Quantitative nanoscale vortex imaging using a cryogenic quantum magnetometer

Abstract

Microscopic studies of superconductors and their vortices play a pivotal role in understanding the mechanisms underlying superconductivity. Local measurements of penetration depths or magnetic stray fields enable access to fundamental aspects such as nanoscale variations in superfluid densities or the order parameter symmetry of superconductors. However, experimental tools that offer quantitative, nanoscale magnetometry and operate over large ranges of temperature and magnetic fields are still lacking. Here, we demonstrate the first operation of a cryogenic scanning quantum sensor in the form of a single nitrogen-vacancy electronic spin in diamond, which is capable of overcoming these existing limitations. To demonstrate the power of our approach, we perform quantitative, nanoscale magnetic imaging of Pearl vortices in the cuprate superconductor YBa2Cu3O7-δ. With a sensor-to-sample distance of ∼10 nm, we observe striking deviations from the prevalent monopole approximation in our vortex stray-field images, and find excellent quantitative agreement with Pearl's analytic model. Our experiments provide a non-invasive and unambiguous determination of the system's local penetration depth and are readily extended to higher temperatures and magnetic fields. These results demonstrate the potential of quantitative quantum sensors in benchmarking microscopic models of complex electronic systems and open the door for further exploration of strongly correlated electron physics using scanning nitrogen-vacancy magnetometry.

Composite Topological Excitations in Ferromagnet-Superconductor Heterostructures

“…We derive conditions on the strength of the external forcing which ensure that the SVP remains bound and moves as a unit. The motion can for example be detected through direct imaging via nanoscale scanning magnetometry [22,23].Coupling mechanism − We expect SVPs to form in arXiv:1603.07550v2 [cond-mat.mes-hall] 9 Jul 2016 2 materials with strong SOC and broken spatial inversion symmetry. Here, the skyrmion-vortex interaction is primarily mediated through the superconducting magnetoelectric effect [24][25][26][27], whereby an induced spin polarization generates a supercurrent.…”

Color center fluorescence and spin manipulation in single crystal, pyramidal diamond tips

“…1 ODMR enables to read out spin states via luminescence, and thus even single centers can be used as low back action, quantum-enhanced sensors. Imaging magnetic fields using NV centers, e.g., contributed insights into superconductivity 2 or magnetic materials for spintronics. 3 In life sciences, highly sensitive measurements of magnetic fields enable nuclear magnetic resonance detection even of single proteins.…”

Nanoscale Sensing Using Point Defects in Single-Crystal Diamond: Recent Progress on Nitrogen Vacancy Center-Based Sensors

“…More recently, versatile approaches with NV centers in single crystal scanning probes have been presented [99,132]. This technology significantly broadens the range of samples for which NV magnetometry can be applied: solid materials present unique phenomena that only occur at cryogenic temperatures such as superconductivity.…”

“…However, real superconductors present points at which magnetic fields penetrate and magnetic vortices form. NV nano-magnetometry was applied for a high-resolution, low-invasive imaging of superconducting vortices (6 K, [99], 4.2 K [132]). To achieve cryogenic operation, the NV microscope is enclosed in a liquid 4 He cryostat with optical access.…”

“…Particular care was taken to avoid heating by microwave (MW) and laser excitation. Superconducting vortices were imaged with a resolution below 100 nm with magnetic field sensitivity of 30 µT·Hz 1/2 [99] and 11.9 µT·Hz 1/2 [132], allowing in [132] to verify vortex models beyond the monopole approximation.…”