Ultrahigh magnetic field spectroscopy reveals the band structure of the 3D topological insulator Bi2_2Se3_3

We have investigated the band structure at the $\Gamma$ point of the three-dimensional (3D) topological insulator Bi$_2$Se$_3$ using magneto-spectroscopy over a wide range of energies ($0.55-2.2$\,eV) and in ultrahigh magnetic fields up to 150\,T. At such high energies ($E>0.6$\,eV) the parabolic approximation for the massive Dirac fermions breaks down and the Landau level dispersion becomes nonlinear. At even higher energies around 0.99 and 1.6 eV, new additional strong absorptions are observed with a temperature and magnetic-field dependence which suggest that they originate from higher band gaps. Spin orbit splittings for the further lying conduction and valence bands are found to be 0.196 and 0.264 eV

Emergence of Dirac-like bands in the monolayer limit of epitaxial Ge films on Au(111)

After the discovery of Dirac fermions in graphene, it has become a natural question to ask whether it is possible to realize Dirac fermions in other two-dimensional (2D) materials as well. In this work, we report the discovery of multiple Dirac-like electronic bands in ultrathin Ge films grown on Au(111) by angle-resolved photoelectron spectroscopy. By tuning the thickness of the films, we are able to observe the evolution of their electronic structure when passing through the monolayer limit. Our discovery may signify the synthesis of germanene, a 2D honeycomb structure made of Ge, which is a promising platform for exploring exotic topological phenomena and enabling potential applications

Diameter-independent skyrmion Hall angle observed in chiral magnetic multilayers

Magnetic skyrmions are topologically non-trivial nanoscale objects. Their topology, which originates in their chiral domain wall winding, governs their unique response to a motion inducing force. When subjected to an electrical current, the chiral winding of the spin texture leads to a deflection of the skyrmion trajectory, characterised by an angle with respect to the applied force direction. This skyrmion Hall angle is predicted to be skyrmion diameter dependent. In contrast, our experimental study finds that the skyrmion Hall angle is diameter independent for skyrmions with diameters ranging from 35 to 825 nm. At an average velocity of 6 ± 1 ms−1, the average skyrmion Hall angle was measured to be 9° ± 2°. In fact, the skyrmion dynamics is dominated by the local energy landscape such as materials defects and the local magnetic configuration

Direct observation of the energy gain underpinning ferromagnetic superexchange in the electronic structure of CrGeTe3

Funding: The Leverhulme Trust (Grant No. RL-2016-006), The Royal Society, and the European Research Council (Grant No. ERC-714193-QUESTDO). Max Planck Research School for Chemistry and Physics of Quantum Materials (IMPRS-CPQM) (I.M. and E.A.M).We investigate the temperature-dependent electronic structure of the van der Waals ferromagnet, CrGeTe3. Using angle-resolved photoemission spectroscopy, we identify atomic- and orbital-specific band shifts upon cooling through TC. From these, together with x-ray absorption spectroscopy and x-ray magnetic circular dichroism measurements, we identify the states created by a covalent bond between the Te 5p and the Cr eg orbitals as the primary driver of the ferromagnetic ordering in this system, while it is the Cr t2g states that carry the majority of the spin moment. The t2g states furthermore exhibit a marked bandwidth increase and a remarkable lifetime enhancement upon entering the ordered phase, pointing to a delicate interplay between localized and itinerant states in this family of layered ferromagnets.PostprintPeer reviewe

Magnetic profile of proximity-coupled (Dy,Bi)2Te3/(Cr,Sb)2Te3 topological insulator heterostructures

Magnetic topological insulators (TIs) are an ideal playground for the study of novel quantum phenomena building on time-reversal symmetry-broken topological surface states. By combining different magnetic TIs in a heterostructure, their magnetic and electronic properties can be precisely tuned. Recently, we have combined high-moment Dy:Bi2Te3 with high transition temperature Cr:Sb2Te3 in a superlattice, and we found, using x-ray magnetic circular dichroism (XMCD), that long-range magnetic order can be introduced in the Dy:Bi2Te3 layers. Accompanying first-principles calculations indicated that the origin of the long-range magnetic order is a strong antiferromagnetic coupling between Dy and Cr magnetic moments at the interface extending over several layers. However, based on XMCD alone, which is either averaging over the entire thin-film stack or is surface-sensitive, this coupling scenario could not be fully confirmed. Here we use polarized neutron reflectometry, which is ideally suited for the detailed study of superlattices, to retrieve the magnetization in a layer- and interface-resolved way. We find that the magnetization is, in contrast to similar recent studies, homogeneous throughout the individual layers, with no apparent interfacial effects. This finding demonstrates that heterostructure engineering is a powerful way of controlling the magnetic properties of entire layers, with the effects of coupling reaching beyond the interface region

Spin-orbit coupled spin-polarised hole gas at the CrSe2-terminated surface of AgCrSe2

Funding: We gratefully acknowledge support from the European Research Council (through the QUESTDO project, 714193), the Engineering and Physical Sciences Research Council (Grant No. EP/T02108X/1), and the Leverhulme Trust (Grant No. RL-2016-006). S.-J.K., E.A.M., A.Z., and I.M. gratefully acknowledge studentship support from the International Max-Planck Research School for Chemistry and Physics of Quantum Materials. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020.In half-metallic systems, electronic conduction is mediated by a single spin species, offering enormous potential for spintronic devices. Here, using microscopic-area angle-resolved photoemission, we show that a spin-polarised two-dimensional hole gas is naturally realised in the polar magnetic semiconductor AgCrSe2 by an intrinsic self-doping at its CrSe2-terminated surface. Through comparison with first-principles calculations, we unveil a striking role of spin-orbit coupling for the surface hole gas, unlocked by both bulk and surface inversion symmetry breaking, suggesting routes for stabilising complex magnetic textures in the surface layer of AgCrSe2.Publisher PDFPeer reviewe

Modification of the van der Waals interaction at the Bi2Te3{\mathrm{Bi}}_{2}{\mathrm{Te}}_{3} and Ge(111) interface

We present a structural and density-functional theory study of the interface of the quasi-twin-free grown three-dimensional topological insulator Bi2Te3 on Ge(111). Aberration-corrected scanning transmission electron microscopy and electron energy-loss spectroscopy in combination with first-principles calculations show that the weak van der Waals adhesion between the Bi2Te3 quintuple layer and Ge can be overcome by forming an additional Te layer at their interface. The first-principles calculations of the formation energy of the additional Te layer show it to be energetically favorable as a result of the strong hybridization between the Te and Ge

STANJE I PERSPEKTIVA RAZVOJA VINOGRADARSTVA I VINARSTVA ISTRE I HRVATSKOG PRIMORJA

Strong many-body interactions in solids yield a host of fascinating and potentially useful physical properties. Here, from angle-resolved photoemission experiments and ab initio many-body calculations, we demonstrate how a strong coupling of conduction electrons with collective plasmon excitations of their own Fermi sea leads to the formation of plasmonic polarons in the doped ferromagnetic semiconductor EuO. We observe how these exhibit a significant tunability with charge carrier doping, leading to a polaronic liquid that is qualitatively distinct from its more conventional lattice-dominated analogue. Our study thus suggests powerful opportunities for tailoring quantum many-body interactions in solids via dilute charge carrier doping

Razlike po spolu u nekim motoričkim sposobnostima djece predškolske dobi

The paper presents the results of the investigation of gender differences in motor abilities of preschool boys (n=106) and girls (n=121), 6-7 years of age. Eighteen composite motor tests adapted for preschool children, three for each hypothetical latent motor dimension (coordination, flexibility, strength, agility, accuracy and balance) were used to measure motor performance of the subjects. Statistically significant gender differences in motor variables were established. In the majority of variables better results were achieved by boys, except for the variable assessing flexibility – straddle seated forward bend, in which girls performed better. The results showed that this set of variables had a relatively high discriminant power. The measures influenced by the motion regulation mechanism had the greatest contribution to the discriminant function. The results indicate occurrence of sexual dimorphism in children’s motor abilities even at the age of six and half years.U radu su ispitane moguće razlike po spolu u motoričkim obilježjima dječaka (n=106) i djevojčica (n=121) predškolske dobi, starosti od 6 do 7 godina. U istraživanju je korištena baterija od osamnaest modificiranih testova za uzrast predškolske dobi, od kojih su za svaku latentnu dimenziju motoričkih sposobnosti bila predviđena po tri testa (koordinacija, fleksibilnost, snaga, agilnost, preciznost, ravnoteža). Utvrđene su značajne razlike po spolu između dječaka i djevojčica u mjerenim varijablama motoričkih sposobnosti. U većini varijabla bolje rezultate postizali su dječaci, osim u jednoj varijabli iz skupine procjene fleksibilnosti – pretklon u sjedu, u čemu su djevojčice bile bolje. Rezultati diskriminacijske analize potvrdili su kako taj skup manifestnih varijabli za procjenu motoričkih sposobnosti dobro razlikuje dječake i djevojčice. Najveći doprinos mogućem razlikovanju djece s obzirom na spolnu pripadnost pokazale su one varijable koje su pod utjecajem mehanizma za regulaciju kretanja. Rezultati ukazuju na to kako je već kod djece od šest i pol godina došlo do pojave spolnog dimorfizma u motoričkim sposobnostima