Electrons in two-dimensional crystals with a honeycomb lattice structure possess a valley degree of freedom (DOF) in addition to charge and spin. These systems are predicted to exhibit an anomalous Hall effect whose sign depends on the valley index. Here, we report the observation of this so-called valley Hall effect (VHE). Monolayer MoS2 transistors are illuminated with circularly polarized light, which preferentially excites electrons into a specific valley, causing a finite anomalous Hall voltage whose sign is controlled by the helicity of the light.

We calculate the ground state of a Bose gas trapped on a two-leg ladder where Raman-induced hopping mimics the effect of a large magnetic field. In the mean-field limit, where there are large numbers of particles per site, this maps onto a uniformly frustrated two-leg ladder classical spin model. The net particle current always vanishes in the ground state, but generically there is a finite "chiral current," corresponding to equal and opposite flow on the two legs. We vary the strength of the hopping across the rungs of the ladder and the interaction between the bosons.

Tiger beetles are fast diurnal predators capable of chasing prey under closed-loop visual guidance. We investigated this control system using statistical analyses of high-speed digital recordings of beetles chasing a moving prey dummy in a laboratory arena. Correlation analyses reveal that the beetle uses a proportional control law in which the angular position of the prey relative to the beetle's body axis drives the beetle's angular velocity with a delay of about 28 ms. The proportionality coefficient or system gain, 12 s -1, is just below critical damping.

In an effort to scale down electronic devices to atomic dimensions, the use of transition-metal oxides may provide advantages over conventional semiconductors. Their high carrier densities and short electronic length scales are desirable for miniaturization, while strong interactions that mediate exotic phase diagrams open new avenues for engineering emergent properties. Nevertheless, understanding how their correlated electronic states can be manipulated at the nanoscale remains challenging.

We demonstrate large optomechanical coupling between a carbon nanotube and an optical microresonator. We measured a dominantly dissipative optomechanical coupling coefficient of gk = 1 MHz/nm. © 2014 Optical Society of America.

We show ability to simultaneously trap micron-size particles in an optical field and freeze their position by rapidly changing the direction of Poynting vector in an optofluidic waveguide using an electrically controlled Mach-Zehnder switch. © 2014 OSA.

Optical trapping is a powerful manipulation and measurement technique widely used in the biological and materials sciences. Miniaturizing optical trap instruments onto optofluidic platforms holds promise for high-throughput lab-on-a-chip applications. However, a persistent challenge with existing optofluidic devices has been achieving controlled and precise manipulation of trapped particles. Here, we report a new class of on-chip optical trapping devices.

We review recent experiments in which superfluid 3He has been studied under highly controlled confinement in nanofluidic sample chambers. We discuss the experimental challenges and their resolution. These methods open the way to a systematic investigation of the superfluidity of 3He films, and the surface and edge excitations of topological superfluids. © 2014 Springer Science+Business Media New York.

Identifying the effects of surface-bulk coupling is a key challenge in exploiting the topological nature of the surface states in many available three-dimensional topological “metals.†Here we combine an effective-model calculation and an ab initio slab calculation to study the effects of the lowest order surface-bulk interaction: hybridization. In the effective-model study, we discretize an established low-energy effective four-band model and introduce hybridization between surface bands and bulk bands in the spirit of the Fano model.