Evidence for Exciton Crystals in a 2D Semiconductor Heterotrilayer.

Two-dimensional (2D) transition metal dichalcogenides (TMDC) and their moir\'e interfaces have been demonstrated for correlated electron states, including Mott insulators and electron/hole crystals commensurate with moir\'e superlattices. Here we present spectroscopic evidences for ordered bosons - interlayer exciton crystals in a WSe2/MoSe2/WSe2 trilayer, where the enhanced Coulomb interactions over those in heterobilayers have been predicted to result in exciton ordering. While the dipolar interlayer excitons in the heterobilayer may be ordered by the periodic moir\'e traps, their mutual repulsion results in de-trapping at exciton density n_ex larger than 10^11 cm^-2 to form mobile exciton gases and further to electron-hole plasmas, both accompanied by broadening in photoluminescence (PL) peaks and large increases in mobility. In contrast, ordered interlayer excitons in the trilayer are characterized by negligible mobility and by sharper PL peaks persisting to n_ex approximately 10^12 cm^-2. We present evidences for the predicted quadrupolar exciton crystal and its transitions to dipolar excitons either with increasing n_ex or by an applied electric field. These ordered interlayer excitons may serve as models for the exploration of quantum phase transitions and quantum coherent phenomena.

[1]  J. Finley,et al.  Twist-Dependent Intra- and Interlayer Excitons in Moiré MoSe_{2} Homobilayers. , 2022, Physical review letters.

[2]  Ajit K. Srivastava,et al.  Quadrupolar excitons in a tunnel-coupled van der Waals heterotrilayer , 2022, 2208.05490.

[3]  J. Shan,et al.  Exciton density waves in Coulomb-coupled dual moiré lattices , 2022, Nature Materials.

[4]  Kenji Watanabe,et al.  Localized interlayer excitons in MoSe2–WSe2 heterostructures without a moiré potential , 2022, Nature Communications.

[5]  Kenji Watanabe,et al.  Free Trions with Near-Unity Quantum Yield in Monolayer MoSe2. , 2021, ACS nano.

[6]  B. Gerardot,et al.  Optical dipole orientation of interlayer excitons in MoSe2−WSe2 heterostacks , 2021, Physical Review B.

[7]  J. Shan,et al.  Dipolar excitonic insulator in a moiré lattice , 2021, Nature Physics.

[8]  L. Pfeiffer,et al.  Mott insulator of strongly interacting two-dimensional semiconductor excitons , 2021, Nature Physics.

[9]  I. L. Kurbakov,et al.  Quantum phase transition of a two-dimensional quadrupolar system , 2020, 2012.14008.

[10]  Kenji Watanabe,et al.  Signatures of a degenerate many-body state of interlayer excitons in a van der Waals heterostack , 2020, Physical Review Research.

[11]  A. Georges,et al.  Moiré heterostructures as a condensed-matter quantum simulator , 2020, Nature Physics.

[12]  J. Shan,et al.  Correlated insulating states at fractional fillings of moiré superlattices , 2020, Nature.

[13]  Kenji Watanabe,et al.  Signatures of Wigner crystal of electrons in a monolayer semiconductor , 2020, Nature.

[14]  M. Lukin,et al.  Bilayer Wigner crystals in a transition metal dichalcogenide heterostructure , 2020, Nature.

[15]  B. Gerardot,et al.  Highly energy-tunable quantum light from moiré-trapped excitons , 2020, Science Advances.

[16]  L. Orozco,et al.  Many-Body Signatures of Collective Decay in Atomic Chains. , 2020, Physical review letters.

[17]  Xuedan Ma,et al.  Strain-Induced Trapping of Indirect Excitons in MoSe2/WSe2 Heterostructures , 2020 .

[18]  Xiaodong Xu,et al.  Excitons in strain-induced one-dimensional moiré potentials at transition metal dichalcogenide heterojunctions , 2020, Nature Materials.

[19]  Kenji Watanabe,et al.  Correlated electronic phases in twisted bilayer transition metal dichalcogenides , 2020, Nature Materials.

[20]  R. Rapaport,et al.  Quantum Phase Transitions of Trilayer Excitons in Atomically Thin Heterostructures. , 2020, Physical review letters.

[21]  Kenji Watanabe,et al.  Strongly correlated electrons and hybrid excitons in a moiré heterostructure , 2020, Nature.

[22]  J. Shan,et al.  Simulation of Hubbard model physics in WSe2/WS2 moiré superlattices , 2020, Nature.

[23]  J. Hone,et al.  Diffusivity Reveals Three Distinct Phases of Interlayer Excitons in MoSe_{2}/WSe_{2} Heterobilayers. , 2020, Physical review letters.

[24]  Kenji Watanabe,et al.  Mott and generalized Wigner crystal states in WSe2/WS2 moiré superlattices , 2019, Nature.

[25]  Luka M. Devenica,et al.  Dipolar interactions between localized interlayer excitons in van der Waals heterostructures , 2019, Nature Materials.

[26]  J. Shan,et al.  Evidence of high-temperature exciton condensation in two-dimensional atomic double layers , 2019, Nature.

[27]  Xiaodong Xu,et al.  Optical generation of high carrier densities in 2D semiconductor heterobilayers , 2019, Science Advances.

[28]  L. Balicas,et al.  Approaching the Intrinsic Limit in Transition Metal Diselenides via Point Defect Control. , 2019, Nano letters.

[29]  K. Novoselov,et al.  Resonantly hybridized excitons in moiré superlattices in van der Waals heterostructures , 2019, Nature.

[30]  Xiaodong Xu,et al.  Signatures of moiré-trapped valley excitons in MoSe2/WSe2 heterobilayers , 2018, Nature.

[31]  B. Shklovskii,et al.  Attraction of indirect excitons in van der Waals heterostructures with three semiconducting layers , 2019, Physical Review B.

[32]  M. Lukin,et al.  Electrical control of interlayer exciton dynamics in atomically thin heterostructures , 2018, Science.

[33]  Jiaqiang Yan,et al.  Signatures of moiré-trapped valley excitons in MoSe2/WSe2 heterobilayers , 2018, Nature.

[34]  S. Banerjee,et al.  Evidence for moiré excitons in van der Waals heterostructures , 2018, Nature.

[35]  E. Tutuc,et al.  Hubbard Model Physics in Transition Metal Dichalcogenide Moiré Bands. , 2018, Physical review letters.

[36]  G. Rainò,et al.  Superfluorescence from lead halide perovskite quantum dot superlattices , 2018, Nature.

[37]  M. L. Van de Put,et al.  Dielectric properties of hexagonal boron nitride and transition metal dichalcogenides: from monolayer to bulk , 2018, npj 2D Materials and Applications.

[38]  Xiaodong Xu,et al.  Moiré excitons: From programmable quantum emitter arrays to spin-orbit–coupled artificial lattices , 2017, Science Advances.

[39]  A. K. Vinod,et al.  Enhanced interlayer neutral excitons and trions in trilayer van der Waals heterostructures , 2017, npj 2D Materials and Applications.

[40]  Jiaqiang Yan,et al.  Directional interlayer spin-valley transfer in two-dimensional heterostructures , 2016, Nature Communications.

[41]  Xiaodong Xu,et al.  Anomalous Light Cones and Valley Optical Selection Rules of Interlayer Excitons in Twisted Heterobilayers. , 2015, Physical review letters.

[42]  S. Larentis,et al.  Band Alignment in WSe2-Graphene Heterostructures. , 2015, ACS nano.

[43]  C. A. Nelson,et al.  Time-, Energy-, and Phase-Resolved Second-Harmonic Generation at Semiconductor Interfaces , 2014 .

[44]  K. L. Shepard,et al.  One-Dimensional Electrical Contact to a Two-Dimensional Material , 2013, Science.

[45]  M. Bonitz,et al.  Crystallization of an exciton superfluid , 2011, 1101.1757.

[46]  S. Girvin,et al.  Continuous quantum phase transitions , 1996, cond-mat/9609279.

[47]  J. Hubbard.  On the Interaction of Electrons in Metals , 1955 .