arXiv subjects

Hamid Mosadeq

Publications and source records attributed to Hamid Mosadeq.

8 recordsLinked to original sources

arXiv2025

Interplay of Rashba and Dresselhaus Spin-Orbit Couplings on the Stability of Topological FFLO Phases in 1D Fermi Gases

We investigate the stabilization of topological Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phases, with a specific emphasis on the intraband FFLO phase, in a one-dimensional (1D) Fermi gas subjected to an external magnetic field. This research highlights the crucial role of the interplay between Rashba spin-orbit coupling (RSOC) and Dresselhaus spin-orbit coupling (DSOC). Employing a Fermi-Hubbard model alongside the density matrix renormalization group (DMRG) method, we examine the combined effects of RSOC and DSOC on these exotic superfluid phases, taking into account attractive fermionic interactions. Our principal finding reveals that while RSOC primarily stabilizes conventional zero-momentum pairing, DSOC performs a distinct and crucial role in selectively stabilizing the intraband FFLO phase. This stabilization is achieved by enhancing spin polarization within a single helicity band and suppressing interband coherence, thereby facilitating the formation of finite-momentum FFLO pairs within the same band and resulting in the emergence of a topologically nontrivial superfluid. This targeted control of intraband FFLO pairing paves the way for new strategies in the manipulation of superfluid phases in spin-orbit coupled systems and offers essential insights for experimental realizations in ultracold atomic gases, with implications for topological quantum computing and Majorana fermions.

cond-mat.quant-gas↗

arXiv2024

Unveiling Non-Kitaev Interactions and Field-Angle Dependence in Topological Magnon Transport of $\alpha$-RuCl$_3$

Honeycomb lattice Kitaev magnets exhibit exotic magnetic properties governed by the Kitaev interaction. This study delves into $\alpha$-RuCl$_3$, a prototypical example described by effective Hamiltonians encompassing bond-dependent Kitaev interactions alongside additional terms such as the Heisenberg interaction and symmetric off-diagonal exchange interactions. These non-Kitaev terms significantly influence $\alpha$-RuCl$_3$'s low-temperature magnetism, impacting both magnetic order and excitations. We employ spin-wave theory to elucidate the topological nature of magnetic excitations within the polarized state of $\alpha$-RuCl$_3$ under an external magnetic field. Our focus lies on transverse magnon conductivities, specially the thermal Hall conductivity and spin Nernst coefficient. The calculations unveil a pronounced dependence of the magnitude and sign structure of the low-temperature transverse thermal conductivities on both the applied magnetic field's orientation and the exchange parameters within the nearest neighbor Heisenberg-Kitaev-Gamma-Gamma$'$ $(JK\Gamma\Gamma')$ model, which govern the nature and strength of spin interactions. This theoretical framework facilitates critical comparisons with experimental observations, ultimately aiding the identification of an effective Hamiltonian for Kitaev magnets exemplified by $\alpha$-RuCl$_3$.

cond-mat.str-el↗

arXiv2023

Ground state of the staggered Heisenberg-$\Gamma$ honeycomb model in a magnetic field

We study the ground state properties of the $S=\frac{1}{2}$ staggered Heisenberg-$\Gamma$ honeycomb model under a magnetic field based on analytical and numerical methods. Our calculations show that the conventional zigzag and stripy phases are favored because of the staggered Heisenberg interaction away from the pure $\Gamma$ limit. In our classical analysis, we find that the field induces a series of competing magnetic phases with relatively large unit cells in the region sandwiched between the two magnetic phases with long-range ordering. In the quantum treatment, these large magnetic unit cells are destabilized by strong quantum fluctuations that result in the stabilization of a gapless quantum spin liquid behavior. In a honeycomb $\Gamma$ magnet, we disclose an intermediate-field gapless quantum spin liquid phase driven by a tilted field away from the out-of-plane direction only for a narrow region between the low-field zigzag and high-field fully polarized phases.

cond-mat.str-el↗

arXiv2021

Spin liquid in twisted homobilayers group-VI gichalcogenides

Twisted transition metal dichalcogenide (TMD) homobilayers have recently emerged as a powerful platform for studying correlated insulating states. In the strongly correlated limit, we construct an effective spin Hamiltonian on a honeycomb lattice that includes the Heisenberg interaction and nonsymmetric interactions such as a Dzyaloshinskii-Moriya interaction and a Kane-Mele coupling for the Mott-insulating phase at half-filling. For the twisted TMD homobilayers, the spin-orbit coupling in the Hubbard model, which is expected to induce the antisymmetric exchange couplings in the effective spin Hamiltonian, is a highly tunable and experimentally accessible quantity that can be tuned by an applied electric field. In this study, we investigate classical and quantum phase diagrams of the effective spin Hamiltonian using analytical and numerical methods. We show that the model exhibits a rich classical phase diagram including an antiferromagnetic (AFM) phase, a planar spiral ordered phase with high classical degeneracy, a $z$-AFM phase, a noncoplanar phase, a noncollinear phase, and a 120$^{\circ}$-AFM phase. In the quantum treatment, we calculate low-energy magnon excitation spectrum, ground state energy, and static spin structure factor using linear spin-wave theory and density matrix renormalization group methods to compose the quantum phase diagram of the effective spin Hamiltonian. Beyond the Heisenberg interaction, we find that the existence of these antisymmetric couplings is responsible for the quantum spin liquid, $z$-AFM, noncoplanar, and 120$^{\circ}$ phases. Twisted TMD homobilayers, therefore, offer rich platforms for realizing rich phases of matter such as quantum spin liquid, noncoplanar, and 120$^{\circ}$, resulting from the spin-orbit coupling.

cond-mat.str-el↗

arXiv2017

Origin of magnetic frustration in Bi$_3$Mn$_4$O$_{12}$(NO$_3$)

Bi$_3$Mn$_4$O$_{12}$(NO$_3$) (BMNO) is a honeycomb bilayers anti-ferromagnet, not showing any ordering down to very low temperatures despite having a relatively large Curie-Weiss temperature. Using ab initio density functional theory, we extract an effective spin Hamiltonian for this compound. The proposed spin Hamiltonian consists of anti-ferrimagnetic Heisenberg terms with coupling constants ranging up to third intra-layer and fourth inter-layer neighbors. Performing Monte Carlo simulation, we obtain the temperature dependence of magnetic susceptibility and so the Curie-Weiss temperature and find the coupling constants which best matches with the experimental value. We discover that depending on the strength of the interlayer exchange couplings, two collinear spin configurations compete with each other in this system. Both states have in plane N{é}el character, however, at small interlayer coupling spin directions in the two layers are antiparallel (N$_1$ state) and discontinuously transform to parallel (N$_2$ state) by enlarging the interlayer couplings at a first order transition point. Classical Monte Carlo simulation and density matrix renormalization group calculations confirm that exchange couplings obtained for BMNO are in such a way that put this material {at the phase boundary of a first order phase transition}, where the trading between these two collinear spin states prevents it from setting in a magnetically ordered state.

cond-mat.str-el↗

arXiv2016

Quantum phase diagram of $J_1-J_2$ Heisenberg $S=1/2$ antiferromagnet in honeycomb lattice: a modified spin wave study

Using modified spin wave (MSW) method, we study the $J_1-J_2$ Heisenberg model with first and second neighbor antiferromagnetic exchange interactions. For symmetric $S=1/2$ model, with the same couplings for all the equivalent neighbors, we find three phase in terms of frustration parameter ${\barα=J_2/J_1}$: (1) a commensurate collinear ordering with staggered magnetization (N{é}el.I state) for $0\leq{\barα}\lesssim 0.207$ , (2) a magnetically gapped disordered state for $0.207\lesssim{\barα}\lesssim 0.369$, preserving all the symmetries of the Hamiltonian and lattice, hence by definition is a quantum spin liquid (QSL) state and (3) a commensurate collinear ordering in which two out of three nearest neighbor magnetizations are antiparallel and the remaining pair are parallel (N{é}el.II state), for $0.396\lesssim{\barα}\leq 1$. We also explore the phase diagram of distorted $J_1-J_2$ model with $S=1/2$. Distortion is introduced as an inequality of one nearest neighbor coupling with the other two. This yields a richer phase diagram by the appearance of a new gapped QSL, a gapless QSL and also a valence bond crystal (VBC) phase in addition to the previously three phases found for undistorted model.

cond-mat.str-el↗

arXiv2015

Quantum phases of a one-dimensional dipolar Fermi gas

We quantitatively obtain the quantum ground-state phases of a Fermi system with on-site and dipole-dipole interactions in one-dimensional lattice chains within the density matrix renormalization group. We show, at a given spin polarization, the existence of six phases in the phase diagram and find that the phases are highly dependent on the spin degree of freedom. These phases can be constructed using available experimental techniques.

cond-mat.str-el↗

arXiv2014

Valence Bond Phases in $S=1/2$ Kane-Mele-Heisenberg Model

The phase diagram of Kane-Mele-Heisenberg (KMH) model in classical limit~\cite{zare}, contains disordered regions in the coupling space, as the result of to competition among different terms in the Hamiltonian, leading to frustration in finding a unique ground state. In this work we explore the nature of these phase in the quantum limit, for a $S=1/2$. Employing exact diagonalization (ED) in $S_z$ and nearest neighbor valence bond (NNVB) bases, bond and plaquette valence bond mean field theories, We show that the disordered regions are divided into ordered quantum states in the form of plaquette valence bond crystal(PVBC) and staggered dimerized (SD) phases.

cond-mat.str-el↗