Unconventional superconducting pairing states are very sensitive to the scattering of quasiparticles by impurities or interfaces. This sensitivity arises from the dependence of the order parameter’s phase on direction of quasiparticle’s momentum. As the quasiparticle propagates in an effective pair potential, before and after the scattering event it experiences different phases of that potential (and magnitudes, in general).As a result new states of condensate excitations appear near surfaces, and in spatially small samples they can completely change the energy landscape of the phase diagram, leading to appearance of new exotic phases. 

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