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T Shiroka, T Shang, C Wang, G-H Cao, I Eremin, H-R Ott, J Mesot
Unlike the widely studied ReFeAsO series, the newly discovered iron-based superconductor ThFeAsN exhibits a remarkably high critical temperature of 30 K, without chemical doping or external pressure. Here we investigate in detail its magnetic and superconducting properties via muon-spin rotation/relaxation and nuclear magnetic resonance techniques and show that ThFeAsN exhibits strong magnetic fluctuations, suppressed below ~35 K, but no magnetic order. This contrasts strongly with the ReFeAsO series, where stoichiometric parent materials order antiferromagnetically and superconductivity appears only upon doping...
July 31, 2017: Nature Communications
Monique Mesot Liljehult, Lise Buus, Jacob Liljehult, Birthe Krogh Rasmussen
Primary brain tumors frequently cause considerable functional impairments and the survival time when diagnosed with glioblastoma is 14.6 months. The aim of this study was to examine if baseline postural control and walking ability in patients with glioblastoma could predict long term walking ability and 1 year mortality. Data were gathered from prospective recordings in a brain cancer database supplemented by retrospective review of electronic patient records. We included 109 patients with glioblastoma, 47 women and 62 men with mean age 65 years...
November 2017: Journal of Neuro-oncology
N Xu, G Autès, C E Matt, B Q Lv, M Y Yao, F Bisti, V N Strocov, D Gawryluk, E Pomjakushina, K Conder, N C Plumb, M Radovic, T Qian, O V Yazyev, J Mesot, H Ding, M Shi
The Weyl semimetal phase is a recently discovered topological quantum state of matter characterized by the presence of topologically protected degeneracies near the Fermi level. These degeneracies are the source of exotic phenomena, including the realization of chiral Weyl fermions as quasiparticles in the bulk and the formation of Fermi arc states on the surfaces. Here, we demonstrate that these two key signatures show distinct evolutions with the bulk band topology by performing angle-resolved photoemission spectroscopy, supported by first-principles calculations, on transition-metal monophosphides...
March 10, 2017: Physical Review Letters
Z Wang, Z Zhong, S McKeown Walker, Z Ristic, J-Z Ma, F Y Bruno, S Riccò, G Sangiovanni, G Eres, N C Plumb, L Patthey, M Shi, J Mesot, F Baumberger, M Radovic
Engineering the electronic band structure of two-dimensional electron liquids (2DELs) confined at the surface or interface of transition metal oxides is key to unlocking their full potential. Here we describe a new approach to tailoring the electronic structure of an oxide surface 2DEL demonstrating the lateral modulation of electronic states with atomic scale precision on an unprecedented length scale comparable to the Fermi wavelength. To this end, we use pulsed laser deposition to grow anatase TiO2 films terminated by a (1 × 4) in-plane surface reconstruction...
March 16, 2017: Nano Letters
E Razzoli, T Jaouen, M-L Mottas, B Hildebrand, G Monney, A Pisoni, S Muff, M Fanciulli, N C Plumb, V A Rogalev, V N Strocov, J Mesot, M Shi, J H Dil, H Beck, P Aebi
Spin- and angle-resolved photoemission spectroscopy is used to reveal that a large spin polarization is observable in the bulk centrosymmetric transition metal dichalcogenide MoS_{2}. 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...
February 24, 2017: Physical Review Letters
C E Matt, N Xu, Baiqing Lv, Junzhang Ma, F Bisti, J Park, T Shang, Chongde Cao, Yu Song, Andriy H Nevidomskyy, Pengcheng Dai, L Patthey, N C Plumb, M Radovic, J Mesot, M Shi
In the studies of iron pnictides, a key question is whether their bad-metal state from which the superconductivity emerges lies in close proximity with a magnetically ordered insulating phase. Recently, it was found that at low temperatures, the heavily Cu-doped NaFe_{1-x}Cu_{x}As (x>0.3) iron pnictide is an insulator with long-range antiferromagnetic order, similar to the parent compound of cuprates but distinct from all other iron pnictides. Using angle-resolved photoemission spectroscopy, we determined the momentum-resolved electronic structure of NaFe_{1-x}Cu_{x}As (x=0...
August 26, 2016: Physical Review Letters
N C Plumb, D J Gawryluk, Y Wang, Z Ristić, J Park, B Q Lv, Z Wang, C E Matt, N Xu, T Shang, K Conder, J Mesot, S Johnston, M Shi, M Radović
We investigate the band structure of BaBiO_{3}, an insulating parent compound of doped high-T_{c} superconductors, using in situ angle-resolved photoemission spectroscopy on thin films. The data compare favorably overall with density functional theory calculations within the local density approximation, demonstrating that electron correlations are weak. The bands exhibit Brillouin zone folding consistent with known BiO_{6} breathing distortions. Though the distortions are often thought to coincide with Bi^{3+}/Bi^{5+} charge ordering, core level spectra show that bismuth is monovalent...
July 15, 2016: Physical Review Letters
Z Wang, S McKeown Walker, A Tamai, Y Wang, Z Ristic, F Y Bruno, A de la Torre, S Riccò, N C Plumb, M Shi, P Hlawenka, J Sánchez-Barriga, A Varykhalov, T K Kim, M Hoesch, P D C King, W Meevasana, U Diebold, J Mesot, B Moritz, T P Devereaux, M Radovic, F Baumberger
Surfaces and interfaces offer new possibilities for tailoring the many-body interactions that dominate the electrical and thermal properties of transition metal oxides. Here, we use the prototypical two-dimensional electron liquid (2DEL) at the SrTiO3(001) surface to reveal a remarkably complex evolution of electron-phonon coupling with the tunable carrier density of this system. At low density, where superconductivity is found in the analogous 2DEL at the LaAlO3/SrTiO3 interface, our angle-resolved photoemission data show replica bands separated by 100 meV from the main bands...
August 2016: Nature Materials
N Xu, H M Weng, B Q Lv, C E Matt, J Park, F Bisti, V N Strocov, D Gawryluk, E Pomjakushina, K Conder, N C Plumb, M Radovic, G Autès, O V Yazyev, Z Fang, X Dai, T Qian, J Mesot, H Ding, M Shi
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...
2016: Nature Communications
B Q Lv, S Muff, T Qian, Z D Song, S M Nie, N Xu, P Richard, C E Matt, N C Plumb, L X Zhao, G F Chen, Z Fang, X Dai, J H Dil, J Mesot, M Shi, H M Weng, H Ding
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...
November 20, 2015: Physical Review Letters
M Pikulski, T Shiroka, H-R Ott, J Mesot
We report on the design and implementation of a new digital, broad-band nuclear magnetic resonance (NMR) spectrometer suitable for probing condensed matter. The spectrometer uses direct sampling in both transmission and reception. It relies on a single, commercially-available signal processing device with a user-accessible field-programmable gate array (FPGA). Its functions are defined exclusively by the FPGA firmware and the application software. Besides allowing for fast replication, flexibility, and extensibility, our software-based solution preserves the option to reuse the components for other projects...
September 2014: Review of Scientific Instruments
N C Plumb, M Salluzzo, E Razzoli, M Månsson, M Falub, J Krempasky, C E Matt, J Chang, M Schulte, J Braun, H Ebert, J Minár, B Delley, K-J Zhou, T Schmitt, M Shi, J Mesot, L Patthey, M Radović
Using angle-resolved photoemission spectroscopy, we show that the recently discovered surface state on SrTiO(3) consists of nondegenerate t(2g) states with different dimensional characters. While the d(xy) bands have quasi-2D dispersions with weak k(z) dependence, the lifted d(xz)/d(yz) bands show 3D dispersions that differ significantly from bulk expectations and signal that electrons associated with those orbitals permeate the near-surface region. Like their more 2D counterparts, the size and character of the d(xz)/d(yz) Fermi surface components are essentially the same for different sample preparations...
August 22, 2014: Physical Review Letters
E Razzoli, G Drachuck, A Keren, M Radovic, N C Plumb, J Chang, Y-B Huang, H Ding, J Mesot, M Shi
Using angle-resolved photoemission spectroscopy (ARPES), it is revealed that the low-energy electronic excitation spectra of highly underdoped superconducting and nonsuperconducting La(2-x)Sr(x)CuO(4) cuprates are gapped along the entire underlying Fermi surface at low temperatures. We show how the gap function evolves to a d(x(2)-y(2)) form with increasing temperature or doping, consistent with the vast majority of ARPES studies of cuprates. Our results provide essential information for uncovering the symmetry of the order parameter(s) in strongly underdoped cuprates, which is a prerequisite for understanding the pairing mechanism and how superconductivity emerges from a Mott insulator...
January 25, 2013: Physical Review Letters
M E Zayed, Ch Rüegg, Th Strässle, U Stuhr, B Roessli, M Ay, J Mesot, P Link, E Pomjakushina, M Stingaciu, K Conder, H M Rønnow
The temperature dependence of the gapped triplet excitations (triplons) in the 2D Shastry-Sutherland quantum magnet SrCu(2)(BO(3))(2) is studied by means of inelastic neutron scattering. The excitation amplitude rapidly decreases as a function of temperature, while the integrated spectral weight can be explained by an isolated dimer model up to 10 K. Analyzing this anomalous spectral line shape in terms of damped harmonic oscillators shows that the observed damping is due to a two-component process: one component remains sharp and resolution limited while the second broadens...
August 8, 2014: Physical Review Letters
N Xu, P K Biswas, J H Dil, R S Dhaka, G Landolt, S Muff, C E Matt, X Shi, N C Plumb, M Radović, E Pomjakushina, K Conder, A Amato, S V Borisenko, R Yu, H-M Weng, Z Fang, X Dai, J Mesot, H Ding, M Shi
Topological Kondo insulators have been proposed as a new class of topological insulators in which non-trivial surface states reside in the bulk Kondo band gap at low temperature due to strong spin-orbit coupling. In contrast to other three-dimensional topological insulators, a topological Kondo insulator is truly bulk insulating. Furthermore, strong electron correlations are present in the system, which may interact with the novel topological phase. By applying spin- and angle-resolved photoemission spectroscopy, here we show that the surface states of SmB6 are spin polarized...
2014: Nature Communications
J Chang, M Månsson, S Pailhès, T Claesson, O J Lipscombe, S M Hayden, L Patthey, O Tjernberg, J Mesot
High-temperature superconductivity emerges from an un-conventional metallic state. This has stimulated strong efforts to understand exactly how Fermi liquids breakdown and evolve into an un-conventional metal. A fundamental question is how Fermi liquid quasiparticle excitations break down in momentum space. Here we show, using angle-resolved photoemission spectroscopy, that the Fermi liquid quasiparticle excitations of the overdoped superconducting cuprate La1.77Sr0.23CuO4 is highly anisotropic in momentum space...
2013: Nature Communications
F Casola, T Shiroka, A Feiguin, S Wang, M S Grbić, M Horvatić, S Krämer, S Mukhopadhyay, K Conder, C Berthier, H-R Ott, H M Rønnow, Ch Rüegg, J Mesot
Based on high-field (31)P nuclear magnetic resonance experiments and accompanying numerical calculations, it is argued that in the frustrated S=1/2 ladder compound BiCu(2)PO(6) a field-induced soliton lattice develops above a critical field of μ(0)H(c1)=20.96(7) T. Solitons result from the fractionalization of the S=1, bosonlike triplet excitations, which in other quantum antiferromagnets are commonly known to experience Bose-Einstein condensation or to crystallize in a superstructure. Unlike in spin-Peierls systems, these field-induced quantum domain walls do not arise from a state with broken translational symmetry and are triggered exclusively by magnetic frustration...
May 3, 2013: Physical Review Letters
Marwan Masri, Mehmet Haberal
No abstract text is available yet for this article.
April 2013: Experimental and Clinical Transplantation
T Shiroka, F Casola, J Mesot, W Bachmann, H-R Ott
We report on the construction of a two-axis goniometer intended for low-temperature, single-crystal nuclear magnetic resonance (NMR) measurements. With the use of home-made and commercially available parts, our simple probe-head design achieves good sensitivity, while maintaining a high angular precision and the ability to orient samples also when cooled to liquid helium temperatures. The probe with the goniometer is adapted to be inserted into a commercial (4)He-flow cryostat, which fits into a wide-bore superconducting solenoid magnet...
September 2012: Review of Scientific Instruments
E Razzoli, M Kobayashi, V N Strocov, B Delley, Z Bukowski, J Karpinski, N C Plumb, M Radovic, J Chang, T Schmitt, L Patthey, J Mesot, M Shi
We present a soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) study of the stoichiometric pnictide superconductor LaRu_{2}P_{2}. The observed electronic structure is in good agreement with density functional theory (DFT) calculations. However, it is significantly different from its counterpart in high-temperature superconducting Fe pnictides. In particular, the bandwidth renormalization present in the Fe pnictides (∼2-3) is negligible in LaRu_{2}P_{2} even though the mass enhancement is similar in both systems...
June 22, 2012: Physical Review Letters
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