Materials that exhibit both strong spin–orbit coupling and electron correlation effects are predicted to host numerous new electronic states. One prominent example is the Jeff = 1/2 Mott state in Sr2IrO4, where introducing carriers is predicted to manifest high temperature superconductivity analogous to the S = 1/2 Mott state of La2CuO4. While bulk superconductivity currently remains elusive, anomalous quasiparticle behaviors paralleling those in the cuprates such as pseudogap formation and the formation of a d-wave gap are observed upon electron-doping Sr2IrO4. Here we establish a magnetic parallel between electron-doped Sr2IrO4 and hole-doped La2CuO4 by unveiling a spin density wave state in electron-doped Sr2IrO4. Our magnetic resonant X-ray scattering data reveal the presence of an incommensurate magnetic state reminiscent of the diagonal spin density wave state observed in the monolayer cuprate (La1−xSrx)2CuO4. This link supports the conjecture that the quenched Mott phases in electron-doped Sr2IrO4 and hole-doped La2CuO4 support common competing electronic phases.
The floating zone technique is a well-established single crystal growth method in materials research, able to produce volumetrically large specimens with extremely high purities. However, traditional furnace designs have relied on heating from highpowered bulb sources in combination with parabolic mirrors, and hence are constrained to transparent growth chambers with large solid angles of optical access.This results in a stark limitation on achievable processing gas pressures, and in turn renders a range of compounds unsuitable for crystal growth by the floating zone technique, either due to excessive volatility or due to metastability. Here, we demonstrate a novel high-pressure laser-based floating zone system (HP-LFZ). The use of lasers for heating allows implementation of a high-strength metal growth chamber, permitting greatly enhanced processing pressures over conventional mirror-based designs, with the current design allowing for pressures up to 1000 bar. We demonstrate a series of example single crystal growths using this design in pressures up to 675 bar, a significant increase over processing pressures attainable in commercially available floating zone systems. The general utility of the HP-LFZ is also illustrated via growths of a range of complex oxides.
We review recent advances in crystal growth techniques, focusing on the development of novel quantum materials. Recent progress in instrumentation design, opening new avenues in bulk crystal growth of oxide and intermetallic compounds, is highlighted. Specifically, we illustrate leading techniques that allow for the active control of crystal nucleation/growth and provide platforms for the realization of single crystals with ultrahigh purity and minimized defects. Advances in the postgrowth manipulation of crystals, as well as the impact of purification techniques on the stabilization of delicate quantum phases, are also discussed. Throughout, we highlight new scientific avenues opened by access to high-purity single-crystal samples.
We report a combined infrared and angle-resolved photoemission study of the electronic response of Sr 3 (Ir 1-x Ru x ) 2 O 7 (x=0, 0.22, 0.34). The low-temperature optical conductivities of the three compounds exhibit the characteristic feature of the effective total angular momentum J eff =1/2 antiferromagnetic Mott state. As the temperature increases across the antiferromagnetic ordering temperature T N , the indirect gap gradually closes whereas the direct gap remains open. In the optical conductivity of Sr 3 (Ir 0.66 Ru 0.34 ) 2 O 7 which shows a thermally driven insulator-metal transition at T N , a Drude-like response from itinerant carriers is registered in the paramagnetic phase. We observe in angle-resolved photoemission data of Sr 3 (Ir 0.66 Ru 0.34 ) 2 O 7 that the valence band shifts continuously toward the Fermi energy with the weakening of the antiferromagnetic order and crosses the Fermi level in the paramagnetic phase. Our findings demonstrate that the temperature-induced metalinsulator transition of the Sr 3 (Ir 1-x Ru x ) 2 O 7 system should be attributed to a magnetically driven band shift. * These two authors contributed equally. † yeongkwan@kaist.ac.kr ‡ soonjmoon@hanyang.ac.kr A discovery of the relativistic Mott state in Sr 2 IrO 4 [1,2] suggested that the Mott physics can be applicable in 5d transition metal oxides and stimulated extensive studies on the nature of their metal-insulator transitions. While the electromagnetic properties of Sr 2 IrO 4 were successfully explained in terms of an effective total angular momentum J eff =1/2 Mott state [1-5], a number of experimental and theoretical studies suggested that its ground state should instead be envisioned as a Slater insulator or as an intermediate phase between the Mott and Slater insulators [6-9]. In the Slater picture, the metal-insulator transition occurs at antiferromagnetic ordering temperature T N via a continuous opening of the band gap due to the appearance of a magnetic supercell [10]. Pyrochlore iridates R 2 Ir 2 O 7 (R=Nd, Sm, and Eu) which have attracted much attention as potential candidates for realizing correlated topological insulators/semimetals [11-13] exhibit a continuous metal-insulator transition accompanying the onset of antiferromagnetic order [14]. A recent angle-resolved photoemission spectroscopy (ARPES) experiment on Nd 2 Ir 2 O 7 [15] observed a gap opening at T N with an energy shift of quasiparticle peaks in a fashion similar to the Slater transition. The continuous metal-insulator transitions at T N in Cd 2 Os 2 O 7 andNaOsO 3 were also attributed to the Slater transition in early studies [16][17][18][19]. Recently, however, the metalinsulator transitions of the two osmates were revisited and ascribed to the Lifshitz-type transition [20][21][22][23].Density-functional-theory calculations showed that the metal-insulator transitions of Cd 2 Os 2 O 7 [20] and NaOsO 3 [21] involved a continuous shift of the bands away from the Fermi level and the resulting vanishing of the Fermi surface with decreasing the t...
The unconventional electronic ground state of Sr3IrRuO7 is explored via resonant x-ray scattering techniques and angle-resolved photoemission measurements. As the Ru content approaches x = 0.5 in Sr3(Ir1-xRux)2O7, intermediate to the J ef f = 1/2 Mott state in Sr3Ir2O7 and the quantum critical metal in Sr3Ru2O7, a thermodynamically distinct metallic state emerges. The electronic structure of this intermediate phase lacks coherent quasiparticles, and charge transport exhibits a linear temperature dependence over a wide range of temperatures. Spin dynamics associated with the long-range antiferromagnetism of this phase show nearly local, overdamped magnetic excitations and an anomalously large energy scale of 200 meV-an energy far in excess of exchange energies present within either the Sr3Ir2O7 or Sr3Ru2O7 solid-solution endpoints. Overdamped quasiparticle dynamics driven by strong spin-charge coupling are proposed to explain the incoherent spectral features of the strange metal state in Sr3IrRuO7.
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