scholarly journals Imaging Generalized Wigner Crystal States in a WSe2/WS2 Moiré Superlattice

2021 ◽  
Author(s):  
Feng Wang ◽  
Hongyuan Li ◽  
Shaowei Li ◽  
Emma Regan ◽  
Danqing Wang ◽  
...  
Keyword(s):  
Electrical Transport ◽  
Nearest Neighbor ◽  
Real Space ◽  
Wigner Crystal ◽  
Scanning Tunneling ◽  
Honeycomb Lattice ◽  
Transition Metal Dichalcogenide ◽  
Tunneling Microscopy ◽  
Eugene Wigner ◽  
Wigner Crystals

Abstract The Wigner crystal state, first predicted by Eugene Wigner in 19341, has fascinated condensed matter physicists for nearly 90 years2-10. Studies of two-dimensional (2D) electron gases first revealed signatures of the Wigner crystal in electrical transport measurements at high magnetic fields2-4. More recently optical spectroscopy has provided evidence of generalized Wigner crystal states in transition metal dichalcogenide (TMDC) moiré superlattices6-9. Direct observation of the 2D Wigner crystal lattice in real space, however, has remained an outstanding challenge. Scanning tunneling microscopy (STM) in principle has sufficient spatial resolution to image the Wigner crystal, but conventional STM measurements can potentially alter fragile Wigner crystal states in the process of measurement. Here we demonstrate real-space imaging of 2D Wigner crystals in WSe2/WS2 moiré heterostructures using a novel non-invasive STM spectroscopy technique. We employ a graphene sensing layer in close proximity to the WSe2/WS2 moiré superlattice for Wigner crystal imaging, where local STM tunneling current into the graphene sensing layer is modulated by the underlying electron lattice of the Wigner crystal in the WSe2/WS2 heterostructure. Our measurement directly visualizes different lattice configurations associated with Wigner crystal states at fractional electron fillings of n = 1/3, 1/2, and 2/3, where n is the electron number per site. The n=1/3 and n=2/3 Wigner crystals are observed to exhibit a triangle and a honeycomb lattice, respectively, in order to minimize nearest-neighbor occupations. The n = 1/2 state, on the other hand, spontaneously breaks the original C3 symmetry and forms a stripe structure in real space. Our study lays a solid foundation toward the fundamental understanding of rich Wigner crystal states in WSe2/WS2 moiré heterostructures. Furthermore, this new STM technique is generally applicable to imaging novel correlated electron lattices in different van der Waals moiré heterostructures.

scholarly journals Imaging the electronic Wigner crystal in one dimension

Science ◽  
2019 ◽  
Vol 364 (6443) ◽  
pp. 870-875 ◽  
Author(s):  
I. Shapir ◽  
A. Hamo ◽  
S. Pecker ◽  
C. P. Moca ◽  
Ö. Legeza ◽  
...  
Keyword(s):  
Real Space ◽  
Wigner Crystal ◽  
One Dimension ◽  
Many Body ◽  
Quantum Crystal ◽  
Electronic Density ◽  
Eugene Wigner ◽  
Minimal Invasiveness ◽  
Wigner Crystals ◽  
The Many

The quantum crystal of electrons, predicted more than 80 years ago by Eugene Wigner, remains one of the most elusive states of matter. In this study, we observed the one-dimensional Wigner crystal directly by imaging its charge density in real space. To image, with minimal invasiveness, the many-body electronic density of a carbon nanotube, we used another nanotube as a scanning-charge perturbation. The images we obtained of a few electrons confined in one dimension match the theoretical predictions for strongly interacting crystals. The quantum nature of the crystal emerges in the observed collective tunneling through a potential barrier. These experiments provide the direct evidence for the formation of small Wigner crystals and open the way for studying other fragile interacting states by imaging their many-body density in real space.

scholarly journals Surface science at the PEARL beamline of the Swiss Light Source

2017 ◽  
Vol 24 (1) ◽  
pp. 354-366 ◽  
Author(s):  
Matthias Muntwiler ◽  
Jun Zhang ◽  
Roland Stania ◽  
Fumihiko Matsui ◽  
Peter Oberta ◽  
...  
Keyword(s):  
Light Source ◽  
Surface Science ◽  
Photoelectron Spectroscopy ◽  
Hexagonal Boron Nitride ◽  
Real Space ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
X Ray ◽  
Photoelectron Diffraction ◽  
Swiss Light Source

The Photo-Emission and Atomic Resolution Laboratory (PEARL) is a new soft X-ray beamline and surface science laboratory at the Swiss Light Source. PEARL is dedicated to the structural characterization of local bonding geometry at surfaces and interfaces of novel materials, in particular of molecular adsorbates, nanostructured surfaces, and surfaces of complex materials. The main experimental techniques are soft X-ray photoelectron spectroscopy, photoelectron diffraction, and scanning tunneling microscopy (STM). Photoelectron diffraction in angle-scanned mode measures bonding angles of atoms near the emitter atom, and thus allows the orientation of small molecules on a substrate to be determined. In energy scanned mode it measures the distance between the emitter and neighboring atoms; for example, between adsorbate and substrate. STM provides complementary, real-space information, and is particularly useful for comparing the sample quality with reference measurements. In this article, the key features and measured performance data of the beamline and the experimental station are presented. As scientific examples, the adsorbate–substrate distance in hexagonal boron nitride on Ni(111), surface quantum well states in a metal-organic network of dicyano-anthracene on Cu(111), and circular dichroism in the photoelectron diffraction of Cu(111) are discussed.

scholarly journals Real-space imaging of the atomic-scale magnetic structure of Fe1+yTe

Science ◽  
2014 ◽  
Vol 345 (6197) ◽  
pp. 653-656 ◽  
Author(s):  
Mostafa Enayat ◽  
Zhixiang Sun ◽  
Udai Raj Singh ◽  
Ramakrishna Aluru ◽  
Stefan Schmaus ◽  
...  
Keyword(s):  
Magnetic Structure ◽  
Magnetic Order ◽  
Parent Compound ◽  
Iron Concentration ◽  
Orthorhombic Phase ◽  
Real Space ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Excess Iron

Spin-polarized scanning tunneling microscopy (SP-STM) has been used extensively to study magnetic properties of nanostructures. Using SP-STM to visualize magnetic order in strongly correlated materials on an atomic scale is highly desirable, but challenging. We achieved this goal in iron tellurium (Fe1+yTe), the nonsuperconducting parent compound of the iron chalcogenides, by using a STM tip with a magnetic cluster at its apex. Our images of the magnetic structure reveal that the magnetic order in the monoclinic phase is a unidirectional stripe order; in the orthorhombic phase at higher excess iron concentration (y > 0.12), a transition to a phase with coexisting magnetic orders in both directions is observed. It may be possible to generalize the technique to other high-temperature superconductor families, such as the cuprates.

A UNION OF THE REAL-SPACE AND RECIPROCAL-SPACE VIEW OF THE GaAs(001) SURFACE

2001 ◽  
Vol 15 (17) ◽  
pp. 2301-2333 ◽  
Author(s):  
V. P. LaBELLA ◽  
Z. DING ◽  
D. W. BULLOCK ◽  
C. EMERY ◽  
P. M. THIBADO
Keyword(s):  
Density Functional ◽  
Lattice Gas ◽  
Real Space ◽  
Reciprocal Space ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Functional Theory ◽  
The Real ◽  
Reconstructed Surface ◽  
Temperature Measurement System

A union of the real-space and reciprocal space view of the GaAs(001) surface is presented. An optical transmission temperature measurement system allowed fast and accurate temperature determinations of the GaAs(001) substrate. The atomic features of the Ga A s (001)-(2×4) reconstructed surface are resolved with scanning tunneling microscopy and first principles density functional theory. In addition, the 2D lattice-gas Ising model within the grand canonical ensemble can be applied to this surface to understand the thermodynamics. An algorithm for using electron diffraction on the GaAs(001) surface to determine the substrate temperature and tune the nanoscale surface roughness is presented.

scholarly journals Unraveling the atomic structure, ripening behavior, and electronic structure of supported Au20 clusters

2020 ◽  
Vol 6 (1) ◽  
pp. eaay4289 ◽  
Author(s):  
Zhe Li ◽  
Hsin-Yi Tiffany Chen ◽  
Koen Schouteden ◽  
Thomas Picot ◽  
Ting-Wei Liao ◽  
...  
Keyword(s):  
Molecular Orbital ◽  
Gold Nanoclusters ◽  
Real Space ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Free Standing ◽  
Fundamental Information ◽  
Temperature Scanning ◽  
Homo Lumo

The free-standing Au20 cluster has a unique tetrahedral shape and a large HOMO-LUMO (highest occupied molecular orbital–lowest unoccupied molecular orbital) gap of around 1.8 electron volts. The “magic” Au20 has been intensively used as a model system for understanding the catalytic and optical properties of gold nanoclusters. However, direct real-space ground-state characterization at the atomic scale is still lacking, and obtaining fundamental information about the corresponding structural, electronic, and dynamical properties, is challenging. Here, using cluster-beam deposition and low-temperature scanning tunneling microscopy, atom-resolved topographic images and electronic spectra of supported Au20 clusters are obtained. We demonstrate that individual size-selected Au20 on ultrathin NaCl films maintains its pyramidal structure and large HOMO-LUMO gap. At higher cluster coverages, we find sintering of the clusters via Smoluchowski ripening to Au20n agglomerates. The evolution of the electron density of states deduced from the spectra reveals gap reduction with increasing agglomerate size.

Real Space Observation of Double-Helix DNA Structure Using a Low Temperature Scanning Tunneling Microscopy

1999 ◽  
Vol 38 (Part 2, No. 6A/B) ◽  
pp. L606-L607 ◽  
Author(s):  
Takashi Kanno ◽  
Hiroyuki Tanaka ◽  
Tomohiko Nakamura ◽  
Hitoshi Tabata ◽  
Tomoji Kawai
Keyword(s):  
Low Temperature ◽  
Scanning Tunneling Microscopy ◽  
Double Helix ◽  
Dna Structure ◽  
Real Space ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Temperature Scanning

On The Stability of Triangular Janus MoSSe Quantum-Dots: Shape and Size Effects

2021 ◽  
Author(s):  
J. I. Paez-Ornelas ◽  
R. Ponce-Perez ◽  
H. N. Fernández-Escamilla ◽  
D. M. Hoat ◽  
E. A. Murillo-Bracamontes ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Scanning Tunneling ◽  
Transition Metal Dichalcogenide ◽  
Tunneling Microscopy ◽  
Shape Stability ◽  
Catalytic Material ◽  
Catalytic Sites ◽  
Density Concentration ◽  
The Stability ◽  
Reaction Processes

Abstract Asymmetric Janus transition metal dichalcogenide MoSSe is a promising catalytic material due to the intrinsic in-plane dipole of its opposite faces. The atomic description of the structures observed by experimental techniques is relevant to tune and optimize the reaction processes on its surfaces. Furthermore, the experimentally observed triangular morphologies in MoSSe suggest that an analysis of the chemical environment of its edges is vital to understand its reactivity. Here we analyze the size-shape stability among different triangular structures-quantum dots-proposed from the ideal S(-1010) and Mo(10-10) terminations. Our stability analysis evidenced that the S-Se termination is more stable than Mo; moreover, as the size of the quantum dot increases, its stability increases as well. Besides, a trend is observed, with the appearance of elongated Mo-S/Se bonds at symmetric positions of the edges. Tersoff-Hamann scanning tunneling microscopy images for both faces of the stablest models are presented. Electrostatic potential isosurfaces denote that the basal plane on the S face of both configurations remains the region with more electron density concentration. These results point toward the differentiated activity over both faces. Finally, our study denotes the exact atomic arrangement on the edges of MoSSe quantum dots corresponding with the formation of S/Se dimmers who decorates the edges and their role along with the faces as catalytic sites.

Surface Reconstructions of Strained Epitaxial CoSi2/Si(100) Layers Studied by Scanning Tunneling Microscopy.

1991 ◽  
Vol 237 ◽  
Author(s):  
R. Stalder ◽  
C. Schwarz ◽  
H. Sirringhaus ◽  
H. VON Känel
Keyword(s):  
Electron Diffraction ◽  
Scanning Tunneling Microscopy ◽  
High Energy ◽  
Real Space ◽  
Scanning Tunneling ◽  
High Energy Electron ◽  
Tunneling Microscopy ◽  
Detailed Surface ◽  
Surface Reconstructions

ABSTRACTEpitaxial single-domain CoSi2(100) layers were grown on Si(100) by use of a template technique. In-situ scanning tunneling microscopy (STM) and reflection high energy electron diffraction (RHEED) were used for a detailed surface study. The (√2×√2)R45 reconstruction of the Co-rich “C-surface” and the (3√2×√2)R45 as well as a newly discovered (√2×√2)R45 of the Si-rich “S-surface” were resolved in real space and are discussed in detail. The transition from the C- to the S-surface above 500 °C is related to a (2×2) reconstruction.

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