arXiv subjects

Nicola Manca

Publications and source records attributed to Nicola Manca.

21 records · Page 2Linked to original sources

arXiv2017

Reversible oxygen vacancies doping in (La$_{0.7}$,Sr$_{0.3}$)MnO$_3$ microbridges by combined self-heating and electromigration

Combination of electric fields and Joule self-heating is used to change the oxygen stoichiometry and promote oxygen vacancy drift in a free-standing $\mathrm{(La,Sr)MnO_3}$ thin film microbridge placed in controlled atmosphere. By controlling the local oxygen vacancies concentration, we can reversibly switch our LSMO-based microbridges from metallic to insulating behavior on timescales lower than 1 s and with small applied voltages (<5 V). The strong temperature gradients given by the microbridge geometry strongly confine the motion of oxygen vacancies, limiting the modified region within the free-standing area. Multiple resistive states can be set by selected current pulses that determine different oxygen vacancies profiles within the device . Qualitative analysis of device operation is also provided with the support of Finite Element Analysis.

cond-mat.str-el↗

arXiv2017

Influence of thermal boundary conditions on the current-driven resistive transition in $\mathbf{VO_2}$ microbridges

We investigate the resistive switching behaviour of $\mathrm{VO_2}$ microbridges under current bias as a function of temperature and thermal coupling with the heat bath. Upon increasing the electrical current bias, the formation of the metallic phase can progress smoothly or through sharp jumps. The magnitude and threshold current values of these sharp resistance drops show random behaviour and are dramatically influenced by thermal dissipation conditions. Our results also evidence how the propagation of the metallic phase induced by electrical current in $\mathrm{VO_2}$, and thus the shape of the resulting high-conductivity path, are not predictable. We discuss the origin of the switching events through a simple electro-thermal model based on the domain structure of $\mathrm{VO_2}$ films that can be useful to improve the stability and controllability of future $\mathrm{VO_2}$-based devices.

cond-mat.str-el↗

arXiv2016

Striped nanoscale phase separation at the metal-insulator transition of heteroepitaxial nickelates

Nucleation processes of mixed-phase states are an intrinsic characteristic of first-order phase transitions, typically related to local symmetry breaking. Direct observation of emerging mixed-phase regions in materials showing a first-order metal-insulator transition (MIT) offers unique opportunities to uncover their driving mechanism. Using photoemission electron microscopy, we image the nanoscale formation and growth of insulating domains across the temperature-driven MIT in NdNiO3 epitaxial thin films. Heteroepitaxy is found to strongly determine the nanoscale nature of the phase transition, inducing preferential formation of striped domains along the terraces of atomically flat stepped surfaces. We show that the distribution of transition temperatures is an intrinsic local property, set by surface morphology and stable across multiple temperature cycles. Our data provides new insights into the MIT of heteroepitaxial nickelates and points to a rich, nanoscale phenomenology in this strongly correlated material.

cond-mat.str-el↗