A5018769752- Topological Materials and Phenomena
- Graphene research and applications
- 2D Materials and Applications
- Advanced Condensed Matter Physics
- Rare-earth and actinide compounds
- Quantum and electron transport phenomena
- Iron-based superconductors research
- Physics of Superconductivity and Magnetism
- Magnetic and transport properties of perovskites and related materials
- Multiferroics and related materials
- Quantum many-body systems
- Magnetic properties of thin films
- Cold Atom Physics and Bose-Einstein Condensates
- Magnetic Properties of Alloys
- Inorganic Chemistry and Materials
- MXene and MAX Phase Materials
- Machine Learning in Materials Science
- Quantum Mechanics and Non-Hermitian Physics
- Organic and Molecular Conductors Research
- Ferroelectric and Piezoelectric Materials
- Chalcogenide Semiconductor Thin Films
- Theoretical and Computational Physics
- Magnetic Properties and Synthesis of Ferrites
- Ferroelectric and Negative Capacitance Devices
- Quantum, superfluid, helium dynamics
National Sun Yat-sen University
2015-2024
National Center for Theoretical Sciences
2021-2024
National Center for Theoretical Sciences, Physics Division
2023-2024
National Tsing Hua University
2011-2021
Institute of Physics, Academia Sinica
2021
National University of Singapore
2015-2017
Princeton University
2017
Instituto Sapientia
2011
Medecell (Brazil)
2011
Medical University of Lublin
2011
Weyl physics emerges in the laboratory fermions—massless particles with half-integer spin—were once mistakenly thought to describe neutrinos. Although not yet observed among elementary particles, fermions may exist as collective excitations so-called semimetals. These materials have an unusual band structure which linearly dispersing valence and conduction bands meet at discrete “Weyl points.” Xu et al. used photoemission spectroscopy identify TaAs a semimetal capable of hosting fermions. In...
Abstract Weyl fermions are massless chiral that play an important role in quantum field theory but have never been observed as fundamental particles. A semimetal is unusual crystal hosts quasiparticle excitations and features Fermi arcs on its surface. Such a not only provides condensed matter realization of the anomalies theories also demonstrates topological classification beyond gapped insulators. Here, we identify state transition metal monopnictide materials class. Our first-principles...
Abstract Topological semimetals can support one-dimensional Fermi lines or zero-dimensional Weyl points in momentum space, where the valence and conduction bands touch. While degeneracy are robust against any perturbation that preserves translational symmetry, nodal require protection by additional crystalline symmetries such as mirror reflection. Here we report, based on a systematic theoretical study detailed experimental characterization, existence of topological nodal-line states...
Abstract Weyl semimetals provide the realization of fermions in solid-state physics. Among all physical phenomena that are enabled by semimetals, chiral anomaly is most unusual one. Here, we report signatures magneto-transport measurements on first semimetal TaAs. We show negative magnetoresistance under parallel electric and magnetic fields, is, unlike metals whose resistivity increases an external field, observe our high mobility TaAs samples become more conductive as a field applied along...
Magnetic Weyl semimetals (WSMs)—materials that host exotic quasiparticles called fermions—must break either spatial inversion or time-reversal symmetry. A number of WSMs symmetry have been identified, but showing unambiguously a material is time-reversal-breaking WSM tricky. Three groups now provide spectroscopic evidence for this latter state in magnetic materials (see the Perspective by da Silva Neto). Belopolski et al. probed Co 2 MnGa using angle-resolved photoemission spectroscopy,...
Weyl semimetals are expected to open up new horizons in physics and materials science because they provide the first realization of fermions exhibit protected Fermi arc surface states. However, had been found be extremely rare nature. Recently, a family compounds, consisting tantalum arsenide, phosphide (TaP), niobium phosphide, was predicted as semimetal candidates. We experimentally realize state TaP. Using photoemission spectroscopy, we directly observe fermion cones nodes bulk, arcs on...
The theoretical proposal of chiral fermions in topological semimetals has led to a significant effort towards their experimental realization. In particular, the Fermi surfaces carry quantized Chern numbers, making them an attractive platform for observation exotic transport and optical phenomena. While simplest example fermion condensed matter is conventional $|C|=1$ Weyl fermion, recent works have proposed number unconventional beyond standard model which are protected by unique...
We identify a Weyl semimetal state in an inversion breaking, stoichiometric compound strontium silicide, SrSi$_2$, with many new and novel properties that are distinct from the TaAs family. theoretically show SrSi$_2$ is even without spin-orbit coupling that, after inclusion of coupling, two fermions stick together forming exotic double fermion quadratic dispersions higher chiral topological charge 2. Moreover, we find nodes opposite charges located at different energies due to absence...
A topological nodal-line semimetal is a state of matter with one-dimensional bulk nodal lines and two-dimensional so-called drumhead surface bands. Based on first-principles calculations an effective $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ model, we theoretically propose the existence fermions in ternary transition-metal chalcogenide ${\mathrm{TlTaSe}}_{2}$. The noncentrosymmetric structure strong spin-orbit coupling give rise to spinful states which are protected...
Weyl semimetals may open a new era in condensed matter physics because they provide the first example of fermions, realize topological classification even though system is gapless, exhibit Fermi arc surface states and demonstrate chiral anomaly other exotic quantum phenomena. So far, only known are TaAs class materials. Here, we propose existence tunable metallic state Mo$_x$W$_{1-x}$Te$_2$ via our first-principles calculations. We that 2% Mo doping sufficient to stabilize metal not at low...
Weyl semimetals are conductors whose low-energy bulk excitations fermions, whereas their surfaces possess metallic Fermi arc surface states. These states protected by a topological invariant associated with the electronic wave functions of material. Recently, it has been shown that TaAs and NbAs classes materials harbor such state matter. We review basic phenomena experimental history discovery first semimetals, starting observation arcs nodes in angle spin-resolved sensitive photoemission...
Topological semimetals can be classified by the connectivity and dimensionality of band crossings in momentum space. The a Dirac, Weyl, or an unconventional fermion semimetal are zero-dimensional (0D) points, whereas nodal-line one-dimensional (1D) closed loops. Here we propose that presence perpendicular crystalline mirror planes protect three-dimensional (3D) characterized nontrivial links such as Hopf link coupled chain, giving rise to variety new types topological semimetals. We show...
In quantum field theory, Weyl fermions are relativistic particles that travel at the speed of light and strictly obey celebrated Lorentz symmetry. Their low-energy condensed matter analogs semimetals, which conductors whose electronic excitations mimic fermion equation motion. Although traditional (type I) emergent observed in TaAs still approximately respect symmetry, recently, so-called type II semimetal has been proposed, where quasiparticles break symmetry so strongly they cannot be...
Abstract The recent discovery of a Weyl semimetal in TaAs offers the first fermion observed nature and dramatically broadens classification topological phases. However, it has proven challenging to study rich transport phenomena arising from emergent fermions. series Mo x W 1− Te 2 are inversion-breaking, layered, tunable semimetals already under as promising platform for new electronics recently proposed host Type II, or strongly Lorentz-violating, Here we report at =25%. We use pump-probe...
Abstract Platinum-based transition metal dichalcogenides have been gaining renewed interest because of the development a new method to synthesize thin film structures. Here, using first-principles calculation, we explore electronic properties PtX 2 (X = S, Se, and Te) with respect thickness. For bulk layered structures (1 10 layers), octahedral 1T is most stable. Surprisingly, also find that 3R structure has comparable stability relative 1T, implying possible synthesis 3R. structure, PtS...
Weyl semimetals are novel topological conductors that host fermions as emergent quasiparticles. In this Rapid Communication, we propose a new type of semimetal state breaks both time-reversal symmetry and inversion in the $R\mathrm{AlGe}$ ($R=\mathrm{rare}\ensuremath{-}\mathrm{earth}$) family. Compared to previous predictions magnetic candidates, prediction nodes is more robust less dependent on details magnetism because generated already by breaking ferromagnetism acts simple Zeeman...
The recent proposal of the type-II Weyl semimetal state has attracted significant interest. In this Letter, we propose concept three-dimensional Dirac fermion and theoretically identify new symmetry-protected topological in large family transition-metal icosagenides, MA3 (M=V, Nb, Ta; A=Al, Ga, In). We show that VAl3 features a pair strongly Lorentz-violating nodes each node can be split into four with chiral charge ±1 via symmetry breaking. Furthermore, predict Landau level spectrum arising...
The recent discovery of the first Weyl semimetal in TaAs provides observation a fermion nature and demonstrates novel type anomalous surface state, Fermi arc. Like topological insulators, bulk invariants are uniquely fixed by states sample. Here we present set distinct conditions, accessible angle-resolved photoemission spectroscopy (ARPES), each which arcs state band structure, with minimal reliance on calculation. We apply these results to NbP. For time, rigorously demonstrate nonzero...
The family of binary compounds including TaAs, TaP, NbAs, and NbP was recently discovered as the first realization Weyl semimetals. In order to develop a comprehensive description charge carriers in these semimetals, we performed systematic electronic structure calculations which reveal nature Fermi surfaces their complex interconnectivity NbP. Our work report comparative study surface topology band details all known members semimetal provide necessary building blocks for advancing our...
Topological metals and semimetals (TMs) have recently drawn significant interest. These materials give rise to condensed matter realizations of many important concepts in high-energy physics, leading wide-ranging protected properties transport spectroscopic experiments. The most studied TMs, i.e., Weyl Dirac semimetals, feature quasiparticles that are direct analogues the textbook elementary particles. Moreover, TMs known so far can be characterized based on dimensionality band crossing....
Members of the Mo${}_{x}$W${}_{1-x}$Te${}_{2}$ series are predicted to be Weyl semimetals, hosting type-II fermions, which have yet experimentally realized and unusual because they strongly violate Lorentz invariance. Crucially, points in this system sit above Fermi level. Here, authors show that for a cone, although not type-I if point is level, then it's necessary see band structure level observe topological arc. The also discover pump-probe angle-resolved photoemission beautifully...
A Weyl semimetal is a new state of matter that hosts fermions as quasiparticle excitations. The at zero energy correspond to points bulk-band degeneracy, called nodes, which are separated in momentum space and connected only through the crystal's boundary by an exotic Fermi arc surface state. We experimentally measure spin polarization arcs first discovered TaAs. Our data, for time, reveal arcs' spin-polarization magnitude large 80% lies completely plane surface. Moreover, we demonstrate...