Non-centrosymmetric transition metal monopnictides, including TaAs, TaP, NbAs, and NbP, are emergent topological Weyl semimetals (WSMs) hosting exotic relativistic Weyl fermions. In this letter, we elucidate the physical origin of the unprecedented charge carrier mobility of NbP, which can reach 1 × 10 7 cm 2 V −1 s −1 at 1.5 K. Angle-and temperature-dependent quantum oscillations, supported by density function theory calculations, reveal that NbP has the coexistence of p-and n-type WSM pockets in the kz=1.16π/c plane (W1-WSM) and in the kz=0 plane near the high symmetry points Σ (W2-WSM), respectively. Uniquely, each W2-WSM pocket forms a large dumbbell-shaped Fermi surface (FS) enclosing two neighboring Weyl nodes with the opposite chirality. The magneto-transport in NbP is dominated by these highly anisotropic W2-WSM pockets, in which Weyl fermions are well protected from defect backscattering by real spin conservation associated to the chiral nodes. However, with a minimal doping of ∼1% Cr, the mobility of NbP is degraded by more than two order of magnitude, due to the invalid of helicity protection to magnetic impurities. Helicity protected Weyl fermion transport is also manifested in chiral anomaly induced negative magnetoresistance, controlled by the W1-WSM states. In the quantum regime below 10 K, the intervalley scattering time by impurities becomes a large constant, producing the sharp and nearly identical conductivity enhancement at low magnetic field.Topological Weyl semimetals (WSMs) are regarded as the next wonderland in condensed matter physics [1][2][3][4] for exploring fascinating quantum phenomena [5][6][7][8][9][10]. Unlike Dirac semimetals (DSMs) [11,12], band crossing points in WSMs, i.e. Weyl nodes, always appear in pair with opposite chirality, due to the lifting of spin degeneracy by breaking either time reversal symmetry [1] or inversion symmetry [3,4]. Fermi surfaces (FSs) enclosing the chiral Weyl nodes are characterized by helicity, i.e. the spin orientation is either parallel or antiparallel to the momentum. Such helical Weyl fermions are expected to be remarkably robust against non-magnetic disorders, and may lead to novel device concepts for spintronics and quantum computing.The recent proposed non-centrosymmetric TaAs, TaP, NbAs and NbP, have stimulated immense interests, due to the binary, non-magnetic crystal structure. The existence of Weyl nodes has soon been discovered in TaAs by angle-resolved photoemission spectroscopy (ARPES) [13,14], and by quantum transport measurements of NMR and a non-trivial Berry's phase (Φ B ) of π [15,16]. Transport studies of NbAs [17] and NbP [18] also show ultrahigh mobility and non-saturating MR, but no convincing evidence on the existence of Weyl fermions in these two compounds. However, ARPES resolves tadpoleshaped Fermi arcs on the (001) surface of both NbAs [19] and NbP [20]. It also shows pronounced changes in the * phyzhengyi@zju.edu.cn † zhuan@zju.edu.cn electronic structures of NbAs and NbP compared to TaAs [19], mainly due to weaker sp...

To bridge the gap between laboratory research and commercial applications, it is vital to develop scalable methods to produce large quantities of high-quality and solution-processable few-layer phosphorene (FLBP). Here, we report an ultrafast cathodic expansion (in minutes) of bulk black phosphorus in the nonaqueous electrolyte of tetraalkylammonium salts that allows for the high-yield (>80%) synthesis of nonoxidative few-layer BP flakes with high crystallinity in ambient conditions. Our detailed mechanistic studies reveal that cathodic intercalation and subsequent decomposition of solvated cations result in the ultrafast expansion of BP toward the high-yield production of FLBP. The FLBPs thus obtained show negligible structural deterioration, excellent electronic properties, great solution processability, and high air stability, which allows us to prepare stable BP inks (2 mg/mL) in low-boiling point solvents for large-area inkjet printing and fabrication of optoelectronic devices.

SnSe is a promising thermoelectric material with record-breaking figure of merit. However, to date a comprehensive understanding of the electronic structure and most critically, the self-hole-doping mechanism in SnSe is still absent. Here we report the highly anisotropic electronic structure of SnSe investigated by angle-resolved photoemission spectroscopy, in which a unique pudding-mould-shaped valence band with quasi-linear energy dispersion is revealed. We prove that p-type doping in SnSe is extrinsically controlled by local phase segregation of SnSe2 microdomains via interfacial charge transferring. The multivalley nature of the pudding-mould band is manifested in quantum transport by crystallographic axis-dependent weak localisation and exotic non-saturating negative magnetoresistance. Strikingly, quantum oscillations also reveal 3D Fermi surface with unusual interlayer coupling strength in p-SnSe, in which individual monolayers are interwoven by peculiar point dislocation defects. Our results suggest that defect engineering may provide versatile routes in improving the thermoelectric performance of the SnSe family.

Understanding the remarkable excitonic effects and controlling the exciton binding energies in two-dimensional (2D) semiconductors are crucial in unlocking their full potential for use in future photonic and optoelectronic devices. Here, we demonstrate large excitonic effects and gate-tunable exciton binding energies in single-layer rhenium diselenide (ReSe2) on a back-gated graphene device. We used scanning tunneling spectroscopy and differential reflectance spectroscopy to measure the quasiparticle electronic and optical bandgap of single-layer ReSe2, respectively, yielding a large exciton binding energy of 520 meV. Further, we achieved continuous tuning of the electronic bandgap and exciton binding energy of monolayer ReSe2 by hundreds of milli–electron volts through electrostatic gating, attributed to tunable Coulomb interactions arising from the gate-controlled free carriers in graphene. Our findings open a new avenue for controlling the bandgap renormalization and exciton binding energies in 2D semiconductors for a wide range of technological applications.

The ability to precisely engineer the doping of sub-nanometer bimetallic clusters offers exciting opportunities for tailoring their catalytic performance with atomic accuracy. However, the fabrication of singly dispersed bimetallic cluster catalysts with atomic-level control of dopants has been a long-standing challenge. Herein, we report a strategy for the controllable synthesis of a precisely doped single cluster catalyst consisting of partially ligandenveloped Au 4 Pt 2 clusters supported on defective graphene. This creates a bimetal single cluster catalyst (Au 4 Pt 2 /G) with exceptional activity for electrochemical nitrogen (N 2) reduction. Our mechanistic study reveals that each N 2 molecule is activated in the confined region between cluster and graphene. The heteroatom dopant plays an indispensable role in the activation of N 2 via an enhanced back donation of electrons to the N 2 LUMO. Moreover, besides the heteroatom Pt, the catalytic performance of single cluster catalyst can be further tuned by using Pd in place of Pt as the dopant.