arXiv subjects

Mohammad Alipourzadeh

Publications and source records attributed to Mohammad Alipourzadeh.

3 recordsLinked to original sources

arXiv2025

Opto- and magneto-tunable exceptional degeneracies in non-Hermitian ferromagnet/$p$-wave magnet junctions

Unconventional $p$-wave magnets (UPMs) with odd-parity spin textures have attracted interest for their zero net magnetization and anisotropic spin-split Fermi surfaces. Here, we explore a non-Hermitian open quantum system composed of a ferromagnet and a UPM, subjected to an external magnetic field and off-resonant circularly polarized light (CPL), serving as tunable control parameters. We demonstrate the emergence of exceptional points (EPs) in the proposed junction, whose locations can be modulated by the intrinsic properties of the UPM. These EPs exhibit different multiplicities and formation conditions compared to those in even-parity magnets (dubbed $d$- wave altermagnets), a distinction attributable to the preserved time-reversal and broken inversion symmetries characteristic of UPMs. We find that both the unidirectional magnetic field (with adjustable strength and orientation) and the CPL induce momentum-direction-dependent modifications to the EPs, such as their shifting, tilting, merging, or annihilation, supported by analyses of spin projection and eigenvector overlap. Although both perturbations influence the EP structure, they operate via distinct mechanisms: CPL induces a global Floquet re-normalization, enabling dynamic tunability through light, whereas the unidirectional magnetic field selectively alters orientation-aligned terms, lacking such tunability. Beyond revealing EP dynamics in UPM-based junctions, our results highlight UPMs as promising platforms for non-Hermitian phenomena in future spintronics.

cond-mat.mes-hall↗

arXiv2025

Andreev bound states and supercurrent in an unconventional superconductor-altermagnetic Josephson junction

Motivated by the orientation-dependent properties of d-wave superconductors (SCs), we investigate Andreev bound states (ABSs) and Josephson current in s-wave SC/altermagnet/d-wave SC (S/AM/D) and d-wave SC/altermagnet/d-wave SC (D/AM/D) junctions. The asymmetric S/AM/D junction exhibits a node-less ABSs spectrum with distinct spin states, arising from AM manipulation. In contrast, a symmetric D/AM/D junction with $\pm 45^\circ$-oriented order parameters exhibits a nodal ABSs spectrum, characterized by spin-split sinusoidal curves. This behavior arises from the angular dependence of the d-wave pairing potential, which introduces a $π$-shift in the ABSs spectrum of the D/AM/D junction compared to that of conventional S/AM/S junctions. Additionally, the positions of the ABSs nodes in the D/AM/D junction can be controlled by adjusting the length and strength of the AM layer. Analysis of the free energy and Josephson current reveals additional extrema in the free energy at intermediate phase differences, leading to skewness and a non-sinusoidal behavior in the current-phase relationship of both configurations. These zero-supercurrent phase differences can be tuned by adjusting the properties of the AM layer such as AM strength and length. These findings provide new insights into AM-based Josephson junctions.

cond-mat.supr-con↗

arXiv2024

Quantum Anomalous Hall Effect in $d$-Electron Kagome Systems: Chern Insulating States from Transverse Spin-Orbit Coupling

The possibility of quantum anomalous Hall effect (QAHE) in two-dimensional kagome systems with $d$-orbital electrons is studied within a multi-orbital tight-binding model. We concentrate on the case of isotropic Slater-Koster integrals which is realized in a recently discovered class of metal-organic frameworks TM$_3$C$_6$O$_6$ with transition metals (TM) in the beginning of the 3$d$ series. Furthermore, in the absence of exchange-type spin-orbit coupling, only isotropic Slater-Koster integrals give a perfect flatband in addition to the two dispersive bands hosting relativistic (Dirac) and quadratic band crossing points at high symmetry spots in the Brillouin zone. A quantized topological invariant requires a flux-creating spin-orbit coupling, giving Chern number (per spin sector) $C=1$ not only from the familiar Dirac points at the six corners of the Brillouin zone, but also from the quadratic band crossing point at the center $Γ$. In the case of isotropic Slater-Koster integrals the on-site spin-orbit coupling (SOC) is ineffective to create the QAHE and it is only the transfer or exchange-type SOC which can lead to a QAHE. Surprisingly, this QAHE comes from the nontrivial effective flux induced by the \textit{transverse} part of the spin-orbit coupling, exhibited by electrons in the $d$-orbital state with $m_l=0$ ($d_{z^2}$ orbital), in stark contrast to the more familiar form of QAHE due to the $d$-orbitals with $m_l \neq 0$, driven by the Ising part of spin-orbit coupling. The $C=1$ Chern plateau (per spin sector) due to Dirac point extends over a smaller region of Fermi energy than that due to quadratic band crossing. Our result hints at the promising potential of kagome $d$-electron systems as a platform for dissipationless electronics by virtue of its unique QAHE.

cond-mat.str-el↗