Yong Zhong

All Publications

• Controlling structure and interfacial interaction of monolayer TaSe2 on bilayer graphene. Nano convergence Lee, H., Im, H., Choi, B. K., Park, K., Chen, Y., Ruan, W., Zhong, Y., Lee, J. E., Ryu, H., Crommie, M. F., Shen, Z. X., Hwang, C., Mo, S. K., Hwang, J. 2024; 11 (1): 14

  Abstract

  Tunability of interfacial effects between two-dimensional (2D) crystals is crucial not only for understanding the intrinsic properties of each system, but also for designing electronic devices based on ultra-thin heterostructures. A prerequisite of such heterostructure engineering is the availability of 2D crystals with different degrees of interfacial interactions. In this work, we report a controlled epitaxial growth of monolayer TaSe2 with different structural phases, 1H and 1 T, on a bilayer graphene (BLG) substrate using molecular beam epitaxy, and its impact on the electronic properties of the heterostructures using angle-resolved photoemission spectroscopy. 1H-TaSe2 exhibits significant charge transfer and band hybridization at the interface, whereas 1 T-TaSe2 shows weak interactions with the substrate. The distinct interfacial interactions are attributed to the dual effects from the differences of the work functions as well as the relative interlayer distance between TaSe2 films and BLG substrate. The method demonstrated here provides a viable route towards interface engineering in a variety of transition-metal dichalcogenides that can be applied to future nano-devices with designed electronic properties.

  View details for DOI 10.1186/s40580-024-00422-9

  View details for PubMedID 38622355

  View details for PubMedCentralID PMC11018566

• From Stoner to local moment magnetism in atomically thin Cr2Te3. Nature communications Zhong, Y., Peng, C., Huang, H., Guan, D., Hwang, J., Hsu, K. H., Hu, Y., Jia, C., Moritz, B., Lu, D., Lee, J. S., Jia, J. F., Devereaux, T. P., Mo, S. K., Shen, Z. X. 2023; 14 (1): 5340

  Abstract

  The field of two-dimensional (2D) ferromagnetism has been proliferating over the past few years, with ongoing interests in basic science and potential applications in spintronic technology. However, a high-resolution spectroscopic study of the 2D ferromagnet is still lacking due to the small size and air sensitivity of the exfoliated nanoflakes. Here, we report a thickness-dependent ferromagnetism in epitaxially grown Cr2Te3 thin films and investigate the evolution of the underlying electronic structure by synergistic angle-resolved photoemission spectroscopy, scanning tunneling microscopy, x-ray absorption spectroscopy, and first-principle calculations. A conspicuous ferromagnetic transition from Stoner to Heisenberg-type is directly observed in the atomically thin limit, indicating that dimensionality is a powerful tuning knob to manipulate the novel properties of 2D magnetism. Monolayer Cr2Te3 retains robust ferromagnetism, but with a suppressed Curie temperature, due to the drastic drop in the density of states near the Fermi level. Our results establish atomically thin Cr2Te3 as an excellent platform to explore the dual nature of localized and itinerant ferromagnetism in 2D magnets.

  View details for DOI 10.1038/s41467-023-40997-1

  View details for PubMedID 37660171

  View details for PubMedCentralID PMC10475109

• 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