scholarly journals Experimental discovery of a topological Weyl semimetal state in TaP

2015 ◽  
Vol 1 (10) ◽  
pp. e1501092 ◽  
Author(s):  
Su-Yang Xu ◽  
Ilya Belopolski ◽  
Daniel S. Sanchez ◽  
Chenglong Zhang ◽  
Guoqing Chang ◽  
...  
Keyword(s):  
Materials Science ◽  
Surface States ◽  
Photoemission Spectroscopy ◽  
New Horizons ◽  
Weyl Semimetal ◽  
Fermi Arcs ◽  
Experimental Discovery ◽  
Boundary Correspondence ◽  
First Time ◽  
Weyl Fermion

Weyl semimetals are expected to open up new horizons in physics and materials science because they provide the first realization of Weyl fermions and exhibit protected Fermi arc surface states. However, they had been found to be extremely rare in nature. Recently, a family of compounds, consisting of tantalum arsenide, tantalum phosphide (TaP), niobium arsenide, and niobium phosphide, was predicted as a Weyl semimetal candidates. We experimentally realize a Weyl semimetal state in TaP. Using photoemission spectroscopy, we directly observe the Weyl fermion cones and nodes in the bulk, and the Fermi arcs on the surface. Moreover, we find that the surface states show an unexpectedly rich structure, including both topological Fermi arcs and several topologically trivial closed contours in the vicinity of the Weyl points, which provides a promising platform to study the interplay between topological and trivial surface states on a Weyl semimetal’s surface. We directly demonstrate the bulk-boundary correspondence and establish the topologically nontrivial nature of the Weyl semimetal state in TaP, by resolving the net number of chiral edge modes on a closed path that encloses the Weyl node. This also provides, for the first time, an experimentally practical approach to demonstrating a bulk Weyl fermion from a surface state dispersion measured in photoemission.

scholarly journals Fermi-arc diversity on surface terminations of the magnetic Weyl semimetal Co3Sn2S2

Science ◽  
2019 ◽  
Vol 365 (6459) ◽  
pp. 1286-1291 ◽  
Author(s):  
Noam Morali ◽  
Rajib Batabyal ◽  
Pranab Kumar Nag ◽  
Enke Liu ◽  
Qiunan Xu ◽  
...  
Keyword(s):  
Electronic Properties ◽  
Time Reversal ◽  
Surface States ◽  
Time Reversal Symmetry ◽  
Fermi Arc ◽  
Weyl Semimetal ◽  
Fermi Arcs ◽  
Bulk Surface ◽  
Weyl Semimetals ◽  
Node Connectivity

Bulk–surface correspondence in Weyl semimetals ensures the formation of topological “Fermi arc” surface bands whose existence is guaranteed by bulk Weyl nodes. By investigating three distinct surface terminations of the ferromagnetic semimetal Co3Sn2S2, we verify spectroscopically its classification as a time-reversal symmetry-broken Weyl semimetal. We show that the distinct surface potentials imposed by three different terminations modify the Fermi-arc contour and Weyl node connectivity. On the tin (Sn) surface, we identify intra–Brillouin zone Weyl node connectivity of Fermi arcs, whereas on cobalt (Co) termination, the connectivity is across adjacent Brillouin zones. On the sulfur (S) surface, Fermi arcs overlap with nontopological bulk and surface states. We thus resolve both topologically protected and nonprotected electronic properties of a Weyl semimetal.

scholarly journals Discovery of topological Weyl fermion lines and drumhead surface states in a room temperature magnet

Science ◽  
2019 ◽  
Vol 365 (6459) ◽  
pp. 1278-1281 ◽  
Author(s):  
Ilya Belopolski ◽  
Kaustuv Manna ◽  
Daniel S. Sanchez ◽  
Guoqing Chang ◽  
Benedikt Ernst ◽  
...  
Keyword(s):  
Room Temperature ◽  
Surface States ◽  
Photoemission Spectroscopy ◽  
Topological Invariants ◽  
Fermion Line ◽  
Berry Curvature ◽  
Quantum Matter ◽  
Interacting Electrons ◽  
Strongly Interacting Electrons ◽  
Weyl Fermion

Topological matter is known to exhibit unconventional surface states and anomalous transport owing to unusual bulk electronic topology. In this study, we use photoemission spectroscopy and quantum transport to elucidate the topology of the room temperature magnet Co2MnGa. We observe sharp bulk Weyl fermion line dispersions indicative of nontrivial topological invariants present in the magnetic phase. On the surface of the magnet, we observe electronic wave functions that take the form of drumheads, enabling us to directly visualize the crucial components of the bulk-boundary topological correspondence. By considering the Berry curvature field associated with the observed topological Weyl fermion lines, we quantitatively account for the giant anomalous Hall response observed in this magnet. Our experimental results suggest a rich interplay of strongly interacting electrons and topology in quantum matter.

scholarly journals A strongly robust type II Weyl fermion semimetal state in Ta3S2

2016 ◽  
Vol 2 (6) ◽  
pp. e1600295 ◽  
Author(s):  
Guoqing Chang ◽  
Su-Yang Xu ◽  
Daniel S. Sanchez ◽  
Shin-Ming Huang ◽  
Chi-Cheng Lee ◽  
...  
Keyword(s):  
Surface States ◽  
Insulator Transition ◽  
Type Ii ◽  
Weyl Semimetal ◽  
Tantalum Sulfide ◽  
Weyl Semimetals ◽  
Device Applications ◽  
Metal To Insulator Transition ◽  
Weyl Fermion ◽  
Topological Metal

Weyl semimetals are of great interest because they provide the first realization of the Weyl fermion, exhibit exotic quantum anomalies, and host Fermi arc surface states. The separation between Weyl nodes of opposite chirality gives a measure of the robustness of the Weyl semimetal state. To exploit the novel phenomena that arise from Weyl fermions in applications, it is crucially important to find robust separated Weyl nodes. We propose a methodology to design robust Weyl semimetals with well-separated Weyl nodes. Using this methodology as a guideline, we search among the material parameter space and identify by far the most robust and ideal Weyl semimetal candidate in the single-crystalline compound tantalum sulfide (Ta3S2) with new and novel properties beyond TaAs. Crucially, our results show that Ta3S2has the largestk-space separation between Weyl nodes among known Weyl semimetal candidates, which is about twice larger than the measured value in TaAs and 20 times larger than the predicted value in WTe2. Moreover, all Weyl nodes in Ta3S2are of type II. Therefore, Ta3S2is a type II Weyl semimetal. Furthermore, we predict that increasing the lattice by <4% can annihilate all Weyl nodes, driving a novel topological metal-to-insulator transition from a Weyl semimetal state to a topological insulator state. The robust type II Weyl semimetal state and the topological metal-to-insulator transition in Ta3S2are potentially useful in device applications. Our methodology can be generally applied to search for new Weyl semimetals.

Zero-loss omega-filtered REM and RHEED on the new Zeiss 912

1991 ◽  
Vol 49 ◽  
pp. 616-617
Author(s):  
J.C.H. Spence ◽  
J. Mayer
Keyword(s):  
Electron Microscopy ◽  
Materials Science ◽  
Surface States ◽  
Ccd Camera ◽  
Dark Field ◽  
Ion Pump ◽  
Magnetic Imaging ◽  
Reflection Electron Microscopy ◽  
Diffraction Patterns ◽  
Large Background

The Zeiss 912 is a new fully digital, side-entry, 120 Kv TEM/STEM instrument for materials science, fitted with an omega magnetic imaging energy filter. Pumping is by turbopump and ion pump. The magnetic imaging filter allows energy-filtered images or diffraction patterns to be recorded without scanning using efficient parallel (area) detection. The energy loss intensity distribution may also be displayed on the screen, and recorded by scanning it over the PMT supplied. If a CCD camera is fitted and suitable new software developed, “parallel ELS” recording results. For large fields of view, filtered images can be recorded much more efficiently than by Scanning Reflection Electron Microscopy, and the large background of inelastic scattering removed. We have therefore evaluated the 912 for REM and RHEED applications. Causes of streaking and resonance in RHEED patterns are being studied, and a more quantitative analysis of CBRED patterns may be possible. Dark field band-gap REM imaging of surface states may also be possible.

Electron spectroscopic imaging and diffraction

1991 ◽  
Vol 49 ◽  
pp. 706-707
Author(s):  
M. Rühle ◽  
J. Mayer ◽  
J.C.H. Spence ◽  
J. Bihr ◽  
W. Probst ◽  
...  
Keyword(s):  
Materials Science ◽  
Electron Spectroscopic Imaging ◽  
Magnetic Filter ◽  
Magnetic Imaging ◽  
Illumination System ◽  
Probe Size ◽  
Diffraction Patterns ◽  
Fritz Haber ◽  
Koehler Illumination ◽  
First Time

A new Zeiss TEM with an imaging Omega filter is a fully digitized, side-entry, 120 kV TEM/STEM instrument for materials science. The machine possesses an Omega magnetic imaging energy filter (see Fig. 1) placed between the third and fourth projector lens. Lanio designed the filter and a prototype was built at the Fritz-Haber-Institut in Berlin, Germany. The imaging magnetic filter allows energy-filtered images or diffraction patterns to be recorded without scanning using efficient area detection. The energy dispersion at the exit slit (Fig. 1) results in ∼ 1.5 μm/eV which allows imaging with energy windows of ≤ 10 eV. The smallest probe size of the microscope is 1.6 nm and the Koehler illumination system is used for the first time in a TEM. Serial recording of EELS spectra with a resolution < 1 eV is possible. The digital control allows X,Y,Z coordinates and tilt settings to be stored and later recalled.

scholarly journals Cobalt-based magnetic Weyl semimetals with high-thermodynamic stabilities

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Wei Luo ◽  
Yuma Nakamura ◽  
Jinseon Park ◽  
Mina Yoon
Keyword(s):  
Tight Binding ◽  
Three Dimensional ◽  
Interlayer Coupling ◽  
First Principles Calculation ◽  
Optimization Approach ◽  
Binding Model ◽  
Nodal Lines ◽  
Weyl Semimetal ◽  
Topological Quantum ◽  
First Time

AbstractRecent experiments identified Co3Sn2S2 as the first magnetic Weyl semimetal (MWSM). Using first-principles calculation with a global optimization approach, we explore the structural stabilities and topological electronic properties of cobalt (Co)-based shandite and alloys, Co3MM’X2 (M/M’ = Ge, Sn, Pb, X = S, Se, Te), and identify stable structures with different Weyl phases. Using a tight-binding model, for the first time, we reveal that the physical origin of the nodal lines of a Co-based shandite structure is the interlayer coupling between Co atoms in different Kagome layers, while the number of Weyl points and their types are mainly governed by the interaction between Co and the metal atoms, Sn, Ge, and Pb. The Co3SnPbS2 alloy exhibits two distinguished topological phases, depending on the relative positions of the Sn and Pb atoms: a three-dimensional quantum anomalous Hall metal, and a MWSM phase with anomalous Hall conductivity (~1290 Ω−1 cm−1) that is larger than that of Co2Sn2S2. Our work reveals the physical mechanism of the origination of Weyl fermions in Co-based shandite structures and proposes topological quantum states with high thermal stability.

scholarly journals Observation of a singular Weyl point surrounded by charged nodal walls in PtGa

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
J.-Z. Ma ◽  
Q.-S. Wu ◽  
M. Song ◽  
S.-N. Zhang ◽  
E. B. Guedes ◽  
...  
Keyword(s):  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Photoemission Spectroscopy ◽  
Functional Theory ◽  
Fermi Arc ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Fermi Arcs ◽  
Surface Projection ◽  
Applicable Range ◽  
Opposite Chirality

AbstractConstrained by the Nielsen-Ninomiya no-go theorem, in all so-far experimentally determined Weyl semimetals (WSMs) the Weyl points (WPs) always appear in pairs in the momentum space with no exception. As a consequence, Fermi arcs occur on surfaces which connect the projections of the WPs with opposite chiral charges. However, this situation can be circumvented in the case of unpaired WP, without relevant surface Fermi arc connecting its surface projection, appearing singularly, while its Berry curvature field is absorbed by nontrivial charged nodal walls. Here, combining angle-resolved photoemission spectroscopy with density functional theory calculations, we show experimentally that a singular Weyl point emerges in PtGa at the center of the Brillouin zone (BZ), which is surrounded by closed Weyl nodal walls located at the BZ boundaries and there is no Fermi arc connecting its surface projection. Our results reveal that nontrivial band crossings of different dimensionalities can emerge concomitantly in condensed matter, while their coexistence ensures the net topological charge of different dimensional topological objects to be zero. Our observation extends the applicable range of the original Nielsen-Ninomiya no-go theorem which was derived from zero dimensional paired WPs with opposite chirality.

scholarly journals 2D weak anti-localization in thin films of the topological semimetal Pd$$_{3}$$Bi$$_{2}$$S$$_{2}$$

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Shama ◽  
R. K. Gopal ◽  
Goutam Sheet ◽  
Yogesh Singh
Keyword(s):  
Thin Films ◽  
Phonon Scattering ◽  
Surface States ◽  
Relaxation Mechanism ◽  
Transport Studies ◽  
Bulk Carriers ◽  
Topological Semimetal ◽  
Topological Surface ◽  
First Time ◽  
Electron Phonon Scattering

AbstractPd$$_{3}$$ 3 Bi$$_{2}$$ 2 S$$_{2}$$ 2 (PBS) is a recently proposed topological semimetal candidate. However, evidence for topological surface states have not yet been revealed in transport measurements due to the large mobility of bulk carriers. We report the growth and magneto-transport studies of PBS thin films where the mobility of the bulk carriers is reduced by two orders of magnitude, revealing for the first time, contributions from the 2-dimensional (2D) topological surface states in the observation of the 2D weak anti-localization (WAL) effect in magnetic field and angle dependent conductivity measurements. The magnetotransport data is analysed within the 2D Hikami-Larkin-Nagaoka (HLN) theory. The analysis suggests that multiple conduction channels contribute to the transport. It is also found that the temperature dependence of the dephasing length can’t be explained only by electron-electron scattering and that electron-phonon scattering also contributes to the phase relaxation mechanism in PBS films.

scholarly journals APASL Single Topic Conference DELTA HEPATITIS, 27-28 June 2019, Baku, Azerbaijan

2019 ◽  
Vol 2 (2) ◽  
pp. 1-46
Author(s):  
Gulnara Aghayeva
Keyword(s):  
Hepatitis B ◽  
Current Treatment ◽  
Hbv Infection ◽  
Good Chance ◽  
Hepatitis Delta ◽  
New Horizons ◽  
History Of ◽  
Pharmaceutical Agents ◽  
Work Up ◽  
First Time

As Delta problem moved from the shadow up on the stage, becoming one of the most crucial disease in Hepatology area, our STC 2019 is dedicated to hepat itis D, for the first time in the history of APASL STC topics. As hepatitis Delta occurs only with HBV infection, we will discuss hepatitis B, its epidemiology, work - up, current treatment and new horizons in the developing pharmaceutical agents. The scient ific program will include the topics presented by the best speakers and the experts in Delta and B hepatitis. This conference is a good chance to meet and interact with leading clinical professionals and researches and to obtain latest information for hepa tologists.

scholarly journals Evolution of Metastable Structures at Bimetallic Surfaces from Microscopy and Machine-Learning Molecular Dynamics

2020 ◽  
Author(s):  
Jin Soo Lim ◽  
Jonathan Vandermause ◽  
Matthijs A. van Spronsen ◽  
Albert Musaelian ◽  
Yu Xie ◽  
...  
Keyword(s):  
Machine Learning ◽  
Molecular Dynamics ◽  
Materials Science ◽  
Automated Analysis ◽  
Layer By Layer ◽  
Surface Restructuring ◽  
Bimetallic Systems ◽  
Metastable Structures ◽  
Mechanistic Investigation ◽  
First Time

Restructuring of interfaces plays a crucial role in materials science and heterogeneous catalysis. Bimetallic systems, in particular, often adopt very different composition and morphology at surfaces compared to the bulk. For the first time, we reveal a detailed atomistic picture of long-timescale restructuring of Pd deposited on Ag, using microscopy, spectroscopy, and novel simulation methods. By developing and performing accelerated machine-learning molecular dynamics followed by an automated analysis method, we discover and characterize previously unidentified surface restructuring mechanisms in an unbiased fashion, including Pd-Ag place exchange and Ag pop-out, as well as step ascent and descent. Remarkably, layer-by-layer dissolution of Pd into Ag is always preceded by an encapsulation of Pd islands by Ag, resulting in a significant migration of Ag out of the surface and a formation of extensive vacancy pits within a period of microseconds. These metastable structures are of vital catalytic importance, as Ag-encapsulated Pd remains much more accessible to reactants than bulk-dissolved Pd. Our approach is broadly applicable to complex multimetallic systems and enables the previously intractable mechanistic investigation of restructuring dynamics at atomic resolution.

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