Yong Zhong

All Publications

• Differentiated roles of Lifshitz transition on thermodynamics and superconductivity in La2-xSrxCuO4. Proceedings of the National Academy of Sciences of the United States of America Zhong, Y., Chen, Z., Chen, S., Xu, K., Hashimoto, M., He, Y., Uchida, S., Lu, D., Mo, S., Shen, Z. 2022; 119 (32): e2204630119

  Abstract

  The effect of Lifshitz transition on thermodynamics and superconductivity in hole-doped cuprates has been heavily debated but remains an open question. In particular, an observed peak of electronic specific heat is proposed to originate from fluctuations of a putative quantum critical point p* (e.g., the termination of pseudogap at zero temperature), which is close to but distinguishable from the Lifshitz transition in overdoped La-based cuprates where the Fermi surface transforms from hole-like to electron-like. Here we report an in situ angle-resolved photoemission spectroscopy study of three-dimensional Fermi surfaces in La2-xSrxCuO4 thin films (x = 0.06 to 0.35). With accurate kz dispersion quantification, the said Lifshitz transition is determined to happen within a finite range around x = 0.21. Normal state electronic specific heat, calculated from spectroscopy-derived band parameters, reveals a doping-dependent profile with a maximum at x = 0.21 that agrees with previous thermodynamic microcalorimetry measurements. The account of the specific heat maximum by underlying band structures excludes the need for additionally dominant contribution from the quantum fluctuations at p*. A d-wave superconducting gap smoothly across the Lifshitz transition demonstrates the insensitivity of superconductivity to the dramatic density of states enhancement.

  View details for DOI 10.1073/pnas.2204630119

  View details for PubMedID 35914123

• A Novel 19*19 Superstructure in Epitaxially Grown 1T-TaTe2. Advanced materials (Deerfield Beach, Fla.) Hwang, J., Jin, Y., Zhang, C., Zhu, T., Kim, K., Zhong, Y., Lee, J., Shen, Z., Chen, Y., Ruan, W., Ryu, H., Hwang, C., Lee, J., Crommie, M. F., Mo, S., Shen, Z. 2022: e2204579

  Abstract

  The spontaneous formation of electronic orders is a crucial element for understanding complex quantum states and engineering heterostructures in two-dimensional materials. We report a novel 19*19 charge order in few-layer thick 1T-TaTe2 transition metal dichalcogenide films grown by molecular beam epitaxy, which has not been realized. Our photoemission and scanning probe measurements demonstrate that monolayer 1T-TaTe2 exhibits a variety of metastable charge density wave orders, including the 19*19 superstructure, which can be selectively stabilized by controlling the post-growth annealing temperature. Moreover, we find that only the 19*19 order persists in 1T-TaTe2 films thicker than a monolayer, up to 8 layers. Our findings identify the previously unrealized novel electronic order in a much-studied transition metal dichalcogenide and provide a viable route to control it within the epitaxial growth process. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/adma.202204579

  View details for PubMedID 35902365

• Large-gap insulating dimer ground state in monolayer IrTe2. Nature communications Hwang, J., Kim, K., Zhang, C., Zhu, T., Herbig, C., Kim, S., Kim, B., Zhong, Y., Salah, M., El-Desoky, M. M., Hwang, C., Shen, Z., Crommie, M. F., Mo, S. 2022; 13 (1): 906

  Abstract

  Monolayers of two-dimensional van der Waals materials exhibit novel electronic phases distinct from their bulk due to the symmetry breaking and reduced screening in the absence of the interlayer coupling. In this work, we combine angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy to demonstrate the emergence of a unique insulating 2 * 1 dimer ground state in monolayer 1T-IrTe2 that has a large band gap in contrast to the metallic bilayer-to-bulk forms of this material. First-principles calculations reveal that phonon and charge instabilities as well as local bond formation collectively enhance and stabilize a charge-ordered ground state. Our findings provide important insights into the subtle balance of interactions having similar energy scales that occurs in the absence of strong interlayer coupling, which offers new opportunities to engineer the properties of 2D monolayers.

  View details for DOI 10.1038/s41467-022-28542-y

  View details for PubMedID 35173153