Feng Liang, Liu Xiao-Ping, Lu Ming-Hui, Chen Yan-Bin, Chen Yan-Feng, Mao Yi-Wei, Zi Jian, Zhu Yong-Yuan, Zhu Shi-Ning, Ming Nai-Ben
National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China.
Phys Rev Lett. 2006 Jan 13;96(1):014301. doi: 10.1103/PhysRevLett.96.014301. Epub 2006 Jan 6.
Acoustic negative refractions with backward-wave (BW) effects were both theoretically and experimentally established in the second band of a two-dimensional (2D) triangular sonic crystal (SC). Intense Bragg scatterings result in the extreme deformation of the second band equifrequency surface (EFS) into two classes: one around the K point and the other around the point of the reduced Brillouin zone. The two classes can lead to BW negative refractions (BWNRs) but with reverse negative refraction dependences on frequencies and incident angles. Not only BWNR but BW positive refraction can be present at EFSs around the K point, so it is possible to enhance the resolution of acoustic waves with a subdiffraction limit regardless of refractions, which is no analogy in both left-handed material and SCs' first band. These abundant characters make refractions in the second band distinguished.
在二维三角形声子晶体（SC）的第二能带中，从理论和实验两方面证实了具有背向波（BW）效应的声学负折射现象。强烈的布拉格散射导致第二能带等频面（EFS）极度变形为两类：一类围绕K点，另一类围绕简约布里渊区的该点。这两类会导致背向波负折射（BWNR），但负折射对频率和入射角的依赖关系相反。不仅在围绕K点的EFS处会出现BWNR，还会出现BW正折射，因此，无论折射情况如何，都有可能提高具有亚衍射极限的声波分辨率，这在左手材料和SC的第一能带中都没有类似情况。这些丰富的特性使得第二能带中的折射现象与众不同。
