Abstract. The spectrum of the Dirichlet problem for Laplace operator is studied in three terminal tubes. The cross-section of the tubes is either a circle or a square. We show that these Y-shaped waveguides always have at least one eigenvalue in the discrete spectrum. In the regular case, that is, the angle between the cylinders is 2 3 π, there exists exactly one eigenvalue in the discrete spectrum. While the angle 2α between the arms is varying, we show that the number of the bound states remains to be one for α ∈ arctan 3 4 , π 2 when the cross-section of the tubes is square. However, when the angle becomes sharp enough, the number of eigenvalues in the discrete spectrum increases. Moreover, it is shown that the eigenvalues are monotonously increasing when the angle 2α is in the interval 0, 2 3 π and are monotonously decreasing when 2α ∈ 2 3 π, π .
Physical backgroundThe development of nanotechnology has lead to smaller and smaller devices in electrical engineering. Over the last few decades there have been several both theoretical and applied studies to understand the physical behavior of such small nanometer sized waveguides.The nanometer scale devices have attracted due to their excellent attributes. They have light weight, but they are still strong because of their elasticity. Moreover, they have exceptional electrical properties. These waveguides have either metallic or semi-conducting behavior depending on their geometrical structure.These devices have a high purity and crystalline structure. Thus, the electron mean free path is greater than the diameter of the system. Therefore the scattering is unsubstantial and derives us to model the electron motion as a free particle in the infinite waveguide where the motion is limited inside the waveguide by posing the Dirichlet condition on the boundaries.In this study we concentrate on the three-dimensional and three terminal nanotubes with either rectangular or circular cross-section. These waveguides are often called Y-junctions. Our intention is to investigate the existence of the non-trivial solutions of the Helmholtz equation:In particular, those solutions which have the finite energy and the eigenvalue corresponding to such an eigenfunction is located below the continuous spectrum. The continuous spectrum is where the electron propagation can occur as the contrary to the discrete spectrum where the eigenfunction is localized.