Exploring the intricate interplay between magnetism and superconductivity is crucial for unveiling the underlying mechanisms of unconventional superconductivity. Here, we report on the magnetotransport evidence for the coexistence of a two-dimensional (2D) superconducting state and a 2D ferromagnetic state at the interface between amorphous CaZrO₃ film and (111)-oriented KTaO₃ single crystal. Remarkably, the fingerprint of ferromagnetism, i.e., hysteretic magnetoresistance loops, is observed in the superconducting state. The butterfly-shaped hysteresis with twin peaks emerges against the background of superconducting zero resistance, and the peak amplitude increases with the sweep rate of the magnetic field, indicating that the magnetization dynamics are at play in the superconducting state. Moreover, the magnetoresistance hysteresis is strongly dependent on temperature, achieving a maximum near the superconducting transition temperature. This behavior is well described by the thermal activated phase slip model. Density function theory (DFT) calculations suggest that the magnetic moment is primarily contributed by the Ta 5d_yz orbital, and the Stoner ferromagnetism is identified. Our findings provide new insights into the interaction of magnetism and superconductivity at KTaO₃-based oxide heterointerfaces.

Spin-to-charge interconversion has been extensively investigated to improve its efficiency of charge-to-spin conversion, realizing magnetic switching by the technique of low-power spin-orbit torque (SOT). The quasi-two-dimensional electron gas (q2DEG) formed at the interface between insulating ${\mathrm{SrTiO}}_3$ (STO) and ${\mathrm{LaTiO}}_{3+\delta }$ (LTO) is supposed to possess strong Rashba spin-orbit coupling. Here, we show that a charge current flowing along the LTO/STO interface, which hosts a q2DEG, can efficiently generate a spin current, producing a strong SOT on adjacent NiFe layer as confirmed by spin-torque ferromagnetic resonance. The maximal charge-to-spin conversion efficiency is as large as $\sim 2.4$ at room temperature, appearing in the NiFe/LTO/STO structure with a LTO thickness of 4 nm. This efficiency is much larger than that of heavy meals. With the decrease of temperature, the conversion efficiency only exhibits a slight decrease, remaining $\sim 1.5$ at 20 K. The present work reveals the great potential of conducting oxide interface for oxide-based spintronics.

Despite intensive research, the mechanism determining the terahertz (THz) emission of the ferromagnetic (FM) metallic monolayers remains elusive. Here, we report on the results of a systematic investigation on the THz emission generated by pumping Ni80Fe20 monolayers on Al2O3 substrates with a femtosecond laser. We found solid evidence that the THz emission is dominated by the anomalous Nernst effect (ANE), in which a transient spin-polarized charge current can be induced by an ultrafast electron temperature gradient on the picosecond timescale, outputting THz emission. We found a polarity reversal of the THz waveform after the introduction of a SiO2 buffer layer to the sample and found that, based on ultrafast temperature simulation, it was a consequence of direction reversal of temperature gradient. Comparing the THz emission of different FM monolayers further confirms that the THz polarity also strongly depends on the sign of the ANE coefficient. These phenomena unambiguously indicate that the ANE plays a decisive role in the process of THz emission. The present work shows the importance of ultrafast spin caloritronics for a spintronic THz emitter. The principle demonstrated here can be applied to other FM metallic materials.

Charge-to-spin conversion is crucial for the application of emerging spintronic devices. A two-dimensional electron gas (2DEG) at a complex oxide interface usually possesses strong Rashba spin-orbit coupling, and spin-momentum locking offers a great possibility for efficient charge-to-spin conversion through the Rashba-Edelstein effect. Here, we report the fabrication of metallic 2DEGs in γ-${\mathrm{Al}}_2{\mathrm{O}}_3/{\mathrm{KTaO}}_3$ spinel/perovskite heterostructures and investigate the charge-to-spin conversion for Py/γ-${\mathrm{Al}}_2{\mathrm{O}}_3/{\mathrm{KTaO}}_3$ devices using the technique of spin-torque ferromagnetic resonance. The sizable spin splitting of the band structure results in a large current-induced spin-orbit torque efficiency with values up to around 3.6 at 5 K and about 1.1 at 300 K, which are more than an order of magnitude higher than those of heavy metals (0.07 for $\mathrm{Pt}$ at 300 K). Moreover, both theoretical and experimental results show that the charge-to-spin conversion is strongly dependent on the position of the Fermi level. These results demonstrate that optimizing the band filling of a ${\mathrm{KTaO}}_3$-based 2DEG is crucial for maximizing the conversion efficiency.

Oxide two-dimensional electron gas (2DEG) is a low-dimensional carrier system formed at the interface of oxide heterojunctions with strong and tunable Rashba spin–orbit coupling which makes oxide 2DEG an ideal platform for converting spin current and charge current. This review provides a summary of the recent advances on the 2DEGs at oxide interfaces for spin-charge interconversion. On one hand, we analyze properties and the efficiency of the spin-to-charge conversion through different ways of spin current injection. On the other hand, the conversion of charge current to spin current under different experimental methods has been summarized. These research achievements provide perspectives and methods for understanding and regulating the spin-charge interconversion of the 2DEG at the oxide interface.

The nonlinear Hall effect (NLHE), an emergent phenomenon in noncentrosymmetric systems, enables the generation of a transverse voltage without an external magnetic field through a second-order electrical response. However, achieving a sizable NLHE signal remains a critical challenge for its application in frequency-doubling and rectifying devices. Here, we report a light-induced giant enhancement of the NLHE in the two-dimensional electron gas (2DEG) at the CaZrO3/KTaO3 (111) interface. Under light illumination, the second harmonic Hall voltage (V2ω y) increases substantially and undergoes a sign reversal. Correspondingly,the second-order transverse conductivity increases by nearly five orders of magnitude, reaching 2.4 um V-1 omega-1, while also reversing its sign. Scaling analysis indicates that skew scattering is the dominant mechanism underlying the NLHE and is highly tunable via optical gating. Photoexcitation pumps electrons from in-gap states into the higher-lying Ta 5d conduction band, generating high-mobility photocarriers that significantly increase the cubic transport scattering time, thereby driving a dramatic enhancement of σ(2) yxx. First-principles calculations further reveal that the Berry curvature distribution on the Fermi surface strongly depends on band filling. As the Fermi level approaches a band crossing in the Ta 5d subband near the M point, the Berry curvature triple undergoes a sign change, accounting for the experimentally observed sign reversal of the nonlinear Hall response. Our work offers a new strategy to optically boost and tune the nonlinear Hall effect in oxide 2DEG systems, paving the way for applications in light-controlled rectification and nonlinear electronic devices.