An official website of the United States government
Abstract Vanadium dioxide (VO2) is a well‐studied Mott‐insulator because of the very abrupt physical property switching during its semiconductor‐to‐metal transition (SMT) around 341 K (68 °C). In this work, through novel oxide‐metal nanocomposite designs (i.e., Au:VO2and Pt:VO2), a very broad range of SMT temperature tuning from≈323.5 to≈366.7 K has been achieved by varying the metallic secondary phase in the nanocomposites (i.e., Au:VO2and Pt:VO2thin films, respectively). More surprisingly, the SMTTccan be further lowered to≈301.8 K (near room temperature) by reducing the Au particle size from 11.7 to 1.7 nm. All the VO2nanocomposite thin films maintain superior phase transition performance, i.e., large transition amplitude, very sharp transition, and narrow width of thermal hysteresis. Correspondingly, a twofold variation of the complex dielectric function has been demonstrated in these metal‐VO2nanocomposites. The wide range physical property tuning is attributed to the band structure reconstruction at the metal‐VO2phase boundaries. This demonstration paved a novel approach for tuning the phase transition property of Mott‐insulating materials to near room temperature transition, which is important for sensors, electrical switches, smart windows, and actuators.
more »
« less
Quantum cluster algorithm for data classification
Abstract We present a quantum algorithm for data classification based on the nearest-neighbor learning algorithm. The classification algorithm is divided into two steps: Firstly, data in the same class is divided into smaller groups with sublabels assisting building boundaries between data with different labels. Secondly we construct a quantum circuit for classification that contains multi control gates. The algorithm is easy to implement and efficient in predicting the labels of test data. To illustrate the power and efficiency of this approach, we construct the phase transition diagram for the metal-insulator transition ofVO2, using limited trained experimental data, whereVO2is a typical strongly correlated electron materials, and the metallic-insulating phase transition has drawn much attention in condensed matter physics. Moreover, we demonstrate our algorithm on the classification of randomly generated data and the classification of entanglement for various Werner states, where the training sets can not be divided by a single curve, instead, more than one curves are required to separate them apart perfectly. Our preliminary result shows considerable potential for various classification problems, particularly for constructing different phases in materials.
more »
« less
- Award ID(s):
- 1955907
- PAR ID:
- 10307989
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Materials Theory
- Volume:
- 5
- Issue:
- 1
- ISSN:
- 2509-8012
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
VO2-based MEMS tunable optical shutters are demonstrated. The design consists of a VO2-based cantilever attached to a VO2-based optical window with integrated resistive heaters for individual mechanical actuation of the cantilever structure, tuning of the optical properties of the window, or both. Optical transmittance measurements as a function of current for both heaters demonstrates that the developed devices can be used as analog optical shutters, where the intensity of a light beam can be tuned to any value within the range of VO2phase transition. A transmittance drop off 30% is shown for the optical window, with tuning capabilities greater than 30% upon actuation of the cantilever. Unlike typical mechanical shutters, these devices are not restricted to binary optical states. Optical modulation of the optical window is demonstrated with an oscillating electrical input. This produces a transmittance signal that oscillates around an average value within the range off VO2’s phase transition. For an input current signal with fixed amplitude (fel= 0.28 Hz), tuned to be at the onset of the phase transition, a transmittance modulation of 14% is shown. Similarly, by modulating the DC-offset, a transmittance modulation of VO2along the hysteresis is obtained.more » « less
-
Abstract Mott insulator VO2exhibits an ultrafast and reversible semiconductor‐to‐metal transition (SMT) near 340 K (67 °C). In order to fulfill the multifunctional device applications, effective transition temperature (Tc) tuning as well as integrated functionality in VO2is desired. In this study, multifunctionalities including tailorable SMT characteristics, ferromagnetic (FM) integration, and magneto‐optical (MO) coupling, have been demonstrated via metal/VO2nanocomposite designs with controlled morphology, i.e., a two‐phase Ni/VO2pillar‐in‐matrix geometry and a three‐phase Au/Ni/VO2particle‐in‐matrix geometry. EvidentTcreduction of 20.4 to 54.9 K has been achieved by morphology engineering. Interestingly, the Au/Ni/VO2film achieves a record‐lowTcof 295.2 K (22.2 °C), slightly below room temperature (25 °C). The change in film morphology is also correlated with unique property tuning. Highly anisotropic magnetic and optical properties have been demonstrated in Ni/VO2film, whereas Au/Ni/VO2film exhibits isotropic properties because of the uniform distribution of Au/Ni nanoparticles. Furthermore, a strong MO coupling with enhanced magnetic coercivity and anisotropy is demonstrated for both films, indicating great potential for optically active property tuning. This demonstration opens exciting opportunities for the VO2‐based device implementation towards smart windows, next‐generation optical‐coupled switches, and spintronic devices.more » « less
-
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 VO2thin film devices are studied by performing optically detected NV electron spin resonance measurements. These measurements probe thelocaltemperature and magnetic field in electrically biased VO2devices, which are in agreement with theglobaltransport 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.more » « less
-
Abstract The characteristic metal–insulator phase transition (MIT) in vanadium dioxide results in nonlinear electrical transport behavior, allowing VO2devices to imitate the complex functions of neurological behavior. Chemical doping is an established method for varying the properties of the MIT, and interstitial dopant boron has been shown to generate a unique dynamic relaxation effect in individual B‐VO2particles. This paper describes the first demonstration of an electrically stimulated B‐VO2proto‐device which manifests a time‐dependent critical transformation temperature and switching voltage derived from the coupling of dopant diffusion dynamics and the metal–insulator transition of VO2. During quasi‐steady current‐driven transitions, the electrical responses of B‐VO2proto‐devices show a step‐by‐step progression through the phase transformation, evidencing domain transformations within individual particles. The dynamic relaxation effect is shown to increase the critical switching voltage by up to 41% (ΔVcrit =0.13 V) and also to increase the resistivity of the M1 phase of B‐VO2by 14%, imbuing a memristive response derived from intrinsic material properties. These observations demonstrate the dynamic relaxation effect in B‐VO2proto‐devices whose electrical transport responses can be adjusted by electronic phase transitions triggered by temperature but also by time as a result of intrinsic dynamics of interstitial dopants.more » « less
