Browsing by Author "Hossain, Md Shafayat"

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    Imaging real-space flat band localization in kagome magnet FeSn
    (Springer Nature, 2023) Multer, Daniel; Yin, Jia-Xin; Hossain, Md Shafayat; Yang, Xian; Sales, Brian C.; Miao, Hu; Meier, William R.; Jiang, Yu-Xiao; Xie, Yaofeng; Dai, Pengcheng; Liu, Jianpeng; Deng, Hanbin; Lei, Hechang; Lian, Biao; Zahid Hasan, M.; Rice Center for Quantum Materials
    Kagome lattices host flat bands due to their frustrated lattice geometry, which leads to destructive quantum interference of electron wave functions. Here, we report imaging of the kagome flat band localization in real-space using scanning tunneling microscopy. We identify both the Fe3Sn kagome lattice layer and the Sn2 honeycomb layer with atomic resolution in kagome antiferromagnet FeSn. On the Fe3Sn lattice, at the flat band energy determined by the angle resolved photoemission spectroscopy, tunneling spectroscopy detects an unusual state localized uniquely at the Fe kagome lattice network. We further show that the vectorial in-plane magnetic field manipulates the spatial anisotropy of the localization state within each kagome unit cell. Our results are consistent with the real-space flat band localization in the magnetic kagome lattice. We further discuss the magnetic tuning of flat band localization under the spin–orbit coupled magnetic kagome lattice model.
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    Tunable unconventional kagome superconductivity in charge ordered RbV3Sb5 and KV3Sb5
    (Springer Nature, 2023) Guguchia, Z.; Mielke, C.; Das, D.; Gupta, R.; Yin, J.-X.; Liu, H.; Yin, Q.; Christensen, M.H.; Tu, Z.; Gong, C.; Shumiya, N.; Hossain, Md Shafayat; Gamsakhurdashvili, Ts; Elender, M.; Dai, Pengcheng; Amato, A.; Shi, Y.; Lei, H.C.; Fernandes, R.M.; Hasan, M.Z.; Luetkens, H.; Khasanov, R.
    Unconventional superconductors often feature competing orders, small superfluid density, and nodal electronic pairing. While unusual superconductivity has been proposed in the kagome metals AV3Sb5, key spectroscopic evidence has remained elusive. Here we utilize pressure-tuned and ultra-low temperature muon spin spectroscopy to uncover the unconventional nature of superconductivity in RbV3Sb5 and KV3Sb5. At ambient pressure, we observed time-reversal symmetry breaking charge order below $${T}_{{{{{{{{\rm{1}}}}}}}}}^{*}\simeq$$110 K in RbV3Sb5 with an additional transition at $${T}_{{{{{{{{\rm{2}}}}}}}}}^{*}\simeq$$50 K. Remarkably, the superconducting state displays a nodal energy gap and a reduced superfluid density, which can be attributed to the competition with the charge order. Upon applying pressure, the charge-order transitions are suppressed, the superfluid density increases, and the superconducting state progressively evolves from nodal to nodeless. Once optimal superconductivity is achieved, we find a superconducting pairing state that is not only fully gapped, but also spontaneously breaks time-reversal symmetry. Our results point to unprecedented tunable nodal kagome superconductivity competing with time-reversal symmetry-breaking charge order and offer unique insights into the nature of the pairing state.