Infinite Magnetoresistance and Vortex Coupling in the Pb/BSCCO Heterostructure

Combining superconductivity with spintronics provides exciting opportunities to realize low-dissipation quantum devices. Here we report the synthesis, characterization and magnetotransport measurements of the Pb/Bi$_2$Sr$2$CaCu$2$O${8+δ}$ (BSCCO) superconducting heterostructures, where an insulating PbO${x}$ layer spontaneously forms at the interface. Non-volatile switching between superconducting (logical “0”) and normal (“1”) states in Pb films by an external field, i.e., infinite magnetoresistance (IMR), can be realized and are attributed to the strong trapping and pinning of vortices in BSCCO. Furthermore, butterfly-shaped hysteresis loops in magnetoresistance, pronounced resistance dips/jumps and thermal reset to superconducting states can be observed and are direct manifestations of the peculiar vortex dynamics in BSCCO and vortex coupling across the Pb/BSCCO interface. Our work demonstrates a simple and effective way to realize IMR through superconducting vortices and opens up new opportunities to study the vortex interactions across the superconducting interfaces.

💡 Research Summary

In this work the authors report the synthesis, structural characterization, and magnetotransport properties of a novel superconducting heterostructure consisting of a lead (Pb) thin film deposited on an optimally‑doped Bi₂Sr₂CaCu₂O₈₊δ (BSCCO) single crystal. A key observation is that a few‑angstrom‑thick insulating PbOₓ layer forms spontaneously at the Pb/BSCCO interface during molecular‑beam epitaxy. Angle‑resolved photoemission spectroscopy (ARPES) and core‑level scans confirm the presence of this interfacial oxide, which acts as a thin barrier separating the metallic Pb overlayer from the cuprate substrate while still allowing epitaxial growth of Pb(111) crystallites.

Because the barrier prevents direct electrical shorting, the four‑probe transport measurement probes the parallel combination of the Pb film, the thin insulating layer, and the BSCCO bulk. Consequently two distinct superconducting transitions are observed: the high‑temperature transition near 90 K (BSCCO) and a low‑temperature transition near 7 K (Pb).

When an out‑of‑plane magnetic field is applied, BSCCO enters the mixed state (H > Hc1) and a dense lattice of Abrikosov vortices is generated. The vortices are strongly pinned in the cuprate due to intrinsic defects and the layered crystal structure. The magnetic flux associated with these pinned vortices penetrates the interfacial PbOₓ layer and produces an effective local magnetic field on the Pb overlayer. This field suppresses the superconductivity of Pb much more efficiently than the external field alone because the vortices act as a built‑in magnetic bias.

The authors demonstrate a striking “infinite magnetoresistance” (IMR) effect: after zero‑field cooling to 2 K the Pb film is in a zero‑resistance state (logical “0”). Applying a modest out‑of‑plane field (≈3 kOe) drives the Pb into a normal‑resistive state; when the field is subsequently removed the resistance remains finite (logical “1”). The state is non‑volatile because the trapped vortices in BSCCO retain their magnetization, providing a persistent bias field. Re‑applying a field of opposite polarity can reset the device, enabling repeatable binary switching.

Magnetoresistance versus field (R–H) curves display pronounced hysteresis. At low maximal applied fields (MAF ≈ 5–6 kOe) the hysteresis loops are narrow and the zero‑resistance state can be recovered on field removal. At higher MAF (≥ 8 kOe) the loops become “butterfly‑shaped”: the resistance never returns to zero, indicating that the vortex configuration in BSCCO has been irreversibly rearranged and continues to suppress Pb superconductivity. The authors identify a characteristic field Hc2,eff ≈ 6 kOe where a sharp change in the slope of the R–H curve occurs, which they attribute to a crossover in the vortex state of the Pb film itself (formation of secondary vortices) that is strongly coupled to the underlying BSCCO vortex lattice.

Thermal cycling experiments reveal a “reset” mechanism: heating the sample above ~30 K (well below the BSCCO Tc) releases the pinned vortices, allowing the Pb film to revert to the superconducting state upon cooling. This demonstrates that the vortex pinning energy is comparable to the thermal energy at modest temperatures, and that the insulating PbOₓ layer does not introduce excessive additional pinning centers beyond a few atomic layers.

The paper highlights three major contributions: (1) the discovery that a self‑formed PbOₓ interfacial layer creates a clean S/I/S′ junction without the need for complex fabrication; (2) the exploitation of high‑Tc cuprate vortex pinning as an internal magnetic bias to achieve non‑volatile, field‑controlled switching of a conventional low‑Tc superconductor; and (3) the demonstration that such a system yields an effectively infinite magnetoresistance, offering a new route to superconducting spintronic memory elements that do not rely on ferromagnetic layers.

Beyond device implications, the work provides a simple yet sensitive transport‑based probe of vortex dynamics across a superconductor–superconductor interface. The observed hysteresis, butterfly loops, and thermal reset give direct insight into vortex trapping, depinning, and interlayer coupling in a heterostructure that combines a high‑Tc layered cuprate with a conventional metallic superconductor. Future directions suggested include engineering the thickness and composition of the interfacial oxide, exploring other low‑Tc superconductors (e.g., Nb, Al) on BSCCO, and integrating current‑ or light‑induced vortex manipulation to realize more complex logic or quantum‑coherent functionalities. Overall, the study opens a promising pathway toward low‑dissipation, vortex‑based superconducting electronics.