fabrication-magnetic-platforms-for-micron-scale-organization

Fabrication of Magnetic Platforms for Micron-Scale Organization of Interconnected Neurons

The ability to direct neurons into organized neural networks has great implications for regenerative medicine, tissue engineering, and bio-interfacing. ...

Transition metal oxides are complex electronic systems that exhibit a multitude of collective phenomena. Two archetypal examples are VO and NdNiO , which undergo a metal-insulator phase transition (MIT), the origin of which is still under debate. Here this study reports the discovery of a memory effect in both systems, manifested 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, electron-glass or magnetic systems. From a broad range of experimental features, supported by theoretical modelling, it is found that the main ingredients for the effect to arise are the spatial phase separation of metallic and insulating regions during the MIT and the coupling of lattice strain to the local transition 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.

Ramp-Reversal Memory and Phase-Boundary Scarring in Transition Metal Oxides.

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.

Scanning SQUID microscopy in a cryogen-free cooler.

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 LaAlO/SrTiO 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.

Article	Year
Ramp-Reversal Memory and Phase-Boundary Scarring in Transition Metal Oxides. Advanced materials (Deerfield Beach, Fla.)\| PubMed ID: 28332323	2017
Scanning SQUID microscopy in a cryogen-free cooler. The Review of scientific instruments\| PubMed ID: 31153251	2019
Non-universal current flow near the metal-insulator transition in an oxide interface. Nature communications\| PubMed ID: 34083533	2021

Naor Vardi

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