scholarly journals Atomic-scale interface engineering of Majorana edge modes in a 2D magnet-superconductor hybrid system

2019 ◽  
Vol 5 (7) ◽  
pp. eaav6600 ◽  
Author(s):  
Alexandra Palacio-Morales ◽  
Eric Mascot ◽  
Sagen Cocklin ◽  
Howon Kim ◽  
Stephan Rachel ◽  
...  
Keyword(s):  
Hybrid System ◽  
Theoretical Calculations ◽  
Real Space ◽  
Scanning Tunneling Spectroscopy ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Edge States ◽  
Interface Engineering ◽  
New Paradigm ◽  
Topological Quantum

Topological superconductors are predicted to harbor exotic boundary states—Majorana zero-energy modes—whose non-Abelian braiding statistics present a new paradigm for the realization of topological quantum computing. Using low-temperature scanning tunneling spectroscopy, here, we report on the direct real-space visualization of chiral Majorana edge states in a monolayer topological superconductor, a prototypical magnet-superconductor hybrid system composed of nanoscale Fe islands of monoatomic height on a Re(0001)-O(2 × 1) surface. In particular, we demonstrate that interface engineering by an atomically thin oxide layer is crucial for driving the hybrid system into a topologically nontrivial state as confirmed by theoretical calculations of the topological invariant, the Chern number.

scholarly journals Evidence for one-dimensional chiral edge states in a magnetic Weyl semimetal Co3Sn2S2

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Sean Howard ◽  
Lin Jiao ◽  
Zhenyu Wang ◽  
Noam Morali ◽  
Rajib Batabyal ◽  
...  
Keyword(s):  
Practical Interest ◽  
Interlayer Coupling ◽  
Scanning Tunneling Spectroscopy ◽  
Scanning Tunneling ◽  
Edge States ◽  
New Paradigm ◽  
Linear Dispersion ◽  
Weyl Semimetal ◽  
Chern Insulators ◽  
Higher Temperature

AbstractThe physical realization of Chern insulators is of fundamental and practical interest, as they are predicted to host the quantum anomalous Hall (QAH) effect and topologically protected chiral edge states which can carry dissipationless current. Current realizations of the QAH state often require complex heterostructures and sub-Kelvin temperatures, making the discovery of intrinsic, high temperature QAH systems of significant interest. In this work we show that time-reversal symmetry breaking Weyl semimetals, being essentially stacks of Chern insulators with inter-layer coupling, may provide a new platform for the higher temperature realization of robust chiral edge states. We present combined scanning tunneling spectroscopy and theoretical investigations of the magnetic Weyl semimetal, Co3Sn2S2. Using modeling and numerical simulations we find that depending on the strength of the interlayer coupling, chiral edge states can be localized on partially exposed kagome planes on the surfaces of a Weyl semimetal. Correspondingly, our dI/dV maps on the kagome Co3Sn terraces show topological states confined to the edges which display linear dispersion. This work provides a new paradigm for realizing chiral edge modes and provides a pathway for the realization of higher temperature QAH effect in magnetic Weyl systems in the two-dimensional limit.

scholarly journals Moiréless correlations in ABCA graphene

2021 ◽  
Vol 118 (4) ◽  
pp. e2017366118 ◽  
Author(s):  
Alexander Kerelsky ◽  
Carmen Rubio-Verdú ◽  
Lede Xian ◽  
Dante M. Kennes ◽  
Dorri Halbertal ◽  
...  
Keyword(s):  
Theoretical Calculations ◽  
Van Der Waals ◽  
Bilayer Graphene ◽  
Scanning Tunneling Spectroscopy ◽  
Scanning Tunneling ◽  
Van Hove Singularity ◽  
Natural Interfaces ◽  
Simple Material ◽  
Electronic Band ◽  
Topological Quantum

Atomically thin van der Waals materials stacked with an interlayer twist have proven to be an excellent platform toward achieving gate-tunable correlated phenomena linked to the formation of flat electronic bands. In this work we demonstrate the formation of emergent correlated phases in multilayer rhombohedral graphene––a simple material that also exhibits a flat electronic band edge but without the need of having a moiré superlattice induced by twisted van der Waals layers. We show that two layers of bilayer graphene that are twisted by an arbitrary tiny angle host large (micrometer-scale) regions of uniform rhombohedral four-layer (ABCA) graphene that can be independently studied. Scanning tunneling spectroscopy reveals that ABCA graphene hosts an unprecedentedly sharp van Hove singularity of 3–5-meV half-width. We demonstrate that when this van Hove singularity straddles the Fermi level, a correlated many-body gap emerges with peak-to-peak value of 9.5 meV at charge neutrality. Mean-field theoretical calculations for model with short-ranged interactions indicate that two primary candidates for the appearance of this broken symmetry state are a charge-transfer excitonic insulator and a ferrimagnet. Finally, we show that ABCA graphene hosts surface topological helical edge states at natural interfaces with ABAB graphene which can be turned on and off with gate voltage, implying that small-angle twisted double-bilayer graphene is an ideal programmable topological quantum material.

Development of the UHV-STM

1990 ◽  
Vol 48 (1) ◽  
pp. 322-323
Author(s):  
M. Iwatsuki ◽  
S. Kitamura ◽  
A. Mogami
Keyword(s):  
Surface Science ◽  
Real Space ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Great Promise ◽  
Force Microscopy ◽  
Atomic Force ◽  
Stm Image ◽  
Surface Construction ◽  
Very High

Since Binnig, Rohrer and associates observed real-space topographic images of Si(111)-7×7 and invented the scanning tunneling microscope (STM),1) the STM has been accepted as a powerful surface science instrument.Recently, many application areas for the STM have been opened up, such as atomic force microscopy (AFM), magnetic force microscopy (MFM) and others. So, the STM technology holds a great promise for the future.The great advantages of the STM are its high spatial resolution in the lateral and vertical directions on the atomic scale. However, the STM has difficulty in identifying atomic images in a desired area because it uses piezoelectric (PZT) elements as a scanner.On the other hand, the demand to observe specimens under UHV condition has grown, along with the advent of the STM technology. The requirment of UHV-STM is especially very high in to study of surface construction of semiconductors and superconducting materials on the atomic scale. In order to improve the STM image quality by keeping the specimen and tip surfaces clean, we have built a new UHV-STM (JSTM-4000XV) system which is provided with other surface analysis capability.

Simultaneous observation of surface- and edge-states of a 2D topological insulator through scanning tunneling spectroscopy and differential conductance imaging

2017 ◽  
Vol 19 (15) ◽  
pp. 9872-9878 ◽  
Author(s):  
Hrishikesh Bhunia ◽  
Abhijit Bar ◽  
Abhijit Bera ◽  
Amlan J. Pal
Keyword(s):  
Topological Insulator ◽  
Fermi Energy ◽  
Topological Insulators ◽  
Dirac Point ◽  
Scanning Tunneling Spectroscopy ◽  
Tunneling Spectroscopy ◽  
Differential Conductance ◽  
Scanning Tunneling ◽  
Edge States ◽  
Simultaneous Observation

Gapless edge-states with a Dirac point below the Fermi energy and band-edges at the interior observed in 2D topological insulators.

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.

scholarly journals Zero-energy bound states in the high-temperature superconductors at the two-dimensional limit

2020 ◽  
Vol 6 (13) ◽  
pp. eaax7547 ◽  
Author(s):  
Chaofei Liu ◽  
Cheng Chen ◽  
Xiaoqiang Liu ◽  
Ziqiao Wang ◽  
Yi Liu ◽  
...  
Keyword(s):  
High Temperature ◽  
Bound States ◽  
High Temperature Superconductors ◽  
Scanning Tunneling Spectroscopy ◽  
Scanning Tunneling ◽  
Two Dimensional ◽  
Zero Energy ◽  
Topological Superconductors ◽  
Topological Quantum ◽  
Energy Bound

Majorana zero modes (MZMs) that obey the non-Abelian statistics have been intensively investigated for potential applications in topological quantum computing. The prevailing signals in tunneling experiments “fingerprinting” the existence of MZMs are the zero-energy bound states (ZEBSs). However, nearly all of the previously reported ZEBSs showing signatures of the MZMs are observed in difficult-to-fabricate heterostructures at very low temperatures and additionally require applied magnetic field. Here, by using in situ scanning tunneling spectroscopy, we detect the ZEBSs upon the interstitial Fe adatoms deposited on two different high-temperature superconducting one-unit-cell iron chalcogenides on SrTiO3(001). The spectroscopic results resemble the phenomenological characteristics of the MZMs inside the vortex cores of topological superconductors. Our experimental findings may extend the MZM explorations in connate topological superconductors toward an applicable temperature regime and down to the two-dimensional (2D) limit.

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.

Scanning Tunneling Spectroscopy

2021 ◽  
pp. 363-378
Author(s):  
C. Julian Chen
Keyword(s):  
Sample Surface ◽  
Experimental Methods ◽  
Scanning Tunneling Spectroscopy ◽  
Tunneling Spectroscopy ◽  
Atomic Scale ◽  
Detailed Account ◽  
Atomic Resolution ◽  
Scanning Tunneling ◽  
High Tc ◽  
Spectroscopy Experiment

This chapter discusses various aspects of scanning tunneling spectroscopy (STS). It is an extension of the classical tunneling spectroscopy experiment to nanometer-scale or atomic-scale features on the sample surface. First, the electronics for STS is presented. The nature of STS as a convolution of tip DOS and sample DOS is discussed. Special tip treatment for the STS experiment, often different from the atomic-resolution STM, is described. The purpose is to produce tips with flat DOS, instead of special tip orbitals. Experimental methods to determine tip DOS is discussed. A detailed account of the inelastic scanning tunneling spectroscopy, or STM-IETS, is then discussed. It includes the principles, the electronics, and the instrumental broadening of the features. This chapter concludes with the STS study of superconductors, especially High-Tc supercondoctors.

scholarly journals Evidence for a quantum spin Hall phase in graphene decorated with Bi2Te3 nanoparticles

2018 ◽  
Vol 4 (11) ◽  
pp. eaau6915 ◽  
Author(s):  
K. Hatsuda ◽  
H. Mine ◽  
T. Nakamura ◽  
J. Li ◽  
R. Wu ◽  
...  
Keyword(s):  
Scanning Tunneling Spectroscopy ◽  
Quantum Spin ◽  
Orbit Coupling ◽  
Photoelectron Spectra ◽  
Scanning Tunneling ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Edge States ◽  
Graphene Devices ◽  
Quantum Spin Hall

Realization of the quantum spin Hall effect in graphene devices has remained an outstanding challenge dating back to the inception of the field of topological insulators. Graphene’s exceptionally weak spin-orbit coupling—stemming from carbon’s low mass—poses the primary obstacle. We experimentally and theoretically study artificially enhanced spin-orbit coupling in graphene via random decoration with dilute Bi2Te3 nanoparticles. Multiterminal resistance measurements suggest the presence of helical edge states characteristic of a quantum spin Hall phase; the magnetic field and temperature dependence of the resistance peaks, x-ray photoelectron spectra, scanning tunneling spectroscopy, and first-principles calculations further support this scenario. These observations highlight a pathway to spintronics and quantum information applications in graphene-based quantum spin Hall platforms.

scholarly journals Nearly quantized conductance plateau of vortex zero mode in an iron-based superconductor

Science ◽  
2019 ◽  
pp. eaax0274 ◽  
Author(s):  
Shiyu Zhu ◽  
Lingyuan Kong ◽  
Lu Cao ◽  
Hui Chen ◽  
Michał Papaj ◽  
...  
Keyword(s):  
Bound States ◽  
Zero Mode ◽  
Finite Energy ◽  
Scanning Tunneling Spectroscopy ◽  
Scanning Tunneling ◽  
Tunneling Conductance ◽  
Zero Energy ◽  
Tunnel Coupling ◽  
Topological Quantum ◽  
The Continuum

Majorana zero modes (MZMs) are spatially-localized zero-energy fractional quasiparticles with non-Abelian braiding statistics that hold promise for topological quantum computing. Owing to the particle-antiparticle equivalence, MZMs exhibit quantized conductance at low temperature. By utilizing variable-tunnel-coupled scanning tunneling spectroscopy, we study tunneling conductance of vortex bound states on FeTe0.55Se0.45 superconductors. We report observations of conductance plateaus as a function of tunnel coupling for zero-energy vortex bound states with values close to or even reaching the 2e2/h quantum conductance (here e is the electron charge and h is Planck’s constant). In contrast, no plateaus were observed on either finite energy vortex bound states or in the continuum of electronic states outside the superconducting gap. This behavior of the zero-mode conductance supports the existence of MZMs in FeTe0.55Se0.45.

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