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Non-Equilibrium Green's Function based Circuit Models for Coherent Spin Devices
摘要： With recent developments in spintronics, it is now possible to envision 'spin-driven' devices with magnets and interconnects that require a new class of transport models using generalized Fermi functions and currents, each with four components: one for charge and three for spin. The corresponding impedance elements are not pure numbers but 4 × 4 matrices. Starting from the Non-Equilibrium Green's Function (NEGF) formalism in the elastic, phase-coherent transport regime, we develop spin generalized Landauer-Büttiker formulas involving such 4 × 4 conductances, for multi-terminal devices in the presence of Normal-Metal (NM) leads. In addition to usual 'terminal' conductances describing currents at the contacts, we provide 'spin-transfer torque' conductances describing the spin currents absorbed by ferromagnetic (FM) regions inside the conductor, specifying both of these currents in terms of Fermi functions at the terminals. We derive universal sum rules and reciprocity relations that would be obeyed by such matrix conductances. Finally, we apply our formulation to two example Hamiltonians describing the Rashba and the Hanle effect in 2D. Our results allows the use of pure quantum transport models as building blocks in constructing circuit models for complex spintronic and nano-magnetic structures and devices for simulation in SPICE-like simulators.
关键词： Rashba effect,spintronics,Landauer-Büttiker formula,spin-transfer torque,Non-Equilibrium Green's Function,Hanle effect,SPICE simulation
更新于2025-09-23 15:23:52
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A generalised approach to calculate various transport observables for a linear array of series and parallel quantum dots
摘要： A systematic generalised approach to ?nd transport observables for a linear array of different quantum dot (QD) systems has been discussed, using non-equilibrium Green function (NEGF) formalism, in the presence of on-dot Coulomb interaction and inter-dot tunnelling. The equation of motion (EOM) method has been used to derive expressions for Green functions (GFs) within the simplest mean-?eld approximation to tackle the Coulomb correlation term. Starting from the mathematical structures of GFs for single, double and triple quantum dot systems, the expressions for GFs and transport observables have been generalised for the quantum dot systems containing N number of quantum dots in series as well as parallel linear array of dots. Further, the formulae so obtained have been used for numerical calculations of transmission probability and the I –V characteristics of linear arrays of quantum dots in series as well as parallel con?guration containing up to three dots. The results show that, with the increase in number of dots in the scattering region, transmission probability and electron current decrease in series case, while both quantities increase in parallel con?guration of dots. The inter-dot tunnelling leads to the splitting of transmission peaks in double QD system in series case whereas, it induces Fano effect in triple QD system in parallel con?guration.
关键词： quantum dots,Quantum transport,non-equilibrium Green function,Landauer–Buttiker formula,linear array of dots
更新于2025-09-23 15:21:01