arXiv subjects

Takeyuki Tsuji

Publications and source records attributed to Takeyuki Tsuji.

5 recordsLinked to original sources

arXiv2026

Observation of individual vortex penetration in a coplanar superconducting resonator

We demonstrate the microwave signatures of individual Abrikosov-vortex penetration events in superconducting microwave resonators. $λ/4$ resonators with a narrowed region near the grounded end acting as a vortex trap were fabricated and studied using microwave transmission spectroscopy at millikelvin temperatures. Sharp stepwise drops in resonance frequency are detected as a function of increasing external magnetic field, attributed to the entry of individual Abrikosov vortices in the narrow region. This interpretation is confirmed by NV center magnetometry revealing discrete vortex entry events on increasing field and the absence of such drops in a device with a wider narrowed region. Our results establish a method to investigate and manipulate the states of Abrikosov vortices with microwaves access and readout vortex configurations using magnetic-field sweeps and microwave drive.

cond-mat.supr-con↗

arXiv2026

Wide-field magnetic imaging of shielding-current-driven vortex rearrangement under local heating using diamond quantum sensors

Understanding and controlling vortex motion in superconductors are important both for suppressing dissipation in superconducting devices and for device applications that exploit vortices. In this work, we quantitatively imaged the stray magnetic field distribution of vortices in an NbN thin film by wide-field magnetic imaging using a perfectly aligned diamond nitrogen-vacancy ensemble. By continuously measuring while stepwise varying the applied magnetic field under local laser heating, we captured a rearrangement of the vortex configuration in real space and in real time over more than 100 min. The observed vortex rearrangement is consistent with a reduction of the pinning force due to local laser heating and with the Lorentz force exerted by shielding currents induced by the field variation. These results provide insight into vortex dynamics and suggest potential applications, including vortex exclusion from sensitive regions of superconducting devices.

cond-mat.supr-con↗

arXiv2026

Direct imaging of stress tensor around single dislocation in diamond

Dislocations are fundamental crystal defects whose stress fields govern a wide range of material properties. The analytical form of the stress tensor around single dislocation was established by elasticity theory more than 80 years ago and has provided a theoretical basis for evaluating essential characteristics of dislocations. However, direct experimental verification has long remained out of reach because it has been difficult to measure the components of the stress tensor with conventional methods. Here, we present the experimental visualization of the stress tensor around single dislocation in diamond. Using quantum sensors based on nitrogen-vacancy (NV) centers, we mapped the shear components ($σ_{xy}$, $σ_{yz}$, $σ_{zx}$) together with the trace of the stress tensor ($σ_{xx}+σ_{yy}+σ_{zz}$) around single 45° dislocation. The observed distributions exhibited good agreement with predictions from elasticity theory, thus providing experimental validation of this theoretical framework.

cond-mat.mtrl-sci↗

arXiv2025

Visualization of Current-Driven Vortex Formation in High-$T_c$ Cuprate Superconductors

Type-II superconductors exhibit hysteretic behavior due to the presence of quantum vortices, and the order in which temperature and external field are varied plays a decisive role. Here we take current, rather than magnetic field, as the external drive. We image the magnetic field of a high-$T_c$ cuprate superconductor strip after cooling. We confirm that even in zero magnetic field, current-biased cooling nucleates vortices within the strip. With a small external magnetic field, the distribution is polarized opposite to the Lorentz-force direction. These behaviors follow from the self-consistent relation between current and local field in steady flux flow. Our findings show that current history is encoded as vortices. This reveals self-field effects that influence dc measurements and glassy transitions under drive.

cond-mat.supr-con↗

arXiv2023

Wide-field quantitative magnetic imaging of superconducting vortices using perfectly aligned quantum sensors

Various techniques have been applied to visualize superconducting vortices, providing clues to their electromagnetic response. Here, we present a wide-field, quantitative imaging of the stray field of the vortices in a superconducting thin film using perfectly aligned diamond quantum sensors. Our analysis, which mitigates the influence of the sensor inhomogeneities, visualizes the magnetic flux of single vortices in YBa$_2$Cu$_3$O$_{7-δ}$ with an accuracy of $\pm10~\%$. The obtained vortex shape is consistent with the theoretical model, and penetration depth and its temperature dependence agree with previous studies, proving our technique's accuracy and broad applicability. This wide-field imaging, which in principle works even under extreme conditions, allows the characterization of various superconductors.

cond-mat.supr-con↗