Light Erases Superconductivity in KTaO₃ Interfaces, Enabling Novel Memory Control

Controlling superconductivity without energy consumption represents a major goal in future information technologies, and researchers are now demonstrating a pathway towards achieving this through innovative material design. Zhihao Chen, Pengxu Ran, and Jiexiong Sun, from Beijing National Laboratory for Condensed Matter Physics, alongside colleagues, have discovered a method to both enhance and erase superconductivity at the interface of specially engineered materials. Their work focuses on structures built from potassium tantalate oxide, which uniquely combines superconducting properties with a sensitive underlying lattice structure, allowing them to encode information directly into the superconducting state. The team reveals that applying electrical voltages progressively strengthens superconductivity, creating a form of memory, and crucially, this memory can be completely wiped clean using light, offering a reconfigurable and non-volatile superconducting system with potential applications in advanced computing and neuromorphic devices.

Oxygen Vacancies Enable Nonvolatile Memory Effects

This research demonstrates a non-volatile memory effect in a two-dimensional electron gas (2DEG) created within a heterostructure, offering potential for low-power memory applications. Scientists demonstrate the ability to ‘write’ information by cycling gate voltage, altering the charge state of oxygen vacancies (OVs), and ‘read’ it by measuring sheet resistance and carrier properties. Light illumination resets the system to a known state. Gate voltage cycling induces changes in superconducting transition temperature, sheet resistance, carrier density, and mobility, stabilizing after a few cycles.

The memory effect remains robust across a wide temperature range, from 5K to 180K, and is not limited to low temperatures. Asymmetric current flow through the gate electrode during cycling suggests irreversible charge displacement related to oxygen vacancy charge states. The magnitude of the memory effect, measured as changes in sheet resistance, can be controlled by adjusting illumination time and gate voltage amplitude. Light illumination resets the system, and subsequent dark relaxation reveals dynamics of carrier density and mobility, providing insights into the underlying mechanisms.

Superconducting Memory Effect via Voltage Cycling

Scientists engineered an aluminum oxide/potassium tantalate oxide heterostructure to create a 2DEG, intentionally introducing oxygen vacancies to form a conductive interface. Applying a gate voltage revealed an unexpected memory effect: the superconducting transition temperature shifted to higher values with each voltage cycle. Repeated cycling consistently elevated both transition temperature and sheet resistance, stabilizing after four cycles and remaining discernible up to approximately 100K. This behavior is attributed to redistribution of charges and internal electric fields near the interface, supported by asymmetric gate current measurements.

Illumination with red light, despite being below the material’s band gap, induced persistent photoconductivity, resetting the enhanced superconducting transition temperature. By alternating illumination and gate cycles, the team demonstrated repeatable switching between resistance states, artificially fine-tuning the effect by adjusting illumination duration and gate voltage amplitude. Hall measurements confirmed that illumination increased carrier mobility and density, while gate cycling decreased both.

Electrostatic Cycling Imprints Superconducting Memory States

Researchers have demonstrated reconfigurable and non-volatile superconductivity in aluminum oxide/potassium tantalate oxide heterostructures. They found that progressive electrostatic cycling enhances the superconducting transition temperature, effectively imprinting a memory within the superconducting state. The team observed a consistent upward drift in transition temperature following repeated voltage sweeps, establishing a reproducible hysteretic loop after just four cycles. Sheet resistance also increases with cycling, indicating a change in the material’s electrical properties. Detailed measurements reveal that this elevation in resistance is primarily due to a decrease in carrier mobility, with a slight increase in carrier density also observed.

The memory effect persists up to approximately 100 Kelvin, demonstrating the robustness of the induced changes. The research identifies two key microscopic mechanisms: flipping of polar nanoregion orientations and switching between oxygen vacancy charge states. These polar nanoregions modulate the internal gating field acting on the 2DEG, while changes in oxygen vacancy charge states alter electron mobility.

Reconfigurable Superconductivity via Gate-Induced Memory

Researchers have demonstrated reconfigurable and non-volatile superconductivity within oxide heterostructures, integrating memory and quantum functionality. They found that progressive electrostatic cycling enhances the superconducting transition temperature, effectively imprinting a memory within the superconducting state. The memory is not permanent and can be erased by illuminating the material at cryogenic temperatures. This behavior arises from an interplay between the superconducting interface and the underlying lattice structure, specifically the reorientation of polar nanoregions and the ionization of oxygen vacancies. Changes in oxygen vacancy charge states and the alignment of polar nanoregions are sensitive to both electric and optical stimuli, creating a pathway to control the superconducting state. The authors acknowledge that thermal fluctuations can randomize lattice behavior at higher temperatures, and future work will focus on disentangling these interactions and exploring the potential for superconducting neuromorphic devices.