A recent study conducted by a team led by Prof. He Junfeng from the University of Science and Technology of China (USTC) has shed new light on the relationship between electronic instability, lattice structural instability, and charge density waves (CDW). Their findings, published in Physical Review Letters, provide insights into the tunability of the van Hove singularity (VHS) in the novel Ti-based kagome metal CsTi3Bi5 without compromising the lattice structure.

Typically, VHS and lattice structural instabilities coexist in kagome metals, making it challenging to discern the specific effects of each instability on CDW. To investigate this, the research team focused on studying CsTi3Bi5, a Ti-based kagome metal with a similar lattice structure to AV3Sb5 (A=K, Rb, Cs) but devoid of charge density wave states.

The researchers initially analyzed the electronic structure of CsTi3Bi5 using advanced techniques such as high-resolution angle-resolved photoemission spectroscopy. The results of these observations were found to be consistent with first-principles calculations. Interestingly, the energy position of the VHS in pristine CsTi3Bi5 was identified to be significantly above the Fermi level, thereby lacking the potential for generating electronic instability.

The team discovered that by introducing Cs surface doping, electrons could be injected into CsTi3Bi5, thereby modulating the VHS across a wide energy range. This modulation of the VHS brings it closer to the Fermi level, consequently allowing the generation of electronic instabilities. Crucially, first-principles calculations demonstrated no lattice structural instability in CsTi3Bi5 even after electron doping, indicating a decoupling of the two instabilities. This unique characteristic makes CsTi3Bi5 an exceptional platform for solely modulating electronic instabilities without interference from structural instabilities.

Despite tuning the VHS to induce electronic instabilities near the Fermi energy level, the researchers observed that it still failed to generate an energy gap in CDW in CsTi3Bi5. Consequently, the electronic instability itself was deemed insufficient to produce charge density waves in CsTi3Bi5. The team’s analysis suggested that the evolution from CsV3Sb5 to CsTi3Bi5, as observed through first-principles calculations, showed a direct correlation between the appearance of CDW and the change in the system’s total energy. Therefore, it became evident that lattice structural instability plays a pivotal role in the CDW phase transition in kagome metals.

This groundbreaking study offers valuable insights into the interplay between electronic instability, lattice structural instability, and CDW in kagome metals. By understanding the decoupling of these instabilities through careful modulation, researchers can potentially foster new approaches to harnessing and controlling CDW. Further research is needed to explore the underlying mechanisms in greater detail and investigate other materials with similar characteristics.

Prof. He Junfeng and his team’s research on CsTi3Bi5 has shed light on the intricate relationship between electronic instability and lattice structural instability in charge density waves. The ability to tune the van Hove singularity without compromising the lattice structure opens up new possibilities for future investigations into CDW in kagome metals. This study serves as a stepping stone for enhancing our understanding of these phenomena and may lead to transformative advances in materials science and condensed matter physics.


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