| Metadata | Details |
|---|
| Publication Date | 2021-03-26 |
| Journal | Advanced Quantum Technologies |
| Authors | Nathan J McLaughlin, Yoav Kalcheim, Albert Suceava, Hailong Wang, Ivan K. Schuller |
| Institutions | University of California, San Diego |
| Citations | 8 |
| Analysis | Full AI Review Included |
- Core Achievement: The research successfully utilized Nitrogen Vacancy (NV) centers in diamond to perform local, nanoscale quantum sensing of the electrically driven Insulator-to-Metal Transition (IMT) in Vanadium Dioxide (VO2) thin films.
- Non-Thermal IMT Evidence: The study provides the first direct evidence for a non-thermal, electrically induced IMT mechanism in ion-irradiated VO2, where the transition occurs up to 35 K below the critical thermal temperature (Tc ~ 335 K).
- Thermal IMT Confirmation: In pristine VO2 devices, the IMT was confirmed to be thermally driven, proceeding through Joule heating until the local temperature reached Tc.
- Dual Sensing Capability: The NV center acts as a sensitive local probe, simultaneously measuring local temperature (via the NV zero-splitting frequency) and the local magnetic field (Oersted field, via Zeeman splitting) generated by the current filament.
- Mechanism Identification: The non-thermal IMT in irradiated VO2 is attributed to field-assisted carrier generation (doping-driven IMT), where in-gap states created by ion irradiation are electrically excited.
- Engineering Impact: This non-thermal mechanism significantly reduces the required critical currents and energy dissipation, highlighting a path toward developing highly energy-efficient Mott-material-based neuromorphic circuits.
| Parameter | Value | Unit | Context |
|---|
| VO2 Film Thickness | 170 | nm | Grown by radio-frequency magnetron sputtering. |
| Substrate Material | Al2O3 (012) | N/A | Used for VO2 film growth. |
| Electrode Material | Ti/Au | N/A | 125 nm thick, used for electrical transport. |
| Electrode Separation | 10 | µm | Distance between the two Au electrical contacts. |
| Diamond Nanobeam Size | 500 x 500 x 10 | nm x nm x µm | Equilateral triangular prism shape containing NV centers. |
| NV-to-Sample Distance | ~100 | nm | Estimated distance ensuring sufficient thermal and field sensitivity. |
| Thermal IMT Critical Temp (Tc) | ~335 | K | Characteristic transition temperature for pristine VO2. |
| Local Temperature Uncertainty | ±1.2 | K | Precision of temperature extracted from NV ESR measurements. |
| Non-Thermal IMT Temp Offset | Up to 35 | K | Local temperature below Tc during electrically induced IMT in ion-irradiated VO2. |
| External Magnetic Field (B//) | 700 | Oe | Applied along the NV-axis for optically detected NV ESR measurements. |
| Critical Current Range (Ic) | 1 to 3 | mA | Range where resistive switching occurs, dependent on base temperature. |
- VO2 Film Preparation: 170-nm-thick VO2 films were deposited onto Al2O3 (012) substrates using radio-frequency magnetron sputtering.
- Device Fabrication: Standard lithography was used to define two 125-nm-thick Ti/Au electrodes separated by 10 µm on the VO2 film for electrical transport measurements.
- Quantum Sensor Integration: Patterned diamond nanobeams containing individually addressable NV centers were transferred onto the VO2 film and positioned between the electrical contacts.
- Microwave Delivery: An Au stripline was fabricated adjacent to the contacts to provide the microwave control necessary for the NV electron spin resonance (ESR) measurements.
- Thermal Characterization: Global electrical transport measurements were performed to determine the resistance-temperature profile and establish the thermal IMT critical temperature (Tc).
- Ion Irradiation (Non-Thermal Study): A focused ion beam was used to irradiate gallium ions onto a ~2 µm wide region connecting the Au contacts in specific devices, creating in-gap states to facilitate non-thermal switching.
- Optically Detected ESR (ODMR/ESR): An external magnetic field (B//) was applied along the NV axis. A continuous green laser initiated the NV spin to the ms = 0 state, and a microwave current was swept in frequency ($f$). The resulting photoluminescence (PL) intensity dips were measured to determine the NV ESR frequencies ($f_+$ and $f_-$).
- Local Parameter Extraction:
- Local Temperature (TL): Extracted from the temperature dependence of the NV zero-splitting frequency, $D(T)$, using the average of the two ESR frequencies ($f_+ + f_-$).
- Local Magnetic Field (ΔB//): Extracted from the Zeeman splitting of the ESR frequencies ($f_+ - f_-$), which corresponds to the Oersted field generated by the current filament.
- Energy-Efficient Neuromorphic Computing: The demonstration of non-thermal, doping-driven IMT in VO2 provides a foundation for designing artificial neurons and synapses that require significantly lower switching energy compared to conventional thermal IMT devices.
- Nanoscale Thermal Management: NV quantum sensing offers unprecedented spatial resolution and sensitivity for mapping heat dissipation and thermal conductivity in complex integrated circuits, microprocessors, and power electronics.
- Advanced Quantum Material Characterization: The NV-based platform is a transformative tool for non-perturbative local sensing of electrical phase transitions, magnetic fields, and temperature in other Mott insulators and correlated electron systems.
- Resistive Switching Memory (RRAM): The ability to control and understand the non-thermal switching mechanism is crucial for developing faster, more reliable, and lower-power resistive memory elements.
- Hybrid Quantum-Classical Devices: The demonstrated coupling between NV centers (a quantum system) and Mott insulators (a classical/correlated system) opens avenues for developing next-generation hybrid devices for computing and sensing.
View Original Abstract
Abstract Nitrogen vacancy (NV) centers, optically active atomic defects in diamond, have attracted tremendous interest for quantum sensing, network, and computing applications due to their excellent quantum coherence and remarkable versatility in a real, ambient environment. Taking advantage of these strengths, this paper reports on NV‐based local sensing of the electrically driven insulator‐to‐metal transition (IMT) in a proximal Mott insulator. The resistive switching properties of both pristine and ion‐irradiated VO 2 thin film devices are studied by performing optically detected NV electron spin resonance measurements. These measurements probe the local temperature and magnetic field in electrically biased VO 2 devices, which are in agreement with the global transport measurement results. In pristine devices, the electrically driven IMT proceeds through Joule heating up to the transition temperature while in ion‐irradiated devices, the transition occurs nonthermally, well below the transition temperature. The results provide direct evidence for nonthermal electrically induced IMT in a Mott insulator, highlighting the significant opportunities offered by NV quantum sensors in exploring nanoscale thermal and electrical behaviors in Mott materials.