Steven G. Louie

The integration of low-energy states into bottom-up engineered graphene nanoribbons (GNRs) is a robust strategy for realizing materials with tailored electronic band structure for nanoelectronics. Low-energy zero-modes (ZMs) can be introduced into nanographenes (NGs) by creating an imbalance between the two sublattices of graphene. This phenomenon is exemplified by the family of [n]triangulenes. Here, we demonstrate the synthesis of [3]triangulene-GNRs, a regioregular one-dimensional (1D) chain of [3]triangulenes linked by five-membered rings. Hybridization between ZMs on adjacent [3]triangulenes leads to the emergence of a narrow band gap, Eg = 0.7 eV, and topological end states that are experimentally verified using scanning tunneling spectroscopy (STS). Tight-binding and first-principles density functional theory (DFT) calculations within the local spin density approximation (LSDA) corroborate our experimental observations. Our synthetic design takes advantage of a selective on-surface head-to-tail coupling of monomer building blocks enabling the regioselective synthesis of [3]triangulene-GNRs. Detailed ab initio theory provides insight into the mechanism of on-surface radical polymerization, revealing the pivotal role of Au-C bond formation/breakage in driving selectivity.

B43. 00001: Novel Excited States in 2D van der Waals Structures and Moiré Superlattices*

M59. 00002: Excitonic effects in nonlinear optical responses: Diagrammatic approach, exciton-state formalism and first-principles calculations*

M10. 00003: Directly layer-resolved observation of flat-band in phononic magic-angle twisted bilayer graphene*

Fabricating new 2D materials from molecular components is desirable because of the extraordinary flexibility of molecular building blocks. This has driven much growth in the fields of covalent organic frameworks (COFs) and metal organic frameworks (MOFs). A common problem with molecular materials, however, is that they are typically insulators and very difficult to electrically dope. Here we describe a new synthesis strategy for growing periodic 2D and 1D molecular networks that exhibit intrinsic metallicity. We achieved this through a unique covalent bonding motif that occurs between N-heterocyclic carbenes (NHCs) and transition metal atoms. A carbene is a molecule with two unpaired electrons (ie, radicals), and when two carbenes bond to a gold atom (ie, NHC-Au-NHC) then this results in frontier molecular orbitals (FMOs) that each contain a single unpaired electron. Periodic structures built from such FMOs …

The behavior of two-dimensional electron gas (2DEG) in extreme coupling limits are reasonably well-understood, but our understanding of intermediate region remains limited. Strongly interacting electrons crystalize into a solid phase known as the Wigner crystal at very low densities, and these evolve to a Fermi liquid at high densities. At intermediate densities, however, where the Wigner crystal melts into a strongly correlated electron fluid that is poorly understood partly due to a lack of microscopic probes for delicate quantum phases. Here we report the first imaging of a disordered Wigner solid and its quantum densification and quantum melting behavior in a bilayer MoSe2 using a non-invasive scanning tunneling microscopy (STM) technique. We observe a Wigner solid with nanocrystalline domains pinned by local disorder at low hole densities. With slightly increasing electrostatic gate voltages, the holes are added quantum mechanically during the densification of the disordered Wigner solid. As the hole density is increased above a threshold (p ~ 5.7 * 10e12 (cm-2)), the Wigner solid is observed to melt locally and create a mixed phase where solid and liquid regions coexist. With increasing density, the liquid regions gradually expand and form an apparent percolation network. Local solid domains appear to be pinned and stabilized by local disorder over a range of densities. Our observations are consistent with a microemulsion picture of Wigner solid quantum melting where solid and liquid domains emerge spontaneously and solid domains are pinned by local disorder.

M59. 00008: Moiré effect on the higher-energy excitonic states in WSe 2/WS 2 superlattice*

The combination of deep learning and ab initio calculation has shown great promise in revolutionizing future scientific research. However, designing neural network models that effectively incorporate symmetry requirements and a priori knowledge of physical systems remains a significant challenge. Here, we present an E (3)-equivariant deep-learning framework that models the density functional theory (DFT) Hamiltonian as a function of material structure [1, 2]. The neural network respects the Euclidean symmetry of material systems and leverages the locality property of electronic matter, allowing us to achieve sub-meV level accuracy in electronic structure calculations with small-sized training structures [1-3]. Our method scales linearly with system size and is applicable to materials with up to 10 4 atoms. Additionally, our method can be integrated with advanced computational techniques beyond the DFT level …