Abstract
Two-dimensional semiconductor moiré superlattices have emerged as a powerful platform for engineering correlated electronic phenomena. On the other hand, optical excitation creates charge neutral interlayer excitons with an out-of-plane electric dipole. Strong onsite dipole–dipole interaction promises the formation of correlated bosonic states, akin to the Mott states of electrons, but has not yet been demonstrated. Here we report a large interaction between excitons occupying the same moiré lattice site—characterized by the Hubbard U parameter—and consequent dipole ladders with spin- and electron-filling dependence in WSe2/WS2 moiré superlattices. Photoluminescence measurements show successive peaks emerging with an energy separation of around 34 meV above the ground state as the exciton density is increased. This corresponds to the sequential injection of excitons into a single site with an energy cost to overcome the large exciton Hubbard U, forming a dipole ladder. Based on findings of local magnetic moments at two holes per moiré cell, we show that excitons can also fill a second moiré orbital, establishing the two-orbital nature of the moiré potential landscape. Our results show that the Bose–Hubbard model with possible exciton crystal phases can be investigated in interacting opto-moiré quantum matter.
| Original language | English |
|---|---|
| Pages (from-to) | 1286-1292 |
| Number of pages | 7 |
| Journal | Nature Physics |
| Volume | 19 |
| Issue number | 9 |
| DOIs | |
| State | Published - Sep 2023 |
Funding
This work was mainly supported by Department of Energy (DOE) Basic Energy Sciences (BES) under award DE-SC0018171. RMCD measurements were supported as part of Programmable Quantum Materials, an Energy Frontier Research Center funded by the U.S. DOE BES, under award DE-SC0019443. Sample fabrication and PFM characterization are partially supported by ARO MURI programme (grant no. W911NF-18-1-0431). The AFM-related measurements were performed using instrumentation supported by the U.S. National Science Foundation through the UW Molecular Engineering Materials Center, a Materials Research Science and Engineering Center (DMR-1719797). W.Y. acknowledges support by the Research Grants Council of Hong Kong SAR (AoE/P-701/20, HKU SRFS2122-7S05). Bulk WSe crystal growth and characterization by J.Y. is supported by the U.S. DOE BES, Materials Sciences and Engineering Division. K.W. and T.T. acknowledge support from JSPS KAKENHI (grant nos. 19H05790, 20H00354 and 21H05233). X.X. acknowledges support from the State of Washington funded Clean Energy Institute and from the Boeing Distinguished Professorship in Physics. 2 This work was mainly supported by Department of Energy (DOE) Basic Energy Sciences (BES) under award DE-SC0018171. RMCD measurements were supported as part of Programmable Quantum Materials, an Energy Frontier Research Center funded by the U.S. DOE BES, under award DE-SC0019443. Sample fabrication and PFM characterization are partially supported by ARO MURI programme (grant no. W911NF-18-1-0431). The AFM-related measurements were performed using instrumentation supported by the U.S. National Science Foundation through the UW Molecular Engineering Materials Center, a Materials Research Science and Engineering Center (DMR-1719797). W.Y. acknowledges support by the Research Grants Council of Hong Kong SAR (AoE/P-701/20, HKU SRFS2122-7S05). Bulk WSe2 crystal growth and characterization by J.Y. is supported by the U.S. DOE BES, Materials Sciences and Engineering Division. K.W. and T.T. acknowledge support from JSPS KAKENHI (grant nos. 19H05790, 20H00354 and 21H05233). X.X. acknowledges support from the State of Washington funded Clean Energy Institute and from the Boeing Distinguished Professorship in Physics.