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Abstract Strain modulation is a crucial way in engineering nanoscale materials. It is even more important for single photon emitters in layered materials, where strain can trap a delocalized exciton, leading to quantum emission. Herein, we apply strain by using the piezoelectric relaxor ferroelectric substrate. In addition to the strain-tuning of energy and polarization, we report on new observations, including the enhanced polarizability and tunable diamagnetic shift, from the charged localized excitons. As indicated from the polarization-resolved measurements, we attribute the formation of charged localized excitons to selenium vacancy defects. The shallow defect trap, supported by the value of g-factor, further allows for strain-modulation of the electron-hole overlap, hence resulting in the tunable diamagnetic shift. Our results provide a new perspective in integrating layered materials with functional substrates. The contrasting features observed from the charged localized excitons also signify the prospect of charged localized emitters for quantum science and technology. 

We fabricate and measure electrically-gated tunnel junctions in which the insulating barrier is a sliding van der Waals ferroelectric made from parallel-stacked bilayer hexagonal boron nitride and the electrodes are single-layer graphene. Despite the nominally-symmetric tunnel-junction structure, these devices can exhibit substantial electroresistance upon reversing the ferroelectric polarization. The magnitude and sign of tunneling electroresistance are tunable by bias and gate voltage. We show that this behavior can be understood within a simple tunneling model that takes into account the quantum capacitance of the graphene electrodes, so that the tunneling densities of states in the electrodes are separately modified as a function of bias and gate voltage. 

Three fluorescent 5’-(p-hydroxyphenyl)pyridylthiazoles (HPPT) with different chelating groups at the 4’ position were synthesized and evaluated for their ability to detect transition metal ions in acetonitrile and aqueous buffers, based on changes in fluorescence intensity and intramolecular charge transfer (ICT). Both 4’-O-picolyloxy-HPPT (Pic-HPPT) and 4’-O-(o-carboxypicolyl)-HPPT (CPic-HPPT) respond strongly to Zn(II), Cd(II), and Pb(II) in CH3CN with a bathochromic shift in emission up to 68 nm, whereas 4’-O-carboxymethyl-HPPT (CM-HPPT) is unresponsive. Only CPic-HPPT responds to d10 metal ions in aqueous phosphate buffered solution (PBS, pH 7.4), attributable to the added chelating power of the ortho-carboxylate. CPic-HPPT forms a 2:1 complex with Zn(II) and a 1:1 complex with Cd(II) and Pb(II) in CH3CN, whereas a 1:1 complex forms with Zn(II), Cd(II), and Hg(II) ions in PBS. X-ray structural analysis of 1:1 Pic-HPPT–metal ion complexes reveals a planar tridentate binding motif with Zn(II) but a nonplanar tridentate geometry with the larger Cd(II) ion. Fluorescence titration of CPic-HPPT in PBS with Zn(NO3)2 established sub-micromolar sensitivity with a limit of quantitation at 50 nM. These results show that CPic-HPPT has promise as a fluorescent probe for d10 metal ions in physiologically relevant media. 

Abstract Perceptual learning can significantly improve visual sensitivity even in fully matured adults. However, the ability to generalize learning to untrained conditions is often limited. While traditionally, perceptual learning is attributed to practice-dependent plasticity mechanisms, recent studies suggest that brief memory reactivations can efficiently improve visual perception, recruiting higher-level brain regions. Here we provide evidence that similar memory reactivation mechanisms promote generalization of offline learning mechanisms. Human participants encoded a visual discrimination task with the target stimulus at retinotopic location A. Then, brief memory reactivations of only five trials each were performed on separate days at location A. Generalization was tested at retinotopic location B. Results indicate remarkable enhancement of location B performance following memory reactivations, pointing to efficient offline generalization mechanisms. A control experiment with no reactivations showed minimal generalization. These findings suggest that reactivation-induced learning further enhances learning efficiency by promoting offline generalization mechanisms to untrained conditions, and can be further tested in additional learning domains, with potential future clinical implications. 

Abstract AB-stacked bilayer graphene has emerged as a fascinating yet simple platform for exploring macroscopic quantum phenomena of correlated electrons. Under large electric displacement fields and near low-density van-Hove singularities, it exhibits a phase with features consistent with Wigner crystallization, including negative dR/dT and nonlinear bias behavior. However, direct evidence for the emergence of an electron crystal at zero magnetic field remains elusive. Here, we explore low-frequency noise consistent with depinning and sliding of a Wigner crystal or solid. At large magnetic fields, we observe enhanced noise at low bias current and a frequency-dependent response characteristic of depinning and sliding, consistent with earlier scanning tunnelling microscopy studies confirming Wigner crystallization in the fractional quantum Hall regime. At zero magnetic field, we detect pronounced AC noise whose peak frequency increases linearly with applied DC current—indicative of collective electron motion. These transport signatures pave the way toward confirming an anomalous Hall crystal.