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Employing X-ray magnetic circular dichroism (XMCD), angle-resolved photoemission spectroscopy (ARPES), and momentum-resolved density fluctuation (MRDF) theory, the magnetic and electronic properties of ultrathin NdNiO3 (NNO) film in proximity to ferromagnetic (FM) La0.67Sr0.33MnO3 (LSMO) layer are investigated. The experimental data shows the direct magnetic coupling between the nickelate film and the manganite layer which causes an unusual ferromagnetic (FM) phase in NNO. Moreover, it is shown the metal–insulator transition in the NNO layer, identified by an abrupt suppression of ARPES spectral weight near the Fermi level (EF), is absent. This observation suggests that the insulating AFM ground state is quenched in proximity to the FM layer. Combining the experimental data (XMCD and AREPS) with the momentum-resolved density fluctuation calculation (MRDF) reveals a direct link between the MIT and the magnetic orders in NNO systems. This work demonstrates that the proximity layer order can be broadly used to modify physical properties and enrich the phase diagram of RENiO3 (RE = rare-earth element).

In many cuprate superconductors rare-earth (R) ions can be placed close to the superconducting copper oxide planes; thus, the crystal-field interaction at the R site constitutes an ideal probe of the local symmetry as well as the local charge distribution and thereby monitors directly changes of the carrier concentration induced by doping. For several compounds the crystal-field spectra observed by inelastic neutron scattering separate into different local components whose spectral weights distinctly depend on the doping level, i.e., there is clear experimental evidence for the formation of clusters which make the systems inhomogeneous. Moreover, it is found that the intrinsic linewidths of crystal-field transitions vary with temperature, which is essentially a reflection of the density of states associated with the charge carriers at the Fermi energy. Linewidth studies can therefore reveal information about the energy gap. For underdoped systems there is evidence for the formation of a pseudogap atT* >T c

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 non-zero Fermi Chern numbers. Combining angle-resolved photoemission spectroscopy and first-principles calculation, here we show that TaP is a Weyl semimetal with only a 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.

In 1929, H. Weyl proposed that the massless solution of the Dirac equation represents a pair of a new type of particles, the so-called Weyl fermions. However, their existence in particle physics remains elusive after more than eight decades. Recently, significant advances in both topological insulators and topological semimetals have provided an alternative way to realize Weyl fermions in condensed matter, as an emergent phenomenon: when two non-degenerate bands in the three-dimensional momentum space cross in the vicinity of the Fermi energy (called Weyl nodes), the low-energy excitations behave exactly as Weyl fermions. Here we report the direct observation in TaAs of the long-sought-after Weyl nodes by performing bulk-sensitive soft X-ray angle-resolved photoemission spectroscopy measurements. The projected locations at the nodes on the (001) surface match well to the Fermi arcs, providing undisputable experimental evidence for the existence of Weyl fermionic quasiparticles in TaAs. © 2015 Macmillan Publishers Limited. All rights reserved.

We have investigated the spin texture of surface Fermi arcs in the recently discovered Weyl semimetal TaAs using spin- and angle-resolved photoemission spectroscopy. The experimental results demonstrate that the Fermi arcs are spin polarized. The measured spin texture fulfills the requirement of mirror and time-reversal symmetries and is well reproduced by our first-principles calculations, which gives strong evidence for the topologically nontrivial Weyl semimetal state in TaAs. The consistency between the experimental and calculated results further confirms the distribution of chirality of the Weyl nodes determined by first-principles calculations. © 2015 American Physical Society.

We present angle-resolved photoelectron spectroscopy data probing the electronic structure of the Nd-substituted high-T-c cuprate La1.48Nd0.4Sr0.12CuO4. Data have been acquired at low and high photon energies, h nu=55 and 500 eV, respectively. The two extracted Fermi surfaces show significant differences. The differences can be attributed to either the change in probing depth suggesting dissimilarity of the intrinsic electronic structure between surface and bulk regions, or a considerable c-axis dispersion signaling a strong interlayer coupling. At both photon energies, considerable spectral weight is observed at all points along the Fermi surface and the intensity distribution as well as Fermi-surface shape observed at low as well as high photon energy is markedly different from what has been previously reported for La1.28Nd0.6Sr0.12CuO4 by Zhou [Science 286, 268 (1999)]. Document Type: Article, QC 20100702

We present angle-resolved photoemission spectroscopy data on moderately underdoped La1.855Sr0.145CuO4 at temperatures below and above the superconducting transition temperature. Unlike previous studies of this material, we observe sharp spectral peaks along the entire underlying Fermi surface in the superconducting state. These peaks trace out an energy gap that follows a simple d-wave form, with a maximum superconducting gap of 14 meV. Our results are consistent with a single gap picture for the cuprates. Furthermore our data on the even more underdoped sample La1.895Sr0.105CuO4 also show sharp spectral peaks, even at the antinode, with a maximum superconducting gap of 26 meV., QC 20100810. Uppdaterad från In press till Published, titel ändrad, tidigare titel: "The coherent d-wave superconducting gap in underdoped La(1.855)Sr(0.145)CuO4) as studied by angle-resolved photoemission" 20100810.

An angle-resolved photoemission study of the scattering rate in the superconducting phase of the high-temperature superconductor La2-xSrxCuO4 with x=0.145 and x=0.17, as a function of binding energy and momentum, is presented. We observe that the scattering rate scales linearly with binding energy up to the high-energy scale E-1 similar to 0.4 eV. The scattering rate is found to be strongly anisotropic, with a minimum along the (0,0)-(pi,pi) direction. A possible connection to a quantum-critical point is discussed., QC 20100810. Uppdaterad från In press till Published. Tidigare titel: Anisotropic scattering in slightly underdoped to optimally doped La(2-x)Sr(x)CuO(4). 20100810.

An on-board sample cleaver has been developed in order to cleave small and hard-to-cleave samples. To acquire good cleaves from rigid samples the alignment of the cleaving blade with respect to the internal crystallographic planes is crucial. To have the opportunity to mount the sample and align it to the blade ex situ has many advantages. The design presented has allowed us to cleave very tiny and rigid samples, e.g., the high-temperature superconductor La(2-x)SrxCuO4. Further, in this design the sample and the cleaver will have the same temperature, allowing us to cleave and keep the sample at low temperature. This is a big advantage over prior cleaver systems. As a result, better surfaces and alignments can be realized, which considerably simplifies and improves the experiments., QC 20100810

The existence of coherent quasiparticles near the Fermi energy in the low-temperature state of high-temperature superconductors has been well established by angle-resolved photoemission spectroscopy (ARPES). We present a study of La1.83Sr0.17CuO4 in the superconducting state and report an abrupt change in the quasiparticle spectral function, as we follow the dispersion of the ARPES signal from the Fermi energy to 0.6 eV. The interruption in the quasiparticle dispersion separates coherent quasiparticle peaks at low energies from broad incoherent excitations at high energies. We find that the boundary between these low-energy and high-energy features exhibits a cosine-shaped momentum dependence, reminiscent of the superconducting d-wave gap. Further intriguing similarities between characteristics of the incoherent excitations and quasiparticle properties suggest a close relation between the electronic response at high and low energies in cuprate superconductors., QC 20100810