The integration of ferroelectric barriers into high-temperature Josephson junctions offers a pathway to tunable superconducting quantum devices. Here, we demonstrate robust Josephson coupling in YBa2Cu3O7-x (YBCO)/Bi0.5Na0.5TiO3 (BNT)/YBCO trilayer junctions incorporating a 40 nm ferroelectric BNT barrier. Epitaxial trilayers were fabricated by pulsed laser deposition on SrTiO3 substrates and investigated under broadband terahertz (THz) irradiation (0.5-2.5 THz). At 1.5 THz, close to the Josephson plasma resonance, the BNT polarization increased from 33.4 to 46.4 uC/cm2 at 30 K, enhancing superconducting transport. The junctions exhibited a well-defined zero-voltage supercurrent branch, with the critical current Ic(T) remaining nearly constant up to 60 K and reaching 468.2 uA under 1.5 THz excitation, evidencing strong phase coherence. Scanning tunneling spectroscopy revealed an enhanced superconducting gap in YBCO/BNT/YBCO (Delta = 1.3 meV) compared with pure YBCO (Delta = 1.05 meV), while optical conductivity measurements showed a reduction in conductivity and gap with increasing temperature, consistent with BCS theory under THz excitation. Atomic force microscopy and X-ray reflectivity confirmed uniform morphology and sharp interfaces, excluding defect-mediated transport. Magnetic field modulation of Ic(B) exhibited a canonical Fraunhofer interference pattern, and resistance mapping revealed alternating lobes of high and low dissipation, indicating coherent Josephson tunneling. These results establish that Josephson coupling is intrinsic to the YBCO/BNT/YBCO junctions, enabled by the dipolar character and dynamic THz response of the BNT barrier. This study identifies BNT as a viable, tunable barrier material for next-generation high-Tc superconducting quantum devices.
The integration of ferroelectric barriers into high-temperature Josephson junctions offers a pathway to tunable superconducting quantum devices. Here, we demonstrate robust Josephson coupling in YBa2Cu3O7-x (YBCO)/Bi0.5Na0.5TiO3 (BNT)/YBCO trilayer junctions incorporating a 40 nm ferroelectric BNT barrier. Epitaxial trilayers were fabricated by pulsed laser deposition on SrTiO3 substrates and investigated under broadband terahertz (THz) irradiation (0.5-2.5 THz). At 1.5 THz, close to the Josephson plasma resonance, the BNT polarization increased from 33.4 to 46.4 uC/cm2 at 30 K, enhancing superconducting transport. The junctions exhibited a well-defined zero-voltage supercurrent branch, with the critical current Ic(T) remaining nearly constant up to 60 K and reaching 468.2 uA under 1.5 THz excitation, evidencing strong phase coherence. Scanning tunneling spectroscopy revealed an enhanced superconducting gap in YBCO/BNT/YBCO (Delta = 1.3 meV) compared with pure YBCO (Delta = 1.05 meV), while optical conductivity measurements showed a reduction in conductivity and gap with increasing temperature, consistent with BCS theory under THz excitation. Atomic force microscopy and X-ray reflectivity confirmed uniform morphology and sharp interfaces, excluding defect-mediated transport. Magnetic field modulation of Ic(B) exhibited a canonical Fraunhofer interference pattern, and resistance mapping revealed alternating lobes of high and low dissipation, indicating coherent Josephson tunneling. These results establish that Josephson coupling is intrinsic to the YBCO/BNT/YBCO junctions, enabled by the dipolar character and dynamic THz response of the BNT barrier. This study identifies BNT as a viable, tunable barrier material for next-generation high-Tc superconducting quantum devices.
Abstract The integration of ferroelectric barriers into high temperature Josephson junctions offers a pathway to tunable superconducting quantum devices. Here, we demonstrate robust Josephson coupling in YBa₂Cu₃O₇₋ₓ (YBCO) | Bi₀.₅Na₀.₅TiO₃ (BNT) | YBCO trilayer junctions incorporating a relatively thick (40 nm) ferroelectric BNT barrier. Epitaxial trilayers were fabricated using pulsed laser deposition on SrTiO₃ substrates and systematically investigated under broadband terahertz (THz) irradiation in the range of 0.5 to 2.5 THz. At 1.5 THz, which is close to the Josephson plasma resonance, the BNT polarization increased significantly, from 33.4 to 46.4 µC/cm² at 30 K, leading to enhanced superconducting transport. The junctions exhibited a well-defined zero voltage supercurrent branch, with critical current Ic(T) remaining nearly constant up to 60 K and reaching a peak value of 468.2 µA under 1.5 THz excitation, evidencing strong phase coherence. Scanning tunneling spectroscopy revealed enhanced superconducting gaps in YBCO|BNT|YBCO (Δ = 1.3 meV) compared to pure YBCO (Δ = 1.05 meV), while optical conductivity measurements showed a systematic reduction in conductivity and gap with increasing temperature, consistent with BCS theory under THz excitation. To exclude defect mediated transport, atomic force microscopy and X ray reflectivity confirmed uniform morphology and sharp interfaces. Magnetic field modulation of Ic(B) exhibited a canonical Fraunhofer interference pattern, and resistance mapping revealed alternating lobes of high and low dissipation, both of which are strong indicators of coherent Josephson tunneling. These results establish that Josephson coupling is intrinsic to the YBCO|BNT|YBCO junctions, enabled by the dipolar character and dynamic THz response of the BNT barrier. This study positions BNT as a viable and tunable barrier material for next generation superconducting quantum devices based on high-Tc materials.
Microscopic theories predict that the critical temperature of a superconducting layer can be strongly modified in proximity to a ferroelectric; however, experimental evidence is lacking. We report on BaTiO3 (BTO)/YBa2Cu3O7-δ (YBCO) heterostructures grown on SrTiO3 (001) substrates using pulsed laser deposition (PLD), with precise control of growth conditions and oxygen stoichiometry. Piezoresponse force microscopy confirms ferroelectric switching within both single-layer and heterostructured films. Neutron reflectometry measurements show low roughness parameters for the buried interfaces, which is critical for mediating the interfacial coupling between superconductivity and ferroelectric polarization. The superconducting transition temperature (TCR) measured from the R(T) curve of the single-layer YBCO was approximately 86 K, and a transition temperature (TCM) of approximately 80-85 K was observed from the M(T) curve. For the heterostructure film (YBCO/BTO/YBCO) grown under the same conditions, both resistivity and magnetization measurements indicate lower transition temperatures of approximately 75 K and approximately 55 K, respectively, as well as a lower overall susceptibility. These findings highlight the need to combine multiple techniques to characterize BTO/YBCO heterostructures and identify subtle features of the ferroelectric--superconducting coupling. This establishes BTO/YBCO heterostructures as promising systems for tunable oxide electronics and reconfigurable superconducting devices.
The Josephson junction, a key component of superconducting quantum circuits, is much less mature, especially for the high-transition (high-Tc) temperature cuprate superconductors. Herein, we report on the realization of high-Tc Josephson junction based on nanoslits on a SrTiO3 substrate. We demonstrate the ability to manipulate the current–voltage characteristics of YBa2Cu3O7−x bridges continuously from superconducting current-dominated to Josephson junction behavior by changing the irradiation parameters of the focused Ga+ ion beam on a single-crystal SrTiO3 substrate. The periodic critical current that depends on the magnetic flux coupled into the superconducting quantum interference devices was observed, which exactly reflects the effects of quantum tunneling and flux quantization. To some extent, this weak link within the framework of the semiconductor manufacturing process shows the potential to provide a cost-effective, highly efficient, and reliable pathway for scaling up quantum mechanical superconducting circuits, which is promising for the fabrication process.
We report on the fabrication and millikelvin char acterization of Nb/Al–AlOx/Nb Josephson junctions directly de posited on X-cut LiNbO3 substrates. Motivated by the strong electro-optic and piezoelectric properties of LiNbO3, such devices are of interest for future hybrid superconducting–electro-optic architectures. The junctions were fabricated using standard processes involving DC magnetron sputtering followed by controlled thermal oxidation of the aluminum layer to form an AlOx tunnel barrier with reproducible junction areas. Insulation of the junctions was achieved by anodization and SiOx deposition. Electrical measurements performed at 30 mK reveal high-quality Josephson tunnel junction behavior with a critical current density ofJc= 70 A/cm2and a characteristic voltage reaching values up toVm= 286 mV. Differential conductance measurements exhibit pronounced quasiparticle peaks corresponding to a sum gap energy of 2Δ = (2.73 ± 0.05) meV, confirming the good quality of the Nb electrodes. Magnetic-field-dependent measure ments yield a Josephson penetration depth of λJ= 45 μm, confirming operation in the small-junction regime, with deviations from the ideal Josephson interference pattern attributed to non-uniform current distribution across the junction area. Compared to our previous characterization at 4.2 K, this work demonstrates reliable Josephson junction operation on LiNbO3 at dilution-refrigerator temperatures relevant for quantum circuits, supporting the suitability of lithium niobate as a promising substrate for future hybrid superconducting–electro-optic device implementations.
The terahertz region of the electromagnetic spectrum [0.3-10THz] has, so far, not been exploited fully due to the lack of suitable sources and detectors. Indeed, THz frequency lies between the frequency range of traditional electronics and photonics where the existing technology cannot be simply extended. SIS Niobium tunnel junctions that are currently used as mixing element in heterodyne receivers are intrinsically limited in frequency by the energy gap of Nb and operate only at low temperature (4.2K). An alternative to these devices consists of using High-Tc superconducting receivers. Over the past years, we have developed a new approach based on ion irradiation to make Josephson nano-junctions and SQUIDs with YBCO thin films [1,2]. In this talk, we will present a study of the high-frequency mixing properties of such junctions up to 400 GHz [3]. Conversion gain has been measured at frequencies spanning the range below and above the characteristic frequency fc = (2e/h)IcRn of the junctions. The transition between two distinct mixing regimes has been clearly evidenced, in good agreement with the prediction of the three ports model.[1] N. Bergeal et al., Appl. Phys. Lett. 87, 102502 (2005)[2] N. Bergeal et al., Appl. Phys. Lett. 89, 1112515 (2006)[3] Luo et al, arXiv:1203.1734 (2012)
We present comprehensive experimental and numerical studies of the subpicosecond switching dynamics of YBa2Cu3O7-x (YBCO) grain-boundary Josephson junctions, excited by single-picosecond electrical pulses. The test structures were patterned in 100-nm- thick YBCO films grown by pulsed laser deposition on (100) MgO bicrystal substrates. Each sample consisted of a coplanar strip (CPS) transmission line, a microbridge acting as the electrical pulse generator, and a single Josephson junction positioned between the CPS lines about 100 micrometer away from the bridge. The junctions were characterized by the nonhysteretic current-voltage characteristics with the characteristic voltage approximately equal to 2.0 mV at 20 K (temperature of our experiments). A train of 100- fs-wide optical pulses from a Ti:sapphire laser photo-excited the microbridge and generated 2-ps-wide electrical pulses, which were then applied to switch the junction. In addition to the input pulse, the junction was dc-biased at +0.7 Ic, -0.7 Ic, +1.5 Ic, -1.5 Ic, and zero-Ic, where Ic is junction critical current. Time-resolved dynamics of the junction response was studied with the help of our cryogenic electro-optic sampling system, which can be regarded as a sampling oscilloscope featuring < 200-fs time resolution and < 150-(mu) V voltage sensitivity. We obtained 0.7-ps-wide single-flux-quantum (SFQ) pulses generated as a result of the junction switching process. The measurements were compared to numerical computations based on the equivalent circuit containing a resistively shunted Josephson junction, and we have found a satisfactory agreement between our simulations and experimental data. We believe our findings provide experimental confirmation of the potential of YBCO Josephson gattes as building blocks of ultrafast (sub-THz) digital electronics.