arXiv subjects

Asliddin Khudoyberdiev

Publications and source records attributed to Asliddin Khudoyberdiev.

12 recordsLinked to original sources

arXiv2026

Control of the Néel vector in the quantum antiferromagnetic honeycomb lattice

The switching of antiferromagnetic order and its efficient control promise to enable ultrafast manipulation of data and large storage capacity. Recently, the time-dependent Schwinger boson mean-field theory has been successfully developed to study the Néel vector switching in hypercubic antiferromagnetic lattices. In the present article, we aim at demonstrating that the approach is a well-justified framework to capture the essentials of the switching process, even in low-symmetry quantum antiferromagnets. To this end, we show the possibility of the sublattice magnetization reorientation in the quantum antiferromagnetic honeycomb lattice. First, equilibrium properties of the honeycomb lattice are analyzed using the Schwinger boson mean-field theory and compared to the continuous similarity transformation method to justify the applicability of the approach. Then, the Schwinger boson mean-field theory is employed for switching process. We provide a comprehensive answer to the question what the threshold switching fields are when the coordination number of the lattice is varied. Indeed, the results of the study reveal a correspondence between lattice structures and the threshold fields by comparing them for the square and the simple cubic lattices and the honeycomb lattice. The findings of the present article extend the foundation for future theoretical and computational advancements in the field of antiferromagnetic switching. These advancements are of particular relevance for the development of ultrafast spintronic or magnonic devices.

cond-mat.str-el↗

arXiv2026

Switching magnetization of quantum antiferromagnets: Schwinger boson mean-field theory compared to exact diagonalization

Antiferromagnets have attracted significant attention because of their considerable potential in engineering high-density and ultrafast memory devices, a crucial and increasingly demanded component of contemporary high-performance information technology. Theoretical and experimental investigations are actively progressing to provide the capability of efficient switching and precise control of the Néel vector, which is crucial for the intended practical applications of antiferromagnets. Recently, a time-dependent Schwinger boson mean-field theory has been successfully developed to study the sublattice magnetization switching in anisotropic quantum antiferromagnets [K. Bolsmann $et \, al.$, \textcolor{blue}{\hyperlink{10.1103/PRXQuantum.4.030332}{PRX Quantum $\mathbf{4}$, 030332 (2023)}}]. Here we use a complementary exact diagonalization method to study such sublattice magnetization switching, but in small-cluster quantum antiferromagnets, by means of an external magnetic field. Furthermore, this article aims to support the findings of the Schwinger boson approach. We show that the results of both approaches are consistent at short time scales, with only about 12.5 $\%$ deviations. The consistency of the outcomes obtained through this alternative exact approach demonstrates that the time-dependent Schwinger boson mean-field theory is a versatile framework to capture the essentials of the switching process in quantum antiferromagnets. Thereby, the findings of current article pave the way for further theoretical and computational progress in the study of antiferromagnets for engineering spintronic devices with ultrahigh density and ultrafast speed.

cond-mat.str-el↗

arXiv2025

The effect of dephasing and spin-lattice relaxation during the switching processes in quantum antiferromagnets

The control of antiferromagnetic order can pave the way to large storage capacity as well as fast manipulation of stored data. Here achieving a steady-state of sublattice magnetization after switching is crucial to prevent loss of stored data. The present theoretical approach aims to obtain instantaneous stable states of the order after reorienting the Néel vector in open quantum antiferromagnets using time-dependent Schwinger boson mean-field theory. The Lindblad formalism is employed to couple the system to the environment. The quantum theoretical approach comprises differences in the effects of dephasing, originating from destructive interference of different wave vectors, and spin-lattice relaxation. We show that the spin-lattice relaxation results in an exponentially fast convergence to the steady-state after full ultrafast switching.

cond-mat.mtrl-sci↗

arXiv2024

Exchange enhanced switching by alternating fields in quantum antiferromagnets

Information can be stored magnetically in antiferromagnets ultrafast since their characteristic times are on the picosecond scale. Various spin torques have proven to be important for efficient and high-speed magnetic memories. So far, this has been understood on the classical level by solving the equations of motion for macrospins describing the collective motion of the sublattice magnetizations. Since spins and hence magnetizations are deeply rooted in quantum mechanics, we show that the exchange enhanced manipulation of sublattice magnetizations extends to quantum antiferromagnets as well. To this end, we solve the time-dependent mean-field equations for Schwinger boson theory under external alternating magnetic fields. Exchange enhancement persists on the quantum level which includes dephasing effects. Significantly lower fields are sufficient to control the sublattice magnetization than for uniform fields which holds great promises for the realization of ultrafast magnetic storage devices.

cond-mat.str-el↗

arXiv2024

Switching of Magnetization in Quantum Antiferromagnets with Time-Dependent Control Fields

Ultrafast manipulation of magnetic states is one of the necessities in modern data storage technology. Quantum antiferromagnets are promising candidates in this respect. The orientation of the order parameter, the sublattice magnetization, can be used to encode "0" and "1" of a bit. Then, the switching of magnetization and the full control of its reorientation are crucial for writing data. We show that the magnetization can be switched efficiently by an external short THz pulses with relatively low amplitude. The coupling to the spin degrees can be direct via the magnetic field or indirect via the electric field inducing spin-polarized charge currents. Our description is based on time-dependent Schwinger boson mean-field theory which includes the intrinsic dephasing mechanisms beyond a macrospin description. The findings help to introduce the use of antiferromagnets in data storage technology.

cond-mat.str-el↗

arXiv2023

Switching the Magnetization in Quantum Antiferromagnets

The orientation of the order parameter of quantum magnets can be used to store information in a dense and efficient way. Switching this order parameter corresponds to writing data. To understand how this can be done, we study a precessional reorientation of the sublattice magnetization in an (an)isotropic quantum antiferromagnet induced by an applied magnetic field. We use a description including the leading quantum and thermal fluctuations, namely Schwinger boson mean-field theory, because this theory allows us to describe both ordered phases and the phases in between them, as is crucial for switching. An activation energy has to be overcome requiring a minimum applied field $h_\text{t}$ which is given essentially by the spin gap. It can be reduced significantly for temperatures approaching the Néel temperature facilitating switching. The time required for switching diverges when the field approaches $h_\text{t}$ which is the signature of an inertia in the magnetization dynamics. The temporal evolution of the magnetization and of the energy reveals signs of dephasing. The switched state has lost a part of its coherence because the magnetic modes do not evolve in phase.

cond-mat.str-el↗

arXiv2023

Hugenholtz -- Pines relations and the critical temperature of a Rabi coupled binary Bose system

Using a theoretical field Gaussian approximation we have studied Rabi coupled binary Bose system at low temperatures. We have derived extended Hugenholtz - Pines relations taking into account one body interaction (e.g. Rabi coupling) and studied the critical temperature $T_c$ of Bose-Einstein condensate transition. We have shown that, the shift of $T_c$ due to this interaction can not exceed $\sim 60 \%$ and goes to a plateau with increasing the parameter $Ω_R/T_{c}^{0}$, where $Ω_R$ is the intensity of the coupling and $T_{c}^{0}$ is the critical temperature of the system with $Ω_R=0$. Moreover, the shift is always positive and does not depend on the sign of the one body interaction.

cond-mat.quant-gas↗

arXiv2022

The transition from Bose-Einstein condensate to supersolid states in Rydberg-dressed gases beyond Bogoliubov approximation

In this paper, we study Bose-Einstein condensation of Rydberg-dressed atoms considering finite range interactions. We use Hartree-Fock-Bogoliubov approximation based on Mean-Field approach. Moreover, within this approximation modified by the finite-range character of the two-body interaction we shall obtain analytical expressions for thermodynamic quantities of Rydberg-dressed Bose gas. The imaginary part of the quasiparticle spectrum of a BEC signals the instability of the roton mode with respect to the formation of supersolid state. Our theory predicts a second-order quantum phase transition from BEC to supersolid phase for Rydberg-dressed bosons in three dimensions.

cond-mat.quant-gas↗

arXiv2022

Defining a critical temperature of a crossover from BEC to the normal phase in anisotropic quantum magnets

We address the problem of identifying the critical temperature in a crossover from the Bose-Einstein condensed (BEC) phase to the normal phase. For this purpose we study the temperature dependence of magnetization of spin-gapped quantum magnets described by BEC of triplons. We have calculated the heat capacity $C_H$ at constant field and fluctuations in magnetization in a spin-gapped quantum magnet using the Hartree-Fock-Bogouliubov approximation and found optimized parameters of the Hamiltonian of triplon gas. In the region of phase transition, the heat capacity $C_H$ is smeared out due to the Dzyaloshinsky-Moriya (DM) interaction. The sharp maximum of the fluctuations in the magnetization is identified as the critical temperature of the crossover.

cond-mat.quant-gas↗

arXiv2021

Effects of exchange and weak Dzyaloshinsky-Moriya anisotropies on thermodynamic characteristics of spin-gapped magnets

We study the modification of low temperature properties of quantum magnets such as magnetization, heat capacity, energy spectrum, and densities of condensed and noncondensed quasiparticles (triplons) due to anisotropies in the framework of mean-field based approach. We show that in contrast to exchange anisotropy (EA) interaction, Dzyaloshinsky-Moriya (DM) interaction modifies the physics dramatically. Particularly, it changes the sign of the anomalous density in the whole range of temperatures. Its critical behavior is slightly modified also by the EA. We have found that the shift of the critical temperature of phase transition (or crossover caused by DM interaction) is positive and significant. Using the experimental data on the magnetization of the compound TlCuCl$_3$, we have found optimal values for the strengths of EA and DM interactions. The spectrum of the energy of low lying excitations has also been investigated and found to develop a linear dispersion similar to Goldstone mode with a negligibly small anisotropy gap.

cond-mat.stat-mech↗

arXiv2020

Spin-gapped magnets with weak anisotropies I: Constraints on the phase of the condensate wave function

We study the thermodynamic properties of dimerized spin-gapped quantum magnets with and without exchange anisotropy (EA) and Dzyaloshinsky and Moriya (DM) anisotropies within the mean-field approximation (MFA). For this purpose we obtain the thermodynamic potential $Ω$ of a triplon gas taking into account the strength of DM interaction up to second order. The minimization of $Ω$ with respect to self-energies $Σ_n$ and $Σ_{an}$ yields the equation for $X_{1,2}=Σ_n\pmΣ_{an}-μ$, which define the dispersion of quasiparticles $E_k=\sqrt{ε_k+X_1}\sqrt{ε_k+X_2}$ where $ε_k$ is the bare dispersion of triplons. The minimization of $Ω$ with respect to the magnitude $ρ_0$ and the phase $Θ$ of triplon condensate leads to coupled equations for $ρ_0$ and $Θ$. We discuss the restrictions on $ρ_0$ and $Θ$ imposed by these equations for systems with and without anisotropy. The requirement of dynamical stability conditions $(X_1>0, X_2>0)$ in equilibrium, as well as the Hugenholtz-Pines theorem, particularly for isotropic Bose condensate, impose certain conditions to the physical solutions of these equations. It is shown that the phase angle of a purely homogenous Bose-Einstein condensate (BEC) without any anisotropy may only take values $Θ=πn $ (n=0,$\pm 1,\pm 2$...) while that of BEC with even a tiny DM interaction results in $Θ=π/2+2πn$. In contrast to the widely used Hartree-Fock-Popov approximation, which allows arbitrary phase angle, our approach predicts that the phase angle may have only discrete values, while the phase of the wave function of the whole system remains arbitrary as expected. The consequences of this phase locking for interference of two Bose condensates and to their possible Josephson junction is studied.

cond-mat.quant-gas↗

arXiv2017

Bose - Einstein condensation of triplons with a weakly broken U(1) symmetry

The low-temperature properties of certain quantum magnets can be described in terms of a Bose-Einstein condensation (BEC) of magnetic quasiparticles (triplons). Some mean-field approaches (MFA) to describe these systems, based on the standard grand canonical ensemble, do not take the anomalous density into account and leads to an internal inconsistency, as it has been shown by Hohenberg and Martin, and may therefore produce unphysical results. Moreover, an explicit breaking of the U(1) symmetry as observed, for example, in TlCuCl3 makes the application of MFA more complicated. In the present work, we develop a self-consistent MFA approach, similar to the Hartree-Fock-Bogolyubov approximation in the notion of representative statistical ensembles, including the effect of a weakly broken U(1) symmetry. We apply our results on experimental data of the quantum magnet TlCuCl3 and show that magnetization curves and the energy dispersion can be well described within this approximation assuming that the BEC scenario is still valid. We predict that the shift of the critical temperature Tc due to a finite exchange anisotropy is rather substantial even when the anisotropy parameter γis small, e.g., ΔT_c \approx 10%$ of Tc in H = 6T and for γ\approx 4 μeV.

cond-mat.quant-gas↗