QUANTUM WELLS
Over the recent years, we have investigated the properties of quantum wells (QWs) at the LaAlO3/SrTiO3 interface, including 2D superconductivity, Rashba spin-orbit fields and lattice vibrational modes [see References 1-3 below].
Among our recent discoveries there is the observation of polar lattice distortions in LaAlO3/SrTiO3 quantum wells due to extreme confinement of phonon modes [3]. We used advanced scanning transmission electron microscopy methods to visualize shifts in the atomic positions in the lattice and first-principles calculations to understand the physics behind these observations [3].
We are also interested in low-dimensional quantum transport, and in particular, with 2D superconductivity. Along these lines, we have recently observed for a first time a multi-condensate superconductor tuneable by electrostatic gating in LaAlO3/SrTiO3 quantum wells, published recently in Nature Materials [4].
More recently we have uncovered persistent photoconductance (PPC), whereby the system changes its conductance in a plastic way, retaining memory from its past history, as in the case of memristors, but using light instead of electric pulses. Our most recent discovery [5] is that light pulses can be used to replicate spike timing-dependent plasticity (STDP). STDP was proposed to emulate time causality of electro-chemical signals in biological neurons: pre-synaptic neurons spiking after post-synaptic neurons are “anti-causal” and learning is weakened; pre-synaptic neurons spiking before post-synaptic neurons are causal, reinforcing learning. STDP enables unsupervised learning, without need of labelling training data.

[1] Pesquera et al., Physical Review Letters 2014. https://doi.org/10.1103/PhysRevLett.113.156802
[2] Herranz et al., Nature Communications 2015. https://doi.org/10.1038/ncomms7028
[3] Gazquez et al., Physical Review Letters 2017. https://doi.org/10.1103/PhysRevLett.119.106102
[4] G. Singh et al., Nature Materials 18, 948–954 (2019). https://doi.org/10.1038/s41563-019-0354-z
[5] Y. Chen et al. Physical Review Letters 124, 246804 (2020) https://doi.org/10.1103/PhysRevLett.124.246804
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