Transition metal oxides (TMOs) are complex electronic systems which exhibit a multitude of collective phenomena. Two archetypal examples are VO2 and NdNiO3, which undergo a metal-insulator phase-transition (MIT), the origin of which is still under debate. Here we report the discovery of a memory effect in both systems, manifest through an increase of resistance at a specific temperature, which is set by reversing the temperature-ramp from heating to cooling during the MIT. The characteristics of this ramp-reversal memory effect do not coincide with any previously reported history or memory effects in manganites, electronglass or magnetic systems. From a broad range of experimental features, supported by theoretical modelling, we find that the main ingredients for the effect to arise are the spatial Submitted to 22222222224222 phase-separation of metallic and insulating regions during the MIT and the coupling of lattice strain to the local critical temperature of the phase transition. We conclude that the emergent memory effect originates from phase boundaries at the reversal-temperature leaving "scars" in the underlying lattice structure, giving rise to a local increase in the transition temperature.The universality and robustness of the effect shed new light on the MIT in complex oxides.TMOs are a hallmark example of complex electron systems; the competition between charge, spin, strain, lattice, oxidation and other degrees of freedom, having similar energy scales, give rise to numerous collective phenomena [1][2][3] including superconductivity, [4] colossal magnetoresistance [5] and metal-insulator transitions (MIT). [6] In many thin film TMOs which exhibit a temperature (T)-driven phase transition, complexity is manifest through the coexistence of multiple phases where a single phase is expected, [7][8][9][10][11] providing the setting required for emergent phenomena to develop.[1]An intriguing feature found in many of the systems that exhibit the aforementioned phenomena, is the appearance of internal memory, where the system's properties (e.g. resistance or magnetization) depend on the measurement history. Such memory effects appear in various forms and measurement settings, having very different microscopic origins, many of which are still poorly understood. Examples include dynamical memory and slow relaxation in electron-glass systems such as amorphous oxides, [12,13] spatially phase-separated memory in colossal-magnetoresistance manganites, [14] shape-memory in martensitic alloys, [15] and more. [16,17] Here we report the appearance of an unexpected memory effect within the MIT in two prototypical examples of complex TMOs, namely VO2 and NdNiO3 (NNO). The characteristics of the observed effect differ substantially from those of previously reported memory effects, indicating a different microscopic origin.VO2 and NNO both exhibit an MIT, however its features and microscopic origin are quite different. In VO2 the MIT occurs above room temperature, ~340 K, and is accompanied by a structural transition from...

Scanning superconducting quantum interference device (SQUID) microscopy is a powerful tool for investigating electronic states at surfaces and interfaces by mapping their magnetic signal. SQUID operation requires cryogenic temperatures, which are typically achieved by immersing the cryostat in liquid helium. Making a transition to cryogen free systems is desirable, but has been challenging, as electric noise and vibrations are increased in such systems. We report on the successful operation of a scanning SQUID microscope in a modified Montana Instruments cryogen-free cooler with a base temperature of 4.3 K. We demonstrate scanning SQUID measurements with flux noise performance comparable to a wet system and correlate the sensor-sample vibrations to the cryocooler operation frequencies. In addition, we demonstrate successful operation in a variety of SQUID operation modes, including mapping static magnetic fields, measurement of local susceptibility, and spatial mapping of current flow distribution.

As most biological tissues, neural networks are organized at the micron-scale, with cells positioned appropriately and arranged in a high spatial resolution. Therefore, an important aspect of creating functional neural networks and network interfaces is the ability to localize neurons and guide nerve cell processes to form predesigned structures at this scale, raising technological challenges. Many studies focus on developing neuronal guidance abilities by using chemical and physical cues. [2,3,11-25] A recent approach for controlling cell motility is by applying magnetic forces. [26-30] Incorporating magnetic nanoparticles (MNPs) within cells turns them into magnetic-sensitive units that can be remotely manipulated through controllable magnetic fields. In previous medical applications MNPs have been used for in vivo tracking of cells by magnetic resonance imaging, [31-34] magnetic cell targeting to sites of tissue damage, [26,35-38] drug delivery, and thermotherapy cancer treatment. [39-43] Magnetic forces have been used to create and orient 3D tissues, [44] to fabricate tubular structures by manipulating magnetically labeled cells [14,45] and to control the delivery of growth factors. [46-48] In the nervous system guiding cells toward target tissue is of special importance, both for neuronal replacement and as a supportive tissue. [49-51] However, magnetic organization of neurons at the single cell level has yet not been demonstrated. In order to form functional networks, there is a need for local control of soma motility and axonal outgrowth, with micron scale resolution. Previously, we fabricated substrates embedded with microarrays of ferromagnetic (FM) pads. [52] FM thin films form magnets with stable in-plane magnetization due to shape anisotropy energies. [53] The in-plane magnetization limited the positioning of cells, demonstrating an attraction of the magnetized cells only to the magnetic poles of the pads due to the magnetic field line distribution (Figure 1). In this study, we design and fabricate micro-patterned multilayered FMs with perpendicular magnetic anisotropy (PMA). Our multilayered structures, inspired by magnetic recording media, [54] show better miniaturization scalability and thermal stability compared to in-plane magnets, [55] and have a substantial magnetization saturation that results in strong magnetic forces. These PMA pads show strong attraction of the MNP-loaded Guiding neuronal migration and outgrowth has great importance for therapeutic applications and for bioelectronics interfaces. Many efforts have been devoted to the development of tools to form predesigned structured neuronal networks. Here, a unique approach to localize cell bodies and direct neurite outgrowth is described based on local magnetic manipulations. Inspired by spintronic devices, a multi-layer deposition process is developed to generate nanometricthick films with perpendicular magnetization that provide stable attraction forces toward the entire magnetic pads. PC12 cells, a common neuronal model, are transform...

In systems near phase transitions, macroscopic properties often follow algebraic scaling laws, determined by the dimensionality and the underlying symmetries of the system. The emergence of such universal scaling implies that microscopic details are irrelevant. Here, we locally investigate the scaling properties of the metal-insulator transition at the LaAlO3/SrTiO3 interface. We show that, by changing the dimensionality and the symmetries of the electronic system, coupling between structural and electronic properties prevents the universal behavior near the transition. By imaging the current flow in the system, we reveal that structural domain boundaries modify the filamentary flow close to the transition point, preventing a fractal with the expected universal dimension from forming.

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We measured the photon count rate (PCR) and dark count rate (DCR) of a superconducting nanowire single photon detector (SNSPD) exposed to either a DC magnetic field (up to 60 mT) or to a low-amplitude oscillating field (0.12–0.48 mT, up to 50 kHz). In both cases, the results show an increase in the PCR and the DCR as the DC field or the frequency of the AC field increase. However, the ratio DCR/(PCR + DCR) increases significantly with an increasing DC field, whereas this ratio is approximately constant as the frequency of the AC field increases up to frequencies in the kHz regime. The results suggest a more favorable effect of AC fields on the operation of the SNSPD.

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