Valley Vortex States in Sonic Crystals

Abstract

Valleytronics is quickly emerging as an exciting field in fundamental and applied research. In this Letter, we study the acoustic version of valley states in sonic crystals and reveal a vortex nature of such states. In addition to the selection rules established for exciting valley polarized states, a mimicked valley Hall effect of sound is proposed further. The extraordinary chirality of valley vortex states, detectable in experiments, may open a new possibility in sound manipulations. This is appealing to scalar acoustics that lacks a spin degree of freedom inherently. In addition, the valley selection enables a handy way to create vortex matter in acoustics, in which the vortex chirality can be controlled flexibly. Potential applications can be anticipated with the exotic interaction of acoustic vortices with matter, such as to trigger the rotation of the trapped microparticles without contact.

Snowflake phononic topological insulator at the nanoscale

“…So far, experimental implementations exist on the centimeter scale, both for the case of time-reversal symmetry broken by external driving [1], such as in coupled gyroscopes, as well as for the case without driving [2][3][4][5][6], such as in coupled pendula. Moreover, a multitude of different implementations have been envisioned theoretically [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. However, it is highly desirable to come up with alternative design ideas that may be realized on the nanoscale, eventually pushing towards applications in integrated phononics.…”

Tunable Acoustic Valley–Hall Edge States in Reconfigurable Phononic Elastic Waveguides

“…However, due to the large separation in k-space of the two valleys, valley-dependent topological invariants can be defined and used to classify the topological states of the different lattices. This approach, usually referred to as quantum valley Hall effect (QVHE), was recently investigated for application to fluidic acoustic waveguides 9,12 , as well as elastic plates with local resonators 28,29 .…”

Geometric valley Hall effect and valley filtering through a singular Berry flux

“…In addition to charge and spin, valley quantum numbers provide an alternative way to distinguish and designate quantum states, leading to the concept of valleytronics 1,2 , an area that has attracted much recent interest [3][4][5][6][7][8][9][10][11] . Take graphene as an example, where the crystalline structure stipulates that uncharged degrees of freedom such as valley isospin can arise 12 .…”

“…Electrons affiliated with the distinct valleys can be exploited for applications, e.g., in quantum information processing 14 . Appealing binary valley characteristics can also arise in other materials such as silicene and MoS 2 6 , graphene-inspired artificial crystals such as photonic graphene 15 that exhibits valley-polarized beams and sonic (phononic) crystals 9 in which valley vortex states can emerge, and valley photonic crystals 16 .…”