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SrTiO3 (STO) is among the most widely used substrates in complex oxide heterostructure research, yet the role of its trace impurity content in determining interface properties remains poorly understood. Here, we show that high-temperature annealing (the standard procedure for preparing TiO2-terminated STO surfaces) universally drives Fe impurities from the substrate bulk to the surface, forming a sharp, delta-like distribution within a few nanometers of the surface. Using time-of-flight secondary ion mass spectrometry with nanometer-scale depth resolution, we find that Fe is largely undetectable before annealing but appears prominently at the surface after annealing in all 16 substrates surveyed from three independent commercial suppliers. A systematic study on pieces diced from a single substrate demonstrates that surface Fe concentration increases with both annealing temperature and duration, following thermally activated, diffusion-limited kinetics with an activation energy of approximately 3 eV. Density functional theory calculations confirm a thermodynamic preference for Fe substitution near the STO surface, establishing the driving force for segregation. This annealing-induced redistribution effectively deposits a hidden layer of magnetic impurities within a few nanometers of the surface. These results have direct implications for complex oxide heterostructures such as LaAlO3/SrTiO3, where annealing-dependent Fe accumulation at the STO surface may account for the widely reported magnetic signatures at such interfaces. 

We present a nematic response function model (NRFM) for fit-free direct extraction of the characteristic time of ultrafast electronic thermalization in iron-based superconductors, materials with electronic nematicity. By combining the NRFM for polarization-dependent pump–probe measurements of electronic nematic response with the two-temperature model (TTM) for sub-picosecond quasiparticle relaxation, we quantify the electronic thermalization timescales and their anisotropy. The nematic response function is modeled as the difference in normalized reflectivity signals, revealing a pronounced sub-picosecond extremum in signal evolution that directly yields the characteristic electronic thermalization time. This method demonstrates that the NRFM is consistent with TTM fits of transient optical response, yielding electronic thermalization time constants on the order of 110–230 fs for the FeSe1−xTex and Ba(Fe0.92Co0.08)2As2 thin films. The proposed approach can be applied to any material that exhibits electronic nematicity, providing a powerful tool for direct mapping of the relaxation time in nematic materials, avoiding complex experimental data-fitting procedures. 

The LaAlO3/SrTiO3 (LAO/STO) interface hosts a gate-tunable superconducting two-dimensional electron gas (2DEG), which can be programmed to create quantum devices, such as ballistic electron waveguides and quantum dots. To fully exploit this platform for quantum transport, a key requirement is the ability to shuttle single electrons, electron pairs, and other exotic states between spatially separated devices with precision. Surface acoustic waves (SAWs), which travel along the surface of a solid, offer a powerful route to achieve this through their moving electrical potential that captures and transfers electrons. In particular, SAWs in the GHz regime enable fast, controlled transport of individual quantum particles. Although this approach is well-explored in GaAs-based 2DEG, SAW generation in STO remains largely unexplored due to the lack of intrinsic piezoelectricity at room temperature. Here, we investigate room-temperature SAWs in LAO/STO and observe SAW modes up to 2.2 GHz with very low propagation loss of the order 10−3 dB per wavelength. To directly visualize these modes, we employ atomic acoustic force microscopy, achieving sub-micron resolution imaging of the SAW wave forms, providing insight into the electrostriction-induced SAW generation mechanism. Our measurements indicate a shear horizontal-type mode, which provides the ability to couple to in-plane degrees of freedom for future acoustoelectric and quantum device applications. This work studies the fundamentals of SAW excitation and propagation on STO, a widely used and commercially available substrate, enabling straightforward coupling of SAWs to a broad range of materials that can be grown or transferred onto STO. 

The 5drare Earth iridate is an intriguing material with exhibiting exotic electronic and magnetic phases due to spin‐orbit coupled states. Ternary iridium oxidesLn₃IrO₇contain an unusual Ir⁵⁺(5d⁴) system, which remain a subject of active research. Fabricating epitaxialLn₃IrO₇films is challenging due to substrate compatibility, but it offers a valuable platform to explore electronic and magnetic behaviors under reduced dimensionality and substrate interactions, revealing novel phenomena based on Ir⁵⁺(5d⁴). In this regard, this demonstrates that Pr₃IrO₇with its highly anisotropic orthorhombic structure can be epitaxially grown on a cubic (111)‐oriented yttrium‐stabilized ZrO₂(YSZ) substrate. Pr₃IrO₇film exhibits six epitaxial domains, where the (220) and (202) planes aligning epitaxially to YSZ (111) with the threefold symmetry. This diverse domain configuration in Pr₃IrO₇film leads to unique magnetic properties, exhibiting spin‐glass‐like behavior. Pr₃IrO₇thin film offers a platform for exploring unconventional magnetic states, and their successful heteroepitaxy on YSZ substrates opens new avenues for discovering novel physical phenomena. 

Conductive atomic force microscope (c-AFM) lithography can be utilized to create a wide range of LaAlO3/SrTiO3 (LAO/STO)-based nanoelectronic devices in a reconfigurable manner. Experiments were generally performed with intrinsically insulating LAO/STO heterostructures, with LAO thickness less than the critical value at which a polar catastrophe takes place [<4 unit cell (u.c.)]. Here, we use inductively coupled plasma reactive ion etching (ICPRIE) to fabricate c-AFM “canvases” on intrinsically conducting LAO/STO samples with ≥4 u.c. LAO. We observe that its interfacial two-dimensional electron gas (2DEG) can be pinched off and then switched back on by c-AFM lithography. Nanowires created with initially conductive LAO/STO interfaces have an order-of-magnitude longer lifetime in ambient conditions, when compared to an identically created 3.4 u.c. LAO/STO nanowire. We also demonstrate key nanoscale properties such as ballistic transport in a quasi-one-dimensional electron waveguide at a 5 u.c. LAO/STO interface. This approach frees c-AFM-written nanodevice designs from time constraints in air associated with <4 u.c. LAO/STO heterostructures.