Three-dimensional topological insulators (TIs) are characterized by their nontrivial surface states, in which electrons have spin locked at a right angle to momentum under the protection of time-reversal symmetry. The topologically ordered phase TIs does not break any interplay between order and symmetry breaking, such as that observed superconductivity, can lead new quantum phenomena devices. We fabricated superconducting TI/superconductor heterostructure growing dibismuth triselenide...

High-quality Bi2Te3 films can be grown on Si by the state-of-art molecular beam epitaxy technique. In situ ARPES measurement reveals that as-grown are intrinsic topological insulators and single-Dirac-cone surface state develops at a thickness of two quintuple layers. The work opens new avenue for engineering materials based well-developed technology.

We theoretically study the three-dimensional topological semimetals with nodal surfaces protected by crystalline symmetries. Different from well-known nodal-point and nodal-line semimetals, in these materials, conduction valence bands cross on closed Brillouin zone. propose different classes of surfaces, both absence presence spin-orbit coupling (SOC). In SOC, a class can be spacetime inversion symmetry sublattice characterized $\mathbb{Z}_2$ index, while another are guaranteed combination...

Topological superconductors (TSCs), featuring fully gapped bulk and gapless surface states as well Majorana fermions, have potential applications in fault-tolerant topological quantum computing. Because TSCs are very rare nature, an alternative way to study the TSC is artificially introduce superconductivity into of a insulator through proximity effect [X. L. Qi, T. Hughse, S. Raghu, C. Zhang, Phys. Rev. Lett. 102, 187001 (2009); Fu Kane, 100, 096407 (2008); J. Alicea, Rep. Prog. 75, 076501...

Nodal loop appears when two bands, typically one electron-like and hole-like, are crossing each other linearly along a one-dimensional manifold in the reciprocal space. Here we propose new type of nodal which emerges from between bands both (or hole-like) certain direction. Close to any point on such (dubbed as type-II loop), linear spectrum is strongly tilted tipped over transverse direction, leading marked differences magnetic, optical, transport responses compared with conventional...

Electrides are a unique class of electron-rich materials where excess electrons localized in interstitial lattice sites as anions, leading to range properties and applications. While hundreds electrides have been discovered recent years, magnetic received limited attention, with few investigations into their fundamental physics practical In this work, 51 (12 antiferromagnetic, 13 ferromagnetic, 26 interstitial-magnetic) were identified using high-throughput computational screening methods...

Effective gravity and gauge fields are emergent properties intrinsic for low-energy quasiparticles in topological semimetals. Here, taking two Dirac semimetals as examples, we demonstrate that applied lattice strain can generate warped spacetime, with fascinating analogues astrophysics. Particularly, study the possibility of simulating black-hole/white-hole event horizons gravitational lensing effect. Furthermore, discover strain-induced phase transitions, both bulk materials their thin...

Nonsymmorphic space group symmetries can generate exotic band crossings in topological metals and semimetals. Here, based on symmetry analysis first-principles calculations, we reveal rich band-crossing features the existing layered compounds ${\mathrm{Ta}}_{3}{\mathrm{SiTe}}_{6}$ ${\mathrm{Nb}}_{3}{\mathrm{SiTe}}_{6}$, enabled by nonsymmorphic symmetries. We show that absence of spin-orbit coupling (SOC), these three-dimensional (3D) bulk materials possess accidental Dirac loops essential...

As a novel type of fermionic state, hybrid nodal loop with the coexistence both type-I and type- II band crossings has attracted intense research interest. However, it remains challenge to realize in two-dimensional (2D) materials ferromagnetic (FM) materials. Here, we propose first FM 2D CrN monolayer. We show that material high Curie temperature (> 600 K) ground out-of-plane [001] magnetization. It shows half-metallic structure two bands spin-up channel crossing each other near Fermi...

Nodal line semimetals in two-dimensional (2-D) materials have attracted intense attention currently. From fundamental physics and spintronic applications points of view, high Curie temperature ferromagnetic (FM) ones with nodal lines robust against spin-orbit coupling (SOC) are significantly desirable. Here, we propose that FM K2N monolayer is such Weyl semimetal. We show dynamically stable, has a ground magnetic state the out-of-plane [001] magnetization. It shows two low-energy band...

Multifold degenerate fermions in electronic structures of topological materials give rise to many interesting physics properties. Among them, three-, six-, and eightfold condensed matter systems are considered important because these not allowed high-energy due restriction posed by Poinc\'are symmetry. Phonons the basic emergent boson crystalline lattice. Moreover, phonons also exist solids, like fermionic electrons, crystal symmetry constraints. Two-, fourfold were predicted previously....

This year, researchers have been on the lookout for real materials with one-nodal, two-nodal (two-NS), and three-nodal surface phonons. However, two-NS phonons scarce until recently. paper contributes to understanding of symmetry conditions Two-NS NS states that are localized two three ${k}_{i}=\ifmmode\pm\else\textpm\fi{}\ensuremath{\pi}$ $(i=x,y,z)$ planes in three-dimensional Brillouin zone). They dominated by twofold screw time-reversal symmetry. also prediction a series their phonon...

Abstract Topological materials have been recently regarded as ideal catalysts for heterogeneous reactions due to their surface metallic states and high carrier mobility. However, the underlying relationship between catalytic performance topological is under debate. It has discovered that electride 12CaO·7Al 2 O 3 (C12A7:4e − ) hosts multifold fermions Fermi arcs on (001) near level interstitial electrons. Through comparison of different doping strain conditions, based hydrogen evolution...

In this paper, we used symmetry analyses and first-principles calculations to discover seven Cs-Te binary systems that have different crystal structures can host symmetry-enforced topologically nontrivial phonons: $P{2}_{1}{2}_{1}{2}_{1}\text{\ensuremath{-}}{\mathrm{Cs}}_{2}\mathrm{Te}, Pbam$-CsTe, $Pnma\text{\ensuremath{-}}{\mathrm{Cs}}_{2}\mathrm{Te}, Pm\overline{3}m$-CsTe, $Cmcm\text{\ensuremath{-}}{\mathrm{Cs}}_{2}{\mathrm{Te}}_{5},...

Abstract Diamond is emerging as an attractive third‐generation wide‐bandgap semiconductor for future on‐chip nonlinear photonics and quantum optics due to its unique thermal, optical, mechanical properties. However, the light‐driven current under below‐band gap excitation from second‐order optical effect in diamond still challenging. Herein, a giant photocurrent observed chemical vapor deposition (CVD) by utilizing terahertz (THz) emission spectroscopy. This ultrafast originates photon drag...

The exploration of topological quantum phases and their transitions has become a focus intense research. In this paper, we introduce family two-dimensional (2D) metal-organic frameworks (MOFs) that host various emergent 2D fermions second-order insulators (SOTIs) while also exhibiting strain-tunable phase transitions. Using first-principles calculations, demonstrate these MOFs can exhibit either narrow-band-gap semiconductor or zero-band-gap semimetal state, with three key bands in the...

The topological flat band close to the Fermi level serves as a promising platform for realizing unique and intriguing phenomena. In theory, such can appear in certain geometrically frustrated lattices under stringent conditions, then generally be destroyed by hybridization with other bands application of external fields. Consequently, realistic materials that host are very rare. Via first-principles calculations, we investigate electronic structure monolayer MOF PTC-Fe, which kagome lattice...

We investigate the effect of a vertical electric field on Dirac semimetal thin film. show that through interplay between quantum confinement and field-induced coupling sub-bands, sub-band gap can be tuned inverted, during which system undergoes topological phase transition trivial band insulator spin Hall insulator. Consequently, one electrically switch edge channels off, making promising platform for constructing transistor.

Dirac points in two-dimensional (2D) materials have been a fascinating subject of research, with graphene as the most prominent example. However, existing 2D materials, including graphene, are vulnerable against spin-orbit coupling (SOC). Here, based on first-principles calculations and theoretical analysis, we propose new family stable HfGeTe-family monolayers, which host so-called (SDPs) close to Fermi level. These special that they formed only under significant SOC, hence intrinsically...

Nonsymmorphic symmetries, which involve fractional lattice translations in crystalline materials, can generate exotic types of fermionic excitations that are robust against spin-orbit coupling. Here we report on a hourglass-type dispersion the bulk three-dimensional rhenium dioxide crystals, as dictated by its nonsymmorphic symmetries. Due to time reversal and inversion each band has an additional two-fold degeneracy, making neck crossing-point hourglass four-fold degenerate. Remarkably,...

Most electronic properties of metals are determined solely by the low-energy states around Fermi level, and for topological metals/semimetals, these become distinct because their unusual energy dispersion emergent pseudospin degree freedom. Here, we propose a class materials which termed as quadratic contact point (QCP) semimetals. In materials, conduction valence bands at isolated points in Brillouin zone, band dispersions along all three directions. We show that absence/presence spin-orbit...

In most Weyl semimetal (WSMs), the nodes with opposite chiralities usually have same type of band dispersions (either type-I or type-II), whereas realistic candidate materials hosting different types not been identified to date. Here we report for first time that, a ternary compound HfCuP, is an excellent WSM coexistence and type-II nodes. Our results show HfCuP totally contains six pairs in Brillouin zone, all locating at H-K path. These situate slightly below Fermi level, do coexist other...

Two-dimensional (2D) Dirac-like electron gases have attracted tremendous research interest ever since the discovery of free-standing graphene. The linear energy dispersion and non-trivial Berry phase play pivotal role in remarkable electronic, optical, mechanical chemical properties 2D Dirac materials. known materials are gapless only within certain approximations, for example, absence SOC. Here we report a route to establishing robust cones with nonsymmorphic crystal lattice. symmetry...

Topological semimetals and metals have been extensively studied in nonmagnetic materials, while those magnetic materials are still quite rare. Here, based on first-principles calculations, we reveal that a family of hexagonal compounds $X{\mathrm{TiO}}_{2}$ ($X$ = Li, Na, K, Rb) with ferromagnetic ground states host excellent topological electronic structures. In their low-energy band structures, they show two Weyl nodal loops surfaces, where each loop surface is contributed by the electron...

Electrides are a hot research topic due to their special electronic distribution. Recently, the coupling effects among electrides, magnetism, and topological states have attracted considerable attention in condensed-matter physics. Here, based on first-principles calculations, we report an electride phase, namely, ${\mathrm{Ba}}_{4}{\mathrm{Al}}_{5}\ifmmode\cdot\else\textperiodcentered\fi{}{e}^{\ensuremath{-}}$, with combing antiferromagnetic magnetism multiple types of nontrivial band...