Electronic structure of correlated topological insulator candidate YbB6 studied by photoemission and quantum oscillation

Angle-resolved photoemission spectroscopy(ARPES)and torque magnetometry(TM)measurements have been carried out to study the electronic structures of a correlated topological insulator(TI)candidate Yb B6.We observed clear surface states on the[001]surface centered at theГ^- and М^- points of the surface Brillouin zone.Interestingly,the fermiology revealed by the quantum oscillation of TM measurements agrees excellently with ARPES measurements.Moreover,the band structures we observed suggest that the band inversion in Yb B6 happens between the Yb5 dand B2bands,instead of the Yb5dand Yb4fbands as suggested by previous theoretical investigation,which will help settle the heavy debate regarding the topological nature of samarium/ytterbium hexaborides.

Perspective:Acoustic Metamaterials in Future Engineering

Acoustic metamaterials(AMMs)are a type of artificial materials that make use of appropriate structural designs and exhibit exotic properties not found in natural materials,such as negative effective material parameters(e.g.,bulk modulus,mass density,and refractive index).These interesting properties offer novel means for sound manipulation and thus have drawn a great deal of attention.Over the past two decades,tremendous progress has been made in the fundamental research of AMMs,which has not only promoted the development of modern acoustics but also shown the potential of AMMs for engineering applications.Here,we review recent developments in AMMs with a focus on their future engineering,especially in the most promising fields of sound absorption/isolation,acoustic imaging,cloaking,and so on,furthermore,we outline the opportunities and challenges they are encountering.

A novel two-dimensional thermal convection based MEMS acoustic vector sensor

An acoustic vector sensor can measure acoustic particle velocity and pressure simultaneously,which is important for capturing sound field information.An integrated twodimensional(2D)vector sensor is desired for various applications;however,its manufacturing remains challenging.In this study,a novel thermal-convection-based acoustic vector sensor comprising multiple crossed wires suspended in an etched cavity is designed.The sensor can directly measure two-dimensional particle velocity,and its performance is optimized using numerical simulations.The integrated sensor was fabricated by the microelectromechanical system process,and the frequency response and directivity pattern were measured,exhibiting high sensitivity and good orthogonal quality.