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Publications (10 of 17) Show all publications
Hasan, M. N., Bharati, R., Hellsvik, J., Delin, A., Pal, S. K., Bergman, A., . . . Karmakar, D. (2023). Magnetism in A V3Sb5 (A=Cs, Rb, and K): Origin and Consequences for the Strongly Correlated Phases. Physical Review Letters, 131(19), Article ID 196702.
Open this publication in new window or tab >>Magnetism in A V3Sb5 (A=Cs, Rb, and K): Origin and Consequences for the Strongly Correlated Phases
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2023 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 131, no 19, article id 196702Article in journal (Refereed) Published
Abstract [en]

The V-based kagome systems AV3Sb5 (A=Cs, Rb, and K) are unique by virtue of the intricate interplay of nontrivial electronic structure, topology, and intriguing fermiology, rendering them to be a playground of many mutually dependent exotic phases like charge-order and superconductivity. Despite numerous recent studies, the interconnection of magnetism and other complex collective phenomena in these systems has yet not arrived at any conclusion. Using first-principles tools, we demonstrate that their electronic structures, complex fermiologies and phonon dispersions are strongly influenced by the interplay of dynamic electron correlations, nontrivial spin-polarization and spin-orbit coupling. An investigation of the first-principles-derived intersite magnetic exchanges with the complementary analysis of q dependence of the electronic response functions and the electron-phonon coupling indicate that the system conforms as a frustrated spin cluster, where the occurrence of the charge-order phase is intimately related to the mechanism of electron-phonon coupling, rather than the Fermi-surface nesting.

Place, publisher, year, edition, pages
American Physical Society (APS), 2023
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-340287 (URN)10.1103/PhysRevLett.131.196702 (DOI)001155751900003 ()38000423 (PubMedID)2-s2.0-85177068595 (Scopus ID)
Note

QC 20231201

Available from: 2023-12-01 Created: 2023-12-01 Last updated: 2024-02-29Bibliographically approved
Karmakar, D., Pereiro, M., Hasan, M. N., Bharati, R., Hellsvik, J., Delin, A., . . . Eriksson, O. (2023). Magnetism in A V3Sb5 (A=Cs, Rb, K): Complex landscape of dynamical magnetic textures. Physical Review B, 108(17), Article ID 174413.
Open this publication in new window or tab >>Magnetism in A V3Sb5 (A=Cs, Rb, K): Complex landscape of dynamical magnetic textures
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2023 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, no 17, article id 174413Article in journal (Refereed) Published
Abstract [en]

We have investigated the dynamical magnetic properties of the V-based kagome stibnite compounds by combining the ab initio-extracted magnetic parameters of a spin-Hamiltonian, like inter-site exchange parameters, magnetocrystalline anisotropy and site projected magnetic moments, with full-fledged simulations of atomistic spin- dynamics. Our calculations reveal that, in addition to a ferromagnetic order along the [001] direction, the system hosts a complex landscape of magnetic configurations comprised of commensurate and incommensurate spin spirals along the [010] direction. The presence of such chiral magnetic textures may be the key toward solving the mystery about the origin of the experimentally observed inherent breaking of the C6 rotational, mirror, and the time-reversal symmetry.

Place, publisher, year, edition, pages
American Physical Society (APS), 2023
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-340288 (URN)10.1103/PhysRevB.108.174413 (DOI)001101171600002 ()2-s2.0-85177045826 (Scopus ID)
Note

QC 20231201

Available from: 2023-12-01 Created: 2023-12-01 Last updated: 2024-02-29Bibliographically approved
Nocerino, E., Stuhr, U., San Lorenzo, I., Mazza, F., Mazzone, D. G., Hellsvik, J., . . . Månsson, M. (2023). Q-dependent electron-phonon coupling induced phonon softening and non-conventional critical behavior in the CDW superconductor LaPt2Si2. Journal of Science: Advanced Materials and Devices, 8(4), Article ID 100621.
Open this publication in new window or tab >>Q-dependent electron-phonon coupling induced phonon softening and non-conventional critical behavior in the CDW superconductor LaPt2Si2
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2023 (English)In: Journal of Science: Advanced Materials and Devices, ISSN 2468-2284, Vol. 8, no 4, article id 100621Article in journal (Refereed) Published
Abstract [en]

This paper reports the first experimental observation of phonons and their softening on single crystalline LaPt2Si2 via inelastic neutron scattering. From the temperature dependence of the phonon frequency in close proximity to the charge density wave (CDW) q-vector, we obtain a CDW transition temperature of TCDW = 230 K and a critical exponent β = 0.28 ± 0.03. This value is suggestive of a non-conventional critical behavior for the CDW phase transition in LaPt2Si2, compatible with a scenario of CDW discommensuration (DC). The DC would be caused by the existence of two CDWs in this material, propagating separately in the non equivalent (Si1–Pt2–Si1) and (Pt1–Si2–Pt1) layers, respectively, with transition temperatures TCDW−1 = 230 K and TCDW−2 = 110 K. A strong q-dependence of the electron-phonon coupling has been identified as the driving mechanism for the CDW transition at TCDW−1 = 230 K while a CDW with 3-dimensional character, and Fermi surface quasi-nesting as a driving mechanism, is suggested for the transition at TCDW−2 = 110 K. Our results clarify some aspects of the CDW transition in LaPt2Si2 which have been so far misinterpreted by both theoretical predictions and experimental observations and give direct insight into its actual temperature dependence.

Place, publisher, year, edition, pages
Elsevier BV, 2023
Keywords
CDW discommensuration, Charge density wave, Inelastic neutron scattering, Phonon softening, Unconventional superconductivity
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-336308 (URN)10.1016/j.jsamd.2023.100621 (DOI)001147608200001 ()2-s2.0-85169506032 (Scopus ID)
Note

QC 20240209

Available from: 2023-09-13 Created: 2023-09-13 Last updated: 2024-02-09Bibliographically approved
John Mukkattukavil, D., Hellsvik, J., Ghosh, A., Chatzigeorgiou, E., Nocerino, E., Wang, Q., . . . Sassa, Y. (2022). Resonant inelastic soft x-ray scattering on LaPt2Si2. Journal of Physics: Condensed Matter, 34(32), 324003, Article ID 324003.
Open this publication in new window or tab >>Resonant inelastic soft x-ray scattering on LaPt2Si2
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2022 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 34, no 32, p. 324003-, article id 324003Article in journal (Refereed) Published
Abstract [en]

X-ray absorption and resonant inelastic x-ray scattering spectra of LaPt2Si2 single crystal at the Si 2p and La 4d edges are presented. The data are interpreted in terms of density functional theory, showing that the Si spectra can be described in terms of Si s and d local partial density of states (LPDOS), and the La spectra are due to quasi-atomic local 4f excitations. Calculations show that Pt d-LPDOS dominates the occupied states, and a sharp localized La f state is found in the unoccupied states, in line with the observations.

Place, publisher, year, edition, pages
IOP Publishing, 2022
Keywords
resonant inelastic x-ray scattering, superconductivity, charge density wave, local partial density of states
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-315229 (URN)10.1088/1361-648X/ac7500 (DOI)000811482300001 ()35640576 (PubMedID)2-s2.0-85132455088 (Scopus ID)
Note

QC 20220701

Available from: 2022-07-01 Created: 2022-07-01 Last updated: 2023-12-07Bibliographically approved
Sadhukhan, B., Bergman, A., Kvashnin, Y. O., Hellsvik, J. & Delin, A. (2022). Spin-lattice couplings in two-dimensional CrI3 from first-principles computations. Physical Review B, 105(10), Article ID 104418.
Open this publication in new window or tab >>Spin-lattice couplings in two-dimensional CrI3 from first-principles computations
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2022 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, no 10, article id 104418Article in journal (Refereed) Published
Abstract [en]

Since thermal fluctuations become more important as dimensions shrink, it is expected that low-dimensional magnets are more sensitive to atomic displacement and phonons than bulk systems are. Here we present a fully relativistic first-principles study on the spin-lattice coupling, i.e., how the magnetic interactions depend on atomic displacement, of the prototypical two-dimensional ferromagnet CrI3. We extract an effective measure of the spin-lattice coupling in CrI3, which is up to ten times larger than what is found for bcc Fe. The magnetic exchange interactions, including Heisenberg and relativistic Dzyaloshinskii-Moriya interactions, are sensitive both to the in-plane motion of Cr atoms and out-of-plane motion of ligand atoms. We find that significant magnetic pair interactions change sign from ferromagnetic (FM) to antiferromagnetic (AFM) for atomic displacements larger than 0.16 (0.18) angstrom for Cr (I) atoms. We explain the observed strong spin-lattice coupling by analyzing the orbital decomposition of isotropic exchange interactions, involving different crystal-field-split Cr-3d orbitals. The competition between the AFM t(2g)-t(2g) and FM t(2g)-e(g) contributions depends on the bond angle formed by Cr and I atoms as well as Cr-Cr distance. In particular, if a Cr atom is displaced, the FM-AFM sign changes when the I-Cr-I bond angle approaches 90 degrees. The obtained spin-lattice coupling constants, along with the microscopic orbital analysis, can act as a guiding principle for further studies of the thermodynamic properties and combined magnon-phonon excitations in two-dimensional magnets.

Place, publisher, year, edition, pages
American Physical Society (APS), 2022
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-313711 (URN)10.1103/PhysRevB.105.104418 (DOI)000800750800002 ()2-s2.0-85126926112 (Scopus ID)
Note

QC 20220610

Available from: 2022-06-10 Created: 2022-06-10 Last updated: 2022-06-25Bibliographically approved
Olsthoorn, B., Hellsvik, J. & Balatsky, A. V. (2020). Finding hidden order in spin models with persistent homology. Physical Review Research, 2(4), Article ID 043308.
Open this publication in new window or tab >>Finding hidden order in spin models with persistent homology
2020 (English)In: Physical Review Research, E-ISSN 2643-1564, Vol. 2, no 4, article id 043308Article in journal (Refereed) Published
Abstract [en]

Persistent homology (PH) is a relatively new field in applied mathematics that studies the components and shapes of discrete data. In this paper, we demonstrate that PH can be used as a universal framework to identify phases of classical spins on a lattice. This demonstration includes hidden order such as spin-nematic ordering and spin liquids. By converting a small number of spin configurations to barcodes we obtain a descriptive picture of configuration space. Using dimensionality reduction to reduce the barcode space to color space leads to a visualization of the phase diagram.

Place, publisher, year, edition, pages
American Physical Society (APS), 2020
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-289550 (URN)10.1103/PhysRevResearch.2.043308 (DOI)000605417800005 ()2-s2.0-85099286295 (Scopus ID)
Note

QC 20210204

Available from: 2021-02-04 Created: 2021-02-04 Last updated: 2024-03-18Bibliographically approved
Hellsvik, J., Perez, R. D., Geilhufe, M., Månsson, M. & Balatsky, A. V. (2020). Spin wave excitations of magnetic metalorganic materials. Physical Review Materials, 4(2), Article ID 024409.
Open this publication in new window or tab >>Spin wave excitations of magnetic metalorganic materials
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2020 (English)In: Physical Review Materials, E-ISSN 2475-9953, Vol. 4, no 2, article id 024409Article in journal (Refereed) Published
Abstract [en]

The Organic Materials Database (OMDB) is an open database hosting about 22 000 electronic band structures, density of states, and other properties for stable and previously synthesized three-dimensional organic crystals. The web interface of the OMDB offers various search tools for the identification of novel functional materials such as band structure pattern matching and density of states similarity search. In this work, the OMDB is extended to include magnetic excitation properties. For inelastic neutron scattering, we focus on the dynamic structure factor S(q, omega) which contains information on the excitation modes of the material. We introduce a new dataset containing atomic magnetic moments and Heisenberg exchange parameters for which we calculate the spin wave spectra and dynamic structure factor with linear spin wave theory and atomistic spin dynamics. We thus develop the materials informatics tools to identify novel functional organic and metalorganic magnets.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2020
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-270883 (URN)10.1103/PhysRevMaterials.4.024409 (DOI)000514191700003 ()2-s2.0-85082840322 (Scopus ID)
Note

QC 20200325

Available from: 2020-03-25 Created: 2020-03-25 Last updated: 2023-01-02Bibliographically approved
Hellsvik, J., Thonig, D., Modin, K., Iusan, D., Bergman, A., Eriksson, O., . . . Delin, A. (2019). General method for atomistic spin-lattice dynamics with first-principles accuracy. Physical Review B, 99(10), Article ID 104302.
Open this publication in new window or tab >>General method for atomistic spin-lattice dynamics with first-principles accuracy
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 10, article id 104302Article in journal (Refereed) Published
Abstract [en]

We present a computationally efficient and general first-principles based method for spin-lattice simulations for solids and clusters. The method is based on a coupling of atomistic spin dynamics and molecular dynamics simulations, expressed through a spin-lattice Hamiltonian, where the bilinear magnetic term is expanded up to second order in displacement. The effect of first-order spin-lattice coupling on the magnon and phonon dispersion in bcc Fe is reported as an example, and we observe good agreement with previous simulations. We also illustrate the coupled spin-lattice dynamics method on a more conceptual level, by exploring dissipation-free spin and lattice motion of small magnetic clusters (a dimer, trimer, and tetramer). The method discussed here opens the door for a quantitative description and understanding of the microscopic origin of many fundamental phenomena of contemporary interest, such as ultrafast demagnetization, magnetocalorics, and spincaloritronics.

Place, publisher, year, edition, pages
American Physical Society, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-248337 (URN)10.1103/PhysRevB.99.104302 (DOI)000461953800003 ()2-s2.0-85063194644 (Scopus ID)
Note

QC 20210602

Available from: 2019-04-10 Created: 2019-04-10 Last updated: 2024-03-18Bibliographically approved
Shirinyan, A. A., Kozin, V. K., Hellsvik, J., Pereiro, M., Eriksson, O. & Yudin, D. (2019). Self-organizing maps as a method for detecting phase transitions and phase identification. Physical Review B, 99(4), Article ID 041108.
Open this publication in new window or tab >>Self-organizing maps as a method for detecting phase transitions and phase identification
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 4, article id 041108Article in journal (Refereed) Published
Abstract [en]

Originating from image recognition, methods of machine learning allow for effective feature extraction and dimensionality reduction in multidimensional datasets, thereby providing an extraordinary tool to deal with classical and quantum models in many-body physics. In this study, we employ a specific unsupervised machine learning technique-self-organizing maps-to create a low-dimensional representation of microscopic states, relevant for macroscopic phase identification and detecting phase transitions. We explore the properties of spin Hamiltonians of two archetype model systems: a two-dimensional Heisenberg ferromagnet and a three-dimensional crystal, Fe in the body-centered-cubic structure. The method of self-organizing maps, which is known to conserve connectivity of the initial dataset, is compared to the cumulant method theory and is shown to be as accurate while being computationally more efficient in determining a phase transition temperature. We argue that the method proposed here can be applied to explore a broad class of second-order phase-transition systems, not only magnetic systems but also, for example, order-disorder transitions in alloys.

Place, publisher, year, edition, pages
American Physical Society, 2019
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-242980 (URN)10.1103/PhysRevB.99.041108 (DOI)000455825600002 ()2-s2.0-85059904004 (Scopus ID)
Funder
EU, Horizon 2020Swedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research Swedish Energy AgencyeSSENCE - An eScience CollaborationStandUp
Note

QC 20190204

Available from: 2019-02-04 Created: 2019-02-04 Last updated: 2022-06-26Bibliographically approved
Paul, S., Iuşan, D., Thunström, P., Kvashnin, Y. O., Hellsvik, J., Pereiro, M., . . . Eriksson, O. (2018). Investigation of the spectral properties and magnetism of BiFeO3 by dynamical mean-field theory. Physical Review B, 97(12), Article ID 125120.
Open this publication in new window or tab >>Investigation of the spectral properties and magnetism of BiFeO3 by dynamical mean-field theory
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2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 12, article id 125120Article in journal (Refereed) Published
Abstract [en]

Using the local density approximation plus dynamical mean-field theory (LDA+DMFT), we have computed the valence-band photoelectron spectra and magnetic excitation spectra of BiFeO3, one of the most studied multiferroics. Within the DMFT approach, the local impurity problem is tackled by the exact diagonalization solver. The solution of the impurity problem within the LDA+DMFT method for the paramagnetic and magnetically ordered phases produces result in agreement with the experimental data on electronic and magnetic structures. For comparison, we also present results obtained by the LDA+U approach which is commonly used to compute the physical properties of this compound. Our LDA+DMFT derived electronic spectra match adequately with the experimental hard x-ray photoelectron spectroscopy and resonant photoelectron spectroscopy for Fe 3d states, whereas the LDA+U method fails to capture the general features of the measured spectra. This indicates the importance of accurately incorporating the dynamical aspect of electronic correlation among Fe 3d orbitals to reproduce the experimental excitation spectra. Specifically, the LDA+DMFT derived density of states exhibits a significant amount of Fe 3d states at the position of Bi lone pairs, implying that the latter are not alone in the spectral scenario. This fact might modify our interpretation about the origin of ferroelectric polarization in this material. Our study demonstrates that the combination of orbital cross sections for the constituent elements and broadening schemes for the spectral functions are crucial to explain the detailed structures of the experimental electronic spectra. Our magnetic excitation spectra computed from the LDA+DMFT result conform well with the inelastic neutron scattering data.

Place, publisher, year, edition, pages
American Physical Society, 2018
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-224813 (URN)10.1103/PhysRevB.97.125120 (DOI)000427602000002 ()2-s2.0-85043987943 (Scopus ID)
Funder
Swedish Energy AgencyCarl Tryggers foundation Swedish Research CouncilKnut and Alice Wallenberg Foundation, 2012.0031 2013.0020
Note

QC 20180327

Available from: 2018-03-27 Created: 2018-03-27 Last updated: 2024-03-18Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-0210-4340

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