scholarly journals Effective Hamiltonian for silicene under arbitrary strain from multi-orbital basis

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Zhuo Bin Siu ◽  
Mansoor B. A. Jalil
Keyword(s):  
Tight Binding ◽  
Spin Torque ◽  
Spin Accumulation ◽  
Effective Hamiltonian ◽  
Fermi Surfaces ◽  
Orbital Basis ◽  
Lattice Symmetry ◽  
Out Of Plane ◽  
Coupling Parameters ◽  
Spin Orbit Interactions

AbstractA tight-binding (TB) Hamiltonian is derived for strained silicene from a multi-orbital basis. The derivation is based on the Slater–Koster coupling parameters between different orbitals across the silicene lattice and takes into account arbitrary distortion of the lattice under strain, as well as the first and second-order spin–orbit interactions (SOI). The breaking of the lattice symmetry reveals additional SOI terms which were previously neglected. As an exemplary application, we apply the linearized low-energy TB Hamiltonian to model the current-induced spin accumulation in strained silicene coupled to an in-plane magnetization. The interplay between symmetry-breaking and the additional SOI terms induces an out-of-plane spin accumulation. This spin accumulation remains unbalanced after summing over the Fermi surfaces of the occupied bands and the two valleys, and can thus be utilized for spin torque switching.

Precession frequency and fast switching dependence on the in-plane and out-of-plane dual spin-torque polarizers

2012 ◽  
Vol 100 (14) ◽  
pp. 142409 ◽  
Author(s):  
Hong Zhang ◽  
Zhiwei Hou ◽  
Jianwei Zhang ◽  
Zongzhi Zhang ◽  
Yaowen Liu
Keyword(s):  
Precession Frequency ◽  
Spin Torque ◽  
Fast Switching ◽  
Out Of Plane

scholarly journals Hamiltonian modelling of macro-economic urban dynamics

2020 ◽  
Vol 7 (9) ◽  
pp. 200667 ◽  
Author(s):  
Bernardo Monechi ◽  
Miguel Ibáñez-Berganza ◽  
Vittorio Loreto
Keyword(s):  
Scaling Laws ◽  
Mutual Influence ◽  
Dynamical Evolution ◽  
Real Data ◽  
Urban Environments ◽  
Effective Hamiltonian ◽  
Economic Variables ◽  
Rapid Urbanization ◽  
Urban Dynamics ◽  
Coupling Parameters

The rapid urbanization makes the understanding of the evolution of urban environments of utmost importance to steer societies towards better futures. Many studies have focused on the emerging properties of cities, leading to the discovery of scaling laws mirroring the dependence of socio-economic indicators on city sizes. However, few efforts have been devoted to the modelling of the dynamical evolution of cities, as reflected through the mutual influence of socio-economic variables. Here, we fill this gap by presenting a maximum entropy generative model for cities written in terms of a few macro-economic variables, whose parameters (the effective Hamiltonian, in a statistical-physical analogy) are inferred from real data through a maximum-likelihood approach. This approach allows for establishing a few results. First, nonlinear dependencies among indicators are needed for an accurate statistical description of the complexity of empirical correlations. Second, the inferred coupling parameters turn out to be quite robust along different years. Third, the quasi time-invariance of the effective Hamiltonian allows guessing the future state of a city based on a previous state. Through the adoption of a longitudinal dataset of macro-economic variables for French towns, we assess a significant forecasting accuracy.

Stability Analysis of Spin-Torque Nano-oscillator in the Rotating Frame

SPIN ◽  
2019 ◽  
Vol 09 (03) ◽  
pp. 1950008
Author(s):  
HaoHsuan Chen ◽  
Lang Zeng ◽  
ChingMing Lee ◽  
Weisheng Zhao
Keyword(s):  
High Performance ◽  
Electrical Current ◽  
Nonstationary Process ◽  
Laboratory Frame ◽  
Spin Torque ◽  
Rotating Frame ◽  
Magnetization Dynamics ◽  
Applied Current ◽  
Frequency Tunability ◽  
Out Of Plane

Spin-torque nano-oscillators (STNOs) have become one of the emerging and novel microwave devices with the high performance and tunability of GHz range frequency. The nanopillar structure with an out-of-plane (OP) spin polarizer and an in-plane (IP) magnetized free layer (FL) has been considered as a good candidate for the STNOs. Using the local rotational coordinate transformation, a nonstationary process describing magnetization dynamics in the laboratory frame is therefore transformed into a stationary one in the rotating frame. In this way, the state phase diagram of this type of STNOs is well established as a function of an applied current and external field, which is also evidenced by the macrospin simulations. Also, we show that the frequency tunability of the STNOs through electrical current can be well elevated by applying a static magnetic field anti-parallel to the spin-polarizer vector.

Impact of Device Variability and Circuit Phase Shift in Synchronized Spin Torque Oscillators

2007 ◽  
Vol 998 ◽  
Author(s):  
Johan Persson ◽  
Yan Zhou ◽  
Johan Akerman
Keyword(s):  
Phase Diagram ◽  
Time Delay ◽  
Process Variations ◽  
Small Time ◽  
Spin Transfer Torque ◽  
Spin Torque ◽  
Plane Anisotropy ◽  
Out Of Plane ◽  
The Impact ◽  
Spin Torque Oscillators

ABSTRACTCurrent-induced magnetization dynamics in a system composed of two electrically coupled spin torque oscillators (STOs) is examined. The dynamics of the STOs is modeled by the Landau–Lifshitz–Gilbert equations modified with a Slonczewski spin-transfer torque term. To study the impact of realistic process variations on STO synchronization we let the two STOs have different in-plane anisotropy fields (Hk). The simulation also provides for a time delay τ. We construct a phase diagram of the STO synchronization as a function of Hk and direct current (Idc) at different τ. The phase diagram turns out to be quite rich with different types of synchronized precession modes. While the synchronized state is originally very sensitive to STO process variations and can only sustain up to 4% Hk variation, the addition of a small time delay dramatically improves its robustness and allows as much as 145% Hk variation in the entire out-of-plane precession regime. It is also shown that the two STOs can not only be locked in frequency, but also in phase at a given τ and the phase difference between the two STOs can be tuned by varying the dc current.

High Q factor over 3000 due to out-of-plane precession in nano-contact spin-torque oscillator based on magnetic tunnel junctions

2014 ◽  
Vol 7 (2) ◽  
pp. 023003 ◽  
Author(s):  
Hiroki Maehara ◽  
Hitoshi Kubota ◽  
Yoshishige Suzuki ◽  
Takayuki Seki ◽  
Kazumasa Nishimura ◽  
...  
Keyword(s):  
Tunnel Junctions ◽  
Magnetic Tunnel Junctions ◽  
Spin Torque ◽  
Q Factor ◽  
High Q ◽  
Out Of Plane

Intrinsic Phase Shift and Novel Dynamic Magnetization States of a Spin Torque Oscillator under ac Current Injection

2007 ◽  
Vol 998 ◽  
Author(s):  
Yan Zhou ◽  
Johan Persson ◽  
Johan Akerman
Keyword(s):  
Phase Shift ◽  
Phase Locking ◽  
Wave Length ◽  
Anisotropy Field ◽  
Spin Torque ◽  
Demagnetizing Field ◽  
Oscillation Modes ◽  
Out Of Plane ◽  
Ac Current ◽  
Dc Current

ABSTRACTWe report on a preferred phase shift ΔΦ0 between a spin torque oscillator (STO) and an ac current (Iac) injected at the intrinsic frequency (fSTO) of the STO. In the in-plane precession mode (IP) the STO adjusts to a state where its resistance (or voltage) lags Iac about a quarter of a wave length (ΔΦ0 = 87°−94°). In the IP mode ΔΦ0 increases somewhat with the dc current. As the precession changes into the Out-Of-Plane (OOP) mode, ΔΦ0 jumps by about 180°, i.e. the STO resistance now precedes Iac by about a quarter of a wave length (|ΔΦ0| = 86°). At the IP/OOP boundary, the ac current mixes the two oscillation modes and both periodic and chaotic oscillations are observed. As a consequence of mixing, subharmonic terms appear in the STO signal. ΔΦ0 can furthermore be tuned by changing one or more of the anisotropy field, the demagnetizing field or the applied field. At the IP/OOP boundary, Iac mixes the two oscillation modes. The intrinsic ΔΦ0 will impact any circuit design based on STO technology and will e.g. have direct consequences for phase locking in networks of serially connected STOs.

scholarly journals Lattice vibrations and disorder in crystalline benzoxazoles undergoing excited state intramolecular proton transfer: DFTB modeling

2018 ◽  
Vol 26 (1) ◽  
pp. 57-62
Author(s):  
Y. Syetov
Keyword(s):  
Density Functional ◽  
Tight Binding ◽  
Intramolecular Proton Transfer ◽  
Lattice Vibrations ◽  
Molecular Vibrations ◽  
Out Of Plane ◽  
Symmetry Structure ◽  
Internal Crystal ◽  
Internal Vibrations ◽  
Isolated Molecules

Structure and crystal lattice vibrations are calculated for 2-(2'-hydroxyphenyl)bezoxazole and bis-(2,5-benzoxazolyl)hydroquinone by density functional based tight-binding methods. Despite lowering of the molecular symmetry, structure parameters of the molecules in crystal and forms of the internal vibrations are similar to those of isolated molecules. Weak interaction between the molecules in the molecular crystals leads to appearance of the external vibrations, splitting and mixing of the vibrations of the isolated molecules into internal crystal vibrations. External and internal vibrations are not separated well; contribution of the translations and librations is noticeable in the region below 150 cm-1. The magnitude ofthe splitting does not exceed 4 cm-1 for the most vibrations. The internal vibrations that correspond to the out-of plane molecular vibrations demonstrate larger molecule-to-crystal frequency shift than in-plane modes, mostly to higher frequencies, whereas the modes involving torsion motion of the OH bond are shifted toward lower frequencies. Mixing occurs for the molecular vibrations with frequencies that are different by less than 16 cm-1. Calculations performed for model molecular clusters show that the defectcaused by different molecule orientation has lower energy than the defect related to the formation ofrotamers.

scholarly journals Magnetic competition in topological kagome magnets

2021 ◽  
Author(s):  
Thanh-Mai Thi Tran ◽  
Duong-Bo Nguyen ◽  
Hong-Son Nguyen ◽  
Minh-Tien Tran
Keyword(s):  
Variational Principle ◽  
Spin Exchange ◽  
Tight Binding ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Zero Temperature ◽  
Electron Dynamics ◽  
Hall Conductance ◽  
Magnetic Phases ◽  
Out Of Plane

Abstract Magnetic competition in topological kagome magnets is studied by incorporating the spin-orbit coupling, anisotropic Hund coupling and spin exchange into a tight-binding electron dynamics in the kagome lattice. Using the Bogoliubov variational principle we find the stable phases at zero and finite temperatures. At zero temperature and in the strong Ising-Hund coupling regime, a magnetic tunability from the out-of-plane ferromagnetism to the in-plane antiferromagnetism is achieved through a universal property of the critical in-plane Hund coupling. At low temperature the out-of-plane ferromagnetism is stable until a finite crossing temperature. Above the crossing temperature the in-plane antiferromagnetism is stable, but the magnetization of the out-of-plane ferromagnetism still survives. This suggests a metastable coexistence of these magnetic phases in a finite temperature range. A large anomalous Hall conductance is observed in the Ising-Hund coupling limit.

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