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Assistant Professor of Physics Zhengguang Lu from Florida State University, along with colleagues, has identified novel states of matter in graphene — a carbon variant composed of a singular atomic layer — exhibiting exceptional electrical properties that may serve as a crucial resource for creating more advanced electronics and quantum computing systems.

In a research paper published in Nature, the scientists elaborated on their construction of structures made from five layers of graphene nestled between sheets of boron nitride, revealing that these structures displayed distinctive electronic behaviors at extremely low temperatures. In this arrangement, electrons flow along the peripheries of the structure as fractions of a complete charge with no energy dissipation, a phenomenon safeguarded by topology, indicating that these characteristics remain constant under bending, stretching, or other alterations of the system.

“This represents one of the remarkable aspects of physics — a slight variation in a material’s structure can lead to a system that operates entirely differently,” Lu remarked, an alumnus of FSU who also participated as a postdoctoral researcher in the team that initially identified this phenomenon in graphite systems at the Massachusetts Institute of Technology in late 2023.

The states of matter uncovered by Lu and his team display what are termed quantum anomalous Hall states, meaning that electric current can flow along the material’s edges with zero resistance and without the necessity of a magnetic field.

More precisely, researchers discovered both an electron crystal state demonstrating integer quantum anomalous Hall states, where electrical conductance values are confined to whole numbers, as well as fractional quantum anomalous Hall states, in which they measured electrical conductance that achieved fractional values rather than solely integers. This result signifies strongly correlated electron behavior.

“Should the fractional quantum anomalous Hall effect be integrated with a superconductor, the resultant quantum computer will surpass current versions in efficiency and lack errors. Even a minor magnetic field will ultimately disrupt a superconductor, making the discovery of these states at zero magnetic field critically important,” Lu added.

To examine the graphene layers, the research team cooled samples to below 40 millikelvin, approximately -460 degrees Fahrenheit. At such temperatures, the electrons arranged themselves into two new phases: fractional quantum anomalous Hall states at 5/9 and 5/11, where electrons carried five-ninths and five-elevenths of a single charge, along with an electron crystal state displaying the integer quantum anomalous Hall effect across a wide range of electron density.

“Envision the fractional states as fluid, akin to flowing water, whereas the electron crystal state — referred to as the extended quantum anomalous Hall state — resembles electron ice,” Lu explained. “These liquid and solid phases occur similarly to a river meandering among glaciers. Remarkably, these two distinct electron phases can coexist within the system at ultra-low temperatures.”

An additional critical element in these discoveries is the moiré pattern, which emerges when the five-layer graphene interacts with adjacent boron nitride. Moiré indicates the recurring spatial arrangement formed when overlaid atomic sheets are slightly misaligned at a specific angle or differ in size.

“The moiré potential acts like a scissor allowing us to extract the most advantageous components of a quantum material,” Lu stated. “By fabricating two-dimensional materials in this ‘twistronics’ manner, we are unlocking new avenues in quantum physics.”

For more than two decades, graphene has been a pivotal material in analyzing unique electron behaviors, yet the identification of new fractional states underscores how much remains unexplored about even the most rudimentary materials. This work showcases the richness of quantum materials. Even common substances like pencil graphite can reveal groundbreaking quantum characteristics.

“The types of multilayer graphene in which Zhengguang identified the new quantum states are all found in natural graphite but were regarded as extremely challenging to pinpoint and isolate,” explained Peng Xiong, a physics professor and an authority on mesoscopic electronic phenomena in quantum materials. “His resourcefulness overcame this daunting challenge and yielded these breakthroughs — these fractional states are viewed as the holy grail of quantum computing.”

The multilayer rhombus-shaped graphene in conjunction with hexagonal boron nitride has evolved into a highly adaptable platform for investigating quantum phenomena, paving the way for future innovations in quantum computing and materials science.

The particles that could potentially create the bits necessary for quantum computers are extraordinarily sensitive to environmental disturbances, such as magnetic fields or temperature fluctuations. Alternative approaches, like those developed by Lu and his team, present new prospects for this burgeoning technology.

“Zhengguang positions FSU at the cutting edge of one of the most thrilling domains of research in physics today,” Xiong remarked. “In my opinion, he has achieved all the successes in quantum materials research because he possesses not only a brilliant understanding of physics but also the ability to make the impossible a reality in the laboratory.”

Further contributors to this research include scientists from MIT and researchers from the Research Center for Electronic and Optical Materials, which is part of the National Institute for Materials Science in Tsukuba, Japan.

To discover more about research conducted in the Department of Physics, visit physics.fsu.edu.

The post FSU scientists uncover exotic states of matter in graphene, presenting new opportunities for quantum computing appeared first on Florida State University News.

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