We study transport across ballistic junctions of materials which host pseudospin-one fermions as emergent low-energy quasiparticles. The effective low-energy Hamiltonians of such fermions are described by integer spin Weyl models. We show that current conservation in such integer spin-$s$ Weyl systems requires continuity across a boundary of only $2s$ (out of $2s+1$) components of the wave function. Using the current conservation conditions, we study the transport between normal metal-barrier-normal metal (NBN) and normal metal-barrier-superconductor (NBS) junctions of such systems in the presence of an applied voltage $eV$. We show that for a specific value of the barrier potential $U_0$, such NBN junctions act as perfect collimators; any quasiparticle which is incident on the barrier with a non-zero angle of incidence is reflected back with unit probability for any barrier width $d$. We discover an interesting symmetry of this system, namely, the conductance is invariant under $U_0 \to 2(μ_L \pm eV)-U_0$, where $μ_L$ is the chemical potential and the +(-) sign corresponds to particle (hole) mediated transport. For NBS junctions with a proximity-induced $s$-wave pairing potential, which also display such a collimation, we chart out the properties of the subgap tunneling conductance $G$ as a function of the barrier strength and applied voltage. We point out the effect of the collimation on the subgap tunneling conductance of these NBS junctions and discuss experiments which can test our theory.
Real fermion modes, impurity entropy, and nontrivial fixed points in the phase diagram of junctions of interacting quantum wires and topological superconductors
Point-contact Andreev reflection spectroscopy of heavy-fermion-metal/superconductor junctions
我们之前使用Au尖端对重费米子超导体CeCoIn $_5$的点接触Andreev反射研究显示了两个明显的特征：降低的Andreev信号和不对称的背景电导[1]。为了探索它们的物理起源，我们已经将我们的测量扩展到单晶重费米子金属和超导Nb尖端之间的点接触结。微分电导谱上采取的结与三个重费米子金属，CeCoIn $_5$，CeRhIn $_5$，和YbAl $_3$，每一个具有不同的电子质量。与Au/CeCoIn $_5$结相比，Andreev信号没有降低，并且没有观察到对有效质量的依赖性。基于重费米子的双流体图像提出了一种可能的解释。[1]W. K. Park等人，Phys. Rev. B 72 052509（2005）; W. K. Park等人，Proc. SPIE-Int. Soc.Opt.Eng.593259321Q（2005）; W. K. Park等，Physica C（印刷中）（cond-mat/0606535）。
