Vertical charge order shapes the electronic properties in layered charge density wave (CDW) materials. Various stacking orders inevitably create nanoscale domains with distinct electronic structures inaccessible to bulk probes. Here, the stacking characteristics of bulk 1T-TaS2 are analyzed using scanning tunneling spectroscopy (STS) and density functional theory (DFT) calculations. It is observed that Mott-insulating domains undergo a transition to band-insulating domains restoring vertical dimerization of the CDWs. Furthermore, STS measurements covering a wide terrace reveal two distinct band insulating domains differentiated by band edge broadening. These DFT calculations reveal that the Mott insulating layers preferably reside on the subsurface, forming broader band edges in the neighboring band insulating layers. Ultimately, buried Mott insulating layers believed to harbor the quantum spin liquid phase are identified. These results resolve persistent issues regarding vertical charge order in 1T-TaS2, providing a new perspective for investigating emergent quantum phenomena in layered CDW materials.
H.Y. and B.L. authors contributed equally to this work. The authors acknowledge T. Benschop and J.\\u2010F. Ge for valuable discussions. This work was supported by the National Research Foundation of Korea (Grant No. 2017R1A5A1014862 (H.Y., B.L., J.B., and D.C.), 2020R1C1C1007895 (H.Y., B.L., J.B., and D.C.), and RS\\u20102023\\u201000251265 (H.Y., B.L., J.B., and D.C.), 2018R1A2B6004044 (S.\\u2010H.L.), 2019K1A3A1A18116063 (S.\\u2010H.L.), 2021R1A6A1A10044950 (S.K.), RS\\u20102023\\u201000285390 (S.K.), and RS\\u20102023\\u201000210828 (S.K.)), the Yonsei University Research Fund of 2019\\u201022\\u20100209 (H.Y., B.L., J.B., and D.C.), and Industry\\u2010Academy joint research program between Samsung Electronics and Yonsei University (H.Y., B.L., J.B., and D.C.). D.W. acknowledges support from the Institute for Basic Science (IBS) (Grant No. IBS\\u2010R009\\u2010Y3).
