Soft-X-ray ARPES facility at the ADRESS beamline of the SLS: concepts, technical realisation and scientific applications

Strocov, Vladimir N.; Wang, X.; Shi, M.; Kobayashi, Masaki; Krempaský, J.; Hess, Cecil F.; Schmitt, Thorsten; Patthey, L.

doi:10.1107/s1600577513019085

Cited by 157 publications

(181 citation statements)

References 31 publications

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“…• ) [41], and the hard x-ray data was obtained at the P09 Beamline of Petra III (∼5000 eV, resolution of 0.30 eV and θ xe = 88…”

Section: Experimental Methodsmentioning

confidence: 99%

Energetic, spatial, and momentum character of the electronic structure at a buried interface: The two-dimensional electron gas between two metal oxides

Nemšák¹,

Conti²,

Gray³

et al. 2016

Phys. Rev. B

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The interfaces between two condensed phases often exhibit emergent physical properties that can lead to new physics and novel device applications and are the subject of intense study in many disciplines. We here apply experimental and theoretical techniques to the characterization of one such interesting interface system: the two-dimensional electron gas (2DEG) formed in multilayers consisting of SrTiO 3 (STO) and GdTiO 3 (GTO). This system has been the subject of multiple studies recently and shown to exhibit very high carrier charge densities and ferromagnetic effects, among other intriguing properties. We have studied a 2DEG-forming multilayer of the form [6 unit cells (u.c.) STO/3 u.c. of GTO] 20 using a unique array of photoemission techniques including soft and hard x-ray excitation, soft x-ray angle-resolved photoemission, core-level spectroscopy, resonant excitation, and standing-wave effects, as well as theoretical calculations of the electronic structure at several levels and of the actual photoemission process. Standing-wave measurements below and above a strong resonance have been exploited as a powerful method for studying the 2DEG depth distribution. We have thus characterized the spatial and momentum properties of this 2DEG in detail, determining via depth-distribution measurements that it is spread throughout the 6 u.c. layer of STO and measuring the momentum dispersion of its states. The experimental results are supported in several ways by theory, leading to a much more complete picture of the nature of this 2DEG and suggesting that oxygen vacancies are not the origin of it. Similar multitechnique photoemission studies of such states at buried interfaces, combined with comparable theory, will be a very fruitful future approach for exploring and modifying the fascinating world of buried-interface physics and chemistry.

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“…• ) [41], and the hard x-ray data was obtained at the P09 Beamline of Petra III (∼5000 eV, resolution of 0.30 eV and θ xe = 88…”

Section: Experimental Methodsmentioning

confidence: 99%

Energetic, spatial, and momentum character of the electronic structure at a buried interface: The two-dimensional electron gas between two metal oxides

Nemšák¹,

Conti²,

Gray³

et al. 2016

Phys. Rev. B

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“…To verify the calculated bulk states experimentally, we performed soft x-ray ARPES (SX-ARPES) measurements of NbP in order to achieve higher bulk sensitivity [49,55]. The bulk origin of the probed electronic states is confirmed by the three-dimensional Fermi surface (FS) seen in the out-of-plane FS map (Fig.…”

Section: Pagementioning

confidence: 99%

“…Bulk-sensitive soft X-ray ARPES measurements were performed at the Advanced Resonant Spectroscopies (ADRESS) beamline at SLS [49] using a SPECS analyser, and data were collected using circular-polarized light with an overall energy resolution in the range of 50-80 meV at T = 10 K. The electronic structure of NbP was computed within the density functional theory (DFT) framework using the generalized gradient approximation (GGA) as implemented in the QUANTUM-ESPRESSO software package [50]. Spin-orbit coupling (SOC) is taken into account with the help of relativistic pseudopotentials [51].…”

Section: Pagementioning

confidence: 99%

Distinct Evolutions of Weyl Fermion Quasiparticles and Fermi Arcs with Bulk Band Topology in Weyl Semimetals

Autès

Matt

et al. 2017

Phys. Rev. Lett.

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Although any evidence of chiral Weyl fermions as fundamental particles in vacuum is still lacking, recent advances in topological condensed matter physics [1,2] provide a new way of realizing them in Weyl semimetals (WSMs). In an ideal WSM, bands without spin degeneracy cross at pairs of points at the Fermi level, the Weyl nodes, and the corresponding low-energy excitations fulfill the Weyl equation [3,4].As a consequence, the quasiparticles in a WSM show the same exotic behaviors as Weyl fermions, such as the chiral anomaly effect [5][6][7] that can induce a negative longitudinal magneto-resistance (MR). Another hallmark of a WSM is the existence of anomalous surface states protected by the bulk band topology, the so-called Fermi arcs [8,9]. The WSM state has been proposed in magnetic systems [8,[10][11][12][13][14][15][16][17][18][19], Dirac semimetals [20][21][22][23][24][25][26][27] under magnetic field [28], as well as photonic crystals [29,30].Recently, non-magnetic transition-metal monopnictides with broken inversion symmetry (the crystal structure and the first Brillouin zone (BZ) of these materials are shown in Fig. 1a-c [35,41] surfaces, the magnetotransport behaviors related to the chiral anomaly effect are distinct among the different compounds. The negative longitudinal MR, which has a maximum value of -30% at ~6 T in TaAs [42] and as large as -3000% at 9T in TaP without any sign of saturation [43,44], has never been observed in NbP [45,46]. The apparent disagreement between the transport and spectroscopic signatures of WSM raises the questions of whether the observation of topological Fermi arcs is sufficient to identify a WSM phase [38,47], and whether the negative longitudinal MR in transition-metal monopnictides is not induced by the chiral anomaly but rather by the axial anomaly effect, which is not related to the Weyl fermion quasiparticles [48].Here, we present a comparative study of transition-metal monopnictides by Polycrystalline NbP (TaP) was synthesized by a solid-state reaction using elemental niobium (tantalum) and red phosphorus with a minimum purity of 99.99 %. The respective amounts of starting reagents were mixed and pressed into pellets in a Heglove box and annealed in an evacuated quartz ampule at 1050 °C for 60 hours.Laboratory x-ray diffraction measurements, which were done at room temperature using Cu Ka radiation on a Brucker D8 diffractometer, have shown that the obtained crystals are single phase with the tetragonal structure of space group I41/amd (N 141).Clean surfaces for ARPES measurements were obtained by cleaving NbP and TaP samples in a vacuum better than 5 × 10 -11 Torr. Surface-sensitive VUV-ARPES measurements were performed with circular-polarized light at the Surface/Interface Spectroscopy (SIS) beamline at the Swiss Light Source (SLS) with a Scienta R4000.Bulk-sensitive soft X-ray ARPES measurements were performed at the Advanced Resonant Spectroscopies (ADRESS) beamline at SLS [49] using a SPECS analyser, and data were collected using circular-polarized light w...

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“…The SX ARPES experiments have been carried out at the ADDRESS beamline [21], at the Swiss Light Source, Paul Scherrer Institute, Switzerland. The photon energy dependence has been investigated for both LH and vertical (LV) polarizations in the energy range 310-510 eV, with energy and angular resolution varying between 60 -70 meV and 0.07…”

mentioning

confidence: 99%

Evidence for a Strong Topological Insulator Phase in ZrTe5

et al. 2016

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The complex electronic properties of ZrTe5 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 ZrTe5, 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 ZrTe5.The discovery of topological insulators (TIs), characterized by metallic spin-polarized surface states connecting the bulk valence and conduction bands [1], has stimulated the search for novel topological phases of matter [2][3][4][5][6]. ZrTe 5 has recently emerged as a challenging system with unique, albeit poorly understood, electronic properties [7][8][9][10][11][12][13][14][15][16][17]. Magneto-transport [11], magneto-infrared [13] and optical spectroscopy [14] studies describe ZrTe 5 in terms of a 3D Dirac semimetal. Theoretical calculations have predicted its bulk electronic properties to lie in proximity of a topological phase transition between a strong and a weak TI (STI and WTI, respectively), where only the former displays topologically protected surface states at the experimentally accessible (010) surface [10]. The monolayer is also computed to be a 2D TI [10] and scanning tunneling microscopy/spectroscopy (STM/STS) experiments suggest the existence of topologically protected states at step edges [18,19]. However, the unambiguous identification of the topological phase of ZrTe 5 is still lacking.In this Letter we report on the STI character of the bulk ZrTe 5 by combining ab initio calculations and multiple experimental techniques, at temperature both above and below the one of the resistivity peak, T * ∼ 160 K [7][8][9]15]. Angleresolved photoelectron spectroscopy (ARPES) experiments in the ultraviolet (UV) and soft x-ray (SX) energy ranges reveal the presence of two distinct states at the top of the valence band (VB). On the basis of photon energy dependent studies, we ascribe the origin of these two states to the bulk and crystal surface, respectively. We have performed ab initio calculations of the topological phase diagram of ZrTe 5 , as a function of the interlayer distance b/2. Our measured band dispersion is in agreement with the calculations and it is consistent with the STI case for b/2 = 7.23 ± 0.02Å. This value has been confirmed for our specimen by x-ray diffraction (XRD) measurements. Furthermore, the 3D Dirac semimetal phase is not protected by crystalline symmetries, and it manifests only for the specific b/2 = 7.35Å at the boundar...

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Soft-X-ray ARPES facility at the ADRESS beamline of the SLS: concepts, technical realisation and scientific applications

Cited by 157 publications

References 31 publications

Energetic, spatial, and momentum character of the electronic structure at a buried interface: The two-dimensional electron gas between two metal oxides

Energetic, spatial, and momentum character of the electronic structure at a buried interface: The two-dimensional electron gas between two metal oxides

Distinct Evolutions of Weyl Fermion Quasiparticles and Fermi Arcs with Bulk Band Topology in Weyl Semimetals

Evidence for a Strong Topological Insulator Phase in ZrTe5

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