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Current-linear emergent induction of pinned skyrmion textures in an oxide bilayer
Authors:
Ludwig Scheuchenpflug,
Sebastian Esser,
Robert Gruhl,
Max Hirschberger,
Philipp Gegenwart
Abstract:
Emergent electromagnetic induction (EEMI) induced through current-driven spin dynamics was recently predicted and subsequently observed in helical spin magnets, opening a new direction in spintronics and paving the way towards further miniaturization of electronic circuit elements. In contrast to conventional inductors consisting of coil-like structures whose inductance $L$ shows a linear dependen…
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Emergent electromagnetic induction (EEMI) induced through current-driven spin dynamics was recently predicted and subsequently observed in helical spin magnets, opening a new direction in spintronics and paving the way towards further miniaturization of electronic circuit elements. In contrast to conventional inductors consisting of coil-like structures whose inductance $L$ shows a linear dependence on the cross-section $A$, emergent inductors exhibit an inverse ($\propto {A}^{-1}$) proportionality, favorable for the miniaturization of electrical devices. However, the expected current-linear response of the EEMI voltage has not been demonstrated. Magnetic skyrmions hold promise as a simple platform to study the conceptual foundations of EEMI from current-driven spin dynamics. We fabricated devices of thin film bilayers of ferromagnetic SrRuO$_3$ and paramagnetic SrIrO$_3$, which are known to host interfacial Néel skyrmions detected by the appearance of a topological Hall-effect (THE). A large, positive and current-linear inductive response is found to accompany the THE. In our experiment, the current-induced dynamics of pinned magnetic skyrmions creates a voltage both parallel and perpendicular to the applied electric current flow, corresponding to longitudinal and transverse induction, respectively. This is the first report of transverse EEMI, indicating an angle of $80^{\circ}$ between skyrmion motion and the applied current. Our observation of current-linear longitudinal and transverse EEMI is a hallmark of pinned dynamics of magnetic skyrmion textures in oxide heterostructures.
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Submitted 13 March, 2025;
originally announced March 2025.
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Lattice-commensurate skyrmion texture in a centrosymmetric breathing kagome magnet
Authors:
Max Hirschberger,
Bertalan G. Szigeti,
Mamoun Hemmida,
Moritz M. Hirschmann,
Sebastian Esser,
Hiroyuki Ohsumi,
Yoshikazu Tanaka,
Leonie Spitz,
Shang Gao,
Kamil K. Kolincio,
Hajime Sagayama,
Hironori Nakao,
Yuichi Yamasaki,
László Forró,
Hans-Albrecht Krug von Nidda,
István Kézsmárki,
Taka-hisa Arima,
Yoshinori Tokura
Abstract:
Skyrmion lattices (SkL) in centrosymmetric materials typically have a magnetic period on the nanometer-scale, so that the coupling between magnetic superstructures and the underlying crystal lattice cannot be neglected. Here, we reveal the commensurate locking of a SkL to the atomic lattice in Gd$_3$Ru$_4$Al$_{12}$ via high-resolution resonant elastic x-ray scattering (REXS). Weak easy-plane magne…
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Skyrmion lattices (SkL) in centrosymmetric materials typically have a magnetic period on the nanometer-scale, so that the coupling between magnetic superstructures and the underlying crystal lattice cannot be neglected. Here, we reveal the commensurate locking of a SkL to the atomic lattice in Gd$_3$Ru$_4$Al$_{12}$ via high-resolution resonant elastic x-ray scattering (REXS). Weak easy-plane magnetic anisotropy, demonstrated here by a combination of ferromagnetic resonance and REXS, penalizes placing a skyrmion core on a site of the atomic lattice. Under these conditions, a commensurate SkL, locked to the crystal lattice, is stable at finite temperatures -- but gives way to a competing incommensurate ground state upon cooling. We discuss the role of Umklapp-terms in the Hamiltonian for the formation of this lattice-locked state, its magnetic space group, the role of slight discommensurations, or (line) defects in the magnetic texture, and contrast our findings with the case of SkLs in noncentrosymmetric material platforms.
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Submitted 8 March, 2024;
originally announced March 2024.
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Strong terahertz third-harmonic generation by kinetic heavy quasiparticles in CaRuO$_3$
Authors:
C. Reinhoffer,
Sven Esser,
Sebastian Esser,
E. A. Mashkovich,
S. Germanskiy,
P. Gegenwart,
F. Anders,
P. H. M. van Loosdrecht,
Zhe Wang
Abstract:
We report on time-resolved nonlinear terahertz spectroscopy of a strongly correlated ruthenate, CaRuO$_3$, as a function of temperature, frequency and terahertz field strength. Third-harmonic radiation for frequencies up to 2.1 THz is observed evidently at low temperatures below 80 K, where the low-frequency linear dynamical response deviates from the Drude model and a coherent heavy quasiparticle…
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We report on time-resolved nonlinear terahertz spectroscopy of a strongly correlated ruthenate, CaRuO$_3$, as a function of temperature, frequency and terahertz field strength. Third-harmonic radiation for frequencies up to 2.1 THz is observed evidently at low temperatures below 80 K, where the low-frequency linear dynamical response deviates from the Drude model and a coherent heavy quasiparticle band emerges by strong correlations associated with the Hund's coupling.Phenomenologically, by taking an experimentally observed frequency-dependent scattering rate, the deviation of the field driven kinetics from the Drude behavior is reconciled in a time-dependent Boltzmann description, which allows an attribution of the observed third-harmonic generation to the terahertz field driven nonlinear kinetics of the heavy quasiparticles.
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Submitted 9 October, 2023;
originally announced October 2023.
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Non-coplanar helimagnetism in the layered van-der-Waals metal DyTe$_3$
Authors:
Shun Akatsuka,
Sebastian Esser,
Shun Okumura,
Ryota Yambe,
Rinsuke Yamada,
Moritz M. Hirschmann,
Seno Aji,
Jonathan S. White,
Shang Gao,
Yoshichika Onuki,
Taka-hisa Arima,
Taro Nakajima,
Max Hirschberger
Abstract:
Magnetic materials with highly anisotropic chemical bonding can be exfoliated to realize ultrathin sheets or interfaces with highly controllable optical or spintronics responses, while also promising novel cross-correlation phenomena between electric polarization and the magnetic texture. The vast majority of these van-der-Waals magnets are collinear ferro-, ferri-, or antiferromagnets, with a par…
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Magnetic materials with highly anisotropic chemical bonding can be exfoliated to realize ultrathin sheets or interfaces with highly controllable optical or spintronics responses, while also promising novel cross-correlation phenomena between electric polarization and the magnetic texture. The vast majority of these van-der-Waals magnets are collinear ferro-, ferri-, or antiferromagnets, with a particular scarcity of lattice-incommensurate helimagnets of defined left- or right-handed rotation sense, or helicity. Here we use polarized neutron scattering to reveal cycloidal, or conical, magnetic structures in DyTe$_3$, with coupled commensurate and incommensurate order parameters, where covalently bonded double-slabs of dysprosium square nets are separated by highly metallic tellurium layers. Based on this ground state and its evolution in a magnetic field as probed by small-angle neutron scattering (SANS), we establish a one-dimensional spin model with off-diagonal on-site terms, spatially modulated by the unconventional charge order in DyTe$_3$. The CDW-driven term couples to antiferromagnetism, or to the net magnetization in applied magnetic field, and creates a complex magnetic phase diagram indicative of competing interactions in an easily cleavable helimagnet. Our work paves the way for twistronics research, where helimagnetic layers can be combined to form complex spin textures on-demand, using the vast family of rare earth chalcogenides and beyond.
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Submitted 28 January, 2024; v1 submitted 7 June, 2023;
originally announced June 2023.
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Electronic reconstruction and charge transfer in strained Sr$_2$CoIrO$_6$ double perovskite
Authors:
Jiongyao Wu,
Marcel Ney,
Sebastian Esser,
Vijaya Begum,
Günther Prinz,
Axel Lorke,
Philipp Gegenwart,
Rossitza Pentcheva
Abstract:
The electronic, magnetic and optical properties of the double perovskite Sr$_2$CoIrO$_6$ (SCIO) under biaxial strain are explored in the framework of density functional theory (DFT) including a Hubbard $U$ term and spin-orbit coupling (SOC) in combination with absorption spectroscopy measurements on epitaxial thin films. While the end member SrIrO$_3$ is a semimetal with a quenched spin and orbita…
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The electronic, magnetic and optical properties of the double perovskite Sr$_2$CoIrO$_6$ (SCIO) under biaxial strain are explored in the framework of density functional theory (DFT) including a Hubbard $U$ term and spin-orbit coupling (SOC) in combination with absorption spectroscopy measurements on epitaxial thin films. While the end member SrIrO$_3$ is a semimetal with a quenched spin and orbital moment and bulk SrCoO$_3$ is a ferromagnetic (FM) metal with spin and orbital moment of 2.50 and 0.13 $μ_{B}$, respectively, the double perovskite SCIO emerges as an antiferromagnetic Mott insulator with antiparallel alignment of Co, Ir planes along the [110]-direction. Co exhibits a spin and enhanced orbital moment of $\sim 2.35-2.45$ and $0.31-$0.45 $μ_{B}$, respectively. Most remarkably, Ir acquires a significant spin and orbital moment of 1.21-1.25 and 0.13 $μ_{B}$, respectively. Analysis of the orbital occupation indicates an electronic reconstruction due to a substantial charge transfer from minority to majority spin states in Ir and from Ir to Co, signaling an Ir$^{4+δ}$, Co$^{4-δ}$ configuration. Biaxial strain, varied from -1.02% ($a_{\rm NdGaO_3}$) through 0% ($a_{\rm SrTiO_3}$) to 1.53% ($a_{\rm GdScO_3}$), influences in partcular the orbital polarization of the $t_{2g}$ states and leads to a nonmonotonic change of the band gap between 163 and 235 meV. The absorption coefficient reveals a two plateau fearure due to transitions from the valence to the lower lying narrow $t_{2g}$ and the higher lying broader $e_{g}$ bands. Inclusion of many body effects, in particular, excitonic effects by solving the Bethe-Salpeter equation (BSE), increases the band gap by $\sim0.2$ and improves the agreement with the measured spectrum concerning the position of the second peak at $\sim 2.6$ eV.
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Submitted 19 October, 2021;
originally announced October 2021.
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Angular dependence of Hall effect and magnetoresistance in SrRuO$_3$-SrIrO$_3$ heterostructures
Authors:
Sven Esser,
Jiongyao Wu,
Sebastian Esser,
Robert Gruhl,
Anton Jesche,
Vladimir Roddatis,
Vasily Moshnyaga,
Rossitza Pentcheva,
Philipp Gegenwart
Abstract:
Perovskite SrRuO$_3$ is a prototypical itinerant ferromagnet which allows interface engineering of its electronic and magnetic properties. We report synthesis and investigation of atomically flat artificial multilayers of SrRuO$_3$ with the spin-orbit semimetal SrIrO$_3$ in combination with band-structure calculations with a Hubbard $U$ term and topological analysis. They reveal an electronic reco…
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Perovskite SrRuO$_3$ is a prototypical itinerant ferromagnet which allows interface engineering of its electronic and magnetic properties. We report synthesis and investigation of atomically flat artificial multilayers of SrRuO$_3$ with the spin-orbit semimetal SrIrO$_3$ in combination with band-structure calculations with a Hubbard $U$ term and topological analysis. They reveal an electronic reconstruction and emergence of flat Ru-4d$_{xz}$ bands near the interface, ferromagnetic interlayer coupling and negative Berry-curvature contribution to the anomalous Hall effect. We analyze the Hall effect and magnetoresistance measurements as a function of the field angle from out of plane towards in-plane orientation (either parallel or perpendicular to the current direction) by a two-channel model. The magnetic easy direction is tilted by about $20^\circ$ from the sample normal for low magnetic fields, rotating towards the out-of-plane direction by increasing fields. Fully strained epitaxial growth enables a strong anisotropy of magnetoresistance. An additional Hall effect contribution, not accounted for by the two-channel model is compatible with stable skyrmions only up to a critical angle of roughly $45^\circ$ from the sample normal. Within about $20^\circ$ from the thin film plane an additional peak-like contribution to the Hall effect suggests the formation of a non-trivial spin structure.
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Submitted 27 May, 2021;
originally announced May 2021.
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Strain induced changes of electronic properties of B-site ordered double perovskite Sr$_2$CoIrO$_6$ thin films
Authors:
S. Esser,
C. F. Chang,
C. -Y. Kuo,
S. Merten,
V. Roddatis,
T. D. Ha,
A. Jesche,
V. Moshnyaga,
H. -J. Lin,
A. Tanaka,
C. T. Chen,
L. H. Tjeng,
P. Gegenwart
Abstract:
B-site ordered thin films of double perovskite Sr$_2$CoIrO$_6$ were epitaxially grown by a metal-organic aerosol deposition technique on various substrates, actuating different strain states. X-ray diffraction, transmission electron microscopy and polarized far-field Raman spectroscopy confirm the strained epitaxial growth on all used substrates. Polarization dependent Co $L_{2,3}$ X-ray absorptio…
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B-site ordered thin films of double perovskite Sr$_2$CoIrO$_6$ were epitaxially grown by a metal-organic aerosol deposition technique on various substrates, actuating different strain states. X-ray diffraction, transmission electron microscopy and polarized far-field Raman spectroscopy confirm the strained epitaxial growth on all used substrates. Polarization dependent Co $L_{2,3}$ X-ray absorption spectroscopy reveals a change of the magnetic easy axis of the antiferromagnetically ordered (high-spin) Co$^{3+}$ sublattice within the strain series. By reversing the applied strain direction from tensile to compressive, the easy axis changes abruptly from in-plane to out-of-plane orientation. The low-temperature magnetoresistance changes its sign respectively and is described by a combination of weak anti-localization and anisotropic magnetoresistance effects.
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Submitted 16 April, 2018; v1 submitted 11 January, 2018;
originally announced January 2018.
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Electronic and Spin States of SrRuO3 Thin Films: an X-ray Magnetic Circular Dichroism Study
Authors:
S. Agrestini,
Z. Hu,
C. -Y. Kuo,
1 M. W. Haverkort,
K. -T. Ko,
N. Hollmann,
Q. Liu,
E. Pellegrin,
M. Valvidares,
J. Herrero-Martin,
P. Gargiani,
P. Gegenwart,
M. Schneider,
S. Esser,
A. Tanaka,
A. C. Komarek,
L. H. Tjeng
Abstract:
We report a study of the local magnetism in thin films of SrRuO3 grown on (111) and (001) oriented SrTiO3 substrates using x-ray magnetic circular dichroism spectroscopy (XMCD) at the Ru-L2,3 edges. The application of the sum rules to the XMCD data gives an almost quenched orbital moment and a spin moment close to the value expected for the low spin state S = 1 . Full-multiplet cluster calculation…
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We report a study of the local magnetism in thin films of SrRuO3 grown on (111) and (001) oriented SrTiO3 substrates using x-ray magnetic circular dichroism spectroscopy (XMCD) at the Ru-L2,3 edges. The application of the sum rules to the XMCD data gives an almost quenched orbital moment and a spin moment close to the value expected for the low spin state S = 1 . Full-multiplet cluster calculations indicate that the low spin state is quite stable and suggest that the occurrence of a transition to the high spin state S = 2 in strained thin films of SrRuO3 is unlikely as it would be too expensive in energy.
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Submitted 27 January, 2015;
originally announced January 2015.
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Nonlinear conductivity in CaRuO3 thin films measured by short current pulses
Authors:
Sven Esser,
Sebastian Esser,
Christian Stingl,
Philipp Gegenwart
Abstract:
Metals near quantum critical points have been predicted to display universal out-of equilibrium behavior in the steady current-carrying state. We have studied the non-linear conductivity of high-quality CaRuO$_3$ thin films with residual resistivity ratio up to 57 using micro-second short, high-field current pulses at low temperatures. Even for the shortest pulses of $5μ$s, Joule heating persists,…
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Metals near quantum critical points have been predicted to display universal out-of equilibrium behavior in the steady current-carrying state. We have studied the non-linear conductivity of high-quality CaRuO$_3$ thin films with residual resistivity ratio up to 57 using micro-second short, high-field current pulses at low temperatures. Even for the shortest pulses of $5μ$s, Joule heating persists, making it impossible to observe a possible universal non-linearity. Much shorter pulses are needed for the investigation of universal non-linear conductivity.
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Submitted 27 February, 2014;
originally announced February 2014.
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Low-energy electronic properties of clean CaRuO$_3$: elusive Landau quasiparticles
Authors:
M. Schneider,
D. Geiger,
S. Esser,
U. S. Pracht,
C. Stingl,
Y. Tokiwa,
V. Moshnyaga,
I. Sheikin,
J. Mravlje,
M. Scheffler,
P. Gegenwart
Abstract:
We have prepared high-quality epitaxial thin films of CaRuO$_3$ with residual resistivity ratios up to 55. Shubnikov-de Haas oscillations in the magnetoresistance and a $T^2$ temperature dependence in the electrical resistivity only below 1.5 K, whose coefficient is substantially suppressed in large magnetic fields, establish CaRuO$_3$ as a Fermi liquid (FL) with anomalously low coherence scale. N…
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We have prepared high-quality epitaxial thin films of CaRuO$_3$ with residual resistivity ratios up to 55. Shubnikov-de Haas oscillations in the magnetoresistance and a $T^2$ temperature dependence in the electrical resistivity only below 1.5 K, whose coefficient is substantially suppressed in large magnetic fields, establish CaRuO$_3$ as a Fermi liquid (FL) with anomalously low coherence scale. Non-Fermi liquid (NFL) $T^{3/2}$ dependence is found between 2 and 25 K. The high sample quality allows access to the intrinsic electronic properties via THz spectroscopy. For frequencies below 0.6 THz, the conductivity is Drude-like and can be modeled by FL concepts, while for higher frequencies non-Drude behavior, inconsistent with FL predictions, is found. This establishes CaRuO$_3$ as a prime example of optical NFL behavior in the THz range.
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Submitted 13 December, 2013;
originally announced December 2013.