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Zhidong Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Spin-wave resonance frequency in a ferromagnetic thin film
    Journal of Magnetism and Magnetic Materials, 2013
    Co-Authors: Rong-ke Qiu, Zhi-yong Wang, Zhidong Zhang
    Abstract:

    Abstract The Spin-wave resonance (SWR) frequency in a ferromagnetic thin film with single-ion surface and bulk anisotropies has been studied by using the linear Spin-wave approximation and Green's function techniques. The effects of surface and bulk anisotropies, film thickness, Spin Quantum Number, and external magnetic field on the SWR frequency have been investigated. It is found that the SWR frequencies all increase, as the external magnetic field, the bulk anisotropy, and the Spin Quantum Number increase, respectively. The surface anisotropy affects strongly the SWR frequencies of the middle and low modes (except for the lowest one). With large bulk anisotropy, the surface anisotropy affects mainly the resonance frequency of the lowest Spin-wave mode. As the film thickness decreases, the SWR frequency of the same mode increases. The present results direct the method to enhance and adjust the SWR frequency of ferromagnetic thin films.

  • Effects of competition between the anisotropy and the Spin Quantum Number on the magnon energy gap in a four-layer ferromagnetic superlattice
    Journal of Magnetism and Magnetic Materials, 2009
    Co-Authors: Rong-ke Qiu, Pan-pan Song, Zhidong Zhang
    Abstract:

    The magnon energy bands are studied for a four-layer ferromagnetic superlattice, with regard to the effects of the competition between the anisotropy and the Spin Quantum Number. A spacial attention is also paid of the effects for the symmetry of the system. It is found that there modulated energy gaps exist in the magnon energy band along K(x) direction perpendicular to the superlattice plane. The magnetic anisotropy affects significantly the magnon energy gaps. The sero energy gap Dw(23) correlates with the conditions between anisotropy constants, D(1) + D(3) = D(2) + D(4) and D(1) + D(3) (or D(2) = D(4)), while the disappearance of the magnon energy gaps Dw(12) and Dw(34) corresponds to a translational symmetry of x-direction in a unit cell. When the parameters of the system deviate from these conditions, the energy gaps Dw(12), Dw(23) and Dw(34) become larger. There is a competition effect of the the anisotropy and the Spin Quantum Number on the magnon energy gaps Dw(12) and Dw(23). When the symmetry of the system is higher, the competition can achieve a balance to cause the sero energy gap. (C) Elsevier B.V. All rights reserved.

  • Quantum competitions between the effects of the interlayer exchange couplings and the magnetically structural symmetry in a four-layer ferrimagnetic superlattice
    Journal of Magnetism and Magnetic Materials, 2008
    Co-Authors: Rong-ke Qiu, Zhidong Zhang, Lian-quan Guo
    Abstract:

    The magnon energy spectra, the sublayer magnetization and the Quantum fluctuations in a ferrimagnetic superlattice consisting of four different magnetic sublayers are studied by employing the linear Spin-wave approach and Green's function technique. The effects of the interlayer exchange couplings and the Spin Quantum Numbers on the sublayer magnetization and the Quantum fluctuations of the systems are discussed for three different Spin configurations. The roles of Quantum competitions among the interlayer exchange couplings and the symmetry of the different Spin configurations have been understood. The magnetizations of some sublayers increase monotonously, while those of others can exhibit their maximum, and the Quantum fluctuations of the whole superlattice system can show a minimum when one of the antiferromagnetic interlayer exchange couplings increases. This is due to the Quantum competition/transmission of effects of the interlayer exchange couplings. When the Spin Quantum Number of sublayers varies, the system goes through from a Quantum region of small Spin Numbers to a classical region of large Spin Numbers. The Quantum fluctuations of the system exhibit a maximum as a function of the Spin Quantum Number of a sublayer, which is related with higher symmetry of the system. It belongs to the type III Shubnikov group of magnetic groups. This magnetically structural symmetry consists of not only the symmetry of space group, but also the symmetry of the direction and strength of Spins.

  • Four‐sublattice ferrimagnetic systems: II. Effects of the Spin Quantum Number
    physica status solidi (b), 2004
    Co-Authors: Rong-ke Qiu, Zhidong Zhang
    Abstract:

    The effects of the Spin Quantum Number of each sublattice on the Quantum fluctuations are discussed for different Spin configurations in four-sublattice ferrimagnetic systems. In multi- sublattice ferrimagnets, although the individual sublattice magnetization vectors do not offset each other, but their deviations vectors can cancel out. Namely, the sum of the deviations of magnetization of sites with same initiate Spin direction, equals to that of sites with opposite initiate Spin direction (Sigma(i) Deltam(0i) = Sigma(j) Deltam(0j), i and j denote respectively the Spins along the up and down initiate Spin directions). The role of the Spin Quantum Number of each site on magnetic properties of the system is correlative with properties of the exchange couplings surrounding the site. The results show that the proportion of ferromagnetic and antiferromagnetic exchange couplings, the Spin Quantum Number of each sublattice and the magnetically structural symmetry of the system all play important roles on the Quantum fluctuations of the systems.

  • four sublattice ferrimagnetic systems ii effects of the Spin Quantum Number
    Physica Status Solidi B-basic Solid State Physics, 2004
    Co-Authors: Rong-ke Qiu, Zhidong Zhang
    Abstract:

    The effects of the Spin Quantum Number of each sublattice on the Quantum fluctuations are discussed for different Spin configurations in four-sublattice ferrimagnetic systems. In multi- sublattice ferrimagnets, although the individual sublattice magnetization vectors do not offset each other, but their deviations vectors can cancel out. Namely, the sum of the deviations of magnetization of sites with same initiate Spin direction, equals to that of sites with opposite initiate Spin direction (Sigma(i) Deltam(0i) = Sigma(j) Deltam(0j), i and j denote respectively the Spins along the up and down initiate Spin directions). The role of the Spin Quantum Number of each site on magnetic properties of the system is correlative with properties of the exchange couplings surrounding the site. The results show that the proportion of ferromagnetic and antiferromagnetic exchange couplings, the Spin Quantum Number of each sublattice and the magnetically structural symmetry of the system all play important roles on the Quantum fluctuations of the systems.

Damian J J Farnell - One of the best experts on this subject based on the ideXlab platform.

  • ground state properties of the triangular lattice heisenberg antiferromagnet with arbitrary Spin Quantum Number s
    Journal of Magnetism and Magnetic Materials, 2016
    Co-Authors: O Gotze, J Richter, Ronald Zinke, Damian J J Farnell
    Abstract:

    We apply the coupled cluster method to high orders of approximation and exact diagonalizations to study the ground-state properties of the triangular-lattice Spin-s Heisenberg antiferromagnet. We calculate the fundamental ground-state quantities, namely, the energy e0, the sublattice magnetization Msub, the in-plane Spin stiffness ρs and the in-plane magnetic susceptibility χ for Spin Quantum Numbers s=1/2,1,…,smax, where smax=9/2 for e0 and Msub, smax=4 for ρs and smax=3 for χ . We use the data for s≥3/2 to estimate the leading Quantum corrections to the classical values of e0, Msub, ρs, and χ. In addition, we study the magnetization process, the width of the 1/3 plateau as well as the sublattice magnetizations in the plateau state as a function of the Spin Quantum Number s.

  • Influence of the Spin Quantum Number $s$ on the zero-temperature phase transition in the square lattice $J$-$J'$ model
    Journal of Physics: Condensed Matter, 2005
    Co-Authors: R. Darradi, Johannes Richter, Damian J J Farnell
    Abstract:

    We investigate the phase diagram of the Heisenberg antiferromagnet on the square lattice with two different nearest-neighbor bonds $J$ and $J'$ ($J$-$J'$ model) at zero temperature. The model exhibits a Quantum phase transition at a critical value $J'_c > J$ between a semi-classically ordered N\'eel and a magnetically disordered Quantum paramagnetic phase of valence-bond type, which is driven by local singlet formation on $J'$ bonds. We study the influence of Spin Quantum Number $s$ on this phase transition by means of a variational mean-field approach, the coupled cluster method, and the Lanczos exact-diagonalization technique. We present evidence that the critical value $J'_c$ increases with growing $s$ according to $J'_c \propto s(s+1)$.

  • influence of the Spin Quantum Number s on the zero temperature phase transition in the square lattice j j model
    arXiv: Strongly Correlated Electrons, 2004
    Co-Authors: R. Darradi, J Richter, Damian J J Farnell
    Abstract:

    We investigate the phase diagram of the Heisenberg antiferromagnet on the square lattice with two different nearest-neighbor bonds $J$ and $J'$ ($J$-$J'$ model) at zero temperature. The model exhibits a Quantum phase transition at a critical value $J'_c > J$ between a semi-classically ordered N\'eel and a magnetically disordered Quantum paramagnetic phase of valence-bond type, which is driven by local singlet formation on $J'$ bonds. We study the influence of Spin Quantum Number $s$ on this phase transition by means of a variational mean-field approach, the coupled cluster method, and the Lanczos exact-diagonalization technique. We present evidence that the critical value $J'_c$ increases with growing $s$ according to $J'_c \propto s(s+1)$.

  • coupled cluster method calculations of Quantum magnets with Spins of general Spin Quantum Number
    arXiv: Strongly Correlated Electrons, 2003
    Co-Authors: Damian J J Farnell, Rf Bishop, K. A. Gernoth
    Abstract:

    We present a new high-order coupled cluster method (CCM) formalism for the ground states of lattice Quantum Spin systems for general Spin Quantum Number, $s$. This new ``general-$s$'' formalism is found to be highly suitable for a computational implementation, and the technical details of this implementation are given. To illustrate our new formalism we perform high-order CCM calculations for the one-dimensional Spin-half and Spin-one antiferromagnetic {\it XXZ} models and for the one-dimensional Spin-half/Spin-one ferrimagnetic {\it XXZ} model. The results for the ground-state properties of the isotropic points of these systems are seen to be in excellent quantitative agreement with exact results for the special case of the Spin-half antiferromagnet and results of density matrix renormalisation group (DMRG) calculations for the other systems. Extrapolated CCM results for the sublattice magnetisation of the Spin-half antiferromagnet closely follow the exact Bethe Ansatz solution, which contains an infinite-order phase transition at $\Delta=1$. By contrast, extrapolated CCM results for the sublattice magnetisation of the Spin-one antiferromagnet using this same scheme are seen to go to zero at $\Delta \approx 1.2$, which is in excellent agreement with the value for the onset of the Haldane phase for this model. Results for sublattice magnetisations of the ferrimagnet for both the Spin-half and Spin-one Spins are non-zero and finite across a wide range of $\Delta$, up to and including the Heisenberg point at $\Delta=1$.

Rong-ke Qiu - One of the best experts on this subject based on the ideXlab platform.

  • Spin-wave resonance frequency in a ferromagnetic thin film
    Journal of Magnetism and Magnetic Materials, 2013
    Co-Authors: Rong-ke Qiu, Zhi-yong Wang, Zhidong Zhang
    Abstract:

    Abstract The Spin-wave resonance (SWR) frequency in a ferromagnetic thin film with single-ion surface and bulk anisotropies has been studied by using the linear Spin-wave approximation and Green's function techniques. The effects of surface and bulk anisotropies, film thickness, Spin Quantum Number, and external magnetic field on the SWR frequency have been investigated. It is found that the SWR frequencies all increase, as the external magnetic field, the bulk anisotropy, and the Spin Quantum Number increase, respectively. The surface anisotropy affects strongly the SWR frequencies of the middle and low modes (except for the lowest one). With large bulk anisotropy, the surface anisotropy affects mainly the resonance frequency of the lowest Spin-wave mode. As the film thickness decreases, the SWR frequency of the same mode increases. The present results direct the method to enhance and adjust the SWR frequency of ferromagnetic thin films.

  • Effects of competition between the anisotropy and the Spin Quantum Number on the magnon energy gap in a four-layer ferromagnetic superlattice
    Journal of Magnetism and Magnetic Materials, 2009
    Co-Authors: Rong-ke Qiu, Pan-pan Song, Zhidong Zhang
    Abstract:

    The magnon energy bands are studied for a four-layer ferromagnetic superlattice, with regard to the effects of the competition between the anisotropy and the Spin Quantum Number. A spacial attention is also paid of the effects for the symmetry of the system. It is found that there modulated energy gaps exist in the magnon energy band along K(x) direction perpendicular to the superlattice plane. The magnetic anisotropy affects significantly the magnon energy gaps. The sero energy gap Dw(23) correlates with the conditions between anisotropy constants, D(1) + D(3) = D(2) + D(4) and D(1) + D(3) (or D(2) = D(4)), while the disappearance of the magnon energy gaps Dw(12) and Dw(34) corresponds to a translational symmetry of x-direction in a unit cell. When the parameters of the system deviate from these conditions, the energy gaps Dw(12), Dw(23) and Dw(34) become larger. There is a competition effect of the the anisotropy and the Spin Quantum Number on the magnon energy gaps Dw(12) and Dw(23). When the symmetry of the system is higher, the competition can achieve a balance to cause the sero energy gap. (C) Elsevier B.V. All rights reserved.

  • Quantum competitions between the effects of the interlayer exchange couplings and the magnetically structural symmetry in a four-layer ferrimagnetic superlattice
    Journal of Magnetism and Magnetic Materials, 2008
    Co-Authors: Rong-ke Qiu, Zhidong Zhang, Lian-quan Guo
    Abstract:

    The magnon energy spectra, the sublayer magnetization and the Quantum fluctuations in a ferrimagnetic superlattice consisting of four different magnetic sublayers are studied by employing the linear Spin-wave approach and Green's function technique. The effects of the interlayer exchange couplings and the Spin Quantum Numbers on the sublayer magnetization and the Quantum fluctuations of the systems are discussed for three different Spin configurations. The roles of Quantum competitions among the interlayer exchange couplings and the symmetry of the different Spin configurations have been understood. The magnetizations of some sublayers increase monotonously, while those of others can exhibit their maximum, and the Quantum fluctuations of the whole superlattice system can show a minimum when one of the antiferromagnetic interlayer exchange couplings increases. This is due to the Quantum competition/transmission of effects of the interlayer exchange couplings. When the Spin Quantum Number of sublayers varies, the system goes through from a Quantum region of small Spin Numbers to a classical region of large Spin Numbers. The Quantum fluctuations of the system exhibit a maximum as a function of the Spin Quantum Number of a sublayer, which is related with higher symmetry of the system. It belongs to the type III Shubnikov group of magnetic groups. This magnetically structural symmetry consists of not only the symmetry of space group, but also the symmetry of the direction and strength of Spins.

  • Four‐sublattice ferrimagnetic systems: II. Effects of the Spin Quantum Number
    physica status solidi (b), 2004
    Co-Authors: Rong-ke Qiu, Zhidong Zhang
    Abstract:

    The effects of the Spin Quantum Number of each sublattice on the Quantum fluctuations are discussed for different Spin configurations in four-sublattice ferrimagnetic systems. In multi- sublattice ferrimagnets, although the individual sublattice magnetization vectors do not offset each other, but their deviations vectors can cancel out. Namely, the sum of the deviations of magnetization of sites with same initiate Spin direction, equals to that of sites with opposite initiate Spin direction (Sigma(i) Deltam(0i) = Sigma(j) Deltam(0j), i and j denote respectively the Spins along the up and down initiate Spin directions). The role of the Spin Quantum Number of each site on magnetic properties of the system is correlative with properties of the exchange couplings surrounding the site. The results show that the proportion of ferromagnetic and antiferromagnetic exchange couplings, the Spin Quantum Number of each sublattice and the magnetically structural symmetry of the system all play important roles on the Quantum fluctuations of the systems.

  • four sublattice ferrimagnetic systems ii effects of the Spin Quantum Number
    Physica Status Solidi B-basic Solid State Physics, 2004
    Co-Authors: Rong-ke Qiu, Zhidong Zhang
    Abstract:

    The effects of the Spin Quantum Number of each sublattice on the Quantum fluctuations are discussed for different Spin configurations in four-sublattice ferrimagnetic systems. In multi- sublattice ferrimagnets, although the individual sublattice magnetization vectors do not offset each other, but their deviations vectors can cancel out. Namely, the sum of the deviations of magnetization of sites with same initiate Spin direction, equals to that of sites with opposite initiate Spin direction (Sigma(i) Deltam(0i) = Sigma(j) Deltam(0j), i and j denote respectively the Spins along the up and down initiate Spin directions). The role of the Spin Quantum Number of each site on magnetic properties of the system is correlative with properties of the exchange couplings surrounding the site. The results show that the proportion of ferromagnetic and antiferromagnetic exchange couplings, the Spin Quantum Number of each sublattice and the magnetically structural symmetry of the system all play important roles on the Quantum fluctuations of the systems.

Bernhard G. Bodmann - One of the best experts on this subject based on the ideXlab platform.

  • A Lower Bound for the Wehrl Entropy of Quantum Spin with Sharp High-Spin Asymptotics
    Communications in Mathematical Physics, 2004
    Co-Authors: Bernhard G. Bodmann
    Abstract:

    A lower bound for the Wehrl entropy of a single Quantum Spin is derived. The high-Spin asymptotics of this bound coincides with Lieb’s conjecture up to, but not including, terms of first and higher order in the inverse Spin Quantum Number. The result presented here may be seen as complementary to the verification of the conjecture in cases of lowest Spin by Schupp [Commun. Math. Phys. 207 , 481 (1999)]. The present result for the Wehrl-entropy is obtained from interpolating a sharp norm bound that also implies a sharp lower bound for the so-called Rényi-Wehrl entropy with certain indices that are evenly spaced by half of the inverse Spin Quantum Number.

  • A lower bound for the Wehrl entropy of Quantum Spin with sharp high-Spin asymptotics
    Communications in Mathematical Physics, 2004
    Co-Authors: Bernhard G. Bodmann
    Abstract:

    A lower bound for the Wehrl entropy of a single Quantum Spin is derived. The high-Spin asymptotics of this bound coincides with Lieb's conjecture up to, but not including, terms of first and higher order in the inverse Spin Quantum Number. The result presented here may be seen as complementary to the verification of the conjecture in cases of lowest Spin by Schupp [Commun. Math. Phys. 207 (1999), 481]. The present result for the Wehrl-entropy is obtained from interpolating a sharp norm bound that also implies a sharp lower bound for the so-called R\'enyi-Wehrl entropy with certain indices that are evenly spaced by half of the inverse Spin Quantum Number.

Takeji Takui - One of the best experts on this subject based on the ideXlab platform.

  • Quantum chemistry on Quantum computers Quantum simulations of the time evolution of wave functions under the s2 operator and determination of the Spin Quantum Number s
    Physical Chemistry Chemical Physics, 2019
    Co-Authors: Kenji Sugisaki, Kazuo Toyota, Kazunobu Sato, Daisuke Shiomi, Shigeaki Nakazawa, Takeji Takui
    Abstract:

    Quantum computers have an enormous impact on Quantum chemical calculations. Approaches to calculate the energies of atoms and molecules on Quantum computers by utilizing Quantum phase estimation (QPE) and the variational Quantum eigensolver (VQE) have been well documented, and dozens of methodological improvements to decrease computational costs and to mitigate errors have been reported until recently. However, the possible methodological implementation of observables on Quantum computers such as calculating the Spin Quantum Numbers of arbitrary wave functions, which is a crucial issue in Quantum chemistry, has been discussed less. Here, we propose a Quantum circuit to simulate the time evolution of wave functions under an S2 operator, exp(−iS2t)|Ψ〉, and integrate it into the QPE circuit enabling us to determine the Spin Quantum Number of the arbitrary wave functions. We demonstrate that the Spin Quantum Numbers of up to three Spins can be determined by only one qubit measurement in QPE.

  • Quantum chemistry on Quantum computers: Quantum simulations of the time evolution of wave functions under the S2 operator and determination of the Spin Quantum Number S.
    Physical chemistry chemical physics : PCCP, 2019
    Co-Authors: Kenji Sugisaki, Kazuo Toyota, Kazunobu Sato, Daisuke Shiomi, Shigeaki Nakazawa, Takeji Takui
    Abstract:

    Quantum computers have an enormous impact on Quantum chemical calculations. Approaches to calculate the energies of atoms and molecules on Quantum computers by utilizing Quantum phase estimation (QPE) and the variational Quantum eigensolver (VQE) have been well documented, and dozens of methodological improvements to decrease computational costs and to mitigate errors have been reported until recently. However, the possible methodological implementation of observables on Quantum computers such as calculating the Spin Quantum Numbers of arbitrary wave functions, which is a crucial issue in Quantum chemistry, has been discussed less. Here, we propose a Quantum circuit to simulate the time evolution of wave functions under an S2 operator, exp(−iS2t)|Ψ〉, and integrate it into the QPE circuit enabling us to determine the Spin Quantum Number of the arbitrary wave functions. We demonstrate that the Spin Quantum Numbers of up to three Spins can be determined by only one qubit measurement in QPE.