Controllable Synthesis of High-Quality Magnetic Topological Insulator MnBiTe and MnBiTe Multilayers by Chemical Vapor Deposition.

With a nontrivial topological band and intrinsic magnetic order, two-dimensional (2D) MnBiTe-family materials exhibit great promise for exploring exotic quantum phenomena and potential applications. However, the synthesis of 2D MnBiTe-family materials via chemical vapor deposition (CVD), which is essential for advancing device applications, still remains a significant challenge since it is difficult to control the reactions among multi-precursors and form pure phases. Here, we report a controllable synthesis of high-quality magnetic topological insulator MnBiTe and MnBiTe multilayers via an evaporation-rate-controlled CVD approach.

Superconductivity at Pd/BiSe Interfaces Due to Self-Formed PdBiSe Interlayers.

Understanding the physical and chemical processes at the interfaces of metals and topological insulators is crucial for the development of the next generation of topological quantum devices. Here, we report the discovery of robust superconductivity in Pd/BiSe bilayers fabricated by sputtering Pd on the surface of BiSe. Through transmission electron microscopy measurements, we identify that the observed interfacial superconductivity originates from the diffusion of Pd into BiSe.

Dominant Charge Density Order in TaTe_{4}.

Electronic orders such as charge density wave (CDW) and superconductivity raise exotic physics and phenomena as evidenced in recently discovered kagome superconductors and transition metal chalcogenides. In most materials, CDW induces a weak, perturbative effect, manifested as shadow bands, minigaps, resistivity kinks, etc. Here we demonstrate a unique example-transition metal tetratellurides TaTe_{4}, in which the CDW order dominates the electronic structure and transport properties.

Versatile Method of Engineering the Band Alignment and the Electron Wavefunction Hybridization of Hybrid Quantum Devices.

Hybrid devices that combine superconductors (S) and semiconductors (Sm) have attracted great attention due to the integration of the properties of both materials, which relies on the interface details and the resulting coupling strength and wavefunction hybridization. However, until now, none of the experiments have reported good control of the band alignment of the interface, as well as its tunability to the coupling and hybridization. Here, the interface is modified by inducing specific argon milling while maintaining its high quality, e.

Tunable even- and odd-denominator fractional quantum Hall states in trilayer graphene.

Fractional quantum Hall (FQH) states are exotic quantum many-body phases whose elementary charged excitations are anyons obeying fractional braiding statistics. While most FQH states are believed to have Abelian anyons, the Moore-Read type states with even denominators - appearing at half filling of a Landau level (LL) - are predicted to possess non-Abelian excitations with appealing potential in topological quantum computation. These states, however, depend sensitively on the orbital contents of the single-particle LL wavefunctions and the LL mixing.

Magnetic field filtering of the boundary supercurrent in unconventional metal NiTe-based Josephson junctions.

Topological materials with boundary (surface/edge/hinge) states have attracted tremendous research interest. Additionally, unconventional (obstructed atomic) materials have recently drawn lots of attention owing to their obstructed boundary states. Experimentally, Josephson junctions (JJs) constructed on materials with boundary states produce the peculiar boundary supercurrent, which was utilized as a powerful diagnostic approach.

The Pathogenesis in Alzheimer's Disease: TREM2 as a Potential Target.

Alzheimer's disease (AD) is ranked as the third-most expensive illness and sixth leading cause of mortality. It is associated with the deposition of extracellular amyloid-β (Aβ) in neural plaques (NPs), as well as intracellular hyperphosphorylated tau proteins that form neurofibrillary tangles (NFTs). As a new target in regulating neuroinflammation in AD, triggering receptor expressed on myeloid cells 2 (TREM2) is highly and exclusively expressed on the microglial surface.

A robust and tunable Luttinger liquid in correlated edge of transition-metal second-order topological insulator TaPdTe.

The interplay between topology and interaction always plays an important role in condensed matter physics and induces many exotic quantum phases, while rare transition metal layered material (TMLM) has been proved to possess both. Here we report a TMLM TaPdTe has the two-dimensional second-order topology (also a quadrupole topological insulator) with correlated edge states - Luttinger liquid. It is ascribed to the unconventional nature of the mismatch between charge- and atomic- centers induced by a remarkable double-band inversion.

Composition and phase engineering of metal chalcogenides and phosphorous chalcogenides.

Two-dimensional (2D) materials with multiphase, multielement crystals such as transition metal chalcogenides (TMCs) (based on V, Cr, Mn, Fe, Cd, Pt and Pd) and transition metal phosphorous chalcogenides (TMPCs) offer a unique platform to explore novel physical phenomena. However, the synthesis of a single-phase/single-composition crystal of these 2D materials via chemical vapour deposition is still challenging. Here we unravel a competitive-chemical-reaction-based growth mechanism to manipulate the nucleation and growth rate.

Dimensionality of the Superconductivity in the Transition Metal Pnictide WP.

We report theoretical and experimental results on the transition metal pnictide WP. The theoretical outcomes based on tight-binding calculations and density functional theory indicate that WP is a three-dimensional superconductor with an anisotropic electronic structure and nonsymmorphic symmetries. On the other hand, magnetoresistance experimental data and the analysis of superconducting fluctuations of the conductivity in external magnetic field indicate a weakly anisotropic three-dimensional superconducting phase.

Discovery of Dome-Shaped Superconducting Phase and Anisotropic Transport in a van der Waals Layered Candidate NbIrTe under Pressure.

The unique electronic structure and crystal structure driven by external pressure in transition metal tellurides (TMTs) can host unconventional quantum states. Here, the discovery of pressure-induced phase transition at ≈2 GPa, and dome-shaped superconducting phase emerged in van der Waals layered NbIrTe is reported. The highest critical temperature (T ) is ≈5.

MoTe: Semiconductor or Semimetal?

Transition metal tellurides (TMTs) have attracted intense interest due to their intriguing physical properties arising from their diverse phase topologies. To date, a wide range of physical properties have been discovered for TMTs, including that they can act as topological insulators, semiconductors, Weyl semimetals, and superconductors. Among the TMT families, MoTe is a representative material because of its Janus nature and rich phases.

Controlled Synthesis of MoWTe Atomic Layers with Emergent Quantum States.

Recently, new states of matter like superconducting or topological quantum states were found in transition metal dichalcogenides (TMDs) and manifested themselves in a series of exotic physical behaviors. Such phenomena have been demonstrated to exist in a series of transition metal tellurides including MoTe, WTe, and alloyed MoWTe However, the behaviors in the alloy system have been rarely addressed due to their difficulty in obtaining atomic layers with controlled composition, albeit the alloy offers a great platform to tune the quantum states. Here, we report a facile CVD method to synthesize the MoWTe with controllable thickness and chemical composition ratios.

Magnitude and Spatial Distribution Control of the Supercurrent in BiOSe-Based Josephson Junction.

Many proposals for exploring topological quantum computation are based on superconducting quantum devices constructed on materials with strong spin-orbit coupling (SOC). For these devices, full control of both the magnitude and the spatial distribution of the supercurrent is highly demanded, but has been elusive up to now. We constructed a proximity-type Josephson junction on nanoplates of BiOSe, a new emerging semiconductor with strong SOC.

Phase Transition and Superconductivity Enhancement in Se-Substituted MoTe Thin Films.

Consecutively tailoring few-layer transition metal dichalcogenides MX from 2H to T phase may realize the long-sought topological superconductivity in a single material system by incorporating superconductivity and the quantum spin Hall effect together. Here, this study demonstrates that a consecutive structural phase transition from T to 1T' to 2H polytype can be realized by increasing the Se concentration in Se-substituted MoTe thin films. More importantly, the Se-substitution is found to dramatically enhance the superconductivity of the MoTe thin film, which is interpreted as the introduction of two-band superconductivity.

Transport evidence of asymmetric spin-orbit coupling in few-layer superconducting 1T-MoTe.

Two-dimensional transition metal dichalcogenides MX (M = W, Mo, Nb, and X = Te, Se, S) with strong spin-orbit coupling possess plenty of novel physics including superconductivity. Due to the Ising spin-orbit coupling, monolayer NbSe and gated MoS of 2H structure can realize the Ising superconductivity, which manifests itself with in-plane upper critical field far exceeding Pauli paramagnetic limit. Surprisingly, we find that a few-layer 1T structure MoTe also exhibits an in-plane upper critical field which goes beyond the Pauli paramagnetic limit.

A library of atomically thin metal chalcogenides.

Investigations of two-dimensional transition-metal chalcogenides (TMCs) have recently revealed interesting physical phenomena, including the quantum spin Hall effect, valley polarization and two-dimensional superconductivity , suggesting potential applications for functional devices. However, of the numerous compounds available, only a handful, such as Mo- and W-based TMCs, have been synthesized, typically via sulfurization, selenization and tellurization of metals and metal compounds. Many TMCs are difficult to produce because of the high melting points of their metal and metal oxide precursors.

High-quality monolayer superconductor NbSe grown by chemical vapour deposition.

The discovery of monolayer superconductors bears consequences for both fundamental physics and device applications. Currently, the growth of superconducting monolayers can only occur under ultrahigh vacuum and on specific lattice-matched or dangling bond-free substrates, to minimize environment- and substrate-induced disorders/defects. Such severe growth requirements limit the exploration of novel two-dimensional superconductivity and related nanodevices.

Large-Area and High-Quality 2D Transition Metal Telluride.

Large-area and high-quality 2D transition metal tellurides are synthesized by the chemical vapor deposition method. The as-grown WTe maintains two different stacking sequences in the bilayer, where the atomic structure of the stacking boundary is revealed by scanning transmission electron microscopy. The low-temperature transport measurements reveal a novel semimetal-to-insulator transition in WTe layers and an enhanced superconductivity in few-layer MoTe .

Enhancement of the ν = 5/2 fractional quantum Hall state in a small in-plane magnetic field.

Using a 50-nm-width ultraclean GaAs/AlGaAs quantum well, we have studied the Landau level filling factor ν=5/2 fractional quantum Hall effect in a perpendicular magnetic field B∼1.7  T and determined its dependence on tilted magnetic fields. Contrary to all previous results, the 5/2 resistance minimum and the Hall plateau are found to strengthen continuously under an increasing tilt angle 0<θ<25° (corresponding to an in-plane magnetic field 0 View Article and Find Full Text PDF

Strong superconducting proximity effect in pb-bi(2)te(3) hybrid structures.

To study the interface between a conventional superconductor and a topological insulator, we fabricated Pb-Bi(2)Te(3)-Pb lateral and sandwiched junctions, and performed electron transport measurements down to low temperatures. The results show that there is a strong superconducting proximity effect between Bi(2)Te(3) and Pb, as that a supercurrent can be established along the thickness direction of the Bi(2)Te(3) flakes (100~300 nm thick) at a temperature very close to the superconducting T(c) of Pb. Moreover, a Josephson current can be established over several microns in the lateral direction between two Pb electrodes on the Bi(2)Te(3 )surface.

Aharonov-casher effect in Bi2Se3 square-ring interferometers.

Electrical control of spin dynamics in Bi(2)Se(3) was investigated in ring-type interferometers. Aharonov-Bohm and Altshuler-Aronov-Spivak resistance oscillations against a magnetic field, and Aharonov-Casher resistance oscillations against the gate voltage were observed in the presence of a Berry phase of π. A very large tunability of spin precession angle by the gate voltage has been obtained, indicating that Bi(2)Se(3)-related materials with strong spin-orbit coupling are promising candidates for constructing novel spintronic devices.

Novel resistance behavior of single-walled carbon nanotubes under large currents.

The resistance of single-walled carbon nanotube (SWNT) bundles has been investigated by two-terminal measurements. We find that the time dependence of resistance (dR/dt) exhibits different behaviors at different currents. At low currents, a positive dR/dt is observed.