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The interface between two-dimensional topological Dirac states and an s-wave superconductor is expected to support Majorana bound states that can be used for quantum computing applications. Realizing these novel states of matter and their applications requires control over superconductivity and spin-orbit coupling to achieve spin-momentum locked topological surface states which are simultaneously superconducting. While signatures of Majorana bound states have been observed in the magnetic vortex cores of bulk FeTe0.55Se0.45, inhomogeneity and disorder from doping makes these signatures unclear and inconsistent between vortices. Here we report superconductivity in monolayer FeTe1-ySey (Fe(Te,Se)) grown on Bi2Te3 by molecular beam epitaxy. Spin and angle resolved photoemission spectroscopy directly resolve the interfacial spin and electronic structure of Fe(Te,Se)/Bi2Te3 heterostructures. We find that for y = 0.25 the Fe(Te,Se) electronic structure overlaps with the topological Bi2Te3 interfacial states which disrupts the desired spin-momentum locking. In contrast, for y = 0.1 a smaller Fe(Te,Se) Fermi surface allows for clear spin-momentum locking observed in the topological states. Hence, we demonstrate the Fe(Te,Se)/Bi2Te3 system is a highly tunable platform for realizing Majorana bound states where reduced doping can improve characteristics important for Majorana interrogation and potential applications.

While the discovery of two-dimensional (2D) magnets opens the door for fundamental physics and next-generation spintronics, it is technically challenging to achieve the room-temperature ferromagnetic (FM) order in a way compatible with potential device applications. Here, we report the growth and properties of single- and few-layer CrTe2, a van der Waals (vdW) material, on bilayer graphene by molecular beam epitaxy (MBE). Intrinsic ferromagnetism with a Curie temperature (TC) up to 300 K, an atomic magnetic moment of ~0.21 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mu }_{{\rm{B}}}$$\end{document}μB/Cr and perpendicular magnetic anisotropy (PMA) constant (Ku) of 4.89 × 105 erg/cm3 at room temperature in these few-monolayer films have been unambiguously evidenced by superconducting quantum interference device and X-ray magnetic circular dichroism. This intrinsic ferromagnetism has also been identified by the splitting of majority and minority band dispersions with ~0.2 eV at Г point using angle-resolved photoemission spectroscopy. The FM order is preserved with the film thickness down to a monolayer (TC ~ 200 K), benefiting from the strong PMA and weak interlayer coupling. The successful MBE growth of 2D FM CrTe2 films with room-temperature ferromagnetism opens a new avenue for developing large-scale 2D magnet-based spintronics devices., The emergence of two dimensional ferromagnetism suffers from an inherent fragility to thermal fluctuations, which typically restricts the Curie temperature to below room temperature. Here, Zhang et al present CrTe2 thin films grown via molecular beam epitaxy with a Curie temperature exceeding 300 K.

Streptococcus agalactiae mastitis is one of the significant threats to the milk industry. The traditional antibiotic treatment method is easy to cause the emergence of resistant strains, and the problem of drug residue is increasingly severe. In this study, we designed and synthesized five lipopeptides. The antibacterial activity of different molecular structure lipopeptides against Streptococcus agalactiae was detected. Furthermore, the mouse mastitis model was established using Streptococcus agalactiae. The lipopeptides with better antibacterial effect were selected for the treatment experiment to evaluate the application value in the treatment of mastitis. The results showed that 4 of the synthesized lipopeptides had specific antibacterial activity. SLP3 and SLP4 have an excellent antibacterial effect and can treat murine mastitis caused by Streptococcus agalactiae infection within the safe concentration range. The results of this study can provide an excellent experimental basis for new antibiotics and clinical application in the treatment of dairy cow mastitis.

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 nontrivial Berry phase play a pivotal role in the electronic, optical, mechanical, and chemical properties of 2D Dirac materials. The known 2D Dirac materials are gapless only within certain approximations, for example, in the absence of spin-orbit coupling (SOC). Here, we report a route to establishing robust Dirac cones in 2D materials with nonsymmorphic crystal lattice. The nonsymmorphic symmetry enforces Dirac-like band dispersions around certain high-symmetry momenta in the presence of SOC. Through μ-ARPES measurements, we observe Dirac-like band dispersions in α-bismuthene. The nonsymmorphic lattice symmetry is confirmed by μ-low-energy electron diffraction and scanning tunneling microscopy. Our first-principles simulations and theoretical topological analysis demonstrate the correspondence between nonsymmorphic symmetry and Dirac states. This mechanism can be straightforwardly generalized to other nonsymmorphic materials. The results enlighten the search of symmetry-enforced Dirac fermions in the vast uncharted world of nonsymmorphic 2D materials.

Two-dimensional (2D) Dirac states with linear band dispersion have attracted enormous interest since the discovery of graphene. However, to date, 2D Dirac semimetals are still very rare due to the fact that 2D Dirac states are generally fragile against perturbations such as spin-orbit couplings. Nonsymmorphic crystal symmetries can enforce the formation of Dirac nodes, providing a new route to establishing symmetry-protected Dirac states in 2D materials. Here we report the symmetry-protected Dirac states in nonsymmorphic alpha-antimonene. The antimonene was synthesized by the method of molecular beam epitaxy. Two Dirac cones with large anisotropy were observed by angle-resolved photoemission spectroscopy. The Dirac state in alpha-antimonene is of spin-orbit type in contrast to the spinless Dirac states in graphene. The result extends the 'graphene' physics into a new family of 2D materials where spin-orbit coupling is present., Comment: 4 figures

Discoveries of interfacial topological Hall effect (THE) provide an ideal platform for exploring physics arising from the interplay between topology and magnetism. The interfacial topological Hall effect is closely related to the Dzyaloshinskii-Moriya interaction (DMI) at interface and topological spin textures. However, it is difficult to achieve a sizable THE in heterostructures due to the stringent constraints on the constituents of THE heterostructures such as strong spin-orbit coupling (SOC). Here we report the observation of a giant THE signal of 1.39 $\mu\Omega\cdot$cm in the van der Waals heterostructures of CrTe2/Bi2Te3 fabricated by molecular beam epitaxy, a prototype of two-dimensional (2D) ferromagnet (FM)/topological insulator (TI). This large magnitude of THE is attributed to an optimized combination of 2D ferromagnetism in CrTe2, strong SOC in Bi2Te3, and an atomically sharp interface. Our work reveals CrTe2/Bi2Te3 as a convenient platform for achieving large interfacial THE in hybrid systems, which could be utilized to develop quantum science and high-density information storage., Comment: 5 figures and 1 table

Discoveries of the interfacial topological Hall effect (THE) provide an ideal platform for exploring the physics arising from the interplay between topology and magnetism. The interfacial topological Hall effect is closely related to the Dzyaloshinskii-Moriya interaction (DMI) at an interface and topological spin textures. However, it is difficult to achieve a sizable THE in heterostructures due to the stringent constraints on the constituents of THE heterostructures, such as strong spin-orbit coupling (SOC). Here, we report the observation of a giant THE signal of 1.39 μΩ·cm in the van der Waals heterostructures of CrTe

Organic–inorganic interfaces in photodiodes have recently gathered significant interest due to the realization of intrinsic p–n junctions and unique physical properties. Nanopatterned sol–gel ZnO f...

Tuning interactions between Dirac states in graphene has attracted enormous interest because it can modify the electronic spectrum of the two-dimensional material, enhance electron correlations, and give rise to novel condensed-matter phases such as superconductors, Mott insulators, Wigner crystals and quantum anomalous Hall insulators. Previous works predominantly focus on the flat band dispersion of coupled Dirac states from different graphene layers. In this work, we propose a new route to realizing flat band physics in monolayer graphene under a periodic modulation from substrates. We take gaphene/SiC heterostructure as a role model and demonstrate experimentally the substrate modulation leads to Dirac fermion cloning and consequently, the proximity of the two Dirac cones of monolayer graphene in momentum space. Our theoretical modeling captures the cloning mechanism of Dirac states and indicates that flat bands can emerge at certain magic lattice constants of substrate when the period of modulation becomes nearly commensurate with the $(\sqrt{3}\times\sqrt{3})R30^{\circ}$ supercell of graphene. The results show that the epitaxial monolayer graphene is a promising platform for exploring exotic many-body quantum phases arising from interactions between Dirac electrons.

Selenium and tellurium are among the few elements that form $AB{\mathrm{O}}_{3}$ perovskite structures with a four valent ion in the $A$ site. This leads to highly distorted structures and unusual magnetic behavior. Here we investigate the Co and Ni selenite and tellurite compounds, ${\mathrm{CoSeO}}_{3}, {\mathrm{CoTeO}}_{3}, {\mathrm{NiSeO}}_{3}$, and ${\mathrm{NiTeO}}_{3}$, using first principles calculations. We find an interplay of crystal field and Jahn-Teller distortions that underpin the electronic and magnetic properties. While all compounds are predicted to show an insulating G-type antiferromagnetic ground state, there is a considerable difference in the anisotropy of the exchange interactions between the Ni and Co compounds. This is related to the Jahn-Teller distortion. Finally, we observe that these four compounds show characteristics generally associated with Mott insulators, even when described at the level of standard density functional theory. These are then dense bulk insulators that are correctly described as insulators in a standard band structure picture but that satisfy the common experimental criteria to classify them as Mott-type insulators.

A new femtosecond, Extreme Ultraviolet (EUV), Time Resolved Spin-Angle Resolved Photo-Emission Spectroscopy (TR-Spin-ARPES) beamline was developed for ultrafast materials research and development. This 50-fs laser-driven, table-top beamline is an integral part of the “Ultrafast Spintronic Materials Facility”, dedicated to engineering ultrafast materials. This facility provides a fast and in-situ analysis and development of new materials. The EUV source based on high harmonic generation process emits 2.3 × 1011 photons/second (2.3 × 108 photons/pulse) at H23 (35.7 eV) and its photon energy ranges from 10 eV to 75 eV, which enables surface sensitive studies of the electronic structure dynamics. The EUV monochromator provides the narrow bandwidth of the EUV beamline while preserving its pulse duration in an energy range of 10–100 eV. Ultrafast surface photovoltaic effect with ~650 fs rise-time was observed in p-GaAs (100) from time-resolved ARPES spectra. The data acquisition time could be reduced by over two orders of magnitude by scaling the laser driver from 1 KHz, 4W to MHz, KW average power.

We have studied the Co2FeAl thin films with different thicknesses epitaxially grown on GaAs (001) by molecular beam epitaxy. The magnetic properties and spin polarization of the films were investigated by in-situ magneto-optic Kerr effect (MOKE) measurement and spin-resolved angle-resolved photoemission spectroscopy (spin-ARPES) at 300 K, respectively. High spin polarization of 58% (±7%) was observed for the film with thickness of 21 unit cells (uc), for the first time. However, when the thickness decreases to 2.5 uc, the spin polarization falls to 29% (±2%) only. This change is also accompanied by a magnetic transition at 4 uc characterized by the MOKE intensity. Above it, the film’s magnetization reaches the bulk value of 1000 emu/cm3. Our findings set a lower limit on the thickness of Co2FeAl films, which possesses both high spin polarization and large magnetization.

The search for a superconductor with non-s-wave pairing is important not only for understanding unconventional mechanisms of superconductivity but also for finding new types of quasiparticles such as Majorana bound states. Materials with both topological band structure and superconductivity are promising candidates as $p+ip$ superconducting states can be generated through pairing the spin-polarized topological surface states. In this work, the electronic and phonon properties of the superconductor molybdenum carbide (MoC) are studied with first-principles methods. Our calculations show that nontrivial band topology and superconductivity coexist in both structural phases of MoC, namely, the cubic $\alpha$ and hexagonal $\gamma$ phases. The $\alpha$ phase is a strong topological insulator and the $\gamma$ phase is a topological nodal line semimetal with drumhead surface states. In addition, hole doping can stabilize the crystal structure of the $\alpha$ phase and elevate the transition temperature in the $\gamma$ phase. Therefore, MoC in different structural forms can be a practical material platform for studying topological superconductivity and elusive Majorana fermions., Comment: 4 figures

We have studied the Co2FeAl thin films with different thicknesses epitaxially grown on GaAs (001) by molecular beam epitaxy. The magnetic properties and spin polarization of the films were investigated by in-situ magneto-optic Kerr effect (MOKE) measurement and spin-resolved angle-resolved photoemission spectroscopy (spin-ARPES) at 300 K, respectively. High spin polarization of 58% (±7%) was observed for the film with thickness of 21 unit cells (uc), for the first time. However, when the thickness decreases to 2.5 uc, the spin polarization falls to 29% (±2%) only. This change is also accompanied by a magnetic transition at 4 uc characterized by the MOKE intensity. Above it, the film’s magnetization reaches the bulk value of 1000 emu/cm3. Our findings set a lower limit on the thickness of Co2FeAl films, which possesses both high spin polarization and large magnetization.

SnSe has emerged as an efficient thermoelectric material since a high value of the thermoelectric figure of merit ($ZT$) has been reported recently. Here we show with systematic angle resolved photoemission spectroscopy data that the low-lying electronic structures of undoped and hole-doped SnSe crystals exhibit noticeable temperature variation from 80 to 600 K. In particular, the hole effective masses for the two lowest lying valence band maxima are found to be very large and increase with decreasing temperature. Thermoelectric parameters derived from such hole-mass enhancement agree well with the transport values, indicating comprehensively a reduced impact of multivalley transport to the system's thermoelectric performance.

The ZrTe5 is known as a high mobility thermoelectric material. In 2014, Weng et al. predicted theoretically that the monolayer ZrTe5 is also a 2D topological insulator. In early works, scientists were focused on the abnormal metal-insulator transition as the temperature decreases. However, the physics nature of this phenomenon is still under debate. Here we have explained this by temperature-induced swapping of the dominating carriers from holes to electrons, evidenced by magneto-transport and angle-resolved photoemission spectroscopy (ARPES) measurements on single crystal ZrTe5 samples. Both methods indicate that the Fermi level of ZrTe5 raises from the top of the valance band across the conduction band as the temperature decreases. This is also accompanied by changes of the lattice constants. Our first principle calculation suggests that the shift of the Fermi level comes from the band structure change caused by the temperature variation.

Monolayer black phosphorus (termed 'phosphorene') possesses intriguing tunable electronic properties. Here we report a theoretical study of the antimony analogue of phosphorene, 'antimonene'. Detailed structural parameters and band structures of antimonene films with thickness up to a few atomic layers are obtained by first-principles calculations. Interestingly, a partially degenerate Dirac band emerges in odd atomic layers, which can be attributed to unsaturated bonds and structural flatness.

The catalytic subunit of herpes simplex virus DNA polymerase (Pol), a member of the B family polymerases, possesses both polymerase and exonuclease activities. We previously demonstrated that a recombinant virus (YD12) containing a double mutation within conserved exonuclease motif III of the Pol was highly mutagenic and rapidly evolved to contain an additional leucine-to-phenylalanine mutation at residue 774 (L774F), which is located within the finger subdomain of the polymerase domain. We further demonstrated that the recombinant L774F virus replicated DNA with increased fidelity and that the L774F mutant Pol exhibited altered enzyme kinetics and impaired polymerase activity to extension from mismatched primer termini. In this study, we demonstrated that addition of the L774F mutation to the YD12 Pol did not restore the exonuclease deficiency. However, the polymerase activity of the YD12 Pol to extension from mismatched primer termini and on the nucleotide incorporation pattern was altered upon addition of the L774F mutation. The L774F mutation-containing YD12 Pol also supported the growth of viral progeny and replicated DNA more efficiently and more accurately than did the YD12 Pol. Together, these studies demonstrate that a herpes simplex virus Pol mutant with a highly mutagenic ability can rapidly acquire additional mutations, which may be selected for their survival and outgrowth. Furthermore, the studies demonstrate that the polymerase activity of HSV-1 Pol on primer extension is influenced by sequence context and that herpes simplex virus type 1 Pol may dissociate more frequently at G·C sites during the polymerization reaction. The implications of the findings are discussed.