Asymmetric water diffusion driven nanotube actuator

Here we report, water vapor driven actuation of polymer nanotubes, embedded in a nanoporous membrane with one end attached to a surface deposited thin polymer layer. The nanotube composite shows oscillatory motion when placed near water. Permeation of water vapor through these nanotube embedded membranes is found to be direction dependent. With the water vapor as the driving force, the actuator can lift a mass 1000 times heavier than itself with a change in relative humidity of less than 40%. The actuation mechanism arises due to efficient absorption of water molecules by polymer nanotubes and their rapid evaporation through the surface deposited polymer layer. This actuator can be used as artificial muscle and the direction dependent water transport may help in understanding the activities of transmembrane channels and pumps of biological cells. With the aid of a nanowire generator, the oscillatory motion can be used to generate electricity too

Review of recent progress on THz spectroscopy of quantum materials: superconductors, magnetic and topological materials

Recently, the THz spectroscopy has been efficiently used to investigate varieties of quantum materials, including superconductors, novel magnetic, and topological materials. These materials often exhibit strong correlation and competing interactions between various degrees of freedom, including charge, spins, orbital, and lattice dynamics, which lead to many exotic phenomena and novel phase transitions whose cause–effect correlations are challenging to determine. Whereas probing the ground state’s excitations can unravel the underlying mechanism of these complex phenomena. The characteristic energy scales of different elementary excitations and collective modes in many of these materials are in the THz frequency range. Therefore, THz spectroscopy has become a very effective probe and directly revealed many exciting physics. Many novel phenomena, including exotic quasiparticle excitations in magnetic systems, topological magneto-electric effect, and topological quantum phase transition in three-dimensional topological insulators, are studied with unprecedented success. Here, we review some recent research reports on many-body quantum materials, including superconductors, novel magnetic, and topological materials probed by few popular THz-spectroscopy techniques. We will also briefly discuss the prospects of using THz spectroscopy for observing some exotic quantum phenomena that are still elusive or under investigation