Microwave response of superconducting YBa2Cu3O(7-δ) nanowire bridges sustaining the critical depairing current: evidence of Josephson-like behavior

Optical vortex induced spatio-temporally modulated superconductivity in a high-Tc cuprate

We report an experimental approach to produce spatially localized photoinduced superconducting state in a cuprate superconductor using optical vortices with ultrafast pulses. The measurements were carried out using coaxially aligned three-pulse time-resolved spectroscopy, in which an intense vortex pulse was used for coherent quenching of superconductivity and the resulting spatially modulated metastable states were analyzed by the pump-probe spectroscopy. The transient response after quenching shows a spatially localized superconducting state that remains unquenched at the dark core of the vortex beam for a few picoseconds. Because the quenching is instantaneously driven by photoexcited quasiparticles, the vortex beam profile can be transferred directly to the electron system. By using the optical vortex-induced superconductor, we demonstrate spatially resolved imaging of the superconducting response and show that the spatial resolution can be improved using the same principle as that of super-resolution microscopy for fluorescent molecules. The demonstration of spatially controlled photoinduced superconductivity is significant for establishing a new method for exploring novel photoinduced phenomena and applications in ultrafast optical devices.

Intrinsic Superconducting Diode Effect

Stimulated by the recent experiment [F. Ando et al., Nature (London) 584, 373 (2020).NATUAS0028-083610.1038/s41586-020-2590-4], we propose an intrinsic mechanism to cause the superconducting diode effect (SDE). SDE refers to the nonreciprocity of the critical current for the metal-superconductor transition. Among various mechanisms for the critical current, the depairing current is known to be intrinsic to each material and has recently been observed in several superconducting systems. We clarify the temperature scaling of the nonreciprocal depairing current near the critical temperature and point out its significant enhancement at low temperatures. It is also found that the nonreciprocal critical current shows sign reversals upon increasing the magnetic field. These behaviors are understood by the nonreciprocity of the Landau critical momentum and the change in the nature of the helical superconductivity. The intrinsic SDE unveils the rich phase diagram and functionalities of noncentrosymmetric superconductors.

Restored strange metal phase through suppression of charge density waves in underdoped YBa2Cu3O7-δ

[Figure: see text].

Hot spot formation in focused-ion-beam-fabricated YBa2Cu3O7-x nanobridges with high critical current densities

We report on the fabrication and evaluation of nanoscale YBa₂Cu₃O_7-x (YBCO) constrictions using focused-ion-beam techniques for potential application as YBCO bolometers. A gold protective layer was found to be critical for supressing contamination from gallium ions in order to obtain high critical current densities. Further processing using a radio-frequency plasma to remove the gold protective layer has also been studied and was found to be effective in minimizing sample damage resulting from overheating. Current-voltage measurement indicate that the nanobridges go through the transition from superconducting to normal state with different dissipation mechanism including flux creep and hot spot formation.

Depairing Current at High Magnetic Fields in Vortex-Free High-Temperature Superconducting Nanowires

Superconductors are essential in many present and future technologies, from large-scale devices for medical imaging, accelerators, or fusion experiments to ultra-low-power superconducting electronics. However, their potential applicability, and particularly that of high-temperature superconductors (HTS), is severely affected by limited performances at large magnetic fields and high temperatures, where their use is most needed. One of the main reasons for these limitations is the presence of quantized vortices, whose movements result in losses, internal noise, and reduced performances. The conventional strategy to overcome the flow of vortices is to pin them along artificial defects. Here, we theoretically and experimentally demonstrate that critical-current density in high-temperature superconductors can reach unprecedented high values at high fields and temperatures by preventing vortex entry. By tailoring the geometry, that is, reducing the width, W, of nanowire-patterned HTS films, the range of the Meissner state, for which no vortices are present, is extended up to very large applied field values, on the order of ∼1 T. Current densities on the order of the depairing current can be sustained under high fields for a wide range of temperatures. Results may be relevant both for devising new conductors carrying depairing-current values at high temperatures and large magnetic fields and for reducing flux noise in sensors and quantum systems.

Grooved Dayem Nanobridges as Building Blocks of High-Performance YBa2Cu3O7-δ SQUID Magnetometers

We present noise measurements performed on a YBa₂Cu₃O_7-δ nanoscale weak-link-based magnetometer consisting of a superconducting quantum interference device (SQUID) galvanically coupled to a 3.5 × 3.5 mm² pick-up loop, reaching white flux noise levels and magnetic noise levels as low as [Formula: see text] and 100 fT/[Formula: see text] at T = 77 K, respectively. The low noise is achieved by introducing grooved Dayem bridges (GDBs), a new concept of a weak link. A fabrication technique has been developed for the realization of nanoscale grooved bridges, which substitutes standard Dayem bridge weak links. The introduction of these novel key blocks reduces the parasitic inductance of the weak links and increases the differential resistance of the SQUIDs. This greatly improves the device performance, thus resulting in a reduction of the white noise.

Vortex Lattice Instabilities in YBa₂Cu₃O7-x Nanowires

High-resolution focused ion beam lithography has been used to fabricate YBa₂Cu₃O_7-x (YBCO) wires with nanometric lateral dimensions. In the present work, we investigate Flux-flow instabilities in nanowires of different widths, showing sudden voltage switching jumps from the superconducting to the normal state. We present an extensive study on the temperature and field dependence of the switching characteristics which reveal that voltage jumps become less abrupt as the temperature increases, and disappear at the vortex-liquid state. On the contrary, the current distribution at the critical point becomes narrower at high temperatures. Sharp voltage switchings very close to the critical current density can be obtained by reducing the width of the nanowires, making them very appealing for practical applications.

Direct-Write X-ray Nanopatterning: A Proof of Concept Josephson Device on Bi2Sr2CaCu2O8+δ Superconducting Oxide

We describe the first use of a novel photoresist-free X-ray nanopatterning technique to fabricate an electronic device. We have produced a proof-of-concept device consisting of a few Josephson junctions by irradiating microcrystals of the Bi2Sr2CaCu2O8+δ (Bi-2212) superconducting oxide with a 17.6 keV synchrotron nanobeam. Fully functional devices have been obtained by locally turning the material into a nonsuperconducting state by means of hard X-ray exposure. Nano-XRD patterns reveal that the crystallinity is substantially preserved in the irradiated areas that there is no evidence of macroscopic crystal disruption. Indications are that O ions have been removed from the crystals, which could make this technique interesting also for other oxide materials. Direct-write X-ray nanopatterning represents a promising fabrication method exploiting material/material rather than vacuum/material interfaces, with the potential for nanometric resolution, improved mechanical stability, enhanced depth of patterning, and absence of chemical contamination with respect to traditional lithographic techniques.