The EQUAL lab is now open at Rice MSNE! I feel very proud to start my new career in a brilliant, friendly and productive team. According to the old saying: All beginnings are difficult, this is going to be a challenging and rewarding period. Lucky enough, the lab is not completely empty. And plus, the warm weather is perfect for staying in shape.
Read the original departmental announcement.
For the first time, we have experimentally demonstrated that the vibration of atomic lattice may possess topological attributes. These chiral phonons are promising for quantum memories and transducers (Zhu et al, Science 359, 579).
In a 2D asymmetric hexagonal lattice, such as monolayer WSe2, the atoms rotate, instead of shaking back and forth, for phonons propagating with a momentum of K and -K.
The valley optical phonon mode LO(K) contains unidirectional atomic rotation.
The direction of the rotation is determined by the direction of the momentum, as seen from the circular polarization of the light absorption that excites the phonons.
Phonons created by a pair of light pulses show circular dichroism.
For more introduction and stories about this research, please visit LBL News Center.
Piezoelectric materials, which convert energy between electricity and mechanical force, are the core of clocks, ultrasonics and microbalances. We have experimentally demonstrated that a single-layer crystal of less than 1-nm thick can be piezoelectric, and are tough enough for constructing Nano-ElectroMechanical Systems (Zhu et al, Nature Nanotechnology 10, 151).
The freestanding single-layer MoS2 NEMS device. A force is generated by electric field and picked up by Atomic Force Microscope.
The ratio between the in-plane stress and the electric field, i.e. piezoelectric coefficient, for this 2D crystal is comparable with conventional 3D crystals like quartz and AlN. The crystal can be chemically engineered to show out-of-plane piezoelectricity as well (Lu et al, Nature Nanotechnology 12, 744).