| 1. |
- Azimi Mousolou, Vahid, et al.
(författare)
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Entanglement duality in spin-spin interactions
- 2022
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 106:3
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Tidskriftsartikel (refereegranskat)abstract
- We examine entanglement of thermal states for spin-1/2 dimers in external magnetic fields. Entanglement transition in the temperature-magnetic-field plane demonstrates a duality in spin-spin interactions. This identifies a pair of dual categories of symmetric and antisymmetric dimers with each category classified into toric entanglement classes. The entanglement transition line is preserved from each toric entanglement class to its dual toric class. The toric classification is an indication of the topological signature of the entanglement, which bring about topological stability that could be relevant for quantum information processing.
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| 2. |
- Azimi Mousolou, Vahid, et al.
(författare)
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Hierarchy of magnon mode entanglement in antiferromagnets
- 2020
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Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 102:22
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Tidskriftsartikel (refereegranskat)abstract
- Continuous variable entanglement between magnon modes in Heisenberg antiferromagnets with Dzyaloshinskii-Moriya (DM) interaction is examined. Different bosonic modes are identified, which allows us to establish a hierarchy of magnon entanglement. We argue that entanglement between magnon modes is determined by a simple lattice-specific parameter, together with the ratio of the strengths of the DM and Heisenberg exchange interactions, and that magnon entanglement can be detected by means of quantum homodyne techniques. As an illustration of the relevance of our findings for possible entanglement experiments in the solid state, a typical antiferromagnet with the perovskite crystal structure is considered, and it is shown that long wave length magnon modes have a maximal degree of entanglement.
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| 3. |
- Azimi Mousolou, Vahid, et al.
(författare)
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Magnon-magnon entanglement and its quantification via a microwave cavity
- 2021
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 104:22
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Tidskriftsartikel (refereegranskat)abstract
- Quantum magnonics is an emerging research field, with great potential for applications in magnon based hybrid systems and quantum information processing. Quantum correlation, such as entanglement, is a central resource in many quantum information protocols that naturally comes about in any study toward quantum technologies. This applies also to quantum magnonics. Here, we investigate antiferromagnetic coupling of two ferromagnetic sublattices that can have two different magnon modes. We show how this may lead to experimentally measurable bipartite continuous-variable magnon-magnon entanglement. The entanglement can be fully characterized via a single squeezing parameter or, equivalently, entanglement parameter. The clear relation between the entanglement parameter and the Einstein, Podolsky, and Rosen (EPR) function of the ground state opens up for experimental quantification magnon-magnon continuous-variable entanglement and EPR nonlocality. We propose a practical experimental realization to measure the EPR function of the ground state, in a setting that relies on magnon-photon interaction in a microwave cavity.
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| 4. |
- Azimi Mousolou, Vahid, et al.
(författare)
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Transmon probe for quantum characteristics of magnons in antiferromagnets
- 2023
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 108:9
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Tidskriftsartikel (refereegranskat)abstract
- The detection of magnons and their quantum properties, especially in antiferromagnetic (AFM) materials, is a substantial step to realize many ambitious advances in the study of nanomagnetism and the development of energy efficient quantum technologies. The recent development of hybrid systems based on superconducting circuits provides the possibility to engineer quantum sensors that exploit different degrees of freedom. Here, we examine the magnon-photon-transmon hybridization based on bipartite AFM materials, which gives rise to an effective coupling between a transmon qubit and magnons in a bipartite AFM. We demonstrate how magnon modes, their chiralities, and quantum properties, such as nonlocality and two-mode magnon entanglement in bipartite AFMs, can be characterized through the Rabi frequency of the superconducting transmon qubit.
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| 5. |
- Belotcerkovtceva, Daria, et al.
(författare)
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Insights and Implications of Intricate Surface Charge Transfer and sp3-Defects in Graphene/Metal Oxide Interfaces
- 2022
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 14:31, s. 36209-36216
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Tidskriftsartikel (refereegranskat)abstract
- Adherence of metal oxides to graphene is of fundamental significance to graphene nanoelectronic and spintronic interfaces. Titanium oxide and aluminum oxide are two widely used tunnel barriers in such devices, which offer optimum interface resistance and distinct interface conditions that govern transport parameters and device performance. Here, we reveal a fundamental difference in how these metal oxides interface with graphene through electrical transport measurements and Raman and photoelectron spectroscopies, combined with ab initio electronic structure calculations of such interfaces. While both oxide layers cause surface charge transfer induced p-type doping in graphene, in sharp contrast to TiOx, the AlOx/graphene interface shows the presence of appreciable sp3 defects. Electronic structure calculations disclose that significant p-type doping occurs due to a combination of sp3 bonds formed between C and O atoms at the interface and possible slightly off-stoichiometric defects of the aluminum oxide layer. Furthermore, the sp3 hybridization at the AlOx/graphene interface leads to distinct magnetic moments of unsaturated bonds, which not only explicates the widely observed low spin-lifetimes in AlOx barrier graphene spintronic devices but also suggests possibilities for new hybrid resistive switching and spin valves.
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| 6. |
- Borisov, Vladislav, et al.
(författare)
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Heisenberg and anisotropic exchange interactions in magnetic materials with correlated electronic structure and significant spin-orbit coupling
- 2021
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 103:17
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Tidskriftsartikel (refereegranskat)abstract
- The Dzyaloshinskii-Moriya (DM) interaction, as well as symmetric anisotropic exchange, are important ingredients for stabilizing topologically nontrivial magnetic textures, such as, e.g., skyrmions, merons, and hopfions. These types of textures are currently in focus from a fundamental science perspective and they are also discussed in the context of future spintronics information technology. While the theoretical understanding of the Heisenberg exchange interactions is well developed, it is still a challenge to access, from first principles theory, the DM interaction as well as the symmetric anisotropic exchange, which both require a fully-relativistic treatment of the electronic structure, in magnetic systems where substantial electron-electron correlations are present. Here, we present results of a theoretical framework which allows to compute these interactions in any given system and demonstrate its performance for several selected cases, for both bulk and low-dimensional systems. We address several representative cases, including the bulk systems CoPt and FePt, the B20 compounds MnSi and FeGe as well as the low-dimensional transition metal bilayers Co/Pt(111) andMn/W(001). The effect of electron-electron correlations is analyzed using dynamical mean-field theory on the level of the spin-polarized T -matrix + fluctuating exchange (SPTF) approximation, as regards the strength and character of the isotropic (Heisenberg) and anisotropic (DM) interactions in relation to the underlying electronic structure. Our method can be combined with more advanced techniques for treating correlations, e.g., quantum Monte Carlo and exact diagonalization methods for the impurity solver of dynamical mean-field theory. We find that correlation-induced changes of the DM interaction can be rather significant, with up to fivefold modifications in the most distinctive case.
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| 7. |
- Borisov, Vladislav, et al.
(författare)
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Tuning skyrmions in B20 compounds by 4d and 5d doping
- 2022
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Ingår i: Physical Review Materials. - : American Physical Society (APS). - 2475-9953. ; 6:8
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Tidskriftsartikel (refereegranskat)abstract
- Skyrmion stabilization in novel magnetic systems with the B20 crystal structure is reported here, primarily based on theoretical results. The focus is on the effect of alloying on the 3d sublattice of the B20 structure by substitution of heavier 4d and 5d elements, with the ambition to tune the spin-orbit coupling and its influence on magnetic interactions. State-of-the-art methods based on density functional theory are used to calculate both isotropic and anisotropic exchange interactions. Significant enhancement of the Dzyaloshinskii-Moriya interaction is reported for 5d-doped FeSi and CoSi, accompanied by a large modification of the spin stiffness and spiralization. Micromagnetic simulations coupled to atomistic spin-dynamics and ab initio magnetic interactions reveal the spin-spiral nature of the magnetic ground state and field-induced skyrmions for all these systems. Especially small skyrmions similar to 50 nm are predicted for Co0.75Os0.25Si, compared to similar to 148 nm for Fe0.75Co0.25Si. Convex-hull analysis suggests that all B20 compounds considered here are structurally stable at elevated temperatures and should be possible to synthesize. This prediction is confirmed experimentally by synthesis and structural analysis of the Ru-doped CoSi systems discussed here, both in powder and in single-crystal forms.
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| 8. |
- Cardias, Ramon, et al.
(författare)
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Comment on "Proper and improper chiral magnetic interactions"
- 2022
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Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 105:2
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Tidskriftsartikel (refereegranskat)abstract
- In a recent paper by dos Santos Dias et al. [Phys. Rev. B 103, L140408 (2021)], a critique of earlier works analyzing low-energy spin Hamiltonians is put forth. To be precise, it is the large noncollinear contributions to the Dzyaloshinskii-Moriya interaction (DMI) that is the main concern of dos Santos Dias et al. In this Comment, we clarify the microscopic mechanisms for the large DMI that can be found in noncollinear magnets. Furthermore, we outline the complementary nature of the different parametrizations of a spin Hamiltonian, with strengths and weaknesses of both approaches. Specifically, we stress the physical insight in the interpretation of the DMI, when decomposed in microscopic electron and spin densities and currents.
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| 9. |
- Cardias, Ramon, et al.
(författare)
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Coupled spin-lattice dynamics from the tight-binding electronic structure
- 2024
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 109:14
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Tidskriftsartikel (refereegranskat)abstract
- We developed a method which performs the coupled adiabatic spin and lattice dynamics based on the tight-binding electronic structure model, where the intrinsic magnetic field and ionic forces are calculated from the converged self-consistent electronic structure at every time step. By doing so, this method allows us to explore limits where the physics described by a parameterized spin-lattice Hamiltonian is no longer accurate. We demonstrate how the lattice dynamics is strongly influenced by the underlying magnetic configuration, where disorder is able to induce significant lattice distortions. The presented method requires significantly less computational resources than ab initio methods, such as time-dependent density functional theory (TD-DFT). Compared to parameterized Hamiltonian-based methods, it also describes more accurately the dynamics of the coupled spin and lattice degrees of freedom, which becomes important outside of the regime of small lattice and spin fluctuations.
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| 10. |
- Chimata, Raghuveer, et al.
(författare)
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Magnetism and ultrafast magnetization dynamics of Co and CoMn alloys at finite temperature
- 2017
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 95:21
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Tidskriftsartikel (refereegranskat)abstract
- Temperature-dependent magnetic experiments such as pump-probe measurements generated by a pulsed laser have become a crucial technique for switching the magnetization in the picosecond time scale. Apart from having practical implications on the magnetic storage technology, the research field of ultrafast magnetization poses also fundamental physical questions. To correctly describe the time evolution of the atomic magnetic moments under the influence of a temperature-dependent laser pulse, it remains crucial to know if the magnetic material under investigation has magnetic excitation spectrum that is more or less dependent on the magnetic configuration, e.g., as reflected by the temperature dependence of the exchange interactions. In this paper, we demonstrate from first-principles theory that the magnetic excitation spectra in Co in fcc, bcc, and hcp structures are nearly identical in a wide range of noncollinear magnetic configurations. This is a curious result of a balance between the size of the magnetic moments and the strength of the Heisenberg exchange interactions, that in themselves vary with configuration, but put together in an effective spin Hamiltonian results in a configuration-independent effective model. We have used such a Hamiltonian, together with ab initio calculated damping parameters, to investigate the magnon dispersion relationship as well as ultrafast magnetization dynamics of Co and Co-rich CoMn alloys.
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