arXiv subjects

Gabriel Puebla-Hellmann

Publications and source records attributed to Gabriel Puebla-Hellmann.

4 recordsLinked to original sources

arXiv2026

Quantitative imaging of Abrikosov vortices by scanning quantum magnetometry

Understanding vortex matter in type-II superconductors is central to controlling dissipation and flux pinning in superconducting materials and devices. Here, we use cryogenic scanning nitrogen vacancy magnetometry (NVM) to image Abrikosov vortices in the cuprate superconductors BSCCO-2212 and YBCO under controlled field-cooled conditions. Measurements, which are performed using continuous-wave optically detected magnetic resonance (cw-ODMR) in a closed-cycle cryostat, yield quantitative magnetic-field maps with nanoscale spatial resolution. In BSCCO-2212 at 71 K, we resolve a well-ordered triangular vortex lattice, whose symmetry and spacing are confirmed through 2D Fourier analysis and are consistent with flux quantization. YBCO thin films imaged at 3 K exhibit a more disordered vortex arrangement reflecting stronger pinning, while maintaining quantitative agreement between measured vortex density and the applied magnetic field. These results render our cryogenic scanning NVM a reliable quantitative tool for real-space studies of vortices in high-$T_c$ superconductors, in particular since such a remarkable magnetic resolution has been achieved within relatively short acquisition times of 2 to 4 h.

cond-mat.supr-con↗

arXiv2025

Commercial scanning nitrogen vacancy magnetometer in a closed-cycle cryostat

The ability to measure magnetic fields on the nanometre scale at cryogenic temperatures is key to understand magnetism on the quantum level and to develop materials for new storage devices or quantum computers. Nitrogen vacancy (NV) centres in diamond have proven to be a robust means to harness quantum sensing for such applications. We have developed an instrument to measure the magnetic stray field of a sample with nanometre resolution from 2 K to 300 K and that accepts samples without additional preparation, especially the need to prepare a microwave line on the sample. The instrument features a software-interface for controlling and synchronising all included optical, mechanical and electronic devices and which analyses the acquired information in real time. We present the key features and measurement results achieved with atomic force microscopy (AFM) tips hosting an NV centre and a fully remote controllable microscope platform. The magnetometer is commercially available, and a first demonstrator has been installed in a research facility. We show micro Tesla per square root Hertz sensitivity, low noise AFM tip control and optically detected resonance scans in a closed-cycle cryostat.

quant-ph↗

arXiv2023

Multicone Diamond Waveguides for Nanoscale Quantum Sensing

The long-lived electronic spin of the nitrogen-vacancy (NV) center in diamond is a promising quantum sensor for detecting nanoscopic magnetic and electric fields in a variety of experimental conditions. Nevertheless, an outstanding challenge in improving measurement sensitivity is the poor signal-to-noise ratio (SNR) of prevalent optical spin-readout techniques. Here, we address this limitation by coupling individual NV centers to optimized diamond nanopillar structures, thereby improving optical collection efficiency of fluorescence. First, we optimize the structure in simulation, observing an increase in collection efficiency for tall ($\geq$ 5 $μ$m) pillars with tapered sidewalls. We subsequently verify these predictions by fabricating and characterizing a representative set of structures using a reliable and reproducible nanofabrication process. An optimized device yields increased SNR, owing to improvements in collimation and directionality of emission. Promisingly, these devices are compatible with low-numerical-aperture, long-working-distance collection optics, as well as reduced tip radius, facilitating improved spatial resolution for scanning applications.

quant-ph↗

arXiv2014

The role of titanium in electromigrated tunnel junctions

A standard route for fabrication of nanoscopic tunnel junctions is via electromigration of lithographically prepared gold nanowires. In the lithography process, a thin adhesion layer, typically titanium, is used to promote the adhesion of the gold nanowires to the substrate. Here, we demonstrate that such an adhesion layer plays a vital role in the electrical transport behavior of electromigrated tunnel junctions. We show that junctions fabricated from gold deposited on top of a titanium adhesion layer are electrically stable at ambient conditions, in contrast to gold junctions without a titanium adhesion layer. We furthermore find that electromigrated junctions fabricated from pure titanium are electrically exceptionally stable. Based on our transport data, we provide evidence that the barrier in gold-on-titanium tunnel devices is formed by the native oxide of titanium.

cond-mat.mtrl-sci↗