SCIENTIFIC HIGHLIGHTS RL3, Articles

Probing time correlations with quantum wells

The photoresponse of LaAlO3/SrTiO3 quantum wells is sensitive to time order of optical pulses and replicates the synaptic plasticity observed in neurobiological systems.

Spike-timing dependent plasticity (STDP) is a fundamental concept in neurobiology. Briefly, the relative timing of two neuron spikes reinforces or weakens the synapse between them, so that events caused by another should trigger spikes in a particular time order. A reversal of this order causes the weakening of the synapse, so it penalizes the correlation. This process allows the brain to establish causal correlations from the environment and it is widely used in computational neuroscience. Recently, Yu Chen et al. (ACS Appl. Electron. Mater. 2019, 1, 6, 810–816 (2019)) have found that the photoconductive properties of quantum wells at the LaAlO3/SrTiO3 interface mimic STDP, using time correlations in optical pulses. More specifically, the conductance of the quantum well is increased or decreased depending on the relative timing of optical pulses of short- (blue) and long- (red) wavelengths (Figure). Remarkably, the conductance changes plastically in proportion to the intensity of the optical stimulus, in a way that is reminiscent of synaptic plasticity found in neurobiological systems (Yu Chen, ACS Appl. Electron. Mater. 2019, 1, 6, 810–816 (2019)). The sensitivity of the conductance to these correlations opens up fascinating perspectives on the use of optical synapses for neuromorphic devices based on these photoconductive systems.

Plasticity of Persistent Photoconductance of Amorphous LaAlO3/SrTiO3 Interfaces under Varying Illumination Conditions
Yu Chen, Blai Casals, Gervasi Herranz
ACS Appl. Electron. Mater. 2019, 1, 6, 810–816, 2019
DOI: 10.1021/acsaelm.9b00127

Solid-State Synapses Modulated by Wavelength-Sensitive Temporal Correlations in Optic Sensory Inputs
Yu Chen, Blai Casals, Florencio Sanchez, Gervasi Herranz
ACS Appl. Electron. Mater. 2019, 1, 7, 1189–1197, 2019
DOI: 10.1021/acsaelm.9b00183

Figure: Probing time correlations with quantum wells. We have uncovered photoresponsive quantum wells that mimic spike-timing dependent plasticity using optical pulses as stimuli. The conductance is sensitive to the time order of optical inputs of different wavelengths (see bottom panel, where blue and red arrows indicate different sequences of blue and red pulses). Therefore, these quantum wells can be used as optical synapses in neuromorphic devices.

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