Topological phonons and electronic structure of Li2BaSi class of semimetals

2021 ◽  
Author(s):  
Vineet Kumar Sharma ◽  
Birender Singh ◽  
Anan Bari Sarkar ◽  
Mayanak Kumar Gupta ◽  
Ranjan Mittal ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Transport Properties ◽  
Careful Analysis ◽  
Nodal Line ◽  
Theoretical Modelling ◽  
Spin Orbit Coupling ◽  
Band Inversion ◽  
Device Applications ◽  
Band Crossing ◽  
Nontrivial Topology

Abstract Extension of the topological concepts to the Bosonic systems has led to the prediction of topological phonons in materials. Here we discuss the topological phonons and electronic structure of Li2BaX (X = Si, Ge, Sn, and Pb) materials using first-principles theoretical modelling. A careful analysis of the phonon spectrum of Li2BaX reveals an optical mode inversion with the formation of nodal line states in the Brillouin zone. Our electronic structure results reveal a double band inversion at the Γ point with the formation of inner nodal-chain states in the absence of spin-orbit coupling (SOC). Inclusion of the SOC opens a materials-dependent gap at the band crossing points and transitions the system into a trivial insulator state. We also discuss the lattice thermal conductivity and transport properties of Li2BaX materials. Our results show that coexisting phonon and electron nontrivial topology with robust transport properties would make Li2BaX materials appealing for device applications.

scholarly journals Insight into the Topological Nodal Line Metal YB2 with Large Linear Energy Range: A First-Principles Study

Materials ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 3841
Author(s):  
Yang Li ◽  
Jihong Xia ◽  
Rabah Khenata ◽  
Minquan Kuang
Keyword(s):  
Energy Range ◽  
First Principles ◽  
Phonon Dispersion ◽  
Nodal Line ◽  
Spin Orbit Coupling ◽  
Metallic Material ◽  
Nodal Lines ◽  
Band Crossing ◽  
Crossing Point ◽  
Insight Into

The presence of one-dimensional (1D) nodal lines, which are formed by band crossing points along a line in the momentum space of materials, is accompanied by several interesting features. However, in order to facilitate experimental detection of the band crossing point signatures, the materials must possess a large linear energy range around the band crossing points. In this work, we focused on a topological metal, YB2, with phase stability and a P6/mmm space group, and studied the phonon dispersion, electronic structure, and topological nodal line signatures via first principles. The computed results show that YB2 is a metallic material with one pair of closed nodal lines in the kz = 0 plane. Importantly, around the band crossing points, a large linear energy range in excess of 2 eV was observed, which was rarely reported in previous reports that focus on linear-crossing materials. Furthermore, YB2 has the following advantages: (1) An absence of a virtual frequency for phonon dispersion, (2) an obvious nontrivial surface state around the band crossing point, and (3) small spin–orbit coupling-induced gaps for the band crossing points.

scholarly journals Theoretical Modelling of Charge Transport Properties of Individual Single-Wall Carbon Nanotubes

2018 ◽  
Vol 5 (3) ◽  
pp. 14-34
Author(s):  
G. Ijeomah ◽  
F. Samsuri ◽  
F. Obite ◽  
M.A. Zawawi
Keyword(s):  
Carbon Nanotubes ◽  
Transport Properties ◽  
Mean Free Path ◽  
Channel Length ◽  
Theoretical Modelling ◽  
Computational Time ◽  
Single Wall Carbon Nanotubes ◽  
Boltzmann Transport ◽  
Ohmic Resistance ◽  
Device Applications

Experimental projection of transport properties of semiconductor devices faces a challenge nowadays. As devices scale to nanometre scale range, the classical transport equations used in current device simulators can no longer be applied. Conversely, the use of a more accurate and better non-equilibrium green function (NEGF) is limited by the fact that it requires excessive quantum of memory and computational time, having quasi-separable matrices that are extremely convoluted to solve. This work exploits the Boltzmann Transport Equation (BTE) to assess the transport properties of carbon nanotubes. Previous works on solving the BTE have employed either a stochastic method or an approximate method, both of which do not possess the necessary properties for practical device applications. Therefore, this work represents the first direct theoretical solution of the BTE for one-dimensional carbon nanotubes that can be utilized for practical device applications. The complete spectrum of transport in CNTs extending from ohmic to high-field through ballistic transmission is examined to delineate plethora of transport properties. The transport for arbitrary values of the electric field is based on the BTE applied to experimental data on CNTs. In the limit of low field, the mobility expressions are obtained in terms of the mean free path (mfp) that is distinctly shorter than the length of the sample. The ohmic resistance is quantized a value of 6.453k-ohms consistent with experimental findings with transmission approaching unity as channel length shrinks below the carrier mfp. The emission of a quantum was observed to lower the saturation velocity that is independent of scattering and hence ballistic. Transition to ballistic domain was found to occur when the channel length is scaled below the ballistic limit that is shown to be the extended version of the long-channel mfp modulated by injections from the contacts, yet the mobility degrades. The mobility degradation is shown to be the cause of resistance quantum in the low-channel length limit. These findings are important in predicting the transport properties of low-dimensional CNTs.

scholarly journals Dirac semimetal phase and switching of band inversion in XMg2Bi2 (X = Ba and Sr)

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Daichi Takane ◽  
Yuya Kubota ◽  
Kosuke Nakayama ◽  
Tappei Kawakami ◽  
Kunihiko Yamauchi ◽  
...  
Keyword(s):  
High Reactivity ◽  
Orbit Coupling ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Dirac Semimetal ◽  
Band Inversion ◽  
New Material ◽  
Band Crossing ◽  
Structure Calculations

AbstractTopological Dirac semimetals (TDSs) offer an excellent opportunity to realize outstanding physical properties distinct from those of topological insulators. Since TDSs verified so far have their own problems such as high reactivity in the atmosphere and difficulty in controlling topological phases via chemical substitution, it is highly desirable to find a new material platform of TDSs. By angle-resolved photoemission spectroscopy combined with first-principles band-structure calculations, we show that ternary compound BaMg2Bi2 is a TDS with a simple Dirac-band crossing around the Brillouin-zone center protected by the C3 symmetry of crystal. We also found that isostructural SrMg2Bi2 is an ordinary insulator characterized by the absence of band inversion due to the reduction of spin–orbit coupling. Thus, XMg2Bi2 (X = Sr, Ba, etc.) serves as a useful platform to study the interplay among crystal symmetry, spin–orbit coupling, and topological phase transition around the TDS phase.

scholarly journals Effect of Deformation on Topological Properties of Cobalt Monosilicide

Crystals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 143
Author(s):  
Sergey Nikolaev ◽  
Dmitry Pshenay-Severin ◽  
Yuri Ivanov ◽  
Alexander Burkov
Keyword(s):  
Band Structure ◽  
Ab Initio Calculations ◽  
Topological Charge ◽  
External Stress ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Topological Properties ◽  
Uniaxial Deformation ◽  
Band Crossing ◽  
Topological Charges

Recently, it was shown that materials with certain crystal structures can exhibit multifold band crossings with large topological charges. CoSi is one such material that belongs to non-centrosymmetric space group P213 (#198) and posseses multifold band crossing points with a topological charge of 4. The change of crystal symmetry, e.g., by means of external stress, can lift the degeneracy and change its topological properties. In the present work, the influence of uniaxial deformation on the band structure and topological properties of CoSi is investigated on the base of ab initio calculations. The k·p Hamiltonian taking into account deformation is constructed on the base of symmetry consideration near the Γ and R points both with and without spin-orbit coupling. The transformation of multifold band crossings into nodes of other types with different topological charges, their shift both in energy and in reciprocal space and the tilt of dispersion around nodes are studied in detail depending on the direction of uniaxial deformation.

scholarly journals Heisenberg and anisotropic exchange interactions in magnetic materials with correlated electronic structure and significant spin-orbit coupling

2021 ◽  
Vol 103 (17) ◽  
Author(s):  
Vladislav Borisov ◽  
Yaroslav O. Kvashnin ◽  
Nikolaos Ntallis ◽  
Danny Thonig ◽  
Patrik Thunström ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Magnetic Materials ◽  
Exchange Interactions ◽  
Orbit Coupling ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Anisotropic Exchange

Photo- and exchange-field controlled line-type resonant peaks and enhanced spin and valley polarizations in a magnetic WSe2 junction

2022 ◽  
Author(s):  
Mohammad Alipour zadeh ◽  
Yaser Hajati ◽  
Imam Makhfudz
Keyword(s):  
Transport Properties ◽  
Resonant Tunneling ◽  
High Efficiency ◽  
Oscillatory Behavior ◽  
Spin Orbit Coupling ◽  
Exchange Field ◽  
Ideal Line ◽  
Transmission Resonances ◽  
Filtering Effect ◽  
Line Type

Abstract Existing resonant tunneling modes in the shape of line-type resonances can improve the transport properties of the junction. Motivated by the unique structural properties of monolayer WSe2 e.g. significant spin-orbit coupling (SOC) and large direct bandgap, the transport properties of a normal/ferromagnetic/normal (NFN) WSe2 junction with large incident angles in the presence of exchange field (h), off-resonance light (∆Ω) and gate voltage (U) is studied. In a certain interval of U, the transmission shows a gap with optically controllable width, while outside it, the spin and valley resolved transmissions have an oscillatory behavior with respect to U. By applying ∆Ω (h), an optically (electrically) switchable perfect spin and valley polarizations at all angles of incidence have been found. For large incident angles, the transmission resonances change to spin-valley-dependent separated ideal line-type resonant peaks with respect to U, resulting in switchable perfect spin and valley polarizations, simultaneously. Furthermore, even in the absence of U, applying h or ∆Ω at large incident angles can give some spin-valley dependent ideal transmission peaks, making h or ∆Ω a transmission valve capable of giving a switchable fully spinvalley filtering effect. These findings suggest some alternate methods for providing high-efficiency spin and valley filtering devices based on WSe2.

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