scholarly journals Momentum-space signatures of Berry flux monopoles in the Weyl semimetal TaAs

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
M. Ünzelmann ◽  
H. Bentmann ◽  
T. Figgemeier ◽  
P. Eck ◽  
J. N. Neu ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Magnetic Monopoles ◽  
Weyl Semimetal ◽  
Flux Quantization ◽  
Spin Polarized ◽  
Spectroscopic Signatures ◽  
Spin Detection ◽  
Crossing Point ◽  
Weyl Fermion ◽  
Geometric Effects

AbstractSince the early days of Dirac flux quantization, magnetic monopoles have been sought after as a potential corollary of quantized electric charge. As opposed to magnetic monopoles embedded into the theory of electromagnetism, Weyl semimetals (WSM) exhibit Berry flux monopoles in reciprocal parameter space. As a function of crystal momentum, such monopoles locate at the crossing point of spin-polarized bands forming the Weyl cone. Here, we report momentum-resolved spectroscopic signatures of Berry flux monopoles in TaAs as a paradigmatic WSM. We carried out angle-resolved photoelectron spectroscopy at bulk-sensitive soft X-ray energies (SX-ARPES) combined with photoelectron spin detection and circular dichroism. The experiments reveal large spin- and orbital-angular-momentum (SAM and OAM) polarizations of the Weyl-fermion states, resulting from the broken crystalline inversion symmetry in TaAs. Supported by first-principles calculations, our measurements image signatures of a topologically non-trivial winding of the OAM at the Weyl nodes and unveil a chirality-dependent SAM of the Weyl bands. Our results provide directly bulk-sensitive spectroscopic support for the non-trivial band topology in the WSM TaAs, promising to have profound implications for the study of quantum-geometric effects in solids.

scholarly journals Magnetic and Electronic Properties of Weyl Semimetal Co2MnGa Thin Films

Nanomaterials ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 251
Author(s):  
Peter Swekis ◽  
Aleksandr S. Sukhanov ◽  
Yi-Cheng Chen ◽  
Andrei Gloskovskii ◽  
Gerhard H. Fecher ◽  
...  
Keyword(s):  
Thin Films ◽  
Magnetic Properties ◽  
Electronic Properties ◽  
Photoelectron Spectroscopy ◽  
Magnetic Moments ◽  
Field Orientation ◽  
Weyl Semimetal ◽  
Uniform Magnetization ◽  
Experimental Findings ◽  
High Degree

Magnetic Weyl semimetals are newly discovered quantum materials with the potential for use in spintronic applications. Of particular interest is the cubic Heusler compound Co2MnGa due to its inherent magnetic and topological properties. This work presents the structural, magnetic and electronic properties of magnetron co-sputtered Co2MnGa thin films, with thicknesses ranging from 10 to 80 nm. Polarized neutron reflectometry confirmed a uniform magnetization through the films. Hard x-ray photoelectron spectroscopy revealed a high degree of spin polarization and localized (itinerant) character of the Mn d (Co d) valence electrons and accompanying magnetic moments. Further, broadband and field orientation-dependent ferromagnetic resonance measurements indicated a relation between the thickness-dependent structural and magnetic properties. The increase of the tensile strain-induced tetragonal distortion in the thinner films was reflected in an increase of the cubic anisotropy term and a decrease of the perpendicular uniaxial term. The lattice distortion led to a reduction of the Gilbert damping parameter and the thickness-dependent film quality affected the inhomogeneous linewidth broadening. These experimental findings will enrich the understanding of the electronic and magnetic properties of magnetic Weyl semimetal thin films.

The Generation of Switchable Polarized Currents in Nodal Ring Semimetals Using High-Frequency Periodic Driving

2021 ◽  
Author(s):  
Pei-Hao Fu ◽  
Qianqian Lv ◽  
Xiang-Long Yu ◽  
Jun-Feng Liu ◽  
Jiansheng Wu
Keyword(s):  
High Frequency ◽  
Surface Currents ◽  
Switching Effect ◽  
Fermi Arc ◽  
Periodically Driven ◽  
Weyl Semimetal ◽  
Spin Polarized ◽  
High Frequency Electromagnetic Field ◽  
Polarized Surface ◽  
Lead Device

Abstract A nodal ring semimetal (NRSM) can be driven to a spin-polarized NRSM or a spin-polarized Weyl semimetal (SWSM) by a high-frequency electromagnetic field. We investigate the conditions in realizing these phases and propose a switchable spin-polarized currents generator based on periodically driven NRSMs. Both bulk and surface polarized currents are investigated. The polarization of bulk current is sensitive to the amplitude of the driving field and robust against the direction and polarization of the driving, the opaqueness of the lead-device interface and the misalignment between the nodal ring and the interface, which provides sufficient flexibility in manipulating the devices. Similar switchable polarized surface currents are also expected, which is contributed by the Fermi arc surface state associated with the Weyl semimetal (WSM) phases. The generation of polarized currents and the polarization switching effect offer opportunities to design periodic driving controlled topological spintronics devices based on NRSMs.

Electronic structure and magnetism of epitaxial Fe monolayers on Au(001) by spin-polarized photoelectron spectroscopy

Vacuum ◽  
1990 ◽  
Vol 41 (1-3) ◽  
pp. 493-495 ◽  
Author(s):  
W Heinen ◽  
C Carbone ◽  
T Kachel ◽  
W Gudat
Keyword(s):  
Electronic Structure ◽  
Photoelectron Spectroscopy ◽  
Spin Polarized

scholarly journals Observation of spin-polarized bands and domain-dependent Fermi arcs in polar Weyl semimetal MoTe2

2017 ◽  
Vol 95 (12) ◽  
Author(s):  
M. Sakano ◽  
M. S. Bahramy ◽  
H. Tsuji ◽  
I. Araya ◽  
K. Ikeura ◽  
...  
Keyword(s):  
Weyl Semimetal ◽  
Fermi Arcs ◽  
Spin Polarized

scholarly journals Spin-polarized Weyl cones and giant anomalous Nernst effect in ferromagnetic Heusler films

2020 ◽  
Vol 1 (1) ◽  
Author(s):  
Kazuki Sumida ◽  
Yuya Sakuraba ◽  
Keisuke Masuda ◽  
Takashi Kono ◽  
Masaaki Kakoki ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Remanent Magnetization ◽  
Room Temperature ◽  
High Efficiency ◽  
Quantum Critical Point ◽  
Surface States ◽  
Flat Band ◽  
Zero Field ◽  
Topological Quantum ◽  
Spin Polarized

AbstractWeyl semimetals are characterized by the presence of massless band dispersion in momentum space. When a Weyl semimetal meets magnetism, large anomalous transport properties emerge as a consequence of its topological nature. Here, using in−situ spin- and angle-resolved photoelectron spectroscopy combined with ab initio calculations, we visualize the spin-polarized Weyl cone and flat-band surface states of ferromagnetic Co2MnGa films with full remanent magnetization. We demonstrate that the anomalous Hall and Nernst conductivities systematically grow when the magnetization-induced massive Weyl cone at a Lifshitz quantum critical point approaches the Fermi energy, until a high anomalous Nernst thermopower of  ~6.2 μVK−1 is realized at room temperature. Given this topological quantum state and full remanent magnetization, Co2MnGa films are promising for realizing high efficiency heat flux and magnetic field sensing devices operable at room temperature and zero-field.

Spin-polarized gap in the magnetic Weyl semimetal Co3Sn2S2

2021 ◽  
Vol 104 (10) ◽  
Author(s):  
Fei Sun ◽  
Tan Zhang ◽  
C. J. Yi ◽  
Y. L. Wu ◽  
H. Zhao ◽  
...  
Keyword(s):  
Weyl Semimetal ◽  
Spin Polarized

High-density magnetic-vacancy inclusion in Co2MnGa single crystal probed by spin-polarized positron annihilation spectroscopy

2021 ◽  
Author(s):  
Atsumi Miyashita ◽  
M. Maekawa ◽  
Y. Shimoyama ◽  
N. Seko ◽  
Atsuo Kawasuso ◽  
...  
Keyword(s):  
Single Crystal ◽  
Positron Annihilation ◽  
Electrical Transport ◽  
Positron Annihilation Spectroscopy ◽  
Ordered Structure ◽  
Electrical Transport Properties ◽  
Weyl Semimetal ◽  
Spin Polarized ◽  
B2 Structure

Abstract Co2MnGa is a Weyl semimetal exhibiting giant anomalous Hall and Nernst effects. Using spin-polarized positron annihilation spectroscopy, we examined a Bridgman-grown Co2MnGa single crystal with a nearly perfect L21-ordered structure and a reference Co2MnAl polycrystal with a Mn-Al-disordered B2 structure. We found that a large amount of magnetic vacancies (more than 100 ppm) were included in the Co2MnGa crystal but not the Co2MnAl crystal. We discuss possible reasons for the inclusion of vacancies, the role of vacancies in the development of the ordered structure, and the electronic states associated with the vacancies. Towards the development of Co2MnGa-based devices, the manners for reducing vacancies as well as the influence of vacancies on the electrical transport properties should be considered.

Spin‐polarized electronic structure of cobalt cluster anions studied by photoelectron spectroscopy

1995 ◽  
Vol 102 (15) ◽  
pp. 5960-5965 ◽  
Author(s):  
Hiroyuki Yoshida ◽  
Akira Terasaki ◽  
Katsuyoshi Kobayashi ◽  
Masaru Tsukada ◽  
Tamotsu Kondow
Keyword(s):  
Electronic Structure ◽  
Photoelectron Spectroscopy ◽  
Cluster Anions ◽  
Cobalt Cluster ◽  
Spin Polarized
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