High-symmetry Directions Research Articles

Magnon bands in pyrochlore slabs with Heisenberg exchange and anisotropies

The pyrochlore lattice is a versatile venue to probe the properties of magnetically ordered states induced or perturbed by anisotropic terms like the Dzyaloshinskii–Moriya interactions or single-ion anisotropy. Several such ordered states have been investigated recently as precursors of topological magnons and the associated surface states. In parallel, there has been recent progress in growing thin films of magnetic materials with this lattice structure along high symmetry directions of the lattice. In both cases, an account of the magnetic excitations of relevant Hamiltonians for finite slabs is a necessary step in the analysis of the physics of these systems. While the analysis of bulk magnons for these systems is quite common, a direct evaluation of the magnon spectra in the slab geometry, though required, is less frequently encountered. We study here magnon bands in the slab geometry for a class of spin models on the pyrochlore lattice with Heisenberg exchange, Dzyaloshinskii–Moriya interaction and spin-ice anisotropy. For a range of model parameters, for both ferromagnetic and antiferromagnetic exchange, we compute the classical ground states for different slab orientations and determine the spin wave excitations above them. We analyze the ferromagnetic splay phase, the all-in-all-out (AIAO) phase and a coplanar phase and evaluate magnon dispersions for slabs oriented perpendicular to the [111], [100] and [110] directions. For all the phases considered, depending on the slab orientation, magnon band structures can be non-reciprocal and we highlight the differences in the three orientations from this point-of-view. Finally, we present details of the surface localized magnons for all the three slab orientations in the phases we study. For the ferromagnetic splay phase and the AIAO phase we analyze surface states associated with point degeneracies or nodal lines in the bulk spectrum by computing the magnonic Berry curvature and Weyl charges or Chern numbers associated with it.

Weak electronic correlations observed in magnetic Weyl Semimetal Mn3Ge

Using angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations, we systematically studied the electronic band structure of Mn3Ge in the vicinity of the Fermi level. We observe several bands crossing the Fermi level, confirming the metallic nature of the studied system. We further observe several flat bands along various high symmetry directions, consistent with the DFT calculations. The calculated partial density of states suggests a dominant Mn 3d orbital contribution to the total valence band DOS. With the help of orbital-resolved band structure calculations, we qualitatively identify the orbital information of the experimentally obtained band dispersions. Out-of-plane electronic band dispersions are explored by measuring the ARPES data at various photon energies. Importantly, our study suggests relatively weaker electronic correlations in Mn3Ge compared to Mn3Sn.

Theoretical computation of the phononic vibrational dynamics of Au3Pd, AuPd, and AuPd3 nanostructures at the [AunPdm]/Au(110) bimetallic ordered surface alloy systems

In this work we develop a calculation for the surface phononic dynamical properties of the three ordered bimetallic surface alloy nanostructures [AunPdm]/Au(110) where [AunPdm] = Au3Pd, AuPd, and AuPd3, for the appropriate concentrations of palladium atoms in the proportions 25 %, 50 %, and 75 %, respectively, at the surface boundaries. They are ordered equilibrium structures, which have been characterized, by Atanasov and Hou (2009). Using the phase field matching theory (PFMT), and the Green's function formalism, the surface phonon dispersion curves are computed, in the harmonic approximation, along the high-symmetry directions ΓX, XS, SY and YΓ of the Brillouin zone of the corresponding surface alloy nanostructure. The local vibration densities of states (LDOS) are also calculated for these systems. The results reveal that the number and the dynamic behavior of the surface phonon and resonance modes, are very sensitive to the concentration of the palladium adsorbate atoms in the [AunPdm] nanostructures. The number and characteristics of these modes are modified at the surface and shifted to higher energies as the concentration increases. These phononic results can greatly contribute to our understanding of the dynamic effects underlying potential technological applications of these surface alloy nanostructures.

First-principles calculation of electron-phonon coupling in doped KTaO3.

Background: Motivated by the recent experimental discovery of strongly surface-plane-dependent superconductivity at surfaces of KTaO 3 single crystals, we calculate the electron-phonon coupling strength, λ, of doped KTaO 3 along the reciprocal-space high-symmetry directions. Methods:Using the Wannier-function approach implemented in the EPW package, we calculate λ across the experimentally covered doping range and compare its mode-resolved distribution along the [001], [110] and [111] reciprocal-space directions. Results: We find that the electron-phonon coupling is strongest in the optical modes around the Γ point, with some distribution to higher k values in the [001] direction. The electron-phonon coupling strength as a function of doping has a dome-like shape in all three directions and its integrated total is largest in the [001] direction and smallest in the [111] direction, in contrast to the experimentally measured trends in critical temperatures. Conclusions: This disagreement points to a non-BCS character of the superconductivity. Instead, the strong localization of λ in the soft optical modes around Γ suggests an importance of ferroelectric soft-mode fluctuations, which is supported by our findings that the mode-resolved λ values are strongly enhanced in polar structures. The inclusion of spin-orbit coupling has negligible influence on our calculated mode-resolved λ values.

Confirming the structural stability and reaching the depth of quaternary Heusler alloys LiMgAgZ (Z = Al, Ga) for thermoelectric device applications: A first-principles study

First principles calculations including structural, electronic, elastic, vibrational, thermodynamic and thermoelectric properties of novel quaternary Heusler compounds LiMgAgZ (Z = Al, Ga) have been studied for the first time using density functional theory (DFT). The quaternary Heusler structured LiMgAgAl and LiMgAgGa alloys possess a face centered cubic structure and belong to the space group F-43m (group No. 216). The band structure calculations reveal that these compounds are metallic. Further, the Fermi surface studies have demonstrated their metallic behavior. The mechanical stability is predicted based on calculated elastic constants, Poisson’s ratio as well as other mechanical parameters. The thermoelectric nature of these compounds is studied utilizing BoltzTrap code. The phonon dispersion curves of LiMgAgZ (Z = Al, Ga) are in the high symmetry directions over the Brillouin zone which indicate the vibrational stability of these compounds. The phonon modes are observed to be Raman active or Infrared active based on the representation of Eigenvectors. The stability of the compounds is also analyzed for their thermodynamic applications. The calculated results reveal unique surface topologies and thermoelectric responses for the compounds under investigation. This work is carried out to inspire researchers to synthesize such types of compounds and analyze their potential for the development of modern thermoelectric devices.

A first principles characterization of electronic and optical anisotropy of quasi-one-dimensional transition metal lead sulfides PbMS3 (M [formula omitted] Hf, Zr)

PbMS3 (M = Hf, Zr) are ternary sulfides with the general structure ABX3, where A is a metal, B is a transition metal and X is a chalcogen or halogen element. This work investigates the anisotropy of the optical and electronic properties of PbMS3, and their applicability in optoelectronic devices using first principles DFT calculations. PbHfS3 is an indirect bandgap semiconductor (1.2 eV), whereas PbZrS3 has direct bandgap (1.1 eV). The effective masses of electrons and holes exhibit strong anisotropy along the various high symmetry directions of the Brillouin zone. Important optical parameters are found to be strongly dependent on the direction of the incident radiation, best indicated by the large birefringence value. Considerable optical anisotropy suggests their promising linear and nonlinear optoelectronic applications such as polarizers, wave plates, and phase-matching elements. Small carrier effective masses, large charge recombination rates and suitable bandgap indicate the possibility of solar and photovoltaic applications.

In-plane uniaxial-strain tuning of superconductivity and charge-density wave in CsV3Sb5

The kagome superconductor CsV3Sb5 with exotic electronic properties has attracted substantial research interest, and the interplay between the superconductivity and the charge-density wave is crucial for understanding its unusual electronic ground state. In this work, we performed resistivity and AC magnetic susceptibility measurements on CsV3Sb5 single crystals uniaxially-strained along [100] and [110] directions. We find that the uniaxial-strain tuning effect of T c (dT c/dε) and T CDW (dT CDW/dε) are almost identical along these distinct high-symmetry directions. These findings suggest the in-plane uniaxial-strain-tuning of T c and T CDW in CsV3Sb5 are dominated by associated c-axis strain, whereas the response to purely in-plane strains is likely small.

Low-energy quasi-circular electron correlations with charge order wavelength in Bi2Sr2CaCu2O8+δ.

Most resonant inelastic x-ray scattering (RIXS) studies of dynamic charge order correlations in the cuprates have focused on the high-symmetry directions of the copper oxide plane. However, scattering along other in-plane directions should not be ignored as it may help understand, for example, the origin of charge order correlations or the isotropic scattering resulting in strange metal behavior. Our RIXS experiments reveal dynamic charge correlations over the qx-qy scattering plane in underdoped Bi2Sr2CaCu2O8+δ. Tracking the softening of the RIXS-measured bond-stretching phonon, we show that these dynamic correlations exist at energies below approximately 70 meV and are centered around a quasi-circular manifold in the qx-qy scattering plane with radius equal to the magnitude of the charge order wave vector, qCO. This phonon-tracking procedure also allows us to rule out fluctuations of short-range directional charge order (i.e., centered around [qx = ±qCO, qy = 0] and [qx = 0, qy = ±qCO]) as the origin of the observed correlations.

Implications of phonon anisotropy on thermal conductivity of fluorite oxides

Fluorite oxides are attractive ionic compounds for a range of applications with critical thermal management requirements. In view of recent reports alluding to anisotropic thermal conductivity in this face-centered cubic crystalline systems, we perform a detailed analysis of the impact of direction-dependent phonon group velocities and lifetimes on the thermal transport of fluorite oxides. We demonstrate that the bulk thermal conductivity of this class of materials remains isotropic despite notable anisotropy in phonon lifetime and group velocity. However, breaking the symmetry of the phonon lifetime under external stimuli including boundary scattering present in nonequilibrium molecular dynamics simulations of finite size simulation cell gives rise to apparent thermal conductivity anisotropy. We observe that for accurate determination of thermal conductivity, it is important to consider phonon properties not only along high symmetry directions commonly measured in inelastic neutron or x-ray scattering experiments but also of those along lower symmetry. Our results suggests that certain low symmetry directions have a larger contribution to thermal conductivity compared to high symmetry ones.

Van der Waals Epitaxy of Bi Nanowires and Bi2Se3 Thin Films on an Antiferromagnetic Substrate of CoNb3S6

The combination of a topological insulator and an antiferromagnet is expected to exhibit the quantum anomalous Hall effect due to the breaking of the time-reversal symmetry. As a layered antiferromagnet, CoNb3S6 was recently found to exhibit an anomalous Hall effect below the Néel temperature (TN = 29 K). Here, we report the controllable growth of Bi nanowires and Bi2Se3 thin films on CoNb3S6 substrates using molecular beam epitaxy. The composition and morphology of the as-prepared Bi nanowires and Bi2Se3 thin films were studied by atomic force microscopy, X-ray photoelectron spectroscopy, and scanning tunneling microscopy. We found that the as-grown Bi nanowires with abundant sizes are oriented along high-symmetry directions of the substrate, forming firework-like structures. Such firework-like structures of Bi nanowires exhibit a high edge-to-surface ratio as well as a strong anisotropy, highly desirable for photoelectric devices and industrial catalysts. The absence of oxidation peaks verifies that the as-prepared samples are of high quality and air stability, very promising for applications.

Surface electronic structure of Re(0001): A spin-resolved photoemission study

The surface electronic structure of Re(0001) has been investigated in a combined experimental and theoretical study. Spin- and angle-resolved photoemission was employed to unravel the spin-dependent $E({\mathbf{k}}_{\ensuremath{\parallel}})$ dispersion of electronic states along the $\overline{\mathrm{\ensuremath{\Gamma}}}\phantom{\rule{0.16em}{0ex}}\overline{\mathrm{M}}$ and $\overline{\mathrm{\ensuremath{\Gamma}}}\phantom{\rule{0.16em}{0ex}}\overline{\mathrm{K}}$ directions. The results are compared with band-structure calculations based on density-functional theory. Additional calculations include transitions into final states by taking into account the corresponding matrix elements. Recently, Shockley- and Tamm-type surface states close to ${E}_{\mathrm{F}}$ were identified, which were found to be mixed by spin-orbit coupling. Here, we determined the Rashba parameter ${\ensuremath{\alpha}}_{\mathrm{R}}$ of the surface state around $\overline{\mathrm{\ensuremath{\Gamma}}}$ to 0.32 and $0.34\phantom{\rule{4pt}{0ex}}\mathrm{eV}\phantom{\rule{0.16em}{0ex}}\stackrel{\ifmmode \mathring{}\else \r{}\fi{}}{\mathrm{A}}$ along $\overline{\mathrm{\ensuremath{\Gamma}}}\phantom{\rule{0.16em}{0ex}}\overline{\mathrm{M}}$ and $\overline{\mathrm{\ensuremath{\Gamma}}}\phantom{\rule{0.16em}{0ex}}\overline{\mathrm{K}}$, respectively. Furthermore, we extend our analysis to a wider $E({\mathbf{k}}_{\ensuremath{\parallel}})$ range revealing a multitude of electronic states along both high-symmetry directions. In particular, Rashba-type spin splittings are observed around the high-symmetry $\overline{\mathrm{\ensuremath{\Gamma}}}$ and $\overline{\mathrm{M}}$ points. At variance with theoretical predictions for a perfect hcp(0001) surface, we do not find any out-of-plane spin polarization. This is caused by monatomic steps of a real Re(0001) surface with alternating terminations, leading on average to an effective sixfold surface symmetry and vanishing net out-of-plane spin polarization.

Effects of Zinc Substitution on the Microstructural and Magnetic Characteristics of Cubic Symmetry Nickel Ferrite System

The preparation of ZnxNi1−xFe2O4 (x = 0 and 0.3) nanoparticles using glycine-mediated combustion route was successfully completed depending on the zwitterion and combustion characteristics of glycine. Using a variety of methods, including XRD, FTIR, SEM/EDX, and TEM, the investigated ferrites were characterized. XRD and FTIR analyses confirm that Zn0.3Ni0.7Fe2O4 and NiFe2O4 nanoparticles crystallize in the cubic symmetry in the space group Fd3m. An increase in the lattice parameters and a subsequent decrease in crystallite size were caused by the process of replacing Ni ions with Zn ions. In accordance with Waldron’s hypothesis, FTIR spectra demonstrate that the ferrites have a spinel-type structure as they are produced. The substitution process by Zn led to different changes in the half band widths with subsequent in splitting in the absorption band around 400 cm−1. The examined ferrites’ cation distribution showed that Zn2+ and Ni2+ ions favored the tetrahedral (A) and octahedral (B) sites, respectively, while Fe3+ ions occupied both A- and B-sites, providing mixed spinel ferrite. TEM analysis indicates the formation of spinel nanocrystalline particles with low agglomerations. The particle size of the as-synthesized ferrites did not exceed 16 nm. By applying the VSM approach at room temperature, the magnetic characteristics of the ferrites under investigation were established. The magnetization of Zn0.3Ni0.7Fe2O4 nanoparticles was found to be higher than that of NiFe2O4 nanoparticles according to the magnetic data. Increasing the magnetization and the experimental magnetic moment of Zn0.3Ni0.7Fe2O4 were accompanied by a decreasing of its coercivity. The net magnetization is oriented along different high symmetry directions. On the other hand, the anisotropy of the nickel ferrite increases by substituting Ni with a Zn ion.

Nematic single-component superconductivity and loop-current order from pair-density wave instability

We investigate the nematic and loop-current type orders that may arise as vestigial precursor phases in a model with an underlying pair-density wave (PDW) instability. We discuss how such a vestigial phase gives rise to a highly anisotropic stiffness for a coexisting single-component superconductor with low intrinsic stiffness, as is the case for the underdoped cuprate superconductors. Next, focusing on a regime with a mean-field PDW ground state with loop-current and nematic $xy$ (B$_{2g}$) order, we find a preemptive transition into a low and high-temperature vestigial phase with loop-current and nematic order corresponding to $xy$ (B$_{2g}$) and $x^2-y^2$ (B$_{1g}$) symmetry respectively. Near the transition between the two phases, a state of soft nematic order emerges for which we expect that the nematic director is readily pinned away from the high-symmetry directions in the presence of an external field. Results are discussed in relation to findings in the cuprates, especially to the recently inferred highly anisotropic superconducting fluctuations [W{\aa}rdh {\em et al.}, ``Colossal transverse magnetoresistance due to nematic superconducting phase fluctuations in a copper oxide'', arXiv:2203.06769], giving additional evidence for an underlying ubiquitous PDW instability in these materials.

Tunable zero-energy Dirac and Luttinger nodes in a two-dimensional topological superconductor

Cooper pairing in ultrathin films of topological insulators, induced intrinsically or by proximity effect, can produce an energetically favorable spin-triplet superconducting state. The spin–orbit coupling acts as an SU(2) gauge field and stimulates the formation of a spin-current vortex lattice in this superconducting state. Here we study the Bogoliubov quasiparticles in such a state and find that the quasiparticle spectrum consists of a number of Dirac nodes pinned to zero energy by the particle-hole symmetry. Some nodes are ‘accidental’ and move through the first Brillouin zone along high-symmetry directions as the order parameter magnitude or the strength of the spin–orbit coupling are varied. At special parameter values, nodes forming neutral quadruplets merge and become gapped out, temporarily producing a quadratic band-touching spectrum. All these features are tunable by controlling the order parameter magnitude via a gate voltage in a heterostructure device. In addition to analyzing the spectrum at the mean-field level, we briefly discuss a few experimental signatures of this spectrum.

Influence of vacancy on the elastic, thermodynamic and electronic properties of LaMgNi4 alloys from first-principles calculations

In this work, the structural stability, mechanical, electronic, and thermodynamic characteristics of LaMgNi4 alloys with different vacancies are discussed in detail. The calculated results of formation enthalpy (ΔH) of LaMgNi4 alloys with Mg-Va, Ni-Va2, La-Va1 and La-Va2 vacancies are −0.294eV/atom, −0.273eV/atom, −0.241eV/atom and −0.241eV/atom, respectively, and the results of phonon dispersion curves show that these vacancy models do not exhibit imaginary frequency in any high symmetry direction, which indicates that these models have stable structure. In addition, different vacancies have different effects on the mechanical properties of LaMgNi4 alloys. For example, the existence of Mg-Va, La-Va1, and La-Va2 vacancies enhances the mechanical properties of LaMgNi4 alloys, while the existence of Ni-Va2 vacancy weakens its mechanical properties. From the perspective of electronic structure, the change of mechanical properties of LaMgNi4 alloys is probably caused by the change of electronic state density at the Fermi level due to the existence of different vacancies. The thermodynamic properties such as the specific heat (Cv) and Debye temperature (ΘD) of the LaMgNi4 alloys with different vacancies are calculated by phonon calculations for wide temperature range from 0 K to 1000 K, and further discussed in detail. Finally, the adsorption of O atom on LaMgNi4 (110) surface and the elastic constants and the elastic modulus of random solid solution alloys of La4Mg4Ni14Cu2 are also investigated.

Valley-polarized nematic order in twisted moiré systems: In-plane orbital magnetism and crossover from non-Fermi liquid to Fermi liquid

The interplay between strong correlations and non-trivial topology in twisted moir\'e systems can give rise to a rich landscape of ordered states that intertwine the spin, valley, and charge degrees of freedom. In this paper, we investigate the properties of a system that displays long-range valley-polarized nematic order. Besides breaking the threefold rotational symmetry of the triangular moir\'e superlattice, this type of order also breaks twofold rotational and time-reversal symmetries, which leads to interesting properties. First, we develop a phenomenological model to describe the onset of this ordered state in twisted moir\'e systems and to explore its signatures in their thermodynamic and electronic properties. Its main manifestation is that it triggers the emergence of in-plane orbital magnetic moments oriented along high-symmetry lattice directions. We also investigate the properties of the valley-polarized nematic state at zero temperature. Due to the existence of a dangerously irrelevant coupling $\lambda$ in the six-state clock model that describes the putative valley-polarized nematic quantum critical point, the ordered state displays a pseudo-Goldstone mode. Using a two-patch model, we compute the fermionic self-energy to show that down to very low energies, the Yukawa-like coupling between the pseudo-Goldstone mode and the electronic degrees of freedom promotes the emergence of non-Fermi liquid behavior. Below a crossover energy scale $\Omega^{*}\sim\lambda^{3/2}$, however, Fermi liquid behavior is recovered. Finally, we discuss the applicability of these results to other non-trivial nematic states, such as the spin-polarized nematic phase.

Effect of Residual Carbon on Spin‐Polarized Coupling at a Graphene/Ferromagnet Interface

AbstractVertical stacks of graphene and ferromagnetic layers are predicted to be efficient spin filters, while the experimentally observed figures of merit systematically remain below the theoretical predictions. According to general consensus, a vaguely defined interface contamination is found responsible for this discrepancy. Here, it is demonstrated how the spin‐polarized electronic structure of single‐layer graphene supported on a ferromagnetic cobalt substrate is affected by the presence of an interfacial carbidic buffer layer, formed by residual carbon present in the Co substrate. It is found that the Co‐C hybridized single‐spin state near the Fermi level disappears upon thermal segregation of bulk carbon at the graphene–Co interface, which determines the electronic decoupling of graphene from the ferromagnetic support and consequently, the suppression of net spin polarization. These observations are shown to be independent of the graphene azimuthal orientation with respect to the high symmetry directions of the substrate. The findings provide clear evidence that the realization of highly polarized spin currents in graphene/ferromagnet heterostacks depends on careful control of the graphene growth process in order to eliminate interfacial carbon.

Structural, mechanical, electronic, vibrational and thermoelectric properties of novel double perovskites Ba2MgPdO6 and Ba2MgPtO6 within DFT framework

The first-principles study of novel double perovskites Ba2MgPdO6 and Ba2MgPtO6 has been performed utilizing the concepts of Density Functional Theory (DFT). These materials have been studied for the first time to explore their structural, elastic, electronic, vibrational, thermodynamic and thermoelectric properties. Ba2MgPdO6 and Ba2MgPtO6 possess an FCC (Face centered cubic) crystal structure. The calculated band structure reveals the semiconducting nature of these compounds with the bandgap of 1.18eV and 1.7eV for Ba2MgPdO6 and Ba2MgPtO6 respectively. The elastic stability is predicted based on various calculated mechanical parameters such as Poisson ratio, Bulk modulus and elastic constants. The phonon dispersion curves are analyzed over the high symmetry directions of the Brillouin zone. Phonon vector representation based on Density Functional Perturbation Theory (DFPT) and phonon densities of states indicate the dynamical stability of these compounds. In addition to these properties, the thermoelectric response of Ba2MgPdO6 and Ba2MgPtO6 is investigated with the help of Boltzmann's theory. The figure of merit has been evaluated for both compounds throughout the range from 50 K to 1200 K to analyze their potential for future energy devices. The present study is aimed at providing an overview of many important properties of Ba2MgPdO6 and Ba2MgPtO6 to encourage experimental researchers to synthesize such types of compounds for modern technological devices.

Topological properties of MoP[formula omitted]N[formula omitted] (x = 0, 0.25, 0.5, 0.75, 1) compounds: A density functional approach

Triply Degenerate Point (TDP) fermions in tungsten–carbide-type materials such as MoP which represent new topological states of quantum matter, have generated great interest recently. However, the TDPs in these materials are found to be far below the Fermi level (∼ −1.5eV) leading to the TDP fermions having less contribution to low-energy quasiparticle excitations. Here, we theoretically investigate the existence of TP fermions with TDPs close to the Fermi level in MoN, which has the same structure as MoP, and the ternary MoP1−xNx ordered alloys which their crystal structure is defined by replacing P atoms by N atoms in MoP compound. The topological properties of MoP1−xNx (x = 0, 0.25, 0.5, 0.75, 1) ordered alloys are systematically investigated by combining first-principles calculations and Wannier tight-binding analysis. The obtained Wannier Charge Centers (WCCs) are applied to calculate the topological invariant Z2 number. Our calculations show that hexagonal MoP, MoP0.75N0.25, MoP0.25N0.75, and MoN compounds are topological semimetals hosting triply degenerate nodal points resulting from band crossing between degenerate and nondegenerate bands along the high-symmetry directions of the Brillouin Zone, being protected by crystalline symmetries. Among these compounds, the triple degenerate points in MoP0.75N0.25 are much closer to the Fermi level. MoP0.75N0.25 hosts some points slightly above (42 meV, 73 meV and 87 meV) the Fermi energy. On the other hand, our ab initio calculations suggest that the MoP0.5N0.5 compound with orthorhombic structure does not host any triple degenerate point. It hosts a multitude of topological features including Weyl Points and nodal lines. The calculations indicate that these nodal lines are located in the vicinity of Fermi level.

Epitaxial Growth of High-Quality Monolayer MoS2 Single Crystals on Low-Symmetry Vicinal Au(101) Facets with Different Miller Indices

Epitaxial growth of wafer-scale monolayer semiconducting transition metal dichalcogenide single crystals is essential for advancing their applications in next-generation transistors and highly integrated circuits. Several efforts have been made for the growth of monolayer MoS2 single crystals on high-symmetry Au(111) and sapphire substrates, while more prototype growth systems still need to be discovered for clarifying the internal mechanisms. Herein, we report the epitaxial growth of unidirectionally aligned monolayer MoS2 domains and single-crystal films on low-symmetry Au(101) vicinal facets via a facile chemical vapor deposition method. On-site scanning tunneling microscopy observations reveal the formation of a specific rectangular Moiré pattern along the [101̅] step edge of Au(101) and along its perpendicular direction. The perfect lattice constant matching of MoS2/Au(101) along the substrate high-symmetry directions (i.e., Au[101̅], Au [010]) as well as the step-edge-guiding effect are proposed to facilitate the robust epitaxy. Multiscale characterizations further confirm the domain-boundary-free feature of the monolayer MoS2 films merged by unidirectionally aligned monolayer domains. This work hereby puts forward a symmetry mismatched epitaxial system for the direct synthesis of monolayer MoS2 single crystals, which should deepen our understanding about the epitaxy of 2D layered materials and propel their applications in various fields.