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arXiv:2607.11003

Ferroelectric--Superconducting Interaction in Epitaxial YBa2Cu3O7-δ/BaTiO3 Films

Louis Oppong-Antwi, David L. Cortie, Qi Zhang, Avi Bendavid, Nagarajan Valanoor, Wendy Purches, Golrokh Akhgar

cond-mat.supr-concond-mat.mtrl-sciquant-phSubmitted Jul 13, 2026• Announced Jul 14, 2026
arXivHTMLPDF

Abstract

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 ($T_{\mathrm{C}}^{R}$) measured from the $R(T)$ curve of the single-layer YBCO was approximately 86 K, and a transition temperature ($T_{\mathrm{C}}^{M}$) 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.

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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.

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•Oct 23, 2023•0 citations

Induced superconductivity in hybrid Au/YBa2Cu3O7−x electrodes on vicinal substrates

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We have prepared high-Tc superconducting heterostructures for DC SQUIDs with graphoepitaxial step edge Josephson junctions on single crystal MgO substrates and investigated them using complementary characterization techniques, including atomic force microscopy, scanning electron microscopy and high-resolution transmission electron microscopy. Combined epitaxial (out-of-plane) and graphoepitaxial (in-plane) growth of YBa2Cu3O7-x (YBCO) films on the tilted surfaces of step edges on MgO substrates was observed. The high-Tc step-edge Josephson junctions demonstrated a good reproducibility and an IcRn product of about 600 μV at 77 K. The DC SQUIDs with step edge junctions showed voltage swings δVpp of up to about 60 μV at 77 K. High values of Rn of the graphoepitaxial step edge Josephson junctions can be advantageous for their applications as qubits.

IEEE International Superconductive Electronics Conference (ISEC)•Jul 1, 2013•5 citations
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 (TCRT_{\mathrm{C}}^{R}TCR​) measured from the R(T)R(T)R(T) curve of the single-layer YBCO was approximately 86 K, and a transition temperature (TCMT_{\mathrm{C}}^{M}TCM​) of approximately 80-85 K was observed from the M(T)M(T)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 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.
Superconducting electrodes are an integral part of hybrid Josephson junctions used in many applications including quantum technologies. We report on the fabrication and characterization of superconducting hybrid Au/YBa2Cu3O7-x (YBCO) electrodes on vicinal substrates. In these structures, superconducting CuO2-planes face the gold film, resulting in a higher value and smaller variation of the induced energy gap compared to the conventional Au/YBCO electrodes based on films with the c-axis normal to the substrate surface. Using scanning tunneling microscopy, we observe an energy gap of about 10-17 meV at the surface of the 15- nm-thick gold layer deposited in situ atop the YBCO film. To study the origin of this gap, we fabricate nanoconstrictions from the Au/YBCO heterostructure and measure their electrical transport characteristics. The conductance of the nanoconstrictions shows a series of dips due to multiple Andreev reflections in YBCO and gold providing clear evidence of the superconducting nature of the gap in gold. We consider the Au/YBCO electrodes to be a versatile platform for hybrid Josephson devices with a high operating temperature.
Abstract Superconducting electrodes are an integral part of hybrid Josephson junctions used in many applications including quantum technologies. We report on the fabrication and characterization of superconducting hybrid Au/YBa2Cu3O7 − x (YBCO) electrodes on vicinal substrates. In these structures, superconducting CuO2-planes face the gold film, resulting in a higher value and smaller variation of the induced energy gap compared to the conventional Au/YBCO electrodes based on films with the c-axis normal to the substrate surface. Using scanning tunneling microscopy, we observe an energy gap of about 10–17 meV at the surface of the 15- nm-thick gold layer deposited in situ atop the YBCO film. To study the origin of this gap, we fabricate nanoconstrictions from the Au/YBCO heterostructure and measure their electrical transport characteristics. The conductance of the nanoconstrictions shows a series of dips due to multiple Andreev reflections in YBCO and gold providing clear evidence of the superconducting nature of the gap in gold. We consider the Au/YBCO electrodes to be a versatile platform for hybrid Josephson devices with a high operating temperature.
Abstract Superconducting electrodes are an integral part of hybrid Josephson junctions used in many applications including quantum technologies. We report on the fabrication and characterization of superconducting hybrid Au/YBa2Cu3O7−x (YBCO) electrodes on vicinal substrates. In these structures, superconducting CuO2-planes face the gold film, resulting in a higher value and smaller variation of the induced energy gap compared to conventional Au/YBCO electrodes based on films with the c-axis normal to the substrate surface. Using scanning tunneling microscopy, we observe an energy gap of about 10–17 meV at the surface of the 15- nm-thick gold layer deposited in situ atop the YBCO film. To study the origin of this gap, we fabricate nanoconstrictions from the Au/YBCO heterostructures and measure their electrical transport characteristics. The conductance of the nanoconstrictions shows a series of dips due to multiple Andreev reflections in YBCO and gold, providing clear evidence of the superconducting nature of the gap in gold. We consider the Au/YBCO electrodes to be a versatile platform for hybrid Josephson devices with a high operating temperature.
We have prepared high-Tc superconducting heterostructures for DC SQUIDs with graphoepitaxial step edge Josephson junctions on single crystal MgO substrates and investigated them using complementary characterization techniques, including atomic force microscopy, scanning electron microscopy and high-resolution transmission electron microscopy. Combined epitaxial (out-of-plane) and graphoepitaxial (in-plane) growth of YBa2Cu3O7-x (YBCO) films on the tilted surfaces of step edges on MgO substrates was observed. The high-Tc step-edge Josephson junctions demonstrated a good reproducibility and an IcRn product of about 600 μV at 77 K. The DC SQUIDs with step edge junctions showed voltage swings δVpp of up to about 60 μV at 77 K. High values of Rn of the graphoepitaxial step edge Josephson junctions can be advantageous for their applications as qubits.