TY - JOUR AB - Motivated by properties-controlling potential of the strain, we investigate strain dependence of structure, electronic, and magnetic properties of Sr2IrO4 using complementary theoretical tools: ab-initio calculations, analytical approaches (rigid octahedra picture, Slater-Koster integrals), and extended t−J model. We find that strain affects both Ir-Ir distance and Ir-O-Ir angle, and the rigid octahedra picture is not relevant. Second, we find fundamentally different behavior for compressive and tensile strain. One remarkable feature is the formation of two subsets of bond- and orbital-dependent carriers, a compass-like model, under compression. This originates from the strain-induced renormalization of the Ir-O-Ir superexchange and O on-site energy. We also show that under compressive (tensile) strain, Fermi surface becomes highly dispersive (relatively flat). Already at a tensile strain of 1.5%, we observe spectral weight redistribution, with the low-energy band acquiring almost purely singlet character. These results can be directly compared with future experiments. AU - Paerschke, Ekaterina AU - Chen, Wei-Chih AU - Ray, Rajyavardhan AU - Chen, Cheng-Chien ID - 12213 JF - npj Quantum Materials KW - Condensed Matter Physics KW - Electronic KW - Optical and Magnetic Materials TI - Evolution of electronic and magnetic properties of Sr₂IrO₄ under strain VL - 7 ER - TY - JOUR AB - Despite many efforts to rationalize the strongly correlated electronic ground states in doped Mott insulators, the nature of the doping-induced insulator-to-metal transition is still a subject under intensive investigation. Here, we probe the nanoscale electronic structure of the Mott insulator Sr₂IrO₄δ with low-temperature scanning tunneling microscopy and find an enhanced local density of states (LDOS) inside the Mott gap at the location of individual defects which we interpret as defects at apical oxygen sites. A chiral behavior in the topography for those defects has been observed. We also visualize the local enhanced conductance arising from the overlapping of defect states which induces finite LDOS inside of the Mott gap. By combining these findings with the typical spatial extension of isolated defects of about 2 nm, our results indicate that the insulator-to-metal transition in Sr₂IrO₄−δ could be percolative in nature. AU - Sun, Zhixiang AU - Guevara, Jose M. AU - Sykora, Steffen AU - Paerschke, Ekaterina AU - Manna, Kaustuv AU - Maljuk, Andrey AU - Wurmehl, Sabine AU - van den Brink, Jeroen AU - Büchner, Bernd AU - Hess, Christian ID - 12071 IS - 2 JF - Physical Review Research SN - 2643-1564 TI - Evidence for a percolative Mott insulator-metal transition in doped Sr₂IrO₄ VL - 3 ER - TY - JOUR AB - The concept of the entanglement between spin and orbital degrees of freedom plays a crucial role in our understanding of various phases and exotic ground states in a broad class of materials, including orbitally ordered materials and spin liquids. We investigate how the spin-orbital entanglement in a Mott insulator depends on the value of the spin-orbit coupling of the relativistic origin. To this end, we numerically diagonalize a one-dimensional spin-orbital model with Kugel-Khomskii exchange interactions between spins and orbitals on different sites supplemented by the on-site spin-orbit coupling. In the regime of small spin-orbit coupling with regard to the spin-orbital exchange, the ground state to a large extent resembles the one obtained in the limit of vanishing spin-orbit coupling. On the other hand, for large spin-orbit coupling the ground state can, depending on the model parameters, either still show negligible spin-orbital entanglement or evolve to a highly spin-orbitally-entangled phase with completely distinct properties that are described by an effective XXZ model. The presented results suggest that (i) the spin-orbital entanglement may be induced by large on-site spin-orbit coupling, as found in the 5d transition metal oxides, such as the iridates; (ii) for Mott insulators with weak spin-orbit coupling of Ising type, such as, e.g., the alkali hyperoxides, the effects of the spin-orbit coupling on the ground state can, in the first order of perturbation theory, be neglected. AU - Gotfryd, Dorota AU - Paerschke, Ekaterina AU - Chaloupka, Jiri AU - Oles, Andrzej M. AU - Wohlfeld, Krzysztof ID - 7594 IS - 1 JF - Physical Review Research TI - How spin-orbital entanglement depends on the spin-orbit coupling in a Mott insulator VL - 2 ER - TY - JOUR AB - Several realistic spin-orbital models for transition metal oxides go beyond the classical expectations and could be understood only by employing the quantum entanglement. Experiments on these materials confirm that spin-orbital entanglement has measurable consequences. Here, we capture the essential features of spin-orbital entanglement in complex quantum matter utilizing 1D spin-orbital model which accommodates SU(2)⊗SU(2) symmetric Kugel-Khomskii superexchange as well as the Ising on-site spin-orbit coupling. Building on the results obtained for full and effective models in the regime of strong spin-orbit coupling, we address the question whether the entanglement found on superexchange bonds always increases when the Ising spin-orbit coupling is added. We show that (i) quantum entanglement is amplified by strong spin-orbit coupling and, surprisingly, (ii) almost classical disentangled states are possible. We complete the latter case by analyzing how the entanglement existing for intermediate values of spin-orbit coupling can disappear for higher values of this coupling. AU - Gotfryd, Dorota AU - Paerschke, Ekaterina AU - Wohlfeld, Krzysztof AU - Oleś, Andrzej M. ID - 8726 IS - 3 JF - Condensed Matter SN - 2410-3896 TI - Evolution of spin-orbital entanglement with increasing ising spin-orbit coupling VL - 5 ER - TY - JOUR AB - In the high spin–orbit-coupled Sr2IrO4, the high sensitivity of the ground state to the details of the local lattice structure shows a large potential for the manipulation of the functional properties by inducing local lattice distortions. We use epitaxial strain to modify the Ir–O bond geometry in Sr2IrO4 and perform momentum-dependent resonant inelastic X-ray scattering (RIXS) at the metal and at the ligand sites to unveil the response of the low-energy elementary excitations. We observe that the pseudospin-wave dispersion for tensile-strained Sr2IrO4 films displays large softening along the [h,0] direction, while along the [h,h] direction it shows hardening. This evolution reveals a renormalization of the magnetic interactions caused by a strain-driven cross-over from anisotropic to isotropic interactions between the magnetic moments. Moreover, we detect dispersive electron–hole pair excitations which shift to lower (higher) energies upon compressive (tensile) strain, manifesting a reduction (increase) in the size of the charge gap. This behavior shows an intimate coupling between charge excitations and lattice distortions in Sr2IrO4, originating from the modified hopping elements between the t2g orbitals. Our work highlights the central role played by the lattice degrees of freedom in determining both the pseudospin and charge excitations of Sr2IrO4 and provides valuable information toward the control of the ground state of complex oxides in the presence of high spin–orbit coupling. AU - Paris, Eugenio AU - Tseng, Yi AU - Paerschke, Ekaterina AU - Zhang, Wenliang AU - Upton, Mary H AU - Efimenko, Anna AU - Rolfs, Katharina AU - McNally, Daniel E AU - Maurel, Laura AU - Naamneh, Muntaser AU - Caputo, Marco AU - Strocov, Vladimir N AU - Wang, Zhiming AU - Casa, Diego AU - Schneider, Christof W AU - Pomjakushina, Ekaterina AU - Wohlfeld, Krzysztof AU - Radovic, Milan AU - Schmitt, Thorsten ID - 8699 IS - 40 JF - Proceedings of the National Academy of Sciences of the United States of America SN - 00278424 TI - Strain engineering of the charge and spin-orbital interactions in Sr2IrO4 VL - 117 ER -