arXiv subjects

Sagar Paul

Publications and source records attributed to Sagar Paul.

4 recordsLinked to original sources

arXiv2023

Superconducting nitridized-aluminum thin films

We report the direct observation of superconductivity in nitridized-aluminum thin films. The films are produced by sputtering deposition of aluminum in a controlled mixture of nitrogen diluted in argon. The concentration of applied nitrogen directly determines the properties of the superconducting thin films. We observe samples displaying critical temperatures up to 3.38$\pm$0.01K and resilience to in-plane magnetic fields well above 1T, with good reproducibility of the results. This work represents an unambiguous demonstration of tunable superconductivity in aluminum-based nitridized thin films. Our results put forward nitridized aluminum as a promising material to be employed in superconducting quantum circuits for quantum technology applications.

cond-mat.supr-con↗

arXiv2022

Magnetization Reversal Across Multiple Serial Barriers in a Single Fe$_3$O$_4$ Nanoparticle

Depinning of nanoscale magnetic textures, such as domain walls, vortices and skyrmions, is of paramount importance for magnetic storage and information processing. We measure time-resolved magnetic switching statistics of an individual, non-single-domain Fe$_3$O$_4$ nanoparticle using a micrometer-scale superconducting quantum interference device. Surprisingly, a strong narrowing of the waiting-time distributions before reaching the final state is observed as compared to the exponential distribution expected for a single barrier. The magnetization reversal across the nanostructure is thus shown to result from multiple serial barriers in the minimum energy pathway.

cond-mat.mes-hall↗

arXiv2021

Stochastic resonance in thermally bistable Josephson weak-links and micro-SQUIDs

Constriction-based Josephson weak-links display a thermal bi-stability between two states exhibiting zero and finite voltages. This manifests in experiments either as hysteresis in weak-links current voltage characteristics or as random telegraphic signal in voltage. In the latter case, a noise-driven amplification of a sinusoidal excitation of the device is observed, at frequencies matching the characteristic switching frequency in telegraphic signal, a phenomenon known as stochastic resonance. The observed behavior is understood using a two-state model of stochastic resonance and is exploited to illustrate an enhanced signal-to-noise-ratio in a micro-SQUID as a magnetic field sensor.

cond-mat.supr-con↗

arXiv2016

Micron size superconducting quantum interference devices of lead (Pb)

Micron size superconducting quantum interference devices ($μ$-SQUID) of lead (Pb), for probing nano-magnetism, were fabricated and characterized. In order to get continuous Pb films with small grain size, Pb was thermally evaporated on a liquid nitrogen cooled Si substrate. Pb was sandwiched between two thin Cr layers for improved adhesion and protection. The SQUID pattern was made by e-beam lithography with Pb lift-off after deposition. The current-voltage characteristics of these devices show a critical current, which exhibits the expected SQUID oscillations with magnetic field, and two re-trapping currents. As a result these devices have hysteresis at low temperatures, which disappears just below the critical temperature.

cond-mat.supr-con↗