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Register a new userPhase Instability amid Dimensional Crossover in Artificial Oxide Crystal
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Artificial crystals synthesized by atomic-scale epitaxy provides the ability to control the dimensions of the quantum phases and associated phase transitions via precise thickness modulation. In particular, reduction in dimensionality via quantized control of atomic layers is a powerful approach to revealing hidden electronic and magnetic phases. Here, we demonstrate a dimensionality-controlled and induced metal-insulator transition (MIT) in atomically designed superlattices by synthesizing a genuine two dimensional (2D) SrRuO3 crystal with highly suppressed charge transfer. The tendency to ferromagnetically align the spins in SrRuO3 layer diminishes in 2D as the interlayer exchange interaction vanishes, accompanying the 2D localization of electrons. Furthermore, electronic and magnetic instabilities in the two SrRuO3 unit cell layers induce a thermally-driven MIT along with a metamagnetic transition.
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A sizable transverse thermoelectric coefficient N , large to the extent that it potentially serves applications, is predicted to arise, by means of first-principles calculations, in a Skyrmion crystal assumed on EuO monolayer where carrier electrons are introduced upon a quantum anomalous Hall insulating phase of Chern number C = 2. This encourages future experiments to pursue such an effect.
Layered magnetic transition-metal thiophosphate NiPS3 has unique two-dimensional (2D) magnetic properties and electronic behavior. The electronic band structure and corresponding magnetic state are expected to sensitive to the interlayer interaction, which can be tuned by external pressure. Here, we report an insulator-metal transition accompanied with magnetism collapse during the 2D-3D crossover in structure induced by hydrostatic pressure. A two-stage phase transition from monoclinic (C2=m) to trigonal (P-31m) lattice is identified by ab initio simulation and confirmed by high-pressure XRD and Raman data, corresponding to a layer by layer slip mechanism along the a-axis. Temperature dependence resistance measurements and room temperature infrared spectroscopy show that the insulator-metal transition occurs near 20 GPa as well as magnetism collapse, which is further confirmed by low temperature Raman measurement and theoretical calculation. These results establish a strong correlation among the structural change, electric transport, and magnetic phase transition and expand our understandings about the layered magnetic materials.
Local configurational disorder can have a dominating role in the formation of macroscopic functional responses in strongly correlated materials. Here, we use entropy-stabilization synthesis to create single crystal epitaxial ABO3 perovskite thin films with equal atomic concentration of 3d transition metal cations on the B-site sublattice. X-ray diffraction, atomic force microscopy, and scanning transmission electron microscopy of La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 (L5BO) films demonstrate excellent crystallinity, smooth film surfaces, and uniform mixing of the 3d transition metal cations throughout the B-site sublattice. The magnetic properties are strongly dependent on substrate-induced lattice anisotropy and suggest the presence of long-range magnetic order in these exceptionally disordered materials. The ability to populate multiple elements onto a single sublattice in complex crystal structures opens new possibilities to design functionality in correlated systems and enable novel fundamental studies seeking to understand how diverse local bonding environments can work to generate macroscopic responses, such as those driven by electron-phonon channels and complex exchange interaction pathways.
High-Tc superconductivity in cuprates is generally believed to arise from carrier doping an antiferromagnetic Mott (AFM) insulator. Theoretical proposals and emerging experimental evidence suggest that this process leads to the formation of intriguing electronic liquid crystal phases. These phases are characterized by ordered charge and/or spin density modulations, and thought to be intimately tied to the subsequent emergence of superconductivity. The most elusive, insulating charge-stripe crystal phase is predicted to occur when a small density of holes is doped into the charge-transfer insulator state, and would provide a missing link between the undoped parent AFM phase and the mysterious, metallic pseudogap. However, due to experimental challenges, it has been difficult to observe this phase. Here, we use surface annealing to extend the accessible doping range in Bi-based cuprates and achieve the lightly-doped charge-transfer insulating state of a cuprate Bi2Sr2CaCu2O8+x. In this insulating state with a charge transfer gap at the order of ~1 eV, using spectroscopic-imaging scanning tunneling microscopy, we discover a unidirectional charge-stripe order with a commensurate 4a0 period along the Cu-O-Cu bond. Importantly, this insulating charge-stripe crystal phase develops before the onset of the pseudogap and the formation of the Fermi surface. Our work provides new insights into the microscopic origin of electronic inhomogeneity in high-Tc cuprates.
We report on the transport characterization in dark and under light irradiation of three different interfaces: LaAlO3/SrTiO3, LaGaO3/SrTiO3, and the novel NdGaO3/SrTiO3 heterostructure. All of them share a perovskite structure, an insulating nature of the single building blocks, a polar/non- polar character and a critical thickness of four unit cells for the onset of conductivity. The interface structure and charge confinement in NdGaO3/SrTiO3 are probed by atomic-scale- resolved electron energy loss spectroscopy showing that, similarly to LaAlO3/SrTiO3, extra electronic charge confined in a sheet of about 1.5 nm in thickness is present at the NdGaO3/SrTiO3 interface. Electric transport measurements performed in dark and under radiation show remarkable similarities and provide evidence that the persistent perturbation induced by light is an intrinsic peculiar property of the three investigated oxide-based polar/non-polar interfaces. Our work sets a framework for understanding the previous contrasting results found in literature about photoconductivity in LaAlO3/SrTiO3 and highlights the connection between the origin of persistent photoconductivity and the origin of conductivity itself. An improved understanding of the photo- induced metastable electron-hole pairs might allow to shed a direct light on the complex physics of this system and on the recently proposed perspectives of oxide interfaces for solar energy conversion.
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