Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208, USA.
Phys Rev Lett. 2010 Oct 15;105(16):167003. doi: 10.1103/PhysRevLett.105.167003. Epub 2010 Oct 11.
The normal state properties of the recently discovered ferropnictide superconductors might hold the key to understanding their exotic superconductivity. Using point-contact spectroscopy we show that Andreev reflection between an epitaxial thin film of Ba(Fe(0.92)Co(0.08))₂As₂ and a silver tip can be seen in the normal state of the film up to temperature T∼1.3T(c), where T(c) is the critical temperature of the superconductor. Andreev reflection far above T(c) can be understood only when superconducting pairs arising from strong fluctuation of the phase of the complex superconducting order parameter exist in the normal state. Our results provide spectroscopic evidence of phase-incoherent superconducting pairs in the normal state of the ferropnictide superconductors.
最近发现的铁砷化物超导体的正常态性质可能是理解其奇异超导性的关键。我们使用点接触光谱学表明，在 Ba(Fe(0.92)Co(0.08))₂As₂外延薄膜的正常态中，直到温度 T∼1.3T(c)，其中 T(c)是超导体的临界温度，都可以看到银尖与薄膜之间的安德烈夫反射。只有在正常态中存在由复杂超导序参量相位强涨落引起的超导对时，才能理解远高于 T(c)的安德烈夫反射。我们的结果为铁砷化物超导体正常态中存在相位非相干超导对提供了光谱证据。
