29 research outputs found
In Situ Engineering and Characterization of Correlated Materials with Integrated OMBE–ARPES
Oxide molecular beam epitaxy has emerged as an effective technique to fabricate complex oxide thin films and novel superlattices with atomic‐level precision. In this chapter, we first briefly introduce the oxide molecular beam epitaxy technique and then show how to use this technique to achieve high‐quality thin films with good stoichiometry. Moreover, we exhibit that the combination of oxide molecular beam epitaxy and in situ angle‐resolved photoemission spectroscopy is indeed a versatile toolkit to tailor and characterize properties of novel quantum materials
Novel joint-drift-free scheme at acceleration level for robotic redundancy resolution with tracking error theoretically eliminated
In this article, three acceleration-level joint-drift-free (ALJDF) schemes for kinematic control of redundant manipulators are proposed and analyzed from perspectives of dynamics and kinematics with the corresponding tracking error analyses. First, the existing ALJDF schemes for kinematic control of redundant manipulators are systematized into a generalized acceleration-level joint-drift-free scheme with a paradox pointing out the theoretical existence of the velocity error related to joint drift. Second, to remedy the deficiency of the existing solutions, a novel acceleration-level joint-drift-free (NALJDF) scheme is proposed to decouple Cartesian space error from joint space with the tracking error theoretically eliminated. Third, in consideration of the uncertainty at the dynamics level, a multi-index optimization acceleration-level joint-drift-free scheme is presented to reveal the influence of dynamics factors on the redundant manipulator control. Afterwards, theoretical analyses are provided to prove the stability and feasibility of the corresponding dynamic neural network with the tracking error deduced. Then, computer simulations, performance comparisons, and physical experiments on different redundant manipulators synthesized by the proposed schemes are conducted to demonstrate the high performance and superiority of the NALJDF scheme and the influence of dynamics parameters on robot control. This work is of great significance to enhance the product quality and production efficiency in industrial production
Kagome surface states and weak electronic correlation in vanadium-kagome metals
RV6Sn6 (R = Y and lanthanides) with two-dimensional vanadium-kagome surface
states is an ideal platform to investigate kagome physics and manipulate the
kagome features to realize novel phenomena. Utilizing the micron-scale
spatially resolved angle-resolved photoemission spectroscopy and
first-principles calculations, we report a systematical study of the electronic
structures of RV6Sn6 (R = Gd, Tb, and Lu) on the two cleaved surfaces, i.e.,
the V- and RSn1-terminated (001) surfaces. The calculated bands without any
renormalization match well with the main ARPES dispersive features, indicating
the weak electronic correlation in this system. We observe 'W'-like kagome
surface states around the Brillouin zone corners showing R-element-dependent
intensities, which is probably due to various coupling strengths between V and
RSn1 layers. Our finding suggests an avenue for tuning electronic states by
interlayer coupling based on two-dimensional kagome lattices
Electronic Structure of Superconducting Infinite-Layer Lanthanum Nickelates
Revealing the momentum-resolved electronic structure of infinite-layer
nickelates is essential for understanding this new class of unconventional
superconductors, but has been hindered by the formidable challenges in
improving the sample quality. In this work, we report for the first time the
angle-resolved photoemission spectroscopy of superconducting
LaSrNiO films prepared by molecular beam epitaxy and
atomic-hydrogen reduction. The measured Fermi
topology closely matches theoretical calculations, showing a large
Ni- derived Fermi sheet that evolves from hole-like to
electron-like along , and a three-dimensional (3D) electron pocket
centered at Brillouin zone corner. The Ni- derived bands show a
mass enhancement () of 2-3,while the 3D electron band shows
negligible band renormalization. Moreover, the Ni- derived states
also display a band dispersion anomaly at higher binding energy, reminiscent of
the waterfall feature and kinks observed in cuprates.Comment: 29 pages,13 figure
Observation of electronic nematicity driven by three-dimensional charge density wave in kagome lattice KVSb
Kagome superconductors AVSb (A = K, Rb, Cs) provide a fertile
playground for studying various intriguing phenomena such as non-trivial band
topology, superconductivity, giant anomalous Hall effect, and charge density
wave (CDW). Remarkably, the recent discovery of symmetric nematic phase
prior to the superconducting state in AVSb has drawn enormous
attention, as the unusual superconductivity might inherit the symmetry of the
nematic phase. Although many efforts have been devoted to resolve the charge
orders using real-space microscopy and transport measurements, the direct
evidence on the rotation symmetry breaking of the electronic structure in the
CDW state from the reciprocal space is still rare. The underlying mechanism is
still ambiguous. Here, utilizing the micron-scale spatially resolved
angle-resolved photoemission spectroscopy, we observed the fingerprint of band
folding in the CDW phase of KVSb, which yet demonstrates the
unconventional unidirectionality, and is indicative of the rotation symmetry
breaking from to . We then pinpointed that the interlayer coupling
between adjacent planes with -phase offset in the 222 CDW
phase would lead to the preferred twofold symmetric electronic structure.
Time-reversal symmetry is further broken at temperatures below 40 K as
characterized by giant anomalous Hall effect triggered by weak magnetic fields.
These rarely observed unidirectional back-folded bands with time-reversal
symmetry breaking in KVSb may provide important insights into its
peculiar charge order and superconductivity
Direct observation of topological surface states in the layered kagome lattice with broken time-reversal symmetry
Magnetic topological quantum materials display a diverse range of fascinating
physical properties which arise from their intrinsic magnetism and the breaking
of time-reversal symmetry. However, so far, few examples of intrinsic magnetic
topological materials have been confirmed experimentally, which significantly
hinder our comprehensive understanding of the abundant physical properties in
this system. The kagome lattices, which host diversity of electronic structure
signatures such as Dirac nodes, flat bands, and saddle points, provide an
alternative and promising platform for in-depth investigations into
correlations and band topology. In this article, drawing inspiration from the
stacking configuration of MnBiTe, we conceive and then synthesize a
high-quality single crystal EuTiBi, which is a unique natural
heterostructure consisting of both topological kagome layers and magnetic
interlayers. We investigate the electronic structure of EuTiBi and
uncover distinct features of anisotropic multiple Van Hove singularitie (VHS)
that might prevent Fermi surface nesting, leading to the absence of a charge
density wave (CDW). In addition, we identify the topological nontrivial surface
states that serve as connections between different saddle bands in the vicinity
of the Fermi level. Combined with calculations, we establish that, the
effective time-reversal symmetry S= play a crucial role in
the antiferromagnetic ground state of EuTiBi, which ensures the
stability of the topological surface states and gives rise to their intriguing
topological nature. Therefore, EuTiBi offers the rare opportunity to
investigate correlated topological states in magnetic kagome materials.Comment: 9 pages, 4 figure
Genome-wide identification of the CAD gene family and functional analysis of putative bona fide CAD genes in tobacco (Nicotiana tabacum L.)
Cinnamyl alcohol dehydrogenase (CAD) plays a crucial role in lignin biosynthesis, and the gene family encoding various CAD isozymes has been cloned and characterized in numerous plant species. However, limited information regarding the CAD gene family in tobacco is currently available. In this study, we identified 10 CAD genes in Nicotiana tabacum, four in N. tomentosiformis, and six in N. sylvestris. The nucleotide and amino acid sequences of these tobacco CADs demonstrate high levels of similarity, whereas the putative protein sequences conservatively possessed two Zn2+ binding motifs and an NADP(H) cofactor binding motif. Both NtCAD1 and NtCAD2 had conservative substrate binding sites, similar to those possessed by bona fide CADs, and evidence from phylogenetic analysis as well as expression profiling supported their role as bona fide CADs involved in lignin biosynthesis. NtCAD1 has two paralogous genes, NtCAD1–1 and NtCAD1–2. Enzyme activity analysis revealed that NtCAD1–1 and NtCAD1–2 had a high affinity to coniferyl aldehyde, p-coumaryl aldehyde, and sinapyl aldehyde, whereas NtCAD2 preferred coniferyl aldehyde and p-coumaryl aldehyde as substrates. The kinetic parameter assay revealed that NtCAD1–2 functions as the most efficient enzyme. Downregulation of both NtCAD1–1 and NtCAD1–2 resulted in reddish-brown stems without significant changes in lignin content. Furthermore, NtCAD1–1, NtCAD1–2, and NtCAD2 showed distinct expression patterns in response to biotic and abiotic stresses, as well as different phytohormones. Our findings suggest that NtCAD1–1 and NtCAD1–2 are involved in lignin biosynthesis, with NtCAD1–2 also participating in both biological and abiotic stresses, whereas NtCAD2 plays a distinct role mainly in responding to biological and abiotic stresses in tobacco
Observation of nonrelativistic plaid-like spin splitting in a noncoplanar antiferromagnet
Spatial, momentum and energy separation of electronic spins in condensed
matter systems guides the development of novel devices where spin-polarized
current is generated and manipulated. Recent attention on a set of previously
overlooked symmetry operations in magnetic materials leads to the emergence of
a new type of spin splitting besides the well-studied Zeeman, Rashba and
Dresselhaus effects, enabling giant and momentum dependent spin polarization of
energy bands on selected antiferromagnets independent of relativistic
spin-orbit interaction. Despite the ever-growing theoretical predictions, the
direct spectroscopic proof of such spin splitting is still lacking. Here, we
provide solid spectroscopic and computational evidence for the existence of
such materials. In the noncoplanar antiferromagnet MnTe, the in-plane
components of spin are found to be antisymmetric about the high-symmetry planes
of the Brillouin zone, comprising a plaid-like spin texture in the
antiferromagnetic ground state. Such an unconventional spin pattern, further
found to diminish at the high-temperature paramagnetic state, stems from the
intrinsic antiferromagnetic order instead of the relativistic spin-orbit
coupling. Our finding demonstrates a new type of spin-momentum locking with a
nonrelativistic origin, placing antiferromagnetic spintronics on a firm basis
and paving the way for studying exotic quantum phenomena in related materials.Comment: Version 2, 30 pages, 4 main figures and 8 supporting figure