We have used Raman scattering to investigate the magnetic excitations and lattice dynamics in the prototypical spin-orbit Mott insulators Sr2IrO4 and Sr3Ir2O7. Both compounds exhibit pronounced two-magnon Raman scattering features with different energies, lineshapes, and temperature dependencies, which in part reflect the different influence of long-range frustrating exchange interactions. Additionally, we find strong Fano asymmetries in the lineshapes of low-energy phonon modes in both compounds, which disappear upon cooling below the antiferromagnetic ordering temperatures. These unusual phonon anomalies indicate that the spin-orbit coupling in Mott-insulating iridates is not sufficiently strong to quench the orbital dynamics in the paramagnetic state.
We report the observation of the $A_{\rm g}$-symmetric one-magnon Raman peak in the magnon Bose-Einstein condensation phase of TlCuCl$_{3}$. Its Raman shift traces the one-magnon energy at the magnetic $Γ$ point, and its intensity is proportional to the squared transverse magnetization. The appearance of the one-magnon Raman scattering originates from the exchange magnon Raman process and reflects the change of the magnetic-state symmetry. Using the bond-operator representation, we theoretically clarify the Raman selection rules, being consistent with the experimental results.
Inelastic light scattering spectra of several members of the RFe3(BO3)4 family reveal a cascade of phase transitions as a function of temperature, starting with a structural, weakly first order, phase transition followed by two magnetic phase transitions. Those consist of the ordering of the Fe-spin sublattice revealed by all the compound, and a subsequent spin-reorientational transition for GdFe3(BO3)4. The Raman data evidence a strong coupling between the lattice and magnetic degrees of freedom in these borates. The Fe-sublattice ordering leads to a strong suppression of the low energy magne…
We investigate two-magnon Raman scattering from the $S=1/2$ Heisenberg antiferromagnet on the triangular lattice, considering both the effect of renormalization of the one-magnon spectrum by 1/S corrections and final-state magnon-magnon interactions. The bare Raman intensity displays two peaks related to one-magnon van-Hove singularities. We find that 1/S self-energy corrections to the one-magnon spectrum strongly modify this intensity profile. The central Raman-peak is significantly enhanced due to plateaus in the magnon dispersion, the high frequency peak is suppressed due to magnon damping,…
We study the two-magnon non-resonant Raman scattering in the (pi,pi) and (pi,0) ordered antiferromagnetic phases of a J1x-J1y-J2-Jc Heisenberg model on the tetragonal lattice within the framework of the spin-wave theory. We discuss the effects of various tuning factors to the two-magnon Raman spectra. We find that both the magnetic frustration J2/J1 and the interlayer exchange coupling Jc may significantly affect the spectra in both the B1g and A1g' channels in the (pi,pi) Neel ordered phase. Moreover, we find a splitting of the two-magnon peak in the (pi,0) antiferromagnetic phase. We further…
We calculate the two-magnon Raman scattering spectra in antiferromagnetic phases of several frustrated spin models defined on the honeycomb lattice. These include the Néel antiferromagnetic phase of a $J_1$-$J_2$-$J_3$ model and the stripe phase of the Heisenberg-Kitaev model. We show that both the magnetic frustration and the anisotropy of interactions may significantly affect the Raman spectra. We further discuss the implications of our results to the magnetic excitations of the iron-based compound BaFe$_2$Se$_2$O and show how the magnetic interactions can be extracted from fit to the Raman …
We present a theory for Raman scattering on 2D quantum antiferromagnets. The microscopic Fleury-Loudon Hamiltonian is expressed in terms of an effective $O(3)$ - model. Well within the Néel ordered phase, the Raman spectrum contains a two-magnon and a two-Higgs contribution, which are calculated diagramatically. The vertex functions for both the Higgs and magnon contributions are determined from a numerical solution of the corresponding Bethe-Salpeter equation. Due to the momentum dependence of the Raman vertex in the relevant $B_{1g}+E_{2g}$ symmetry, the contribution from the Higgs mode is s…
We evaluate the Raman light scattering intensity for the square lattice Heisenberg antiferromagnet with plaquette ring exchange J_\Box. With the exchange couplings as fixed before from an accurate fit to the spin-wave dispersion in La2CuO4, leading in particular to J_\Box=0.24J, we demonstrate in a parameter free calculation that the inclusion of the plaquette exchange contribution to the dispersion and the magnon-magnon interaction vertex gives a peak position in $B_{1g}$ scattering geometry E_max = 2.71J which is in excellent agreement with the experimental data. Yet, the intrinsic width and…
We investigate the one-magnon Raman scattering in the layered antiferromagnetic La(2)CuO(4) compound. We find that the Raman signal is composed by two one-magnon peaks: one in the B1g channel, corresponding to the Dzyaloshinskii-Moryia (DM) mode, and another in the B3g channel, corresponding to the XY mode. Furthermore, we show that a peak corresponding to the XY mode can be induced in the planar (RR) geometry when a magnetic field is applied along the easy axis for the sublattice magnetization. The appearance of such field-induced mode (FIM) signals the existence of a new magnetic state above…
Leggett's mode is a collective excitation corresponding to the oscillation of the relative phase of the order parameters in a two band superconductor, with frequency proportional to interband coupling. We report on the existence of modes, similar to Leggett's mode, in magnetic systems with Jahn-Teller distortion. The minimal Kugel-Khomskii model, which describes simultaneously both the spin and the orbital order, is studied. The dynamical degrees of freedom are spin-$s$ operators of localized spins and pseudospin-$τ$ operators, which respond to the orbital degeneracy and satisfy the similar co…
The relation between the electronic excitation and the magnetic excitation for the superconductivity in Bi2Sr2Ca{1-x}YxCu2O{8+δ} was investigated by wide-energy Raman spectroscopy. In the underdoping region the B1g scattering intensity is depleted below the two-magnon peak energy due to the "hot spots" effects. The depleted region decreases according to the decrease of the two-magnon peak energy, as the carrier concentration ncreases. This two-magnon peak energy also determines the B1g superconducting gap energy as $2Δ\approx α\hbar ω_{\rm Two-Magnon} \approx J_{\rm effective}$ $(α=0.34-0.41)$…
Unconventional peak structure in the Raman spectra due to magnon excitation at low temperature is observed in spinel magnet ${\rm MnV_2O_4}$, where a noncollinear spin state is realized by geometrical frustration. We propose a new mechanism to induce such a Raman scattering process due to a one-magnon excitation of the noncollinear spin state. Novel features of the scattering such as selection rules and peak position observed experimentally in ${\rm MnV_2O_4}$ can be explained quite naturally by considering the present one-magnon process. We also discuss that such one-magnon process may exist …
We investigate the resonant two-magnon Raman scattering in two-dimensional (2D) Mott insulators by using a half-filled 2D Hubbard model in the strong coupling limit. By performing numerical diagonalization calculations for small clusters, we find that the Raman intensity is enhanced when the incoming photon energy is not near the optical absorption edge but well above it, being consistent with experimental data. The absence of resonance near the gap edge is associated with the presence of background spins, while photoexcited states for resonance are found to be characterized by the charge degr…
We suggest a family of spin-ladder models with exact singlet-rung vacuum. In addition to the terms describing interactions along legs and rungs the Hamiltonian has frustration and cyclic terms. Using coordinate Bethe ansatze all one- and two-dimensional states are constructed. The explicit formula for zero-temperature Raman scattering cross section is derived. The corresponding line-shapes are strongly asymmetric and have no more than one van-Hove singularity. The results are in good agreement with experimental data.
Nuclear spin-lattice relaxation in one-dimensional Heisenberg ferrimagnets is studied by means of a modified spin-wave theory. We consider the second-order process, where a nuclear spin flip induces virtual spin waves which are then scattered thermally via the four-magnon exchange interaction, as well as the first-order process, where a nuclear spin directly interacts with spin waves via the hyperfine interaction. We point out a possibility of the three-magnon relaxation process predominating over the Raman one and suggest model experiments.
We investigate the resonant two-magnon Raman scattering in the two-dimensional (2D) and ladder-type Mott insulators by using a half-filled Hubbard model in the strong coupling limit. By performing numerical diagonalization calculations for small clusters, we find that the model can reproduce the experimental features in the 2D that the Raman intensity is enhanced when the incoming photon energy is not near the absorption edge but well above it. In the ladder-type Mott insulators, the Raman intensity is found to resonate with absorption spectrum in contrast to the 2D system. The difference betw…
We reported two-magnon Raman scattering from La_{1.9}Sr_{0.1}CuO_4, which has a suppressed Tc=12 K, as the temperature is lowered below 37 K and an ordered spin phase is formed. The two-magnon Raman intensity increases with decreasing temperature. The magnetic scattering in La_{1.9}Sr_{0.1}CuO_4 is totally different from that reported in the parent compound La_2CuO_4. We analyze the line shape of the two-magnon scattering within the traditional Loudon-Fleury theory and find the superexchange constant J=1052 cm^{-1}. The calculation of the frequency moment suggests that the quantum fluctuations…
Although the parent iron-based pnictides and chalcogenides are itinerant antiferromagnets, the use of local moment picture to understand their magnetic properties is still widespread. We study magnetic Raman scattering from a local moment perspective for various quantum spin models proposed for this new class of superconductors. These models vary greatly in the level of magnetic frustration and show a vastly different two-magnon Raman response. Light scattering by two-magnon excitations thus provides a robust and independent measure of the underlying spin interactions. In accord with other rec…
Nuclear spin-lattice relaxation in one-dimensional Heisenberg ferrimagnets is studied by means of a modified spin-wave theory. Calculating beyond the first-order mechanism, where a nuclear spin directly interacts with spin waves through the hyperfine coupling, we demonstrate that the exchange-scattering-enhanced three-magnon nuclear relaxation may generally predominate over the Raman one with increasing temperature and decreasing field. Recent proton spin-lattice relaxation-time (T_1_) measurements on the ferrimagnetic chain compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O suggest that the majo…
We investigate the two-magnon Raman scattering from an anisotropic S=1/2 triangular Heisenberg antiferromagnet Cs2CuCl4. We find that the Raman response is very sensitive to magnon-magnon interactions and to scattering geometries, a feature that is in remarkable contrast with the polarization-independent Raman signal from the isotropic triangular Heisenberg antiferromagnet. Since a spin-liquid ground state gives rise to a similar rotationally invariant Raman response, our results on the polarization dependence of the scattering spectrum suggest that Raman spectroscopy provides a useful probe, …
We study the inelastic neutron scattering cross section in the vicinity of touching points in magnon bands. Among the possible touching points are magnon Weyl points in three dimensional ordered magnets with significant spin-orbit coupling that are characterized by a linear dispersion in their vicinity. A Weyl point is topologically protected by its net chirality and here we show that this leads to a characteristic form for the dynamical structure factor. To address this question, we show that scattering intensities in the vicinity of arbitrary magnon two-band touching points are identical to …
Signature of Magnon-Raman Phonon-Polariton Condensation in a Cavity via Transverse Pumping
Birla Institute of Technology and Science, Pilani-Dubai Campus（比拉理工学院，皮拉尼-迪拜校区）；Birla Institute of Technology and Science, Pilani, Hyderabad Campus（比拉理工学院，海德拉巴校区）
In a magnetic substance the gap in the Raman spectrum, Delta_R, is approximatively twice the value of the neutron scattering gap, Delta_S, if the the magnetic excitations (magnons) are only weakly interacting. But for CuGeO_3 the experimentally observed ratio Delta_R/Delta_S is approximatively 1.49-1.78, indicating attractive magnon-magnon interactions in the quasi-1D Spin-Peierls compound CuGe_3. We present numerical estimates for Delta_R/Delta_S from exact diagonalization studies for finite chains and find agreement with experiment for intermediate values of the frustration parameter alpha. …
Spin-orbit entangled pseudospins hold promise for a wide array of exotic magnetism ranging from a Heisenberg antiferromagnet to a Kitaev spin liquid depending on the lattice and bonding geometry, but many of the host materials suffer from lattice distortions and deviate from idealized models in part due to inherent strong pseudospin-lattice coupling. Here, we report on the synthesis of a magnetic superlattice comprising the single ($n$=1) and the double ($n$=2) layer members of the Ruddlesden-Popper series iridates Sr$_{n+1}$Ir$_{n}$O$_{3n+1}$ alternating along the $c$-axis, and provide a comp…
We present a theory of the Raman scattering from the orbital wave excitations in manganese oxides. Two excitation processes of the Raman scattering are proposed. The Raman scattering cross section is formulated by using the pseudospin operator for orbital degree of freedom in a Mn ion. The Raman spectra from the orbital wave excitations are calculated and their implications in the recent experimental results reported in LaMnO$_3$ are discussed.
Measurement and control of magnetic order and correlations in real time is a rapidly developing scientific area relevant for magnetic memory and spintronics [1,15]. In these experiments an ultra-short laser pulse (pump) is first absorbed by excitations carrying electric dipole moment. These then give their energy to the magnetic subsystem monitored by a time-resolved probe. A lot of progress has been made in investigations of ferromagnets but antiferromagnets are more challenging. Here we introduce time-resolved two-magnon Raman scattering as a novel real time probe of magnetic correlations es…
We present the Raman-scattering spectra of CaV2O5 and MgV2O5. The magnetic contribution in the Raman spectra of CaV2O5 is found in the form of a strong asymmetric line, centered at 2Delta, with a tail on the high-energy side. Our analysis of its spectral shape shows that the magnetic ordering in CaV2O5 can be described using a S=1/2 two-leg ladder Heisenberg antiferromagnetic model with Jparallel/Jperp = 0.1, and a small interladder exchange. The spin gap and exchange constant are estimated to be Delta = 400 cm-1 (570 K) and Jperp = 640 K. No magnon bound states are found. In contrast to CaV2O…
We have studied the magnetic excitations of electron-doped Sr$_{2-x}$La$_x$IrO$_4$ ($0 \leq x \leq 0.10$) using resonant inelastic x-ray scattering (RIXS) at the Ir L$_3$-edge. The long range magnetic order is rapidly lost with increasing $x$, but two-dimensional short-range order (SRO) and dispersive magnon excitations with nearly undiminished spectral weight persist well into the metallic part of the phase diagram. The magnons in the SRO phase are heavily damped and exhibit anisotropic softening. Their dispersions are well described by a pseudospin-1/2 Heisenberg model with exchange interact…
Using Raman spectroscopy, we investigate the lattice phonons, magnetic excitations, and magneto-elastic coupling in the distorted triangular-lattice Heisenberg antiferromagnet alpha-SrCr2O4, which develops helical magnetic order below 43 K. Temperature dependent phonon spectra are compared to predictions from density functional theory calculations which allows us to assign the observed modes and identify weak effects arising from coupled lattice and magnetic degrees of freedom. Raman scattering associated with two-magnon excitations is observed at 20 meV and 40 meV. These energies are in gener…
Towards the First Realization of Weyl Magnons in the Non-Coplanar Antiferromagnet MnTe$_2$
The Ohio State University（俄亥俄州立大学）；National Institute of Standards and Technology（美国国家标准与技术研究院）；Oak Ridge National Laboratory（橡树岭国家实验室）；Duke University（杜克大学）
We apply torque equilibrium spin wave theory (TESWT) to investigate an anisotropic XXZ antiferromagnetic model with Dzyaloshinskii-Moriya (DM) interaction in a triangular lattice. Considering the quasiparticle vacuum as our reference, we provide an accurate analysis of the non-collinear ground state of a frustrated triangular lattice magnet using the TESWT formalism. We elucidate the effects of quantum fluctuations on the ordering wave vector based on model system parameters. We study the single magnon dispersion, the two-magnon continuum using the spectral function, and the Raman spectrum of …
We argue that the Raman intensity in a spin S two-leg spin-ladder has a pseudo-resonance peak, whose width is very small at large S. The pseudo-resonance originates from the existence of a local minimum in the magnon excitation spectrum, and is located slightly below twice the magnon energy at the minimum. The physics behind the peak is similar to the excitonic scenario for the neutron and Raman resonances in a d-wave superconductor.
The effects of phonon anharmonicity, phonon-magnon and electron-phonon interactions on the temperature dependence of Raman optical phonon modes are theoretically investigated. Besides of the Klemens result for the phonon width due to anharmonicity, the corresponding lineshift is derived. We argue that the phonon decay into two magnons has very low intensity in ferromagnets with low Curie temperatures. Therefore, the electron interband transitions accompanied with the ferromagnetic ordering are included in considerations to get a good quantitative agreement with experiments.
We present a comprehensive study of the coupled tetrahedra-compound Cu2Te2O5Br2 by theory and experiments in external magnetic fields. We report the observation of a longitudinal magnon in Raman scattering in the ordered state close to quantum criticality. We show that the excited tetrahedral-singlet sets the energy scale for the magnetic ordering temperature T_N. This energy is determined experimentally. The ordering temperature T_N has an inverse-log dependence on the coupling parameters near quantum criticality.
(Sr$_{2}$,Ba$_{2}$)Cu$_{3}$O$_{4}$Cl$_{2}$ are antiferromagnetic insulators which are akin to the parent compounds of the cuprate superconductors but with two distinct magnetic ordering temperatures related to two magnetic Cu$_{I}$ and Cu$_{II}$ spin sublattices. Here we present a study of these materials by means of Raman spectroscopy. Following the temperature and polarization dependence of the data we readily identify two distinct features at around 3000 cm$^{-1}$ and 300 cm$^{-1}$ that are related to two-magnon scattering from the two sublattices. The estimated spin-exchange coupling const…
We investigated temperature dependent Raman spectra of the one-dimensional spin-ladder compound SrCu2O3. At low temperatures a two-magnon peak is identified at 3160+/-10 cm^(-1) and its temperature dependence analyzed in terms of a thermal expansion model. We find that the two-magnon peak position must include a cyclic ring exchange of J_cycl/J_perp=0.09-0.25 with a coupling constant along the rungs of J_perp approx. 1215 cm^(-1) (1750 K) in order to be consistent with other experiments and theoretical results.
We present and analyze Raman spectra of the Mott insulator Ca$_2$RuO$_4$, whose quasi-two-dimensional antiferromagnetic order has been described as a condensate of low-lying spin-orbit excitons with angular momentum $J_{eff}=1$. In the $A_g$ polarization geometry, the amplitude (Higgs) mode of the spin-orbit condensate is directly probed in the scalar channel, thus avoiding infrared-singular magnon contributions. In the $B_{1g}$ geometry, we observe a single-magnon peak as well as two-magnon and two-Higgs excitations. Model calculations using exact diagonalization quantitatively agree with the…
Raman selection rules for electronic and magnetic excitations in BaFe2As2 were theoretically investigated and applied them to the separate detection of the nodal and anti-nodal gap excitations at the spin density wave (SDW) transition and the separate detection of the nearest and the next nearest neighbor exchange interaction energies. The SDW gap has Dirac nodes, because many orbitals participate in the electronic states near the Fermi energy. Using a two-orbital band model the electronic excitations near the Dirac node and the anti-node are found to have different symmetries. Applying the sy…
We compare the theoretical predictions of the previous article [L. Benfatto and M. B. Silva Neto, cond-mat/0602419], with Raman spectroscopy experiments in Sr(2)CuO(2)Cl(2) and untwinned La(2)CuO(4) single crystals. We construct the magnetic point group for the magnetically ordered phase of the two compounds, Sr(2)CuO(2)Cl(2) and La(2)CuO(4), and we classify all the Raman active one-magnon excitations according to the irreducible co-representations for the associated magnetic point group. We then measure the evolution of the one-magnon Raman energies and intensities for low and moderate magnet…
Two magnon excitations and the nodal spin density wave (SDW) gap were observed in BaFe2As2 by Raman scattering. Below the SDW transition temperature (TSDW) nodal SDW gap opens together with new excitations in reconstructed electronic states. The two-magnon peak remains above TSDW and moreover the energy increases a little. The change from the long-range ordered state to the short-range correlated state is compared to the cuprate superconductors.
We have performed Raman scattering measurements on BiFeO3 nanoparticles and studied both magnetic and lattice modes. We reveal strong anomalies between 140 K and 200 K in the frequency of magnon and E(LO1), E(TO1) and A1(LO1) phonon modes. These anomalies are related to a surface expansion and are enhanced for nanoparticle sizes approaching the spin cycloidal length. These observations point out the strong interplay between the surface, the lattice, and the magnetism for sizes of BiFeO3 nanoparticles close to the cycloid periodicity.
Some well-established examples of itinerant-electron ferromagnetism in one dimension occur in a Mott-insulating phase. We examine the consequences of doping a ferromagnetic insulator and cou- pling magnons to gapless charge fluctuations. Using a bosonization scheme for strongly interacting electrons, we derive an effective field theory for the magnon-holon interaction. When the magnon momentum matches the Fermi momentum of the holons, the backscattering of the magnon at low energies gives rise to a Kondo effect of a pseudospin defined from the chirality degree of freedom (right- or left-moving…
We study experimentally the Raman response of the undoped high-Tc parent compound $YBa_2Cu_3O_6$, and give a unified theory of the two-magnon Raman peak and optical conductivity based on the Hubbard-Holstein model with electron-phonon coupling (EPC). The Hubbard model without EPC can qualitatively account for the experimentally observed resonance of the Raman response, but only the Hubbard-Holstein model (i) reproduces asymmetry of the Raman spectrum, (ii) validates experimental visibility of the two-magnon peak, and (iii) predicts the correct shape and energy of the lower edge of the charge t…
We used Raman and terahertz spectroscopies to investigate lattice and magnetic excitations and their cross-coupling in the hexagonal YMnO3 multiferroic. Two phonon modes are strongly affected by the magnetic order. Magnon excitations have been identified thanks to comparison with neutron measurements and spin wave calculations but no electromagnon has been observed. In addition, we evidenced two additional Raman active peaks. We have compared this observation with the anti-crossing between magnon and acoustic phonon branches measured by neutron. These optical measurements underly the unusual s…
We performed Raman studies and a dielectric characterization of the pseudo-kagome Cu3Bi(SeO3)2O2X (X = Cl, Br). These compounds share competing nearest-neighbour ferromagnetic exchange and frustrating next-nearest-neighbour antiferromagnetic exchange as well as highly noncollinear magnetic ground state. However, at low temperature they differ with respect to the existence of inversion symmetry. For both compounds there exists a pronounced interplay of polar phonon modes with quantum magnetic fluctuations. A novel Raman mode appears for temperatures below the Neel temperature with a Fano linesh…
We report on the lattice and spin dynamics in the monopnictide CrAs using polarized Raman scattering. This system exhibits a first-order magneto-structural phase transition at T_N~ 265 K, below which the magnetic moments of Cr form an incommensurate double helical magnetic structure while the unit cell volume abruptly expands. Across the transition, the frequencies of the fully symmetric Ag phonons strongly renormalize, which along with the results of first-principle calculations suggest the presence of a sizeable coupling of the phonons to the magnetic degrees of freedom in this compound. In …
Plaid-Like Spin Splitting and Chirality of Magnon Bands in Antiferromagnetic MnTe$_2$
Sejong University（世宗大学）；Korea Advanced Institute of Science and Technology (KAIST)（韩国科学技术院）；Sungkyunkwan University（成均馆大学）；Institute of Physics, Academia Sinica（中央研究院物理研究所）
We used a combination of polarized Raman spectroscopy and spin wave calculations to study magnetic excitations in the strong spin-orbit-coupled (SOC) bilayer perovskite antiferromagnet $Sr_3Ir_2O_7$. We observed two broad Raman features at ~ 800 $cm^{-1}$ and ~ 1400 $cm^{-1}$ arising from magnetic excitations. Unconventionally, the ~ 800 $cm^{-1}$ feature is fully symmetric ($A_{1g}$) with respect to the underlying tetragonal ($D_{4h}$) crystal lattice which, together with its broad line shape, definitively rules out the possibility of a single magnon excitation as its origin. In contrast, the…
We measure Raman scattering in an interacting spin-dimer system KCuCl3 under hydrostatic pressures up to 5 GPa mediated by He gas. In the pressure-induced quantum phase, we observe a one-magnon Raman peak, which originates from the longitudinal magnetic excitationand is observable through the second-order exchange interaction Raman process. We report the pressure dependence of the frequency, halfwidth and Raman intensity of this mode.
Nickel oxide (NiO) has been studied extensively for various applications ranging from electrochemistry to solar cells [1,2]. In recent years, NiO attracted much attention as an antiferromagnetic (AF) insulator material for spintronic devices [3-10]. Understanding the spin - phonon coupling in NiO is a key to its functionalization, and enabling AF spintronics' promise of ultra-high-speed and low-power dissipation [11,12]. However, despite its status as an exemplary AF insulator and a benchmark material for the study of correlated electron systems, little is known about the spin - phonon interac…
We have carried out Raman spectroscopy experiments to investigate two-magnon excitations in epitaxial thin films of the quasi-two-dimensional antiferromagnetic Mott insulator Sr$_2$IrO$_4$ under in-plane misfit strain. With in-plane biaxial compression, the energy of the two-magnon peak increases, and the peak remains observable over a wider temperature range above the Néel temperature, indicating strain-induced enhancement of the superexchange interactions between $\it{J}_{eff}$ = 1/2 pseudospins. From density functional theory calculations, we have found an increase of the nearest-neighbor h…
