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The newly synthesized compound Fe[SeO4]OH belongs to the kieserite-like structure. Using the superspace approach, possible polytypes are predicted for R[MO4]Z, where R = Mg, Fe, Ni, Co, Zn, Mn, Al, V, Sb, Y; M = S, Se, P, As; Z = OH, H2O, F, O.

Ba4Fe4ClO9.5−x compounds are built of a Ba2Fe4O9.5−x framework with open hexagonal channels. (Ba–Cl–Ba) trimers located in the channels and the framework O atoms cause incommensurability, which is tuned under different annealing conditions.

In situ Lorentz transmission electron microscopy experiments demonstrate that skyrmions in magnetoelectric helimagnet Cu2OSeO3 can be written and erased locally by electric fields with an ultralow energy barrier.

The structure of Ba5(IO6)2 has been redetermined at two different temperatures, namely 298 and 80 K, with a high crystalline single-crystal. In comparison with previous determinations based on powder diffraction patterns, the present redetermination results are of greatly improved precision of the structural parameters. The ambiguity of the space-group assignment was eliminated with three-dimensional patterns from a single-crystal sample., The crystal structure of Ba5(IO6)2, penta­barium bis­(orthoperiodate), has been re-investigated at room temperature based on single-crystal X-ray diffraction data. In comparison with a previous crystal structure determination by the Rietveld method, an improved precision of the structural parameters was achieved. Additionally, low-temperature measurements allowed the crystal structure evolution to be studied down to 80 K. No evidence of structural transition was found even at the lowest temperature. Upon cooling, the lattice contraction is more pronounced along the b axis. This contraction is found to be inhomogeneous along different crystallographic axes. The inter­atomic distances between different Ba atoms reduce drastically with lowering temperature, resulting in a closer packing around the IO6 octa­hedra, which remain largely unaffected.

Electronic states of iron in the lower mantle's dominant mineral, (Mg,Fe,Al)(Fe,Al,Si)O3 bridgmanite, control physical properties of the mantle including density, elasticity, and electrical and thermal conductivity. However, the determination of electronic states of iron has been controversial, in part due to different interpretations of Mössbauer spectroscopy results used to identify spin state, valence state, and site occupancy of iron. We applied energy-domain Mössbauer spectroscopy to a set of four bridgmanite samples spanning a wide range of compositions: 10–50% Fe/total cations, 0–25% Al/total cations, 12–100% Fe3+/total Fe. Measurements performed in the diamond-anvil cell at pressures up to 76 GPa below and above the high to low spin transition in Fe3+ provide a Mössbauer reference library for bridgmanite and demonstrate the effects of pressure and composition on electronic states of iron. Results indicate that although the spin transition in Fe3+ in the bridgmanite B-site occurs as predicted, it does not strongly affect the observed quadrupole splitting of 1.4 mm/s, and only decreases center shift for this site to 0 mm/s at ~70 GPa. Thus center shift can easily distinguish Fe3+ from Fe2+ at high pressure, which exhibits two distinct Mössbauer sites with center shift ~1 mm/s and quadrupole splitting 2.4–3.1 and 3.9 mm/s at ~70 GPa. Correct quantification of Fe3+/total Fe in bridgmanite is required to constrain the effects of composition and redox states in experimental measurements of seismic properties of bridgmanite. In Fe-rich, mixed-valence bridgmanite at deep-mantle-relevant pressures, up to ~20% of the Fe may be a Fe2.5+ charge transfer component, which should enhance electrical and thermal conductivity in Fe-rich heterogeneities at the base of Earth's mantle.

Topological spin textures such as skyrmions hold high potential for use as magnetically active elements in diverse near-future applications. While skyrmions in metallic multilayers attract great attention in this context, unleashing the myriad potential of skyrmions for various applications requires the discovery and customization of alternative host system paradigms. Here we developed and applied a chemical method to synthesize octahedral particles of the chiral insulating skyrmion host Cu2OSeO3 with both narrow size distribution, and tailored dimensions approaching the nanoscale. Combining magnetometry and neutron scattering experiments with micromagnetic simulations, we show that the bulk phase diagram of Cu2OSeO3 changes dramatically below octahedral heights of 400 nm. Further particle size-dependent regimes are identified where various topological spin textures such as skyrmions, merons and bobbers can stabilize, prior to a lower critical octahedral height of approx. 190 nm below which no topological spin texture is found stable. These findings suggest conditions under which sparse topological spin textures confined to chiral magnet nanoparticles can be stable, and provide fresh potential for insulator-based application paradigms.

The synthesis and X-ray structural study of the new family of compounds Ba

Quantum spin liquids are exotic states of matter that form when strongly frustrated magnetic interactions induce a highly entangled quantum paramagnet far below the energy scale of the magnetic interactions. Three-dimensional cases are especially challenging due to the significant reduction of the influence of quantum fluctuations. Here, we report the magnetic characterization of ${\mathrm{K}}_{2}{\mathrm{Ni}}_{2}({\mathrm{SO}}_{4}{)}_{3}$ forming a three-dimensional network of ${\mathrm{Ni}}^{2+}$ spins. Using density functional theory calculations, we show that this network consists of two interconnected spin-1 trillium lattices. In the absence of a magnetic field, magnetization, specific heat, neutron scattering, and muon spin relaxation experiments demonstrate a highly correlated and dynamic state, coexisting with a peculiar, very small static component exhibiting a strongly renormalized moment. A magnetic field $B\ensuremath{\gtrsim}4\text{ }\text{ }\mathrm{T}$ diminishes the ordered component and drives the system into a pure quantum spin liquid state. This shows that a system of interconnected $S=1$ trillium lattices exhibits a significantly elevated level of geometrical frustration.

Quantum spin liquids are exotic states of matter which form when strongly frustrated magnetic interactions induce a highly entangled quantum paramagnet far below the energy scale of the magnetic interactions. Three-dimensional cases are especially challenging due to the significant reduction of the influence of quantum fluctuations. Here, we report the magnetic characterization of {\kni} forming a three dimensional network of Ni$^{2+}$ spins. Using density functional theory calculations we show that this network consists of two interconnected spin-1 trillium lattices. In the absence of a magnetic field, magnetization, specific heat, neutron scattering and muon spin relaxation experiments demonstrate a highly correlated and dynamic state, coexisting with a peculiar, very small static component exhibiting a strongly renormalized moment. A magnetic field $B \gtrsim 4$ T diminishes the ordered component and drives the system in a pure quantum spin liquid state. This shows that a system of interconnected $S=1$ trillium lattices exhibit a significantly elevated level of geometrical frustration., accepted in PRL

The present paper reports on an experimental investigation of the structural, electrical and optical properties of Ru rich Ru1-xTixO2 thin films. Rutile single-phase Ru1-xTixO2 thin films have been deposited by reactive hybrid High-power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS) at a substrate temperature of 250 °C. The HiPIMS source was applied to the Ru target while the DCMS source was connected to the Ti target in order to vary the Ti content in the films. The films are well crystallized and compact with randomly orientated nanocrystallites. The optical properties have been investigated by ellipsometric measurements in the optical energy range from 1.3 eV to 3.3 eV, while the electrical resistivity has been measured in the Van der Paw configuration at room temperature. The electrical resistivity increases gradually from 70 μΩcm for pure RuO2 to about 243 μΩcm for Ru1-xTixO2 films with x = 0.13. The optical properties are correlated with the Ti doping. The refractive index n changes from a strong dispersion relationship to a moderate one with increasing Ti content.

The nature of the dynamics and structural changes that take place at the ferroelectric phase transition in lead oxides is a rich field of study. Solid-state nuclear magnetic resonance (NMR) of 207Pb is well suited to study the local structure and disorder in lead oxide ferroelectric transitions at the atomic level. However, very large 207Pb shielding anisotropy results in poor resolution in 1D static and magic angle spinning (MAS) NMR spectra. We address this problem by using short high-power adiabatic pulses (SHAPs) with magic-angle-turning sequences to correlate the isotropic and anisotropic parts of the 207Pb chemical shift tensor in a 2D NMR experiment, yielding resolved 207Pb NMR spectra of the nine distinct lead sites in uniaxial ferroelectric lead germanate (Pb5Ge3O11). Using this technique we detect the magnetic environments of displaced Pb2+ ions and unambiguously identify the nature of the phase transition as mixed displacive and order-disorder. We also observe that the atomic-level process responsible for the phase transition in ferroelectric lead germanate is chemical exchange on the kilohertz timescale. We derive an activation energy of 103.4 ± 1.7 kJ mol-1 and compare it to dielectric spectroscopy studies on similar materials. These results show that this method can be used to characterize ferroelectric phase transitions of complex materials with high resolution using nuclei that are typically inaccessible due to their large shielding anisotropy.

We report magnetic properties of a $3{d}^{9}$ $({\mathrm{Cu}}^{2+})$ magnetic insulator ${\mathrm{Cu}}_{2}{\mathrm{OSO}}_{4}$ measured on both powder and single crystal. The magnetic atoms of this compound form layers whose geometry can be described either as a system of chains coupled through dimers or as a kagome lattice where every third spin is replaced by a dimer. Specific heat and DC susceptibility show a magnetic transition at 20 K, which is also confirmed by neutron scattering. Magnetic entropy extracted from the specific heat data is consistent with an $S=1/2$ degree of freedom per ${\mathrm{Cu}}^{2+}$, and so is the effective moment extracted from DC susceptibility. The ground state has been identified by means of neutron diffraction on both powder and single crystal and corresponds to an $\ensuremath{\sim}{120}^{\ensuremath{\circ}}$ spin structure in which ferromagnetic intradimer alignment results in a net ferrimagnetic moment. No evidence is found for a change in lattice symmetry down to 2 K. Our results suggest that ${\mathrm{Cu}}_{2}{\mathrm{OSO}}_{4}$ represents a type of model lattice with frustrated interactions where interplay between magnetic order, thermal and quantum fluctuations can be explored.

The discovery of multiple coexisting magnetic phases in the crystallographically homogeneous compound ${\mathrm{Ca}}_{3}{\mathrm{Co}}_{2}{\mathrm{O}}_{6}$ has stimulated ongoing research activity. In recent years the main focus has been on the zero-field-state properties, where exceedingly long timescales have been established. In this study we report a detailed investigation of static and dynamic properties of ${\mathrm{Ca}}_{3}{\mathrm{Co}}_{2}{\mathrm{O}}_{6}$ across the magnetic field induced transition around 3.5 T. This region has so far been practically neglected, while we argue that in some aspects it represents a simpler version of the transition across the $B=0$ state. Investigating the frequency dependence of the ac susceptibility, we reveal that on the high-field side ($Bg3.5$ T) the response corresponds to a relatively narrow distribution of magnetic clusters. The distribution appears very weakly dependent on magnetic field, with an associated energy barrier of around 200 K. Below 3.5 T a second contribution arises, with much smaller characteristic frequencies and a strong temperature and magnetic field dependence. We discuss these findings in the context of intrachain and interchain clustering of magnetic moments.

The phase transition most commonly observed is probably melting, a transition from ordered crystalline solids to disordered isotropic liquids. In three dimensions, melting is a single, first-order phase transition. In two-dimensional systems, however, theory predicts a general scenario of two continuous phase transitions separated by an intermediate, oriented liquid state, the so-called hexatic phase with short-range translational and quasi-long-range orientational orders. Such hexatic phases occur in colloidal systems, Wigner solids and liquid crystals, all composed of real-matter particles. In contrast, skyrmions are countable soliton configurations with non-trivial topology and these quasi-particles can form two-dimensional lattices. Here we show, by direct imaging with cryo-Lorentz transmission electron microscopy, that magnetic field variations can tune the phase of the skyrmion ensembles in Cu

Coupling of spin-waves with electromagnetic cavity field is demonstrated in an antiferromagnet, dysprosium ferrite (DyFeO3). By measuring transmission at 0.2-0.35 THz and sweeping sample temperature, magnon-photon coupling signatures were found at crossings of spin-wave resonances with Fabry-Perot cavity modes formed in samples. The obtained spectra are explained in terms of classical electrodynamics and a microscopic model., Comment: 3 pages, 2 figures

In nodal-line semimetals linearly dispersing states form Dirac loops in the reciprocal space, with high degree of electron-hole symmetry and almost-vanishing density of states near the Fermi level. The result is reduced electronic screening and enhanced correlations between Dirac quasiparticles. Here we investigate the electronic structure of ZrSiSe, by combining time- and angle-resolved photoelectron spectroscopy with ab initio density functional theory (DFT) complemented by an extended Hubbard model (DFT +U +V). We show that electronic correlations are reduced on an ultrashort timescale by optical excitation of high-energy electrons-hole pairs, which transiently screen the Coulomb interaction. Our findings demonstrate an all-optical method for engineering the band structure of a quantum material., Comment: 6 pages, 3 figures

While in 3D materials melting is a single, first-order phase transition, in 2D systems, it can also proceed via an intermediate phase. For a skyrmion lattice in Cu2OSeO3, magnetic field variations can tune this quasiparticle 2D solid into a skyrmion liquid via an intermediate hexatic phase with short-range translational and quasi-long-range orientational order. The phase transition most commonly observed is probably melting, a transition from ordered crystalline solids to disordered isotropic liquids. In three dimensions, melting is a single, first-order phase transition. In two-dimensional systems, however, theory predicts a general scenario of two continuous phase transitions separated by an intermediate, oriented liquid state, the so-called hexatic phase with short-range translational and quasi-long-range orientational orders. Such hexatic phases occur in colloidal systems, Wigner solids and liquid crystals, all composed of real-matter particles. In contrast, skyrmions are countable soliton configurations with non-trivial topology and these quasi-particles can form two-dimensional lattices. Here we show, by direct imaging with cryo-Lorentz transmission electron microscopy, that magnetic field variations can tune the phase of the skyrmion ensembles in Cu(2)OSeO(3)from a two-dimensional solid through the long-speculated skyrmion hexatic phase to a liquid. The local spin order persists throughout the process. Remarkably, our quantitative analysis demonstrates that the aforementioned topological-defect-induced crystal melting scenario well describes the observed phase transitions.

The crystal structure of [ZnCl2(NH3)2], diamminedichloridozinc, was re-investigated at low temperature, revealing the positions of the hydrogen atoms and thus a deeper insight into the hydrogen-bonding scheme in the crystal packing. In comparison with previous crystal structure determinations [MacGillavry & Bijvoet (1936).Z. Kristallogr.94, 249–255; Yamaguchi & Lindqvist (1981).Acta Chem. Scand.35, 727–728], an improved precision of the structural parameters was achieved. In the crystal, tetrahedral [Zn(NH3)2Cl2] units (point-group symmetrymm2) are linked through N—H...Cl hydrogen bonds into a three-dimensional network.

Anatase TiO2 is among the most studied materials for light-energy conversion applications, but the nature of its fundamental charge excitations is still unknown. Yet it is crucial to establish whether light absorption creates uncorrelated electron-hole pairs or bound excitons and, in the latter case, to determine their character. Here, by combining steady-state angle-resolved photoemission spectroscopy and spectroscopic ellipsometry with state-of-the-art ab initio calculations, we demonstrate that the direct optical gap of single crystals is dominated by a strongly bound exciton rising over the continuum of indirect interband transitions. This exciton possesses an intermediate character between the Wannier-Mott and Frenkel regimes and displays a peculiar two-dimensional wavefunction in the three-dimensional lattice. The nature of the higher-energy excitations is also identified. The universal validity of our results is confirmed up to room temperature by observing the same elementary excitations in defect-rich samples (doped single crystals and nanoparticles) via ultrafast two-dimensional deep-ultraviolet spectroscopy.Here the authors combine steady-state angle-resolved photoemission spectroscopy, ellipsometry and ultrafast two-dimensional ultraviolet spectroscopy to examine the role of many-body correlations in anatase TiO2, revealing the existence of strongly bound excitons in single crystals and nanoparticles.

Topological quantum materials have stimulated growing attention because they reveal novel aspects of condensed matter physics and point to new opportunities in materials science, in particular for thermoelectrics. Here, we experimentally study thermoelectric effects in ${\mathrm{HfTe}}_{5}$, which was predicted to be at the boundary between strong and weak topological insulators. The magnetic field dependence of ${\mathrm{HfTe}}_{5}$ thermoelectric properties attests to the anomalous character of this material, supported by our angle-resolved photoemission spectroscopy (ARPES) measurements. At 36 K, the thermopower of $\ensuremath{-}277\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{V}/\mathrm{K}$ is reached when a field of 0.4 Tesla is applied, while it is $\ensuremath{-}157\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{V}/\mathrm{K}$ at zero field and a large Nernst coefficient up to $600\ensuremath{\mu}\mathrm{V}/\mathrm{K}$ is observed at 100 K with magnetic field of 4 T. A possible topologically nontrivial band structure is proposed to account for our observations. Our results constitute a highly constraining set of data for any model of transport based on ${\mathrm{HfTe}}_{5}$ band structure. Furthermore, the extraordinary thermoelectric properties suggest a new paradigm for the development of thermoelectric applications based on layered transition-metal chalcogenides.

Coupling of magnons with cavity photons at THz frequencies is reported in an antiferromagnet dysprosium ferrite (DyFeO 3 ).

We report electrical conductivity measurements of Polymethyl-methacrylate filled by onion-like carbon particles with primary particle size of $\approx 5$ nm. We shown that the conductivity $\sigma$ is exceptionally high even at very low loadings, and that its low-temperature dependence follows a Coulomb gap regime at atmospheric pressure and an activated behavior at a pressure of $2$ GPa. We interpret this finding in terms of the enhancement under the applied pressure of the effective dielectric permittivity within the aggregates of onion-like carbons, which improves the screening of the Coulomb interaction and reduces the optimal hopping distance of the electrons., Comment: 4 pages, 3 figures, 1 page of supplementary material

The nature of the dynamics and structural changes that take place at the ferroelectric phase transition in lead oxides is a rich field of study. Solid-state nuclear magnetic resonance (NMR) of

Author(s): Jovic, V; Koch, RJ; Panda, SK; Berger, H; Bugnon, P; Magrez, A; Smith, KE; Biermann, S; Jozwiak, C; Bostwick, A; Rotenberg, E; Moser, S | Abstract: The efficiency and stability of RuO2 in electrocatalysis has made this material a subject of intense fundamental and industrial interest. The surface functionality is rooted in its electronic and magnetic properties, determined by a complex interplay of lattice-, spin-rotational, and time-reversal symmetries, as well as the competition between Coulomb and kinetic energies. This interplay was predicted to produce a network of Dirac nodal lines (DNLs), where the valence and conduction bands touch along continuous lines in momentum space. Here we uncover direct evidence for three DNLs in RuO2 by angle-resolved photoemission spectroscopy. These DNLs give rise to a flat-band surface state that is readily tuned by the electrostatic environment, and that presents an intriguing platform for exotic correlation phenomena. Our findings support high spin-Hall conductivities and bulk magnetism in RuO2, and are likely related to its catalytic properties.

Perovskite alkaline niobates, due to their strong nonlinear optical properties, including birefringence and the capability to produce second-harmonic generation (SHG) signals, attract a lot of attention as potential candidates for applications as local nano/microsized mechano-optical probes. Here, we report on an implementation of photonic force microscopy (PFM) to explore the Brownian motion and optical trappability of monocrystalline potassium niobate (KNbO3) nano/microsized particles having sizes within the range of 50 to 750 nm. In particular, we exploit the anisotropic translational diffusive regime of the Brownian motion to quantify thermal fluctuations and optical forces of singly-trapped KNbO3 particles within the optical trapping volume of a PFM microscope. We also show that, under near-infrared (NIR) excitation of the highly focused laser beam of the PFM microscope, a single optically-trapped KNbO3 particle reveals a strong SHG signal manifested by a narrow peak (lambda(em) = 532 nm) at half the excitation wavelength (lambda(ex) = 1064 nm). Moreover, we demonstrate that the thus induced SHG emission can be used as a local light source that is capable of optically exciting molecules of an organic dye, Rose Bengal (RB), which adhere to the particle surface, through the mechanism of luminescence energy transfer (LET).

Using soft x-ray angle-resolved photoemission spectroscopy we probed the bulk electronic structure of T_{d}-MoTe_{2}. We found that on-site Coulomb interaction leads to a Lifshitz transition, which is essential for a precise description of the electronic structure. A hybrid Weyl semimetal state with a pair of energy bands touching at both type-I and type-II Weyl nodes is indicated by comparing the experimental data with theoretical calculations. Unveiling the importance of Coulomb interaction opens up a new route to comprehend the unique properties of MoTe_{2}, and is significant for understanding the interplay between correlation effects, strong spin-orbit coupling and superconductivity in this van der Waals material.

Exploiting additional degrees of freedom in solid-state materials may be the most-promising solution when approaching the quantum limit of Moore's law for the conventional electronic industry. Recently discovered topologically nontrivial spin textures, skyrmions, are outstanding among such possibilities. However, the controlled creation of skyrmions, especially by electric means, remains a pivotal challenge in technological applications. Here, we report that skyrmions can be created locally via electric field in the magnetoelectric helimagnet Cu

Topological magnetic skyrmions are particlelike objects that can be created, moved, and annihilated, making them suitable for information storage and logic applications. Toward this goal, most effort is focused on metallic systems, but here the authors use neutron scattering to study electric field control of skyrmion states in a magnetoelectric insulator. Under electric fields, metastable skyrmion states are created, and switching between competing skyrmion and conical topological phases is demonstrated, as well as the antagonistic interplay of thermal agitation and remnant skyrmion states (important for applications near room temperature).

Magnetic skyrmions are topologically protected spin-whirls currently considered as promising for use in ultra-dense memory devices. Towards achieving this goal, exploration of the skyrmion phase response and under external stimuli is urgently required. Here we show experimentally, and explain theoretically, that in the magnetoelectric insulator Cu2OSeO3 the skyrmion phase can expand and shrink significantly depending on the polarity of a moderate applied electric field (few V/μm). The theory we develop incorporates fluctuations around the mean-field that clarifies precisely how the electric field provides direct control over the free energy difference between the skyrmion and the surrounding conical phase. The quantitative agreement between theory and experiment provides a solid foundation for the development of skyrmionic applications based on magnetoelectric coupling.

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The discovery of Weyl semimetals represents a significant advance in topological band theory. They paradigmatically enlarged the classification of topological materials to gapless systems while simultaneously providing experimental evidence for the long-sought Weyl fermions. Beyond fundamental relevance, their high mobility, strong magnetoresistance, and the possible existence of even more exotic effects, such as the chiral anomaly, make Weyl semimetals a promising platform to develop radically new technology. Fully exploiting their potential requires going beyond the mere identification of materials and calls for a detailed characterization of their functional response, which is severely complicated by the coexistence of surface- and bulk-derived topologically protected quasiparticles, i.e., Fermi arcs and Weyl points, respectively. Here, we focus on the type-II Weyl semimetal class in which we find a stoichiometry-dependent phase transition from a trivial to a nontrivial regime. By exploring the two extreme cases of the phase diagram, we demonstrate the existence of a universal response of both surface and bulk states to perturbations. We show that quasiparticle interference patterns originate from scattering events among surface arcs. Analysis reveals that topologically nontrivial contributions are strongly suppressed by spin texture. We also show that scattering at localized impurities can generate defect-induced quasiparticles sitting close to the Weyl point energy. These give rise to strong peaks in the local density of states, which lift the Weyl node, significantly altering the pristine low-energy spectrum. Remarkably, by comparing the WTe2 and the MoTe2 cases we found that scattering response and topological transition are not directly linked. Visualizing the existence of a universal microscopic response to scattering has important consequences for understanding the unusual transport properties of this class of materials. Overall, our observations provide a unifying picture of the type-II Weyl phase diagram.

We present an experimental investigation of the magnetic structure in a tetramer system SeCuO$_3$ using neutron diffraction and nuclear resonance techniques. We establish a non-collinear, commensurate antiferromagnetic ordering with a propagation vector $\textbf{k} = \left(0,0,1 \right)$. The order parameter follows a critical behavior near $T_N = 8$ K, with a critical exponent $\beta = 0.32$ in agreement with a 3D universality class. Evidence is presented that a singlet state starts to form on tetramers at temperatures as high as 200 K, and its signature is preserved within the ordered state through a strong renormalization of the ordered magnetic moment on two non-equivalent copper sites, $m_{Cu1} \approx 0.4 \mu_B$ and $m_{Cu2} \approx 0.7 \mu_B$ at 1.5 K.

Here we report on experiments performed by linear-dichroism angle resolved photoelectron spectroscopy (LD-ARPES) on septuple layers (SL) topological insulator GeBi2Te4. The linear dichroic signals, both for the valence band states and in the topologically protected surface state are interpreted as a probe of the symmetry of the states. The observation of a change in the LD-ARPES spectrum at the top of VB is attributed to the band parity inversion which is predicted by theory for all materials entering the topologically protected phase. Finally, the opening of a gap in the surface state dispersion along the non-high symmetry direction is reported. This is proposed to originated from the interaction between the surface state and the VB, leading to the formation of surface resonances.