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Zhibo Zhao

Publications and source records attributed to Zhibo Zhao.

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A voltage-responsive strongly dipolar-coupled macrospin network with emergent dynamics for computing

Emergent behavior, which arises from local interactions between simple elements, is pervasive in nature. It underlies the energy-efficient computing in our brains. However, realizing such dynamics in artificial materials, particularly under low-energy stimuli, remains a fundamental challenge. While dipole-dipole interactions are typically suppressed in magnetic storage, here we harness and amplify them to construct a strongly dipolar-coupled network of SmCo5 macrospins at wafer scale, which can exhibit intrinsic interaction-driven collective dynamics in response to voltage pulses. The network combines three essential ingredients: strong dipolar coupling by large single-domain macrospin, giant voltage control of coercivity over nearly 1000-fold, and disordered network topology with frustrated Ising-like energy landscape. When stimulated by 1 V pulses, the network enters a regime where interaction-driven magnetic behaviors emerge, including spontaneous demagnetization, greatly enhanced magnetization modulation, reversible freeze and resume evolution and stochastic convergence toward low-energy magnetic configurations. All these behaviors are completely absent at the single-nanomagnet level. Furthermore, by constructing micromagnetic models of the strongly dipolar-coupled macrospin networks, we show that the resulting nonlinear, high-dimensional collective dynamics, intrinsic to strongly-interacting systems, can enable accurate chaotic Mackey-Glass prediction and multiclass drone-signal classification. Our work establishes the voltage-responsive strongly-coupled SmCo5 network as a mesoscopic platform for probing emergent magnetic dynamics previously inaccessible under ambient conditions. It also suggests a fundamental distinct route towards scalable, low-voltage computing, one rooted in native physical interaction-driven collective dynamics at the network level.

cond-mat.mtrl-sci

Cathodoluminescence as an Effective Probe of Carrier Transport and Deep Level Defects in Droop-Mitigating InGaN/GaN Quantum Well Heterostructures

Commercial InGaN/GaN light emitting diode heterostructures continue to suffer from efficiency droop at high current densities. Droop mitigation strategies target Auger recombination and typically require structural and/or compositional changes within the multi-quantum well active region. However, these modifications are often accompanied by a corresponding degradation in material quality that decreases the expected gains in high-current external quantum efficiency. We study origins of these efficiency losses by correlating chip-level quantum efficiency measurements with structural and optical properties obtained using a combination of electron microscopy tools. The drop in quantum efficiency is not found to be correlated with quantum well (QW) width fluctuations. Rather, we show direct correlation between active region design, deep level defects, and delayed electron beam induced cathodoluminescence (CL) with characteristic rise time constants on the order of tens of seconds. We propose a model in which the electron beam fills deep level defect states and simultaneously drives reduction of the built-in field within the multi-quantum well active region, resulting in a delay in accumulation of carrier populations within the QWs. The CL measurements yield fundamental insights into carrier transport phenomena, efficiency-reducing defects, and quantum well band structure that are important in guiding future heterostructure process development.

cond-mat.mes-hall