arXiv subjects

Amin Naseri

Publications and source records attributed to Amin Naseri.

4 recordsLinked to original sources

arXiv2021

Unconventional supersymmetric quantum mechanics in spin systems

It is shown that the eigenproblem of any $2\times 2$ matrix Hamiltonian with discrete eigenvalues is involved with a supersymmetric quantum mechanics. The energy dependence of the superalgebra marks the disparity between the deduced supersymmetry and the standard supersymmetric quantum mechanics. The components of an eigenspinor are superpartners\textemdash up to a $SU(2)$ transformation\textemdash which allows to derive two reduced eigenproblems diagonalizing the Hamiltonian in the spin subspace. As a result, each component carries all information encoded in the eigenspinor. We also discuss the generalization of the formalism to a system of a single spin-$\frac{p}{2}$ coupled with external fields. The unconventional supersymmetry can be regarded as an extension of the Fulton-Gouterman transformation, which can be established for a two-level system coupled with multi oscillators displaying a mirror symmetry. The transformation is exploited recently to solve Rabi-type models. Correspondingly, we illustrate how the supersymmetric formalism can solve spin-boson models with no need to appeal a symmetry of the model. Furthermore, a pattern of entanglement between the components of an eigenstate of a many-spin system can be unveiled by exploiting the supersymmetric quantum mechanics associated with single spins which also recasts the eigenstate as a matrix product state. Examples of many-spin models are presented and solved by utilizing the formalism.

quant-ph↗

arXiv2019

Spin Vortices and Skyrmions of a Single Electron in Inhomogeneous Magnetic Fields

We study the spin textures of a confined two-dimensional electron in inhomogeneous magnetic fields. These fields can either be external or effective fields due to a background magnetic texture in the plane in which the electron resides. By analytical considerations, WKB-type approximations, and by performing numerical diagonalizations we show that the in-plane spin field components of a single electron can form vortices while the total spin field can become a skyrmion. Most interestingly, we find that topological trivial magnetic fields can induce topological spin field configurations in the eigenstates of the electron due to quantum effects.

cond-mat.mes-hall↗

arXiv2018

Unique Spin Vortices in Quantum Dots with Spin-orbit Couplings

Spin textures of one or two electrons in a quantum dot with Rashba or Dresselhaus spin-orbit couplings reveal several intriguing properties. We show that even at the single-electron level spin vortices with different topological charges exist. These topological textures appear in the {\it ground state} of the dots. The textures are stabilized by time-reversal symmetry breaking and are robust against the eccentricity of the dot. The phenomenon persists for the interacting two-electron dot in the presence of a magnetic field.

cond-mat.mes-hall↗

arXiv2014

Orbital ferromagnetism in interacting few-electron dots with strong spin-orbit coupling

We study the ground state of $N$ weakly interacting electrons (with $N\le 10$) in a two-dimensional parabolic quantum dot with strong Rashba spin-orbit coupling. Using dimensionless parameters for the Coulomb interaction, $λ\lesssim 1$, and the Rashba coupling, $α\gg 1$, the low-energy physics is characterized by an almost flat single-particle dispersion. From an analytical approach for $α\to \infty$ and $N=2$, and from numerical exact diagonalization and Hartree-Fock calculations, we find a transition from a conventional unmagnetized ground state (for $λ<λ_c$) to an orbital ferromagnet (for $λ>λ_c$), with a large magnetization and a circulating charge current. We show that the critical interaction strength, $λ_c=λ_c(α,N)$, vanishes in the limit $α\to \infty$.

cond-mat.mes-hall↗