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Kagome materials with magnetic frustration in two-dimensional networks are known for their exotic properties, such as the anomalous Hall effect (AHE) with non-collinear spin textures. However, the effects of one-dimensional (1D) spin chains within these networks are less understood. Here, we report a distinctive AHE in the bilayer-distorted kagome material GdTi$_3$Bi$_4$, featuring 1D Gd zigzag spin chains, a one-third magnetization plateau, and two successive metamagnetic transitions. At these metamagnetic transitions, Hall resistivity shows abrupt jumps linked to the formation of stripe domain walls, while within the plateau, the absence of detectable domain walls suggests possible presence of skyrmion phase. Reducing the sample size to a few microns reveals additional Hall resistivity spikes, indicating domain wall skew scattering contributions. Magnetic atomistic spin dynamics simulations reveal that the magnetic textures at these transitions have reverse chirality, explaining the evolution of AHE and domain walls with fields. These results underscore the potential of magnetic and crystal symmetry interplay, and magnetic field-engineered spin chirality, for controlling domain walls and tuning transverse properties, advancing spintronic applications.

We synthesize and spectroscopically investigate monolayer C$_{60}$ on the topological insulator (TI) Bi$_4$Te$_3$. This C$_{60}$/Bi$_4$Te$_3$ heterostructure is characterized by excellent translational order in a novel (4 x 4) C$_{60}$ superstructure on a (9 x 9) unit of Bi$_4$Te$_3$. We measure the full two-dimensional energy band structure of C$_{60}$/Bi$_4$Te$_3$ using angle-resolved photoemission spectroscopy (ARPES). We find that C$_{60}$ accepts electrons from the TI at room temperature but no charge transfer occurs at low temperatures. We unravel this peculiar behaviour by Raman spectroscopy of C$_{60}$/Bi$_4$Te$_3$ and density functional theory (DFT) calculations of the electronegativity of C$_{60}$. Both methods are sensitive to orientational order of C$_{60}$. At low temperatures, Raman spectroscopy shows a dramatic intensity increase of the C$_{60}$ Raman signal, evidencing a transition to a rotationally ordered state. DFT reveals that the orientational order of C$_{60}$ at low temperatures has a higher electron affinity than at high temperatures. These results neatly explain the temperature-dependent charge transfer observed in ARPES. Our conclusions are supported by the appearance of a strong photoluminescence from C$_{60}$/Bi$_4$Te$_3$ at low temperatures.

The interplay between topology and superconductivity in quantum materials harbors rich physics ripe for discovery. In this study, we investigate the topological properties and superconductivity of the nonsymmorphic chiral superconductor NbGe$_2$ using high-resolution angle-resolved pho-toemission spectroscopy (ARPES), transport measurements, and ab initio calculations. The ARPES data revealed exotic chiral surface states on the (100) surface originating from the inherent chiral crystal structure. Supporting calculations indicate that NbGe$_2$ likely hosts elusive Weyl fermions in its bulk electronic structure. Furthermore, we uncovered the signatures of van Hove singularities that can enhance many-body interactions. Additionally, transport measurements demonstrated that NbGe$_2$ exhibits superconductivity below 2K. Overall, our comprehensive results provide the first concrete evidence that NbGe$_2$ is a promising platform for investigating the interplay between non-trivial band topology, possible Weyl fermions, van Hove singularities, and superconductivity in chiral quantum materials.

Kagome magnets provide a fascinating platform for the realization of correlated topological quantum phases under various magnetic ground states. However, the effect of the magnetic spin configurations on the characteristic electronic structure of the kagome lattice layer remains elusive. Here, utilizing angle-resolved photoemission spectroscopy and density functional theory calculations, we report the spectroscopic evidence for the spin-reorientation effect of a kagome ferromagnet Fe$_3$Ge, which is composed solely of kagome planes. As the Fe moments cant from the $c$ axis into the $ab$ plane upon cooling, the two kinds of kagome-derived Dirac fermions respond quite differently. The one with less-dispersive bands ($k_z$ $\sim$ 0) containing the $3d_{z^2}$ orbitals evolves from gapped into nearly gapless, while the other with linear dispersions ($k_z$ $\sim$ $\pi$) embracing the $3d_{xz}$/$3d_{yz}$ components remains intact, suggesting that the effect of spin reorientation on the Dirac fermions has an orbital selectivity. Moreover, we demonstrate that there is no signature of charge order formation in Fe$_3$Ge, contrasting with its sibling compound FeGe, a newly established charge-density-wave kagome magnet., Comment: 40 pages, 5 figures

For quantum electronics, the possibility to finely tune the properties of magnetic topological insulators (TIs) is a key issue. We studied solid solutions between two isostructural Z$_2$ TIs, magnetic MnBi$_2$Te$_4$ and nonmagnetic GeBi$_2$Te$_4$, with Z$_2$ invariants of 1;000 and 1;001, respectively. For high-quality, large mixed crystals of Ge$_x$Mn$_{1-x}$Bi$_2$Te$_4$, we observed linear x-dependent magnetic properties, composition-independent pairwise exchange interactions along with an easy magnetization axis. The bulk band gap gradually decreases to zero for $x$ from 0 to 0.4, before reopening for $x>0.6$, evidencing topological phase transitions (TPTs) between topologically nontrivial phases and the semimetal state. The TPTs are driven purely by the variation of orbital contributions. By tracing the x-dependent $6p$ contribution to the states near the fundamental gap, the effective spin-orbit coupling variation is extracted. As $x$ varies, the maximum of this contribution switches from the valence to the conduction band, thereby driving two TPTs. The gapless state observed at $x=0.42$ closely resembles a Dirac semimetal above the Neel temperature and shows a magnetic gap below, which is clearly visible in raw photoemission data. The observed behavior of the Ge$_x$Mn$_{1-x}$Bi$_2$Te$_4$ system thereby demonstrates an ability to precisely control topological and magnetic properties of TIs.

An essential ingredient for the production of Majorana fermions that can be used for quantum computing is the presence of topological superconductivity. As bulk topological superconductors remain elusive, the most promising approaches exploit proximity-induced superconductivity making systems fragile and difficult to realize. Weyl semimetals due to their intrinsic topology belong to potential candidates too, but search for Majorana fermions has always been connected with the superconductivity in the bulk, leaving the possibility of intrinsic superconductivity of the Fermi surface arcs themselves practically without attention, even from the theory side.Here, by means of angle-resolved photoemission spectroscopy and ab-initio calculations, we unambiguously identify topological Fermi arcs on two opposing surfaces of the non-centrosymmetric Weyl material PtBi2. We show that these states become superconducting at different temperatures around 10K. Remarkably, the corresponding coherencepeaks appear as the strongest and sharpest excitations ever detected by photoemission from solids, suggesting significant technological relevance. Our findings indicate that topological superconductivity in PtBi2 occurs exclusively at the surface, which not only makes it an ideal platform to host Majorana fermions, but may also lead to a unique quantum phase - an intrinsic topological SNS Josephson junction., Comment: 8 pages, 4 figures and Supplementary Information

Determining the degree of inherent parallelism in classical sequential algorithms and leveraging it for fast parallel execution is a key topic in parallel computing, and detailed analyses are known for a wide range of classical algorithms. In this paper, we perform the first such analysis for the fundamental Union-Find problem, in which we are given a graph as a sequence of edges, and must maintain its connectivity structure under edge additions. We prove that classic sequential algorithms for this problem are well-parallelizable under reasonable assumptions, addressing a conjecture by [Blelloch, 2017]. More precisely, we show via a new potential argument that, under uniform random edge ordering, parallel union-find operations are unlikely to interfere: $T$ concurrent threads processing the graph in parallel will encounter memory contention $O(T^2 \cdot \log |V| \cdot \log |E|)$ times in expectation, where $|E|$ and $|V|$ are the number of edges and nodes in the graph, respectively. We leverage this result to design a new parallel Union-Find algorithm that is both internally deterministic, i.e., its results are guaranteed to match those of a sequential execution, but also work-efficient and scalable, as long as the number of threads $T$ is $O(|E|^{\frac{1}{3} - \varepsilon})$, for an arbitrarily small constant $\varepsilon > 0$, which holds for most large real-world graphs. We present lower bounds which show that our analysis is close to optimal, and experimental results suggesting that the performance cost of internal determinism is limited.

Magnetic topological materials are a class of compounds with the underlying interplay of nontrivial band topology and magnetic spin configuration. Extensive interests have been aroused due to their application potential involved with an array of exotic quantum states. With angle-resolved photoemission spectroscopy and first-principles calculations, here we study the electronic properties of two magnetic Weyl semimetal candidates PrAlSi and SmAlSi. Though the two compounds harbor distinct magnetic ground states (ferromagnetic and antiferromagnetic for PrAlSi and SmAlSi, respectively) and 4$f$ shell fillings, we find that they share quite analogous low-energy band structure. By the measurements across the magnetic transitions, we further reveal that there is no evident evolution of the band structure in both compounds and the experimental spectra can be well reproduced by the nonmagnetic calculations, together suggesting a negligible effect of the magnetism on their electronic structures and a possibly weak coupling between the localized 4$f$ electrons and the itinerant conduction electrons. Our results offer essential insights into the interactions between magnetism, electron correlations, and topological orders in the $R$Al$X$ ($R$ = light rare earth and $X$ = Si or Ge) family., Comment: 7 pages, 3 figures

The noncentrosymmetric ferromagnetic Weyl semimetal CeAlSi with simultaneous space-inversion (SI) and time-reversal (TR) symmetry breaking provides a unique platform for the exploration of novel topological states. Here, by employing electrical and thermoelectrical transport, angle-resolved photoemission spectroscopy (ARPES), high-pressure techniques, and band calculations, we demonstrate that magnetism and pressure can serve as efficient parameters to tune the positions of Weyl nodes in CeAlSi. At ambient pressure, an anomalous Hall effect (AHE) and an anomalous Nernst effect (ANE) arise in the paramagnetic state, and then are enhanced when temperature approaches the ferromagnetic ordering temperature, evidencing magnetism facilitates the AHE/ANE. Such an enhancement of AHE/ANE can be ascribed to the tuning of the positions of Weyl nodes via magnetism. The ARPES measurements reveal that the ferromagnetism serves as a pivotal knob to tune the band structure of CeAlSi both in the bulk and on the surface. Such magnetism-tunable electronic structure has hitherto not been reported in other magnetic $R$Al$Pn$ ($R$ = rare earth elements, $Pn$ = Si, Ge) siblings, suggesting the great potential of controlling Weyl node positions in CeAlSi. Under pressure, an enhancement and a sign change of AHE are discovered. Based on band calculations, the evolution of AHE may root in the tuning of Weyl nodes via pressure. Moreover, multiple pressure-induced phase transitions are uncovered. These findings indicate that CeAlSi provides a unique and tunable platform for exploring exotic topological physics and electron correlations, as well as catering to an array of potential applications, such as spintronics and thermoelectrics.

Although a wide variety of handcrafted concurrent data structures have been proposed, there is considerable interest in universal approaches (henceforth called Universal Constructions or UCs) for building concurrent data structures. These approaches (semi-)automatically convert a sequential data structure into a concurrent one. The simplest approach uses locks that protect a sequential data structure and allow only one process to access it at a time. The resulting data structures use locks, and hence are blocking. Most work on UCs instead focuses on obtaining non-blocking progress guarantees such as obstruction-freedom, lock-freedom, or wait-freedom. Many non-blocking UCs have appeared. Key examples include the seminal wait-free UC by Herlihy, a NUMA-aware UC by Yi et al., and an efficient UC for large objects by Fatourou et al. We borrow ideas from persistent data structures and multi-version concurrency control (MVCC), most notably path copying, and use them to implement concurrent versions of sequential persistent data structures. Despite our expectation that our data structures would not scale under write-heavy workloads, they scale in practice. We confirm this scaling analytically in our model with private per-process caches.

Typically, topological superconductivity is reachable via proximity effect by a direct deposition of superconductor (S) on top of a topological insulator (TI) surface. Here we observed and analyzed the double critical current in the Josephson junctions based on the topological insulator in the fabricated planar Superconducting Quantum Interference Device. By measuring critical currents as a function of temperature and magnetic field, we show that the second critical current stems from the intrinsic superconductivity of the S/TI interface, which is supported by the modified Resistively Shunted Junction model and Transmission Electron Microscopy studies. This complex structure of the interface should be taken into account when technological process involves Ar-plasma cleaning.

The nematicity in multilayer FeSe/SrTiO$_3$ films has been previously suggested to be enhanced with decreasing film thickness. Motivated by this, there have been many discussions about the competing relation between nematicity and superconductivity. However, the criterion for determining the nematicity strength in FeSe remains highly debated. The understanding of nematicity and its relation to superconductivity in FeSe films is therefore still controversial. Here, we fabricate multilayer FeSe/SrTiO$_3$ films using molecular beam epitaxy and study the nematic properties by combining angle-resolved photoemission spectroscopy, nuclear magnetic resonance, and scanning tunneling microscopy experiments. We unambiguously demonstrate that, near the interface, the nematicity is suppressed by the SrTiO$_3$-induced tensile strain; in the bulk region further away from the interface, the strength of nematicity recovers to the bulk value. Our results not only solve the controversy about the nematicity in multilayer FeSe films, but also offer valuable insights into the relationship between nematicity and superconductivity., Comment: 23 pages, 4 figures

The ultrafast manipulation of magnetic order due to optical excitation is governed by the intricate flow of energy and momentum between the electron, lattice and spin subsystems. While various models are commonly employed to describe these dynamics, a prominent example being the microscopic three temperature model (M3TM), systematic, quantitative comparisons to both the dynamics of energy flow and magnetic order are scarce. Here, we apply a M3TM to the ultrafast magnetic order dynamics of the layered antiferromagnet GdRh$_2$Si$_2$. The femtosecond dynamics of electronic temperature, surface ferromagnetic order, and bulk antiferromagnetic order were explored at various pump fluences employing time- and angle-resolved photoemission spectroscopy and time-resolved resonant magnetic soft x-ray diffraction, respectively. After optical excitation, both the surface ferromagnetic order and the bulk antiferromagnetic order dynamics exhibit two-step demagnetization behaviors with two similar timescales (<1 ps, ~10 ps), indicating a strong exchange coupling between localized 4f and itinerant conduction electrons. Despite a good qualitative agreement, the M3TM predicts larger demagnetization than our experimental observation, which can be phenomenologically described by a transient, fluence-dependent increased N\'eel temperature. Our results indicate that effects beyond a mean-field description have to be considered for a quantitative description of ultrafast magnetic order dynamics., Comment: 19 pages, 10 figures

The Fermi arcs are signatures of exotic states in solids because they defy conventional concept of Fermi surfaces as closed contours in momentum space. Fermi arcs were first discovered in cuprates, and caused by the pseudogap. Weyl semimetals provided another way to generate Fermi arcs by breaking either the time reversal symmetry (TRS) or inversion symmetry of a 3D Dirac semimetal, which can result in a Weyl semimetal with pairs of Weyl nodes that have opposite chirality. The bulk-boundary correspondence associated with the Chern number leads to the emergence of Fermi arcs on the boundary. Here, we present experimental evidence that pairs of magnetically split hole- and electron-like Fermi arcs emerge below the Neel temperature, in the antiferromagnetic (AFM) state of cubic NdBi due to a novel band splitting effect. Whereas TRS is broken by the AFM order, both inversion and nonsymmorphic TRS are preserved in the bulk, precluding the possibility of a Weyl semimetal. The observed magnetic splitting is highly unusual, as it creates bands of opposing curvature, that changes with temperature and follows the antiferromagnetic order parameter. This is completely different from previously reported cases of magnetic splittings such as traditional Zeeman and Rashba, where the curvature of the bands is preserved. Therefore, our finding represents a new Fermionic state created by new type of magnetic band splitting in the presence of a long-range AFM order that are not readily explained by existing theoretical ideas., Comment: 16 pages, 4 figures main text and 20 pages, 12 figures supplement

The entanglement of charge density wave (CDW), superconductivity, and topologically nontrivial electronic structure has recently been discovered in the kagome metal $A$V$_3$Sb$_5$ ($A$ = K, Rb, Cs) family. With high-resolution angle-resolved photoemission spectroscopy, we study the electronic properties of CDW and superconductivity in CsV$_3$Sb$_5$. The spectra around $\bar{K}$ is found to exhibit a peak-dip-hump structure associated with two separate branches of dispersion, demonstrating the isotropic CDW gap opening below $E_{\rm F}$. The peak-dip-hump lineshape is contributed by linearly dispersive Dirac bands in the lower branch and a dispersionless flat band close to $E_{\rm F}$ in the upper branch. The electronic instability via Fermi surface nesting could play a role in determining these CDW-related features. The superconducting gap of $\sim$0.4 meV is observed on both the electron band around $\bar{\Gamma}$ and the flat band around $\bar{K}$, implying the multiband superconductivity. The finite density of states (DOS) at $E_{\rm F}$ in the CDW phase are most likely in favor of the emergence of multiband superconductivity, particularly the enhanced DOS associated with the flat band. Our results not only shed light on the controversial origin of the CDW, but also offer insights into the relationship between CDW and superconductivity., Comment: 6 pages, 4 figures, PRL in press

Fermi surfaces, three-dimensional (3D) abstract interfaces that define the occupied energies of electrons in a solid, are important for characterizing and predicting the thermal, electrical, magnetic, and optical properties of crystalline metals and semiconductors [1]. Angle-resolved photoemission spectroscopy (ARPES) is the only technique directly probing the Fermi surface by measuring the Fermi momenta (kF) from energy and angular distribution of photoelectrons dislodged by monochromatic light [2]. Existing electron analyzers are able to determine a number of kF-vectors simultaneously, but current technical limitations prohibit a direct high-resolution 3D Fermi surface mapping. As a result, no such datasets exist, strongly limiting our knowledge about the Fermi surfaces and restricting a detailed comparison with the widely available nowadays calculated 3D Fermi surfaces. Here we show that using a simpler instrumentation, based on the Fourier electron optics combined with a retardation field of the detector, it is possible to perform 3D-mapping within a very short time interval and with very high resolution. We present the first detailed experimental 3D Fermi surface recorded in the full Brillouin zone along the kz-direction as well as other experimental results featuring multiple advantages of our technique. In combination with various light sources, including synchrotron radiation, our methodology and instrumentation offer new opportunities for high-resolution ARPES in the physical and life sciences., Comment: 14 pages, 4 figures

Dynamic Connectivity is a fundamental algorithmic graph problem, motivated by a wide range of applications to social and communication networks and used as a building block in various other algorithms, such as the bi-connectivity and the dynamic minimal spanning tree problems. In brief, we wish to maintain the connected components of the graph under dynamic edge insertions and deletions. In the sequential case, the problem has been well-studied from both theoretical and practical perspectives. However, much less is known about efficient concurrent solutions to this problem. This is the gap we address in this paper. We start from one of the classic data structures used to solve this problem, the Euler Tour Tree. Our first contribution is a non-blocking single-writer implementation of it. We leverage this data structure to obtain the first truly concurrent generalization of dynamic connectivity, which preserves the time complexity of its sequential counterpart, but is also scalable in practice. To achieve this, we rely on three main techniques. The first is to ensure that connectivity queries, which usually dominate real-world workloads, are non-blocking. The second non-trivial technique expands the above idea by making all queries that do not change the connectivity structure non-blocking. The third ingredient is applying fine-grained locking for updating the connected components, which allows operations on disjoint components to occur in parallel. We evaluate the resulting algorithm on various workloads, executing on both real and synthetic graphs. The results show the efficiency of each of the proposed optimizations; the most efficient variant improves the performance of a coarse-grained based implementation on realistic scenarios up to 6x on average and up to 30x when connectivity queries dominate.

Non-symmorphic chiral topological crystals host exotic multifold fermions, and their associated Fermi arcs helically wrap around and expand throughout the Brillouin zone between the high-symmetry center and surface-corner momenta. However, Fermi-arc splitting and realization of the theoretically proposed maximal Chern number rely heavily on the spin-orbit coupling (SOC) strength. In the present work, we investigate the topological states of a new chiral crystal, PtGa, which has the strongest SOC among all chiral crystals reported to date. With a comprehensive investigation using high-resolution angle-resolved photoemission spectroscopy, quantum-oscillation measurements, and state-of-the-art ab initio calculations, we report a giant SOC-induced splitting of both Fermi arcs and bulk states. Consequently, this study experimentally confirms the realization of a maximal Chern number equal to |4| for the first time in multifold fermionic systems, thereby providing a platform to observe large-quantized photogalvanic currents in optical experiments., Comment: Accepted in Nature Communications

Union-Find (or Disjoint-Set Union) is one of the fundamental problems in computer science; it has been well-studied from both theoretical and practical perspectives in the sequential case. Recently, there has been mounting interest in analyzing this problem in the concurrent scenario, and several asymptotically-efficient algorithms have been proposed. Yet, to date, there is very little known about the practical performance of concurrent Union-Find. This work addresses this gap. We evaluate and analyze the performance of several concurrent Union-Find algorithms and optimization strategies across a wide range of platforms (Intel, AMD, and ARM) and workloads (social, random, and road networks, as well as integrations into more complex algorithms). We first observe that, due to the limited computational cost, the number of induced cache misses is the critical determining factor for the performance of existing algorithms. We introduce new techniques to reduce this cost by storing node priorities implicitly and by using plain reads and writes in a way that does not affect the correctness of the algorithms. Finally, we show that Union-Find implementations are an interesting application for Transactional Memory (TM): one of the fastest algorithm variants we discovered is a sequential one that uses coarse-grained locking with the lock elision optimization to reduce synchronization cost and increase scalability.

Topological superconductors should be able to provide essential ingredients for quantum computing, but are very challenging to realize. Spin-orbit interaction in iron-based superconductors opens the energy gap between the $p$-states of pnictogen and $d$-states of iron very close to the Fermi level, and such $p$-states have been recently experimentally detected. Density functional theory predicts existence of topological surface states within this gap in FeTe$_{1-x}$Se$_x$ making it an attractive candidate material. Here we use synchrotron-based angle-resolved photoemission spectroscopy and band structure calculations to demonstrate that FeTe$_{1-x}$Se$_x$ (x=0.45) is a superconducting 3D Dirac semimetal hosting type-I and type-II Dirac points and that its electronic structure remains topologically trivial. We show that the inverted band gap in FeTe$_{1-x}$Se$_x$ can possibly be realized by further increase of Te content, but strong correlations reduce it to a sub-meV size, making the experimental detection of this gap and corresponding topological surface states very challenging, not to mention exact matching with the Fermi level. On the other hand, the $p-d$ and $d-d$ interactions are responsible for the formation of extremely flat band at the Fermi level pointing to its intimate relation with the mechanism of high-T$_c$ superconductivity in IBS., Comment: 10 pages, 5 figures, 28 references

We report experimental and theoretical evidence that GaGeTe is a basic $Z_2$ topological semimetal with three types of charge carriers: bulk-originated electrons and holes as well as surface state electrons. This electronic situation is qualitatively similar to the primer 3D topological insulator Bi2Se3, but important differences account for an unprecedented transport scenario in GaGeTe. High-resolution angle-resolved photoemission spectroscopy combined with advanced band structure calculations show a small indirect energy gap caused by a peculiar band inversion in the \textit{T}-point of the Brillouin zone in GaGeTe. An energy overlap of the valence and conduction bands brings both electron- and hole-like carriers to the Fermi level, while the momentum gap between the corresponding dispersions remains finite. We argue that peculiarities of the electronic spectrum of GaGeTe have a fundamental importance for the physics of topological matter and may boost the material's application potential.

Nematicity plays an important role in the physics of iron-based superconductors (IBS). Its microscopic origin and in particular its importance for the mechanism of high-temperature superconductivity itself are highly debated. A crucial knowledge in this regard is the degree to which the nematic order influences the electronic structure of these materials. Earlier angle-resolved photoemission spectroscopy (ARPES) studies found that the effect is dramatic in three families of IBS including 11, 111 and 122 compounds: energy splitting reaches 70 meV and Fermi surface becomes noticeably distorted. More recent experiments, however, reported significantly lower energy scale in 11 and 111 families, thus questioning the degree and universality of the impact of nematicity on the electronic structure of IBS. Here we revisit the electronic structure of undoped parent BaFe2As2 (122 family). Our systematic ARPES study including the detailed temperature and photon energy dependencies points to the significantly smaller energy scale also in this family of materials, thus establishing the universal scale of this phenomenon in IBS. Our results form a necessary quantitative basis for theories of high-temperature superconductivity focused on the nematicity., Comment: 14 pages 4 figures

We report on the observation of photoluminescence (PL) with a narrow 18 meV peak width from molecular beam epitaxy grown MoS$_2$ on graphene/Ir(111). This observation is explained in terms of a weak graphene-MoS$_2$ interaction that prevents PL quenching expected for a metallic substrate. The weak interaction of MoS$_2$ with the graphene is highlighted by angle-resolved photoemission spectroscopy and temperature dependent Raman spectroscopy. These methods reveal that there is no hybridization between electronic states of graphene and MoS$_2$ and a different thermal expansion of graphene and MoS$_2$. Molecular beam epitaxy grown MoS2 on graphene is therefore an important platform for optoelectronics which allows for large area growth with controlled properties., Comment: 18 pages, 5 figures, submitted for review