Spin-current Seebeck effect in quantum dot systems

We first bring up the concept of spin-current Seebeck effect based on a recent experiment [Nat. Phys. {\bf 8}, 313 (2012)], and investigate the spin-current Seebeck effect in quantum dot (QD) systems. Our results show that the spin-current Seebeck coefficient $S$ is sensitive to different polarization states of QD, and therefore can be used to detect the polarization state of QD and monitor the transitions between different polarization states of QD. The intradot Coulomb interaction can greatly enhance the $S$ due to the stronger polarization of QD. By using the parameters for a typical QD, we demonstrate that the maximum $S$ can be enhanced by a factor of 80. On the other hand, for a QD whose Coulomb interaction is negligible, we show that one can still obtain a large $S$ by applying an external magnetic field.Comment: 6 pages, 8 figure

Two-component Structure in the Entanglement Spectrum of Highly Excited States

We study the entanglement spectrum of highly excited eigenstates of two known models that exhibit a many-body localization transition, namely the one-dimensional random-field Heisenberg model and the quantum random energy model. Our results indicate that the entanglement spectrum shows a "two-component" structure: a universal part that is associated with random matrix theory, and a nonuniversal part that is model dependent. The non-universal part manifests the deviation of the highly excited eigenstate from a true random state even in the thermalized phase where the eigenstate thermalization hypothesis holds. The fraction of the spectrum containing the universal part decreases as one approaches the critical point and vanishes in the localized phase in the thermodynamic limit. We use the universal part fraction to construct an order parameter for measuring the degree of randomness of a generic highly excited state, which is also a promising candidate for studying the many-body localization transition. Two toy models based on Rokhsar-Kivelson type wave functions are constructed and their entanglement spectra are shown to exhibit the same structure.Comment: published versio

Reduced Graphene Oxide–Based Microsupercapacitors

Recent development in miniaturized electronic devices has been boosting the demand for power sources that are sufficiently thin, flexible/bendable, and even tailorable and can potentially be integrated in a package with other electronic components. Reduced graphene oxide can be a promising electrode material for miniaturized microsupercapacitors due to their excellent electrical conductivity, high surface-to-volume ratio, outstanding intrinsic electrochemical double-layer capacitance, and facile production in large scale and low cost. Therefore, the routes to produce high-quality reduced graphene oxide as electrode materials, along with the typical fabrication techniques for miniaturized electrodes, are deliberately discussed in this chapter. Furthermore, breakthroughs in the area of the advanced packaging technology, deciding the electrochemical performance and stability of these miniaturized microsupercapacitors, are highlighted. Lastly, a summary of the overall electrochemical properties and current development of the reported devices is presented progressively to provide insights into the development of novel miniaturized energy storage technologies