scholarly journals Visualizing weakly bound surface Fermi arcs and their correspondence to bulk Weyl fermions

2016 ◽  
Vol 2 (8) ◽  
pp. e1600709 ◽  
Author(s):  
Rajib Batabyal ◽  
Noam Morali ◽  
Nurit Avraham ◽  
Yan Sun ◽  
Marcus Schmidt ◽  
...  
Keyword(s):  
Wave Function ◽  
Bloch Wave ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Weakly Bound ◽  
Fermi Arc ◽  
Fermi Arcs ◽  
Surface Manifestation ◽  
Energy And Momentum ◽  
Spectroscopic Tool

Fermi arcs are the surface manifestation of the topological nature of Weyl semimetals, enforced by the bulk-boundary correspondence with the bulk Weyl nodes. The surface of tantalum arsenide, similar to that of other members of the Weyl semimetal class, hosts nontopological bands that obscure the exploration of this correspondence. We use the spatial structure of the Fermi arc wave function, probed by scanning tunneling microscopy, as a spectroscopic tool to distinguish and characterize the surface Fermi arc bands. We find that, as opposed to nontopological states, the Fermi arc wave function is weakly affected by the surface potential: it spreads rather uniformly within the unit cell and penetrates deeper into the bulk. Fermi arcs reside predominantly on tantalum sites, from which the topological bulk bands are derived. Furthermore, we identify a correspondence between the Fermi arc dispersion and the energy and momentum of the bulk Weyl nodes that classify this material as topological. We obtain these results by introducing an analysis based on the role the Bloch wave function has in shaping quantum electronic interference patterns. It thus carries broader applicability to the study of other electronic systems and other physical processes.

scholarly journals Nontrivial superconductivity in topological MoTe2−xSx crystals

2018 ◽  
Vol 115 (38) ◽  
pp. 9503-9508 ◽  
Author(s):  
Yanan Li ◽  
Qiangqiang Gu ◽  
Chen Chen ◽  
Jun Zhang ◽  
Qin Liu ◽  
...  
Keyword(s):  
Surface States ◽  
Sample Surface ◽  
Scanning Tunneling Spectroscopy ◽  
Scanning Tunneling ◽  
Fermi Arc ◽  
Topological Features ◽  
Fermi Arcs ◽  
Unique Material ◽  
Pairing Model

Topological Weyl semimetals (TWSs) with pairs of Weyl points and topologically protected Fermi arc states have broadened the classification of topological phases and provide superior platform for study of topological superconductivity. Here we report the nontrivial superconductivity and topological features of sulfur-doped Td-phase MoTe2 with enhanced Tc compared with type-II TWS MoTe2. It is found that Td-phase S-doped MoTe2 (MoTe2−xSx, x ∼ 0.2) is a two-band s-wave bulk superconductor (∼0.13 meV and 0.26 meV), where the superconducting behavior can be explained by the s+− pairing model. Further, measurements of the quasi-particle interference (QPI) patterns and a comparison with band-structure calculations reveal the existence of Fermi arcs in MoTe2−xSx. More interestingly, a relatively large superconducting gap (∼1.7 meV) is detected by scanning tunneling spectroscopy on the sample surface, showing a hint of topological nontrivial superconductivity based on the pairing of Fermi arc surface states. Our work demonstrates that the Td-phase MoTe2−xSx is not only a promising topological superconductor candidate but also a unique material for study of s+− superconductivity.

Wave function imaging of the PbS(001) surface with scanning tunneling microscopy

1993 ◽  
Vol 287-288 ◽  
pp. A439
Author(s):  
A.R.H.F. Ettema ◽  
C. Haas ◽  
P. Moriarty ◽  
G. Hughes
Keyword(s):  
Wave Function ◽  
Scanning Tunneling Microscopy ◽  
Scanning Tunneling ◽  
Tunneling Microscopy

Wave function imaging of the PbS(001) surface with scanning tunneling microscopy

1993 ◽  
Vol 287-288 ◽  
pp. 1106-1111 ◽  
Author(s):  
A.R.H.F. Ettema ◽  
C. Haas ◽  
P. Moriarty ◽  
G. Hughes
Keyword(s):  
Wave Function ◽  
Scanning Tunneling Microscopy ◽  
Scanning Tunneling ◽  
Tunneling Microscopy

scholarly journals Quasiparticle interference evidence of the topological Fermi arc states in chiral fermionic semimetal CoSi

2019 ◽  
Vol 5 (12) ◽  
pp. eaaw9485 ◽  
Author(s):  
Qian-Qian Yuan ◽  
Liqin Zhou ◽  
Zhi-Cheng Rao ◽  
Shangjie Tian ◽  
Wei-Min Zhao ◽  
...  
Keyword(s):  
Density Functional ◽  
Surface States ◽  
High Energy ◽  
Scanning Tunneling ◽  
Wide Energy Range ◽  
Tunneling Microscopy ◽  
Space Resolution ◽  
Fermi Arc ◽  
Quasiparticle Interference ◽  
High Space

Chiral fermions in solid state feature “Fermi arc” states, connecting the surface projections of the bulk chiral nodes. The surface Fermi arc is a signature of nontrivial bulk topology. Unconventional chiral fermions with an extensive Fermi arc traversing the whole Brillouin zone have been theoretically proposed in CoSi. Here, we use scanning tunneling microscopy/spectroscopy to investigate quasiparticle interference at various terminations of a CoSi single crystal. The observed surface states exhibit chiral fermion–originated characteristics. These reside on (001) and (011) but not (111) surfaces with p-rotation symmetry, spiral with energy, and disperse in a wide energy range from ~−200 to ~+400 mV. Owing to the high-energy and high-space resolution, a spin-orbit coupling–induced splitting of up to ~80 mV is identified. Our observations are corroborated by density functional theory and provide strong evidence that CoSi hosts the unconventional chiral fermions and the extensive Fermi arc states.

STM studies of crystal growth

1991 ◽  
Vol 49 ◽  
pp. 374-375
Author(s):  
M. G. Lagally
Keyword(s):  
Crystal Growth ◽  
Molecular Beam ◽  
Chemical Vapor ◽  
Sputter Deposition ◽  
Field Of View ◽  
Scanning Tunneling ◽  
Wide Field ◽  
Tunneling Microscopy ◽  
Wide Field Of View ◽  
The One

It has been recognized since the earliest days of crystal growth that kinetic processes of all Kinds control the nature of the growth. As the technology of crystal growth has become ever more refined, with the advent of such atomistic processes as molecular beam epitaxy, chemical vapor deposition, sputter deposition, and plasma enhanced techniques for the creation of “crystals” as little as one or a few atomic layers thick, multilayer structures, and novel materials combinations, the need to understand the mechanisms controlling the growth process is becoming more critical. Unfortunately, available techniques have not lent themselves well to obtaining a truly microscopic picture of such processes. Because of its atomic resolution on the one hand, and the achievable wide field of view on the other (of the order of micrometers) scanning tunneling microscopy (STM) gives us this opportunity. In this talk, we briefly review the types of growth kinetics measurements that can be made using STM. The use of STM for studies of kinetics is one of the more recent applications of what is itself still a very young field.

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