South America. Xiaomeng describes what it means to him to win this prize, the research that led him to this moment and where he expects he will take his research next. We are really excited to meet Xiaomeng in person at the APS March Meeting and to present him with his award!

1. How does it feel to have won the Lee Osheroff Science Prize?

It is my great honor to join the esteemed scientists who have been awarded the LOR Science Prize. My research focuses on exploring exotic quantum states of matter, such as superfluidity, in simple material systems at low temperatures. Being acknowledged by a prize named after the discoverers of superfluidity in He3, David M. Lee, Douglas D. Osheroff, and Robert C. Richardson, holds a special significance for me. I express my gratitude to Oxford Instruments for establishing this award to support and recognize young scientists, and I am deeply indebted to my advisors and colleagues for their invaluable support and guidance in achieving this honor.

I was in the midst of my job search when my postdoctoral advisor, Dr. Ali Yazdani, nominated me for the LOR Prize. I received the news of my win during an on-site visit, which made for a truly special and memorable moment amidst the challenging process of searching for a faculty position. In addition to the joy of being recognized, winning this award has also heightened my optimism for the future of my academic career, particularly after witnessing the remarkable achievements of past recipients.

2. Can you tell us more about the research you submitted?

I focus on developing innovative methods to create and investigate emergent quantum phenomena using 2D materials and their van der Waals heterostructures. Emergent phenomena refer to new behaviors that arise spontaneously when a large number of particles are brought together, similar to the cultural behaviors that emerge when humans form a society. The 2D material platform provides us with tremendous flexibility to design and construct materials that facilitate the discovery of novel emergent phenomena, paving the way for the development of future quantum technologies.

During my PhD, I designed a superfluid known as an exciton condensate by Coulomb coupling two graphene layers separated by a thin insulator. The tunable pairing strength between the two graphene layers enabled us to access a crucial paradigm called the BEC-BCS crossover. This framework encompasses the behavior of all fermion condensates in a unified manner and is relevant to numerous unconventional superconductors. Under stronger magnetic fields, this double-layered structure also enabled us to observe new types of fractional quantum Hall effects with exotic transport properties. In a different type of heterostructure where two bilayer graphene layers are directly stacked on top of each other with a twist angle, I harnessed the moiré pattern between adjacent atomic layers to create highly-degenerate bands that enable strongly correlated quantum states.

In my postdoctoral research, I am dedicated to deepening our understanding of emergent phenomena in 2D heterostructures using high-resolution imaging techniques, particularly scanning tunneling microscopy (STM). We have developed the necessary technical expertise to perform state-of-the-art STM studies on assembled heterostructures and have illuminated several pressing questions in moiré materials and quantum Hall physics. Notably, we have imaged intriguing structures such as Landau orbits and Skyrmion excitations in the quantum Hall regime. Furthermore, we enabled the first STM measurements of the fractional quantum Hall effect, which holds promise for future opportunities to image exotic emergent particles such as anyons.

3. Is there a particular part of your research of which you are especially proud?

I am proud of my ability to generate innovative ideas and transform them into experiments and discoveries. My journey in the field began with a primitive idea that emerged during my first year of graduate school while studying the quantum field theory. I had the idea of placing hole-doped graphene next to electron-doped graphene, so that the Coulomb attraction of a hole could induce pairing between two electrons in the electron-doped layer, similar to phonon-mediated Cooper pairing. This sparked my persistent pursuit of creating and manipulating superfluidity in double-layer graphene heterostructures. While my efforts were certainly built upon important previous works, I take pride in my ability to identify emerging opportunities for important new discoveries. This story is also repeated in my study of twisted double bilayer graphene and in my STM experiments on 2D heterostructures.

4. What’s next for your research?

I hope to establish my own research group in the near future, focusing on two main directions. The first will be to create new quantum states of matter and quantum devices by taking advantage of the versatile vdW heterostructure. I am particularly excited about the possibility of engineering novel condensates and exploring new magnetic states such as spin liquids. I am also interested in manipulating the mechanical degrees of freedom in these vdW heterostructures and developing coherent quantum devices using the condensates we discover across various platforms.

The second direction of my lab will be to use scanning tunneling microscopy to probe various 2D quantum materials, including graphene quantum Hall states, twisted graphene platforms, and various semiconducting moiré bilayers. This is an underexplored area with immense potential. I am eager to unravel the nature of electron correlations and superconductivity, identify charge and spin orders, and discover exotic emergent particles such as anyons.

5. Any final thoughts?

While research can be challenging, as I personally experienced during my first two years as a postdoc, it can also be incredibly gratifying and fulfilling, including occasions like this. In achieving this honor, I am deeply grateful for the overwhelming support I have received from my advisors and colleagues, especially from Dr. Philip Kim, Dr. Bertrand Halperin, Dr. Ali Yazdani, Zeyu Hao, Cheng-li Chiu, Gelareh Farahi, Dr. J.I.A Li, and Dr. Cory R. Dean. Additionally, I greatly appreciate Oxford Instruments for establishing this award and the committee for recognizing my work.

Xiaomeng Liu

The Lee Osheroff Richardson Science Prize Winner 2023