2024 New's Items

Engineering Small HOMO–LUMO Gaps in Polycyclic Aromatic Hydrocarbons with Topologically Protected States

Slicker K
Delgado A
Jiang J
Cronin A
Tang W
Louie SG
Fischer FR
2024

Topological phases in laterally confined low-dimensional nanographenes have emerged as versatile design tools that can imbue otherwise unremarkable materials with exotic band structures ranging from topological semiconductors and quantum dots to intrinsically metallic bands. The periodic boundary conditions that define the topology of a given lattice have thus far prevented the translation of this technology to the quasi-zero-dimensional (0D) domain of small molecular structures. Here, we describe the synthesis of a polycyclic aromatic hydrocarbon (PAH) featuring two localized zero modes (...

Controlled catalyst-transfer polymerization in graphene nanoribbon synthesis

Pun SH
Delgado A
Dadich C
Cronin A
Fischer FR
2024
Exercising direct control over the unusual electronic structures arising from quantum confinement effects in graphene nanoribbons (GNRs) is intimately linked to geometric boundary conditions imposed by the structure of the ribbon. Besides ...

Gate-Switchable Molecular Diffusion on a Graphene Field-Effect Transistor

Liou F
Tsai HZ
Goodwin ZAH
Yang Y
Aikawa AS
Angeles BRP
Pezzini S
Nguyen L
Trishin S
Cheng Z
Zhou S
Roberts PW
Xu X
Watanabe K
Taniguchi T
Bellani V
Wang F
Lischner J
Crommie MF
2024

Controlling the surface diffusion of particles on 2D devices creates opportunities for advancing microscopic processes such as nanoassembly, thin-film growth, and catalysis. Here, we demonstrate the ability to control the diffusion of F4TCNQ molecules at the surface of clean graphene field-effect transistors (FETs) via electrostatic gating. Tuning the back-gate voltage (VG) of a graphene FET switches molecular adsorbates between negative and neutral charge states, leading to dramatic changes in their diffusion properties. Scanning tunneling microscopy measurements...

Terahertz phonon engineering with van der Waals heterostructures

Yoon Y
Lu Z
Uzundal C
Qi R
Zhao W
Chen S
Feng Q
Kim W
Naik MH
Watanabe K
Taniguchi T
Louie SG
Crommie MF
Wang F
2024

Phonon engineering at gigahertz frequencies forms the foundation of microwave acoustic filters1, acousto-optic modulators2 and quantum transducers...

Imaging tunable Luttinger liquid systems in van der Waals heterostructures

Li H
Xiang Z
Wang T
Naik MH
Kim W
Nie J
Li S
Ge Z
He Z
Ou Y
Banerjee R
Taniguchi T
Watanabe K,
Tongay S
Zettl A
Louie SG
Zaletel MP
Crommie MF
Wang F
2024

One-dimensional (1D) interacting electrons are often described as a Luttinger liquid1,2,...

Synthesis and Polymorph Manipulation of FeSe2 Monolayers

He Z
Poudel SP
Stolz S
Wang T
Rossi A
Wang F
Mo SK
Weber-Bargioni A
Qiu ZQ
Barraza-Lopez S
Zhu T
Crommie MF
2024

Polymorph engineering involves the manipulation of material properties through controlled structural modification and is a candidate technique for creating unique two-dimensional transition metal dichalcogenide (TMDC) nanodevices. Despite its promise, polymorph engineering of magnetic TMDC monolayers has not yet been demonstrated. Here we grow FeSe2 monolayers via molecular beam epitaxy and find that they have great promise for magnetic polymorph engineering. Using scanning tunneling microscopy (STM) and spectroscopy (STS), we find that FeSe2...

Wigner molecular crystals from multielectron moiré artificial atoms

Li H
Xiang Z
Reddy AP
Devakul T
Sailus R
Banerjee R
Taniguchi T
Watanabe K
Tongay S
Zettl A
Fu L
Crommie MF
Wang F
2024

Semiconductor moiré superlattices provide a versatile platform to engineer quantum solids composed of artificial atoms on moiré sites. Previous studies have mostly focused on the simplest correlated quantum solid—the Fermi-Hubbard model—in which intra-atom interactions are simplified to a single onsite repulsion energy U. Here we report the experimental observation of Wigner molecular crystals emerging from multielectron artificial atoms in twisted bilayer tungsten disulfide moiré superlattices. Using scanning tunneling microscopy, we demonstrate that Wigner molecules...

Chern Insulator States with Tunable Chern Numbers in a Graphene Moiré Superlattice

Wang S
Zhang Z
Li H
Sanborn C
Zhao W
Wang S
Watanabe K
Taniguchi T
Crommie MF
Chen G
Wang F
2024

Moiré superlattices, constituted by two-dimensional materials, demonstrate a variety of strongly correlated and topological phenomena including correlated insulators, superconductivity, and integer/fractional Chern insulators. In the realm of topological nontrivial Chern insulators within specific moiré superlattices, previous studies usually observe a single Chern number at a given filling factor in a device. Here we present the observation of gate-tunable Chern numbers within the Chern insulator state of an ABC-stacked trilayer graphene/hexagonal boron nitride moiré superlattice...

Regioselective On-Surface Synthesis of [3]Triangulene Graphene Nanoribbons

Daugherty MC
Jacobse PH
Jiang J
Jornet-Somoza J
Dorit R
Wang Z
Lu J
McCurdy R
Tang W
Rubio A
Louie SG
Crommie MF
Fischer FR
2024

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 (nN). Here, we demonstrate the synthesis of [3]triangulene...

Synthesis and characterization of low-dimensional N-heterocyclic carbene lattices

Qie B
Wang Z
Jiang J
Zhang Z
Jacobse PH
Lu J
Li X
Liu F
Alexandrova AN
Louie SG
Crommie MF
Fischer FR
2024

The covalent interaction of N-heterocyclic carbenes (NHCs) with transition metal atoms gives rise to distinctive frontier molecular orbitals (FMOs). These emergent electronic states have spurred the widespread adoption of NHC ligands in chemical catalysis and functional materials. Although formation of carbene-metal complexes in self-assembled monolayers on surfaces has been explored, design and electronic structure characterization of extended low-dimensional NHC-metal lattices remains elusive. Here we demonstrate a modular approach to engineering one-dimensional (1D) metal-organic...