In the realm of condensed matter systems and metamaterials, non-Hermitian physics has been a game-changer, characterized by its complex band spectra. This field has recently witnessed the deliberate introduction of non-Hermitian gain and nonreciprocity to valley manipulation, leading to phenomena that surpass the capabilities of Hermitian scenarios, such as the amplified topological whispering gallery modes that function as an acoustic laser. However, pure loss, an inevitable factor in practical applications, has typically been viewed as a detrimental element. A recent study, conducted by a team of researchers including Shunda Yin, Qiuyan Zhou, Yuxiang Xi, Weiyin Deng, Wei Chen, Jiuyang Lu, Manzhu Ke, and Zhengyou Liu, challenges this perspective.
The researchers have revealed that coupling loss can actually manipulate valley degrees of freedom in a phononic metamaterial. Through theoretical analysis and airborne sound experiments, they demonstrated three distinct valley-related effects. The first is valley-resolved nonreciprocity, which functions as a valley filter. The second is valley-dependent skin effects, where bulk states from different valleys localize at opposite boundaries. The third is valley-projected edge states with boundary-dependent lifetimes, leading to an anomalous beam splitting.
The ease of preparing loss, as highlighted by the researchers, could significantly facilitate the application of valley-related devices. This study not only sheds new light on non-Hermitian and valley physics but also paves the way for innovative applications in the field. The implications of this research could be far-reaching, potentially revolutionizing the way we manipulate and utilize valley degrees of freedom in various technological applications.
