scholarly journals Weyl fermions, Fermi arcs, and minority-spin carriers in ferromagnetic CoS2

2020 ◽  
Vol 6 (51) ◽  
pp. eabd5000
Author(s):  
Niels B. M. Schröter ◽  
Iñigo Robredo ◽  
Sebastian Klemenz ◽  
Robert J. Kirby ◽  
Jonas A. Krieger ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Surface States ◽  
Anomalous Hall Effect ◽  
Half Metallicity ◽  
Spintronic Devices ◽  
Topological Materials ◽  
Fermi Arcs ◽  
Half Metal ◽  
Minority Spin ◽  
Electron Pocket

Magnetic Weyl semimetals are a newly discovered class of topological materials that may serve as a platform for exotic phenomena, such as axion insulators or the quantum anomalous Hall effect. Here, we use angle-resolved photoelectron spectroscopy and ab initio calculations to discover Weyl cones in CoS2, a ferromagnet with pyrite structure that has been long studied as a candidate for half-metallicity, which makes it an attractive material for spintronic devices. We directly observe the topological Fermi arc surface states that link the Weyl nodes, which will influence the performance of CoS2 as a spin injector by modifying its spin polarization at interfaces. In addition, we directly observe a minority-spin bulk electron pocket in the corner of the Brillouin zone, which proves that CoS2 cannot be a true half-metal.

scholarly journals 2D hybrid CrCl2(N2C4H4)2 with tunable ferromagnetic half-metallicity

2021 ◽  
Author(s):  
Wentao Hu ◽  
Ke Yang ◽  
Alessandro Stroppa ◽  
Alessandra Continenza ◽  
Hua Wu
Keyword(s):  
Magnetic Properties ◽  
Electronic Structure ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Two Dimensional ◽  
Half Metallicity ◽  
Spintronic Devices ◽  
Half Metal

Two-dimensional ferromagnetic (2D FM) half-metal holds great potential for quantum magnetoelectronics and spintronic devices. Here, using density functional calculations and magnetic pictures, we study the electronic structure and magnetic properties...

scholarly journals Giant room temperature anomalous Hall effect and tunable topology in a ferromagnetic topological semimetal Co2MnAl

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Peigang Li ◽  
Jahyun Koo ◽  
Wei Ning ◽  
Jinguo Li ◽  
Leixin Miao ◽  
...  
Keyword(s):  
Hall Effect ◽  
Room Temperature ◽  
Transport Phenomena ◽  
Surface States ◽  
Anomalous Hall Effect ◽  
Spintronic Devices ◽  
Structure Topology ◽  
Weyl Semimetal ◽  
Weyl Semimetals ◽  
Record Value

Abstract Weyl semimetals exhibit unusual surface states and anomalous transport phenomena. It is hard to manipulate the band structure topology of specific Weyl materials. Topological transport phenomena usually appear at very low temperatures, which sets challenges for applications. In this work, we demonstrate the band topology modification via a weak magnetic field in a ferromagnetic Weyl semimetal candidate, Co2MnAl, at room temperature. We observe a tunable, giant anomalous Hall effect (AHE) induced by the transition involving Weyl points and nodal rings. The AHE conductivity is as large as that of a 3D quantum AHE, with the Hall angle (ΘH) reaching a record value ($$\tan {\Theta }^{H}=0.21$$ tan Θ H = 0.21 ) at the room temperature among magnetic conductors. Furthermore, we propose a material recipe to generate large AHE by gaping nodal rings without requiring Weyl points. Our work reveals an intrinsically magnetic platform to explore the interplay between magnetic dynamics and topological physics for developing spintronic devices.

Electronic and Vibrational Properties of Single Crystal Surfaces of NiAl

1986 ◽  
Vol 83 ◽  
Author(s):  
S.-C. Lui ◽  
J. M. Mundenar ◽  
E. W. Plummer ◽  
M. E. Mostoller ◽  
R. M. Nicklow ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Nearest Neighbor ◽  
Surface States ◽  
Active Surface ◽  
Atomic Displacement ◽  
Inelastic Electron ◽  
Crystal Surfaces ◽  
Single Crystal Surfaces ◽  
Nial Alloy ◽  
Bulk Surface

ABSTRACTSurface and bulk electronic structure of the ordered NiAl alloy were measured using angle resolved photoelectron spectroscopy. The measured bulk d-bands (Ni like) were observed to be narrower than theoretically calculated d band widths which are 20 to 40% wider (depending upon what is used as a measure of the width). At least two surface states were observed on both the (110) and (111) surfaces. The nature of these surface states and their relationship to the bulk band structure is discussed. Dispersion of bulk phonons was measured by neutron scattering and fitted with a fourth nearest neighbor Born-von Karman model. Dipole active surface phonons on the (110) and (111) surfaces were observed by inelastic electron scattering and the frequencies also calculated assuming a truncated bulk surface. The calculated surface modes present a qualitative picture of the atomic displacement at each surface and also show that the surface phonon energy and intensity depends upon the structure of the surface.

scholarly journals Interface-induced sign reversal of the anomalous Hall effect in magnetic topological insulator heterostructures

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Fei Wang ◽  
Xuepeng Wang ◽  
Yi-Fan Zhao ◽  
Di Xiao ◽  
Ling-Jie Zhou ◽  
...  
Keyword(s):  
Hall Effect ◽  
Electric Fields ◽  
First Principles ◽  
Berry Phase ◽  
Condensed Matter ◽  
Anomalous Hall Effect ◽  
First Principles Calculations ◽  
Sign Reversal ◽  
Berry Curvature ◽  
Topological Materials

AbstractThe Berry phase picture provides important insights into the electronic properties of condensed matter systems. The intrinsic anomalous Hall (AH) effect can be understood as the consequence of non-zero Berry curvature in momentum space. Here, we fabricate TI/magnetic TI heterostructures and find that the sign of the AH effect in the magnetic TI layer can be changed from being positive to negative with increasing the thickness of the top TI layer. Our first-principles calculations show that the built-in electric fields at the TI/magnetic TI interface influence the band structure of the magnetic TI layer, and thus lead to a reconstruction of the Berry curvature in the heterostructure samples. Based on the interface-induced AH effect with a negative sign in TI/V-doped TI bilayer structures, we create an artificial “topological Hall effect”-like feature in the Hall trace of the V-doped TI/TI/Cr-doped TI sandwich heterostructures. Our study provides a new route to create the Berry curvature change in magnetic topological materials that may lead to potential technological applications.

Multiple Weyl fermions and tunable quantum anomalous Hall effect in 2D half-metal with huge spin-related energy gap

2021 ◽  
Vol 551 ◽  
pp. 149390
Author(s):  
Weizhen Meng ◽  
Xiaoming Zhang ◽  
Weiwang Yu ◽  
Ying Liu ◽  
Lu Tian ◽  
...  
Keyword(s):  
Hall Effect ◽  
Energy Gap ◽  
Anomalous Hall Effect ◽  
Half Metal ◽  
Related Energy ◽  
Quantum Anomalous Hall Effect ◽  
Weyl Fermions

scholarly journals Discovery of a weak topological insulating state and van Hove singularity in triclinic RhBi2

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Kyungchan Lee ◽  
Gunnar F. Lange ◽  
Lin-Lin Wang ◽  
Brinda Kuthanazhi ◽  
Thaís V. Trevisan ◽  
...  
Keyword(s):  
Time Reversal ◽  
Topological Insulators ◽  
Dirac Point ◽  
Saddle Points ◽  
Surface States ◽  
Van Hove Singularity ◽  
Space Group ◽  
Topological Materials ◽  
Topological Surface ◽  
Optimal Space

AbstractTime reversal symmetric (TRS) invariant topological insulators (TIs) fullfil a paradigmatic role in the field of topological materials, standing at the origin of its development. Apart from TRS protected strong TIs, it was realized early on that more confounding weak topological insulators (WTI) exist. WTIs depend on translational symmetry and exhibit topological surface states only in certain directions making it significantly more difficult to match the experimental success of strong TIs. We here report on the discovery of a WTI state in RhBi2 that belongs to the optimal space group P$$\bar{1}$$ 1 ¯ , which is the only space group where symmetry indicated eigenvalues enumerate all possible invariants due to absence of additional constraining crystalline symmetries. Our ARPES, DFT calculations, and effective model reveal topological surface states with saddle points that are located in the vicinity of a Dirac point resulting in a van Hove singularity (VHS) along the (100) direction close to the Fermi energy (EF). Due to the combination of exotic features, this material offers great potential as a material platform for novel quantum effects.

Nonvolatile electrical control of 2D Cr2Ge2Te6 and intrinsic half metallicity in multiferroic hetero-structures

Nanoscale ◽  
2021 ◽  
Author(s):  
Asif Ilyas ◽  
Shuling Xiang ◽  
Miaogen Chen ◽  
Muhammad Yar Khan ◽  
Hua Bai ◽  
...  
Keyword(s):  
Van Der Waals ◽  
Two Dimensional ◽  
Half Metallicity ◽  
Spintronic Devices ◽  
Electrical Control

The electrical control of two-dimensional (2D) van der Waals ferromagnets is a step forward for the realization of spintronic devices.

Ferromagnetic Dirac Half-Metallicity in Transition Metal Embedded Honeycomb Borophene

2021 ◽  
Author(s):  
Yanxia Wang ◽  
Xue Jiang ◽  
Yi Wang ◽  
Jijun Zhao
Keyword(s):  
Transition Metal ◽  
First Principles ◽  
Valence Electron ◽  
Two Dimensional ◽  
First Principles Calculations ◽  
Next Generation ◽  
Half Metallicity ◽  
Counting Rule ◽  
Spintronic Devices ◽  
Electron Counting

Exploring two-dimensional (2D) ferromagnetic materials with intrinsic Dirac half-metallicity is crucial for the development of next-generation spintronic devices. Based on first-principles calculations, here we propose a simple valence electron-counting rule...

scholarly journals A van der Waals antiferromagnetic topological insulator with weak interlayer magnetic coupling

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Chaowei Hu ◽  
Kyle N. Gordon ◽  
Pengfei Liu ◽  
Jinyu Liu ◽  
Xiaoqing Zhou ◽  
...  
Keyword(s):  
Van Der Waals ◽  
Surface States ◽  
Magnetic Coupling ◽  
Anomalous Hall Effect ◽  
Saturation Field ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Ideal System ◽  
Out Of Plane ◽  
Weak Interlayer ◽  
Quantum Phenomena

AbstractMagnetic topological insulators (TI) provide an important material platform to explore quantum phenomena such as quantized anomalous Hall effect and Majorana modes, etc. Their successful material realization is thus essential for our fundamental understanding and potential technical revolutions. By realizing a bulk van der Waals material MnBi4Te7 with alternating septuple [MnBi2Te4] and quintuple [Bi2Te3] layers, we show that it is ferromagnetic in plane but antiferromagnetic along the c axis with an out-of-plane saturation field of ~0.22 T at 2 K. Our angle-resolved photoemission spectroscopy measurements and first-principles calculations further demonstrate that MnBi4Te7 is a Z2 antiferromagnetic TI with two types of surface states associated with the [MnBi2Te4] or [Bi2Te3] termination, respectively. Additionally, its superlattice nature may make various heterostructures of [MnBi2Te4] and [Bi2Te3] layers possible by exfoliation. Therefore, the low saturation field and the superlattice nature of MnBi4Te7 make it an ideal system to investigate rich emergent phenomena.

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