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Magnetic interactions in combination with nontrivial band structures can give rise to several exotic physical properties such as a large anomalous Hall effect, the anomalous Nernst effect, and the topological Hall effect (THE). Antiferromagnetic (AFM) materials exhibit the THE due to the presence of nontrivial spin structures. EuCuAs crystallizes in a hexagonal structure with an AFM ground state (Neel temperature similar to 16 K). In this work, we observe a large topological Hall resistivity of similar to 7.4 mu Omega-cm at 13 K which is significantly higher than the giant topological Hall effect of Gd2PdSi3 (similar to 3 mu Omega-cm). Neutron diffraction experiments reveal that the spins form a transverse conical structure during the metamagnetic transition, resulting in the large THE. In addition, by controlling the magnetic ordering structure of EuCuAs with an external magnetic field, several fascinating topological states such as Dirac and Weyl semimetals have been revealed. These results suggest the possibility of spintronic devices based on antiferromagnets with tailored noncoplanar spin configurations.

Interfacial charge transfer in oxide heterostructures gives rise to a rich variety of electronic and magnetic phenomena. Designing heterostructures where one of the thin-film components exhibits a metal-insulator transition opens a promising avenue for controlling such phenomena both statically and dynamically. In this letter, we utilize a combination of depth-resolved soft X-ray standing-wave and hard X-ray photoelectron spectroscopies in conjunction with polarization-dependent X-ray absorption spectroscopy to investigate the effects of the metal-insulator transition in $LaNiO_{3}$ on the electronic and magnetic states at the $LaNiO_{3}/CaMnO_{3}$ interface. We report on a direct observation of the reduced effective valence state of the interfacial Mn cations in the metallic superlattice with an above-critical $LaNiO_{3}$ thickness (6 u.c.) due to the leakage of itinerant Ni 3d $e_{g}$ electrons into the interfacial $CaMnO_{3}$ layer. Conversely, in an insulating superlattice with a below-critical $LaNiO_{3}$ thickness of 2 u.c., a homogeneous effective valence state of Mn is observed throughout the $CaMnO_{3}$ layers due to the blockage of charge transfer across the interface. The ability to switch and tune interfacial charge transfer enables precise control of the emergent ferromagnetic state at the $LaNiO_{3}/CaMnO_{3}$ interface and, thus, has far-reaching consequences on the future strategies for the design of next-generation spintronic devices.

In the large family of two-dimensional (2D) layered materials including graphene, its honeycomb analogs, and transition-metal dichalcogenides, the interlayer coupling plays a rather intriguing role. On the one hand, the weak van der Waals interaction that holds the layers together endows these compounds with quasi-2D properties, which might imply small interlayer effects on the electronically active bands. On the other hand, the oft-witnessed differences in electronic, optical, and magnetic behaviors of monolayers, bilayers, and multilayers of the same compound must have as their microscopic origin the detailed interlayer hopping parameters. Given the few experimental reports that have attempted to explicitly extract these parameters, we employ soft-x-ray angle-resolved photoemission spectroscopy (SX-ARPES) to probe the interlayer coupling in superconducting 2$H$-NbS$_2$. We visualize the S 3$p_z$ bands that disperse with respect to the out-of-plane momentum and introduce a simple tight-binding model to extract the interlayer hopping parameters. From first-principles calculations, we clarify how atomic distances and the proper accounting for screening via hybrid functionals influence these bands. The knowledge of interlayer hopping parameters is particularly pertinent in NbS$_2$, where recent experiments have uncovered fingerprints of finite-momentum superconductivity in the bulk material and heterostructures., 10 pages, 5 figures + SM

Angle-resolved photoemission spectroscopy, visualizing the superconducting gap in k-space, plays a pivotal role in research on cuprates and other high-T c superconducting materials. However, there has always been an imminent doubt whether this technique truly represents the intrinsic bulk spectral function, whose response can be distorted by energy- and k-dependence of the photoexcitation matrix element, and by a small photoelectron escape depth of few surface atomic layers. Here, we address this fundamental question with soft-X-ray photoemission measurements of the superconducting gap in the paradigm high-T c cuprate Bi2Sr2CaCu2O8. We vary the matrix element by spanning a dense k-space grid, formed by the lattice superstructure, and the probing depth by changing the emission angle. The measured gap appears independent of the matrix element effects, probing depth or photoexcitation energy. This fact proves the relevance of photoemission studies for the bulk superconductivity in Bi2Sr2CaCu2O8, and calls for similar verification experiments on other high-T c compounds, in particular more three-dimensional ones. Bi2Sr2CaCu2O8 shows an anomalously fast decay of the coherent spectral weight with photon energy, tracing back to strong electron–phonon interaction or relaxation of the lattice coherence.

In insulators, the longitudinal resistivity becomes infinitely large at zero temperature. For classical insulators, the Hall conductivity becomes zero at the same time. However, there are special systems, such as two-dimensional quantum Hall insulators, in which a more complex scenario is observed at high magnetic fields. Here, we report experimental evidence for a quasiquantized Hall insulator in the quantum limit of the three-dimensional compound SrSi2. Our measurements reveal a magnetic-field range, in which the longitudinal resistivity diverges with decreasing temperature, while the Hall conductivity approaches a quasiquantized value that is given only by the conductance quantum and the Fermi wave vector in the field direction. The quasiquantized Hall insulator appears in a magnetic field induced insulating ground state of three-dimensional materials and is deeply rooted in quantum Hall physics.

Using spin-resolved and angle-resolved photoemission spectroscopy and first-principles calculations, we have identified bulk band inversion and spin polarized surface state evolved from a weak topological insulator (TI) phase in van der Waals materials Nb3XTe6 (X = Si, Ge). The fingerprints of weak TI homologically emerge with hourglass fermions, as multi nodal chains composed by the same pair of valence and conduction bands gapped by spin orbit coupling. The novel topological state, with a pair of valence and conduction bands encoding both weak TI and hourglass semimetal nature, is essential and guaranteed by nonsymmorphic symmetry. It is distinct from TIs studied previously based on band inversions without symmetry protections., 4 figures

Heterostructures of transition metal oxides perovskites represent an ideal platform to explore exotic phenomena involving the complex interplay between the spin, charge, orbital and lattice degrees of freedom available in these compounds. At the interface between such materials, this interplay can lead to phenomena that are present in none of the original constituents such as the formation of the interfacial two-dimensional electron system (2DES) discovered at the LaAlO3 /SrTiO 3 (LAO/STO) interface. In samples prepared by growing a LAO layer onto a STO substrate, the 2DES is confined in a band bending potential well, whose width is set by the interface charge density and the STO dielectric properties, and determines the electronic band structure. Growing LAO (2 nm) /STO (x nm)/LAO (2 nm) heterostructures on STO substrates allows us to control the extension of the confining potential of the top 2DES via the thickness of the STO layer. In such samples, we explore the electronic structure trend under an increase of the confining potential with using soft x-ray angle-resolved photoemission spectroscopy combined with ab initio calculations. The results indicate that varying the thickness of the STO film modifies the quantization of the 3d t_2g bands and, interestingly, redistributes the charge between the d_xy and d_xz/d_yz bands.

Effects of X-ray irradiation on the electronic structure of LaAlO$_3$/SrTiO$_3$ (LAO/STO) samples, grown at low oxygen pressure and post-annealed ex-situ till recovery of their stoichiometry, were investigated by soft-X-ray ARPES. The irradiation at low sample temperature below ~100K creates oxygen vacancies (VOs) injecting Ti t2g-electrons into the interfacial mobile electron system (MES). At this temperature the oxygen out-diffusion is suppressed, and the VOs are expected to appear mostly in the top STO layer. However, we observe a pronounced three-dimensional (3D) character of the X-ray generated MES in our samples, indicating its large extension into the STO depth, which contrasts to the purely two-dimensional (2D) character of the MES in standard stoichiometric LAO/STO samples. Based on self-interaction-corrected DFT calculations of the MES induced by VOs at the interface and in STO bulk, we discuss possible mechanisms of this puzzling three-dimensionality. They may involve VOs remnant in the deeper STO layers, photoconductivity-induced metallic states as well as more exotic mechanisms such as X-ray induced formation of Frenkel pairs.

Weyl fermions as emergent quasiparticles can arise in Weyl semimetals (WSMs) in which the energy bands are nondegenerate, resulting from inversion or time-reversal symmetry breaking. Nevertheless, experimental evidence for magnetically induced WSMs is scarce. Here, using photoemission spectroscopy, we observe that the degeneracy of Bloch bands is already lifted in the paramagnetic phase of EuCd2As2. We attribute this effect to the itinerant electrons experiencing quasi-static and quasi–long-range ferromagnetic fluctuations. Moreover, the spin-nondegenerate band structure harbors a pair of ideal Weyl nodes near the Fermi level. Hence, we show that long-range magnetic order and the spontaneous breaking of time-reversal symmetry are not essential requirements for WSM states in centrosymmetric systems and that WSM states can emerge in a wider range of condensed matter systems than previously thought., Science Advances, 5 (7), ISSN:2375-2548

We probe the local magnetic properties of interfaces between the insulating ferromagnet EuS and the topological insulator Bi$_2$Se$_3$ using low energy muon spin rotation (LE-$\mu$SR). We compare these to the interface between EuS and the topologically trivial metal, titanium. Below the magnetic transition of EuS, we detect strong local magnetic fields which extend several nm into the adjacent layer and cause a complete depolarization of the muons. However, in both Bi$_2$Se$_3$ and titanium we measure similar local magnetic fields, implying that their origin is mostly independent of the topological properties of the interface electronic states. In addition, we use resonant soft X-ray angle resolved photoemission spectroscopy (SX-ARPES) to probe the electronic band structure at the interface between EuS and Bi$_2$Se$_3$. By tuning the photon energy to the Eu anti-resonance at the Eu $M_5$ pre-edge we are able to detect the Bi$_2$Se$_3$ conduction band, through a protective Al$_2$O$_3$ capping layer and the EuS layer. Moreover, we observe a signature of an interface-induced modification of the buried Bi$_2$Se$_3$ wave functions and/or the presence of interface states.

Currently, there is a flurry of research interest on materials with an unconventional electronic structure, and we have already seen significant progress in their understanding and engineering towards real-life applications. The interest erupted with the discovery of graphene and topological insulators in the previous decade. The electrons in graphene simulate massless Dirac Fermions with a linearly dispersing Dirac cone in their band structure, while in topological insulators, the electronic bands wind non-trivially in momentum space giving rise to gapless surface states and bulk bandgap. Weyl semimetals in condensed matter systems are the latest addition to this growing family of topological materials. Weyl Fermions are known in the context of high energy physics since almost the beginning of quantum mechanics. They apparently violate charge conservation rules, displaying the "chiral anomaly", with such remarkable properties recently theoretically predicted and experimentally verified to exist as low energy quasiparticle states in certain condensed matter systems. Not only are these new materials extremely important for our fundamental understanding of quantum phenomena, but also they exhibit completely different transport phenomena. For example, massless Fermions are susceptible to scattering from non-magnetic impurities. Dirac semimetals exhibit non-saturating extremely large magnetoresistance as a consequence of their robust electronic bands being protected by time reversal symmetry. These open up whole new possibilities for materials engineering and applications including quantum computing. In this review, we recapitulate some of the outstanding properties of WTe$_2$, namely, its non-saturating titanic magnetoresistance due to perfect electron and hole carrier balance up to a very high magnetic field observed for the very first time. (Continued. Please see the main article)., 33 pages, 7 figures

A key issue in heavy fermion research is how subtle changes in the hybridization between the 4$f$ (5$f$) and conduction electrons can result in fundamentally different ground states. CeRhIn$_5$ stands out as a particularly notable example: replacing Rh by either Co or Ir, located above or below Rh in the periodic table, antiferromagnetism gives way to superconductivity. In this photoemission study of CeRhIn$_5$, we demonstrate that the use of resonant ARPES with polarized light allows to extract detailed information on the 4$f$ crystal field states and details on the 4$f$ and conduction electron hybridization which together determine the ground state. We directly observe weakly dispersive Kondo resonances of $f$-electrons and identify two of the three Ce $4f_{5/2}^{1}$ crystal-electric-field levels and band-dependent hybridization, which signals that the hybridization occurs primarily between the Ce $4f$ states in the CeIn$_3$ layer and two more three-dimensional bands composed of the Rh $4d$ and In $5p$ orbitals in the RhIn$_2$ layer. Our results allow to connect the properties observed at elevated temperatures with the unusual low-temperature properties of this enigmatic heavy fermion compound., 6 pages, 5 figures

Rational design of low-dimensional electronic phenomena at oxide interfaces is currently considered to be one of the most promising schemes for realizing new energy-efficient logic and memory devices. An atomically abrupt interface between paramagnetic LaNiO3 and antiferromagnetic CaMnO3 exhibits interfacial ferromagnetism, which can be tuned via a thickness-dependent metal-insulator transition in LaNiO3. Once fully understood, such emergent functionality could turn this archetypal Mott-interface system into a key building block for the above-mentioned future devices. Here, we use depth-resolved standing-wave photoemission spectroscopy in conjunction with scanning transmission electron microscopy and x-ray absorption spectroscopy, to demonstrate a depth-dependent charge reconstruction at the LaNiO3/CaMnO3 interface. Our measurements reveal an increased concentration of Mn3+ and Ni2+ cations at the interface, which create an electronic environment favorable for the emergence of interfacial ferromagnetism mediated via the Mn4+−Mn3+ ferromagnetic double exchange and Ni2+−O−Mn4+ superexchange mechanisms. Our findings suggest a strategy for designing functional Mott oxide heterostructures by tuning the interfacial cation characteristics via controlled manipulation of thickness, strain, and ionic defect states.

Germanium telluride features special spin-electric effects originating from spin-orbit coupling and symmetry breaking by the ferroelectric lattice polarization, which opens up many prospectives for electrically tunable and switchable spin electronic devices. By Mn doping of the {\alpha}-GeTe host lattice, the system becomes a multiferroic semiconductor possessing magnetoelectric properties in which the electric polarization, magnetization and spin texture are coupled to each other. Employing spin- and angle-resolved photoemission spectroscopy in bulk- and surface-sensitive energy ranges and by varying dipole transition matrix elements, we disentangle the bulk, surface and surface-resonance states of the electronic structure and determine the spin textures for selected parameters. From our results, we derive a comprehensive model of the {\alpha}-GeTe surface electronic structure which fits experimental data and first principle theoretical predictions and we discuss the unconventional evolution of the Rashba-type spin splitting upon manipulation by external B- and E-fields., Comment: 7 pages, 7 figures, 1 ancillary file

Spin- and angle-resolved photoemission spectroscopy is used to reveal that a large spin polarization is observable in the bulk centrosymmetric transition metal dichalcogenide MoS2. It is found that the measured spin polarization can be reversed by changing the handedness of incident circularly polarized light. Calculations based on a three-step model of photoemission show that the valley and layer-locked spin- polarized electronic states can be selectively addressed by circularly polarized light, therefore providing a novel route to probe these hidden spin-polarized states in inversion-symmetric systems as predicted by Zhang et al. [Nat. Phys. 10, 387 (2014).].

Condensed matter systems can host quasiparticle excitations that are analogues to elementary particles such as Majorana, Weyl, and Dirac fermions. Recent advances in band theory have expanded the classification of fermions in crystals, and revealed crystal symmetry-protected electron excitations that have no high-energy counterparts. Here, using angle-resolved photoemission spectroscopy, we demonstrate the existence of a triply degenerate point in the electronic structure of MoP crystal, where the quasiparticle excitations are beyond the Majorana-Weyl-Dirac classification. Furthermore, we observe pairs of Weyl points in the bulk electronic structure coexisting with the 'new fermions', thus introducing a platform for studying the interplay between different types of fermions., 12 pages, 4 figures

The recently discovered structural reconstruction in the cuprate superlattice (SrCuO 2) n /(SrTiO 3) 2 has been investigated across the critical value of n = 5 using resonant inelastic x-ray scattering (RIXS). We find that at the critical value of n, the cuprate layer remains largely in the bulk-like two-dimensional structure with a minority of Cu plaquettes being reconstructed. The partial reconstruction leads to quenching of the magnons starting at the Î "-point due to the minority plaquettes acting as scattering points. Although comparable in relative abundance, the doped charge impurities in electron-doped cuprate superconductors do not show this quenching of magnetic excitations.

The recently discovered structural reconstruction in the cuprate superlattice (SrCuO$_2$)$_n$/(SrTiO$_3$)$_2$ has been investigated across the critical value of $n=5$ using resonant inelastic x-ray scattering (RIXS). We find that at the critical value of $n$, the cuprate layer remains largely in the bulk-like two-dimensional structure with a minority of Cu plaquettes being reconstructed. The partial reconstruction leads to quenching of the magnons starting at the $\Gamma$-point due to the minority plaquettes acting as scattering points. Although comparable in relative abundance, the doped charge impurities in electron-doped cuprate superconductors do not show this quenching of magnetic excitations., Comment: Accepted for publication in Scientific Reports

The complex electronic properties of $\mathrm{ZrTe_5}$ have recently stimulated in-depth investigations that assigned this material to either a topological insulator or a 3D Dirac semimetal phase. Here we report a comprehensive experimental and theoretical study of both electronic and structural properties of $\mathrm{ZrTe_5}$, revealing that the bulk material is a strong topological insulator (STI). By means of angle-resolved photoelectron spectroscopy, we identify at the top of the valence band both a surface and a bulk state. The dispersion of these bands is well captured by ab initio calculations for the STI case, for the specific interlayer distance measured in our x-ray diffraction study. Furthermore, these findings are supported by scanning tunneling spectroscopy revealing the metallic character of the sample surface, thus confirming the strong topological nature of $\mathrm{ZrTe_5}$., 5 pages, 4 figures

Chromium dioxide CrO$_2$ belongs to a class of materials called ferromagnetic half-metals, whose peculiar aspect is to act as a metal in one spin orientation and as semiconductor or insulator in the opposite one. Despite numerous experimental and theoretical studies motivated by technologically important applications of this material in spintronics, its fundamental properties such as momentum resolved electron dispersions and Fermi surface have so far remained experimentally inaccessible due to metastability of its surface that instantly reduces to amorphous Cr$_2$O$_3$. In this work, we demonstrate that direct access to the native electronic structure of CrO$_2$ can be achieved with soft-X-ray angle-resolved photoemission spectroscopy whose large probing depth penetrates through the Cr$_2$O$_3$ layer. For the first time the electronic dispersions and Fermi surface of CrO$_2$ are measured, which are fundamental prerequisites to solve the long debate on the nature of electronic correlations in this material. Since density functional theory augmented by a relatively weak local Coulomb repulsion gives an exhaustive description of our spectroscopic data, we rule out strong-coupling theories of CrO$_2$. Crucial for the correct interpretation of our experimental data in terms of the valence band dispersions is the understanding of a non-trivial spectral response of CrO$_2$ caused by interference effects in the photoemission process originating from the non-symmorphic space group of the rutile crystal structure of CrO$_2$.

Interplay of spin, charge, orbital and lattice degrees of freedom in oxide heterostructures results in a plethora of fascinating properties, which can be exploited in new generations of electronic devices with enhanced functionalities. The paradigm example is the interface between the two band insulators LaAlO3 and SrTiO3 that hosts a two-dimensional electron system. Apart from the mobile charge carriers, this system exhibits a range of intriguing properties such as field effect, superconductivity and ferromagnetism, whose fundamental origins are still debated. Here we use soft-X-ray angle-resolved photoelectron spectroscopy to penetrate through the LaAlO3 overlayer and access charge carriers at the buried interface. The experimental spectral function directly identifies the interface charge carriers as large polarons, emerging from coupling of charge and lattice degrees of freedom, and involving two phonons of different energy and thermal activity. This phenomenon fundamentally limits the carrier mobility and explains its puzzling drop at high temperatures.

We present a resonant inelastic x-ray scattering (RIXS) study of spin and charge excitations in overdoped La1.77Sr0.23CuO4 along two high-symmetry directions. The line shape of these excitations is analyzed and they are shown to be highly overdamped. Their spectral weight and damping are found to be strongly momentum dependent. Qualitative agreement between these observations and a calculated random-phase approximation susceptibility is obtained for this overdoped compound, implying that a significant contribution to the RIXS signal stems from a continuum of charge excitations. Furthermore, this suggests that the spin excitations in the overdoped regime can be captured qualitatively by an itinerant picture. Our calculations also predict a low-energy spin-excitation branch to exist along the nodal direction near the zone center. With the energy resolution of the present experiment, this branch is not resolvable, but we show that the next generation of high-resolution spectrometers will be able to test this prediction.

Interplay of spin, charge, orbital and lattice degrees of freedom in oxide heterostructures results in a plethora of fascinating properties, which can be exploited in new generations of electronic devices with enhanced functionalities. The paradigm example is the interface between the two band insulators LaAlO3 and SrTiO3 that hosts a two-dimensional electron system. Apart from the mobile charge carriers, this system exhibits a range of intriguing properties such as field effect, superconductivity and ferromagnetism, whose fundamental origins are still debated. Here we use soft-X-ray angle-resolved photoelectron spectroscopy to penetrate through the LaAlO3 overlayer and access charge carriers at the buried interface. The experimental spectral function directly identifies the interface charge carriers as large polarons, emerging from coupling of charge and lattice degrees of freedom, and involving two phonons of different energy and thermal activity. This phenomenon fundamentally limits the carrier mobility and explains its puzzling drop at high temperatures.

1T−TiSe2 is a quasi-two-dimensional transition metal dichalcogenide, which exhibits a charge density wave transition at a critical temperature of ∼200 K as well as low- temperature superconductivity induced by pressure or intercalation. The electronic energy dispersion measured by soft x-ray angle-resolved photoemission is not only momentum resolved parallel to the surface but also perpendicular to it. Experiments are compared to density functional theory based band structure calculations using different exchange-correlation functionals. The results reveal the importance of including spin-orbit coupling for a good description of the experimental bands. Compared to calculations within the local density approximation, the use of the modified Becke-Johnson (mBJ) exchange functional leads to a band structure that does not need an artificial downwards shift of the valence band to fit the experiment. The mBJ functional thus clearly appears as the most adapted functional for the theoretical description of the 1T−TiSe2 band structure within the DFT framework.

A Weyl semimetal possesses spin-polarized band-crossings, called Weyl nodes, connected by topological surface arcs. The low-energy excitations near the crossing points behave the same as massless Weyl fermions, leading to exotic properties like chiral anomaly. To have the transport properties dominated by Weyl fermions, Weyl nodes need to locate nearly at the chemical potential and enclosed by pairs of individual Fermi surfaces with nonzero Fermi Chern numbers. Combining angle-resolved photoemission spectroscopy and first-principles calculation, here we show that TaP is a Weyl semimetal with only single type of Weyl fermions, topologically distinguished from TaAs where two types of Weyl fermions contribute to the low-energy physical properties. The simple Weyl fermions in TaP are not only of fundamental interests but also of great potential for future applications. Fermi arcs on the Ta-terminated surface are observed, which appear in a different pattern from that on the As-termination in TaAs and NbAs., 20 pages, 5 figures

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In systems with broken inversion symmetry spin-orbit coupling (SOC) yields a Rashba-type spin splitting of electronic states, manifested in a k-dependent splitting of the bands. While most research had previously focused on 2D electron systems, recently a three-dimensional (3D) form of such Rashba-effect was found in a series of bismuth tellurohalides. Whereas these materials exhibit a very large spin-splitting, they lack an important property concerning functionalization, namely the possibility to switch or tune the spin texture. This limitation can be overcome in a new class of functional materials displaying Rashba-splitting coupled to ferroelectricity: the ferroelectric Rashba semiconductors (FERS). Using spin- and angle-resolved photoemission spectroscopy (SARPES) we show that GeTe(111) forms a prime member of this class, displaying a complex spin-texture for the Rashba-split surface and bulk bands arising from the intrinsic inversion symmetry breaking caused by the ferroelectric polarization of the bulk (FE). Apart from pure surface and bulk states we find surface-bulk resonant states (SBR) whose wavefunctions entangle the spinors from the bulk and surface contributions. At the Fermi level their hybridization results in unconventional spin topologies with cochiral helicities and concomitant gap opening. The GeTe(111) surface and SBR states make the semiconductor surface conducting. At the same time our SARPES data confirm that GeTe is a narrow-gap semiconductor, suggesting that GeTe(111) electronic states are endowed with spin properties that are theoretically challenging to anticipate. As the helicity of the spins in Rashba bands is connected to the direction of the FE polarization, this work paves the way to all-electric non-volatile control of spin-transport properties in semiconductors.

We report on the observation of orbital excitations in YVO3 by means of resonant inelastic x-ray scattering (RIXS) at energies across the vanadium L-3 and oxygen K absorption edges. At the V L3 edge, we are able to resolve the full spectrum of orbital excitations up to 5 eV. In order to unravel the effect of superexchange interactions and the crystal field on the orbital excitations, we analyzed the energy and temperature dependence of the intra-t(2g) excitations at 0.1-0.2 eV in detail. While these results suggest a dominant influence of the crystal field, peak shifts of about 13-20 meV observed as a function of the transferred momentum q parallel to a reflect a finite dispersion of the orbital excitations. This is puzzling since theoretical models based on superexchange interactions predict a dispersion only for q parallel to c. Furthermore, we demonstrate that RIXS at the O K edge is very sensitive to intersite excitations. At the O K edge, we observe excitations across the Mott-Hubbard gap and an additional feature at 0.4 eV, which we attribute to two-orbiton scattering, i.e., an exchange of orbitals between adjacent sites. Altogether, our results indicate that both superexchange interactions and the crystal field are important for a quantitative understanding of the orbital excitations in YVO3.