1
|
Stepanov EA, Nomura Y, Lichtenstein AI, Biermann S. Orbital Isotropy of Magnetic Fluctuations in Correlated Electron Materials Induced by Hund's Exchange Coupling. PHYSICAL REVIEW LETTERS 2021; 127:207205. [PMID: 34860069 DOI: 10.1103/physrevlett.127.207205] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Revised: 06/16/2021] [Accepted: 10/01/2021] [Indexed: 06/13/2023]
Abstract
Characterizing nonlocal magnetic fluctuations in materials with strong electronic Coulomb interactions remains one of the major outstanding challenges of modern condensed matter theory. In this Letter, we address the spatial symmetry and orbital structure of magnetic fluctuations in perovskite materials. To this aim, we develop a consistent multiorbital diagrammatic extension of dynamical mean-field theory, which we apply to an anisotropic three-orbital model of cubic t_{2g} symmetry. We find that the form of spatial spin fluctuations is governed by the local Hund's coupling. For small values of the coupling, magnetic fluctuations are anisotropic in orbital space, which reflects the symmetry of the considered t_{2g} model. Large Hund's coupling enhances collective spin excitations, which mixes orbital and spatial degrees of freedom, and magnetic fluctuations become orbitally isotropic. Remarkably, this effect can be seen only in two-particle quantities; single-particle observables remain anisotropic for any value of the Hund's coupling. Importantly, we find that the orbital isotropy can be induced both at half filling and for the case of four electrons per lattice site, where the magnetic instability is associated with different, antiferromagnetic and ferromagnetic, modes, respectively.
Collapse
Affiliation(s)
- Evgeny A Stepanov
- I. Institute of Theoretical Physics, University of Hamburg, Jungiusstrasse 9, 20355 Hamburg, Germany
- Theoretical Physics and Applied Mathematics Department, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
| | - Yusuke Nomura
- RIKEN Center for Emergent Matter Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Alexander I Lichtenstein
- I. Institute of Theoretical Physics, University of Hamburg, Jungiusstrasse 9, 20355 Hamburg, Germany
- Theoretical Physics and Applied Mathematics Department, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
| | - Silke Biermann
- CPHT, CNRS, Ecole Polytechnique, Institut Polytechnique de Paris, F-91128 Palaiseau, France
- Collège de France, 11 place Marcelin Berthelot, 75005 Paris, France
| |
Collapse
|
2
|
Kar U, Singh AK, Yang S, Lin CY, Das B, Hsu CH, Lee WL. High-sensitivity of initial SrO growth on the residual resistivity in epitaxial thin films of SrRuO[Formula: see text] on SrTiO[Formula: see text] (001). Sci Rep 2021; 11:16070. [PMID: 34373527 PMCID: PMC8352924 DOI: 10.1038/s41598-021-95554-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2021] [Accepted: 07/28/2021] [Indexed: 11/09/2022] Open
Abstract
The growth of SrRuO[Formula: see text] (SRO) thin film with high-crystallinity and low residual resistivity (RR) is essential to explore its intrinsic properties. Here, utilizing the adsorption-controlled growth technique, the growth condition of initial SrO layer on TiO[Formula: see text]-terminated SrTiO[Formula: see text] (STO) (001) substrate was found to be crucial for achieving a low RR in the resulting SRO film grown afterward. The optimized initial SrO layer shows a c(2 [Formula: see text] 2) superstructure that was characterized by electron diffraction, and a series of SRO films with different thicknesses (ts) were then grown. The resulting SRO films exhibit excellent crystallinity with orthorhombic-phase down to [Formula: see text] 4.3 nm, which was confirmed by high resolution X-ray measurements. From X-ray azimuthal scan across SRO orthorhombic (02 ± 1) reflections, we uncover four structural domains with a dominant domain of orthorhombic SRO [001] along cubic STO [010] direction. The dominant domain population depends on t, STO miscut angle ([Formula: see text]), and miscut direction ([Formula: see text]), giving a volume fraction of about 92 [Formula: see text] for [Formula: see text] 26.6 nm and [Formula: see text] (0.14[Formula: see text], 5[Formula: see text]). On the other hand, metallic and ferromagnetic properties were well preserved down to t [Formula: see text] 1.2 nm. Residual resistivity ratio (RRR = [Formula: see text]/[Formula: see text]) reduces from 77.1 for t [Formula: see text] 28.5 nm to 2.5 for t [Formula: see text] 1.2 nm, while [Formula: see text] increases from 2.5 [Formula: see text]cm for t [Formula: see text] 28.5 nm to 131.0 [Formula: see text]cm for t [Formula: see text] 1.2 nm. The ferromagnetic onset temperature ([Formula: see text]) of around 151 K remains nearly unchanged down to t [Formula: see text] 9.0 nm and decreases to 90 K for t [Formula: see text] 1.2 nm. Our finding thus provides a practical guideline to achieve high crystallinity and low RR in ultra-thin SRO films by simply adjusting the growth of initial SrO layer.
Collapse
Affiliation(s)
- Uddipta Kar
- Institute of Physics, Academia Sinica, Nankang, 11529 Taipei Taiwan
- Nano Science and Technology, Taiwan International Graduate Program, Academia Sinica and National Taiwan University, Taipei, Taiwan
| | | | - Song Yang
- National Synchrotron Radiation Research Center, Hsinchu, 30076 Taiwan
| | - Chun-Yen Lin
- National Synchrotron Radiation Research Center, Hsinchu, 30076 Taiwan
| | - Bipul Das
- Institute of Physics, Academia Sinica, Nankang, 11529 Taipei Taiwan
| | - Chia-Hung Hsu
- National Synchrotron Radiation Research Center, Hsinchu, 30076 Taiwan
| | - Wei-Li Lee
- Institute of Physics, Academia Sinica, Nankang, 11529 Taipei Taiwan
| |
Collapse
|
3
|
Quantum transport evidence of Weyl fermions in an epitaxial ferromagnetic oxide. Nat Commun 2020; 11:4969. [PMID: 33037206 PMCID: PMC7547107 DOI: 10.1038/s41467-020-18646-8] [Citation(s) in RCA: 39] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2020] [Accepted: 09/06/2020] [Indexed: 11/13/2022] Open
Abstract
Magnetic Weyl semimetals have novel transport phenomena related to pairs of Weyl nodes in the band structure. Although the existence of Weyl fermions is expected in various oxides, the evidence of Weyl fermions in oxide materials remains elusive. Here we show direct quantum transport evidence of Weyl fermions in an epitaxial 4d ferromagnetic oxide SrRuO3. We employ machine-learning-assisted molecular beam epitaxy to synthesize SrRuO3 films whose quality is sufficiently high to probe their intrinsic transport properties. Experimental observation of the five transport signatures of Weyl fermions—the linear positive magnetoresistance, chiral-anomaly-induced negative magnetoresistance, π phase shift in a quantum oscillation, light cyclotron mass, and high quantum mobility of about 10,000 cm2V−1s−1—combined with first-principles electronic structure calculations establishes SrRuO3 as a magnetic Weyl semimetal. We also clarify the disorder dependence of the transport of the Weyl fermions, which gives a clear guideline for accessing the topologically nontrivial transport phenomena. Despite various predictions, the evidence of Weyl fermions in oxide materials remains elusive. Here, the authors show evidence of Weyl fermions in quantum transport measurements in an epitaxial ferromagnetic oxide SrRuO3.
Collapse
|
4
|
Dwivedi GD, Wu CM, Chen BY, Lin ST, Qiu WZ, Sun SJ, Xu G, Lynn JW, Chiou JW, Lee CH, Li WH, Yano S, Chou H. Magnon profile on SrRuO 3 films studied by inelastic neutron scattering. PHYSICAL REVIEW. B 2020; 101:10.1103/PhysRevB.101.054403. [PMID: 38855404 PMCID: PMC11160330 DOI: 10.1103/physrevb.101.054403] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2024]
Abstract
In this study, the inelastic neutron scattering probe of SIKA in ANSTO is employed to investigate the magnon dispersion curve in ferromagnetic SrRuO3 single crystal epitaxial films and to better understand the underlying mechanisms. This report presents the successful measurement of a magnon peak from the SrRuO3 films which contained an amount of material of only 0.9 mg. We reveal one significant magnon dispersion curve along [002] following the quadraticE ∝ Q 2 ) relation, which shows a magnon gap of 0.32 meV. We have discussed several possible mechanisms, such as the higher symmetry structure and the impurity levels, which may contribute to this smaller gap.
Collapse
Affiliation(s)
- G. D. Dwivedi
- Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan, 80424, R.O.C
| | - C.-M. Wu
- National Synchrotron Radiation Research Center, Hsinchu, Taiwan, 30076, R.O.C. and Australian Nuclear Science and Technology Organization, New South Wales, Australia
| | - Bo-Yu Chen
- Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan, 80424, R.O.C
| | - S. T. Lin
- Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan, 80424, R.O.C
| | - W.-Z. Qiu
- Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan, 80424, R.O.C
| | - S. J. Sun
- Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan, 80424, R.O.C
- Department of Applied Physics, National University of Kaohsiung, Kaohsiung, Taiwan, R.O.C
| | - Guangyong Xu
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - J. W. Lynn
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
| | - J. W. Chiou
- Department of Applied Physics, National University of Kaohsiung, Kaohsiung, Taiwan, R.O.C
| | - C.-H Lee
- Department of Physics, National Central University, Taoyuan City, Taiwan, R.O.C
| | - W.-H. Li
- Department of Physics, National Central University, Taoyuan City, Taiwan, R.O.C
| | - S. Yano
- National Synchrotron Radiation Research Center, Hsinchu, Taiwan, 30076, R.O.C. and Australian Nuclear Science and Technology Organization, New South Wales, Australia
| | - H. Chou
- Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan, 80424, R.O.C
- Department of Applied Physics, National University of Kaohsiung, Kaohsiung, Taiwan, R.O.C
| |
Collapse
|