scholarly journals New type of Weyl semimetal with quadratic double Weyl fermions

2016 ◽  
Vol 113 (5) ◽  
pp. 1180-1185 ◽  
Author(s):  
Shin-Ming Huang ◽  
Su-Yang Xu ◽  
Ilya Belopolski ◽  
Chi-Cheng Lee ◽  
Guoqing Chang ◽  
...  
Keyword(s):  
Experimental Studies ◽  
Orbit Coupling ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Experimental Realization ◽  
Weyl Semimetal ◽  
Chiral Magnetic Effect ◽  
Wide Range ◽  
Weyl Semimetals ◽  
Weyl Fermions

Weyl semimetals have attracted worldwide attention due to their wide range of exotic properties predicted in theories. The experimental realization had remained elusive for a long time despite much effort. Very recently, the first Weyl semimetal has been discovered in an inversion-breaking, stoichiometric solid TaAs. So far, the TaAs class remains the only Weyl semimetal available in real materials. To facilitate the transition of Weyl semimetals from the realm of purely theoretical interest to the realm of experimental studies and device applications, it is of crucial importance to identify other robust candidates that are experimentally feasible to be realized. In this paper, we propose such a Weyl semimetal candidate in an inversion-breaking, stoichiometric compound strontium silicide, SrSi2, with many new and novel properties that are distinct from TaAs. We show that SrSi2 is a Weyl semimetal even without spin–orbit coupling and that, after the inclusion of spin–orbit coupling, two Weyl fermions stick together forming an exotic double Weyl fermion with quadratic dispersions and a higher chiral charge of ±2. Moreover, we find that the Weyl nodes with opposite charges are located at different energies due to the absence of mirror symmetry in SrSi2, paving the way for the realization of the chiral magnetic effect. Our systematic results not only identify a much-needed robust Weyl semimetal candidate but also open the door to new topological Weyl physics that is not possible in TaAs.

scholarly journals Realization of an ideal Weyl semimetal band in a quantum gas with 3D spin-orbit coupling

Science ◽  
2021 ◽  
Vol 372 (6539) ◽  
pp. 271-276 ◽  
Author(s):  
Zong-Yao Wang ◽  
Xiang-Can Cheng ◽  
Bao-Zong Wang ◽  
Jin-Yi Zhang ◽  
Yue-Hui Lu ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Orbit Coupling ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Quantum Gas ◽  
Experimental Realization ◽  
Weyl Semimetal ◽  
Minimum Number ◽  
Quench Dynamics ◽  
Bulk Band

Weyl semimetals are three-dimensional (3D) gapless topological phases with Weyl cones in the bulk band. According to lattice theory, Weyl cones must come in pairs, with the minimum number of cones being two. A semimetal with only two Weyl cones is an ideal Weyl semimetal (IWSM). Here we report the experimental realization of an IWSM band by engineering 3D spin-orbit coupling for ultracold atoms. The topological Weyl points are clearly measured via the virtual slicing imaging technique in equilibrium and are further resolved in the quench dynamics. The realization of an IWSM band opens an avenue to investigate various exotic phenomena that are difficult to access in solids.

scholarly journals MAGNETO-GYROTROPIC PHOTOGALVANIC EFFECTS IN SEMICONDUCTOR QUANTUM WELLS

2008 ◽  
Vol 22 (01n02) ◽  
pp. 115-116 ◽  
Author(s):  
S. D. GANICHEV
Keyword(s):  
Hall Effect ◽  
Electric Current ◽  
Electron Gas ◽  
Spin Hall Effect ◽  
Orbit Coupling ◽  
Relaxation Processes ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Wide Range ◽  
Spin Dependent Scattering

The spin-orbit coupling provides a versatile tool to generate and to manipulate the spin degree of freedom in low-dimensional semiconductor structures. The spin Hall effect, where an electric current drives a transverse spin current and causes a nonequilibrium spin accumulation near the sample boundary,1,2 the spin-galvanic effect, where a nonequilibrium spin polarization drives an electric current3,4 or the reverse process, in which an electrical current generates a non-equilibrium spin-polarization,5–9 are all consequences of spin-orbit coupling. In order to observe a spin Hall effect a bias driven current is an essential prerequisite. Then spin separation is caused via spin-orbit coupling either by Mott scattering (extrinsic spin Hall effect) or by spin splitting of the band structure (intrinsic spin Hall effect). Recently an elementary effect causing spin separation which is fundamentally different from that of the spin Hall effect has been observed.10 In contrast to the spin Hall effect it does not require an electric current to flow: it is spin separation achieved by spin-dependent scattering of electrons in media with suitable symmetry. It is show that by free carrier (Drude) absorption of terahertz radiation spin separation is achieved in a wide range of temperatures from liquid helium temperature up to room temperature. Moreover the experimental results demonstrate that simple electron gas heating by any means is already sufficient to yield spin separation due to spin-dependent energy relaxation processes of non-equilibrium carriers. In order to demonstrate the existence of the spin separation due to asymmetric scattering the pure spin current was converted into an electric current. It is achieved by application of a magnetic field which polarizes spins. This is analogues to spin-dependent scattering in transport experiments: spin-dependent scattering in an unpolarized electron gas causes the extrinsic spin Hall effect, whereas in a spin-polarized electron gas a charge current, the anomalous Hall effect, can be observed. As both magnetic fields and gyrotropic mechanisms were used authors introduced the notation "magneto-gyrotropic photogalvanic effects" for this class of phenomena. The effect is observed in GaAs and InAs low dimensional structures at free-carrier absorption of terahertz radiation in a wide range of temperatures from liquid helium temperature up to room temperature. The results are well described by the phenomenological description based on the symmetry. Experimental and theoretical analysis evidences unumbiguously that the observed photocurrents are spin-dependent. Microscopic theory of this effect based on asymmetry of photoexcitation and relaxation processes are developed being in a good agreement with experimental data. Note from Publisher: This article contains the abstract only.

scholarly journals Strong spin depolarization in the ferromagnetic Weyl semimetal Co3Sn2S2 : Role of spin-orbit coupling

2020 ◽  
Vol 102 (10) ◽  
Author(s):  
Sandeep Howlader ◽  
Surabhi Saha ◽  
Ritesh Kumar ◽  
Vipin Nagpal ◽  
Satyabrata Patnaik ◽  
...  
Keyword(s):  
Orbit Coupling ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Weyl Semimetal ◽  
Spin Depolarization ◽  
Strong Spin

scholarly journals Experimental realization of two-dimensional synthetic spin–orbit coupling in ultracold Fermi gases

2016 ◽  
Vol 12 (6) ◽  
pp. 540-544 ◽  
Author(s):  
Lianghui Huang ◽  
Zengming Meng ◽  
Pengjun Wang ◽  
Peng Peng ◽  
Shao-Liang Zhang ◽  
...  
Keyword(s):  
Orbit Coupling ◽  
Fermi Gases ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Two Dimensional ◽  
Experimental Realization ◽  
Ultracold Fermi Gases

scholarly journals Spin-orbit coupling effect on electronic, linear and nonlinear optical properties of Bi2S3 and the Ternary Bismuth Sulfide Bi2S2.75Se0.25: Ab-initio calculations

2021 ◽  
Author(s):  
Houda Ben Abdallah ◽  
Walid Ouerghui
Keyword(s):  
Optical Properties ◽  
Nonlinear Optical ◽  
Experimental Studies ◽  
Orbit Coupling ◽  
Optical Absorption Coefficient ◽  
Optical Parameters ◽  
High Electron ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Bismuth Sulfide

Abstract Although the relevant properties of the bismuthinite \({Bi}_{2}{S}_{3}\), it was recently approved that the substitution of Se atoms in the \({Bi}_{2}{S}_{3}\) lattice can significantly enhance its electro-optical properties. In the present work, a detailed study on the structural, electronic and optical properties of \({Bi}_{2}{S}_{2.75}{Se}_{0.25}\) has been carried out based on first principle calculations. The simultaneous effect of Se-doping and spin-orbit coupling (SOC) on bismuth sulfide \({Bi}_{2}{S}_{3}\) was investigated. Our calculations show that \({Bi}_{2}{S}_{2.75}{Se}_{0.25}\) exhibits a narrow direct band gap of 1.062 eV after inclusion of the (SOC). The calculation of the carrier effective masses indicates that \({Bi}_{2}{S}_{2.75}{Se}_{0.25}\) may possess a high electron mobility material which is in accordance with experimental studies. The linear absorption optical spectra for both \({Bi}_{2}{S}_{3}\) and \({Bi}_{2}{S}_{2.75}{Se}_{0.25}\)show that doping bismuthinite with (Se) increases the optical absorption coefficient in the visible range and takes a value up to \(10 {10}^{5}{cm}^{-1}\). In addition, the dielectric function, optical conductivity and the energy loss function of \({Bi}_{2}{S}_{3}\) and \({Bi}_{2}{S}_{2.75}{Se}_{0.25}\)were also derived. The addition of the (Se) content induces a red shift in agreement with experimental studies. A noticeable effect of the (SOC) on the linear optical parameters was observed. The stability of the excitons was also studied by the estimation of the binding energy value. The dispersion energy parameters of \({Bi}_{2}{S}_{3}\) and \({Bi}_{2}{S}_{2.75}{Se}_{0.25}\)were estimated using a single oscillator model. Some nonlinearities have been computed with and without inclusion of (SOC) showing that \({Bi}_{2}{S}_{2.75}{Se}_{0.25}\)with large nonlinear optical parameters is promising candidate in photonic switching applications.

scholarly journals Experimental evidence for Zeeman spin–orbit coupling in layered antiferromagnetic conductors

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
R. Ramazashvili ◽  
P. D. Grigoriev ◽  
T. Helm ◽  
F. Kollmannsberger ◽  
M. Kunz ◽  
...  
Keyword(s):  
Industrial Applications ◽  
Orbit Coupling ◽  
Organic Superconductor ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Experimental Proof ◽  
Spin Modulation ◽  
Wide Range ◽  
Spin Degeneracy ◽  
State Spin

AbstractMost of solid-state spin physics arising from spin–orbit coupling, from fundamental phenomena to industrial applications, relies on symmetry-protected degeneracies. So does the Zeeman spin–orbit coupling, expected to manifest itself in a wide range of antiferromagnetic conductors. Yet, experimental proof of this phenomenon has been lacking. Here we demonstrate that the Néel state of the layered organic superconductor κ-(BETS)2FeBr4 shows no spin modulation of the Shubnikov–de Haas oscillations, contrary to its paramagnetic state. This is unambiguous evidence for the spin degeneracy of Landau levels, a direct manifestation of the Zeeman spin–orbit coupling. Likewise, we show that spin modulation is absent in electron-doped Nd1.85Ce0.15CuO4, which evidences the presence of Néel order in this cuprate superconductor even at optimal doping. Obtained on two very different materials, our results demonstrate the generic character of the Zeeman spin–orbit coupling.

Spin-Orbit Coupling Induced Chemical Reactivity and Spin-Catalysis Phenomena

1995 ◽  
Vol 60 (3) ◽  
pp. 339-371 ◽  
Author(s):  
Boris F. Minaev ◽  
Hans Ågren
Keyword(s):  
Chemical Reactivity ◽  
Open Shell ◽  
Orbit Coupling ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Activation Barriers ◽  
Metal Compounds ◽  
Wide Range ◽  
Magnetic Perturbations

The crucial role of electron spin in the control of the reaction channels in the region of activated complexes can easily be inferred from the general principles of chemical bonding. Magnetic perturbations could change spin at the intermediate stages of a reaction or in the region of activation barriers and could hence influence the reaction rate through spin switching of the reaction paths. Spin-orbit coupling is one of the most important intrinsic magnetic perturbations in molecules; its role in chemical reactivity is here shown by a few typical examples. Spin-orbit coupling induced spin flip could also be important in catalysis by transition metals. General qualitative arguments predict great enhancements of the spin-orbit coupling in catalytic complexes with transition metal compounds. The concept of spin-catalysis is introduced in order to describe and classify a wide range of phenomena in which chemical reactions are promoted by substances assisting in inducing spin changes and overcoming spin-prohibition. This concept is based on results of quantum chemical calculations with account of spin-orbit coupling and configuration interaction in the intermediate complexes. Besides spin-orbit coupling, the role of intermolecular exchange interaction with open shell catalysts is stressed. The catalytic action would definitely depend on the efficiency of spin uncoupling inside the reacting substrate molecule and this could be induced by magnetic and exchange perturbations.

scholarly journals Field-like spin–orbit torque induced by bulk Rashba channels in GeTe/NiFe bilayers

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Jeehoon Jeon ◽  
Seong Won Cho ◽  
OukJae Lee ◽  
Jinki Hong ◽  
Joon Young Kwak ◽  
...  
Keyword(s):  
Theoretical Study ◽  
Orbit Coupling ◽  
Large Field ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Rashba Effect ◽  
Rashba Spin ◽  
Wide Range ◽  
Nife Layer ◽  
20 Nm

AbstractMost studies of the Rashba effect have focused on interfacial Rashba spin–orbit coupling. Recently, bulk Rashba materials have attracted considerable interest owing to their potential to enhance the Rashba spin–orbit torque. By employing a bulk Rashba material, GeTe, as a spin–orbit channel in GeTe/NiFe bilayers, a large field-like spin–orbit torque up to 15.8 mT/(107 A cm−2) is measured. This value is one of the largest reported field-like torques and is attributed to the interfacial spin–orbit coupling being enhanced by the bulk Rashba effect in the GeTe channel. Furthermore, the large field-like torque is maintained even for a 20-nm-thick NiFe layer. This unconventional dependence on the thickness of both the GeTe and NiFe layers cannot be described by conventional theory, but it is believed to stem from the additional bulk Rashba effect-induced term. The large field-like torque over a wide range of ferromagnet thicknesses results in scalable in-plane spin–orbit torque devices. This result calls for a further theoretical study on spin transport in heterostructures, including bulk Rashba materials.

scholarly journals Spin-orbit coupling driven crossover from a starfruitlike nodal semimetal to Dirac and Weyl semimetal state in CaAuAs

2018 ◽  
Vol 98 (8) ◽  
Author(s):  
Bahadur Singh ◽  
Sougata Mardanya ◽  
Chenliang Su ◽  
Hsin Lin ◽  
Amit Agarwal ◽  
...  
Keyword(s):  
Orbit Coupling ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Weyl Semimetal
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