Tunneling Spectroscopy of Deintercalated Layered Nitride Superconductor ZrNCl_<0.7>(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

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Break junction tunneling spectroscopy measurements have been carried out on the novel layered nitride superconductor ZrNCl_<1-x> (x≅0.3) with T_c=12-14K. Two kinds of gap structures are reproducibly observed, both of which can be described by the BCS density of states. Values of the gap parameters at 4K are obtained to be Δ=1.6-2.3meV and 4.0-5.1meV. Upon warming, these gap structures disappear at T_c, thereby giving the ratio 2Δ/k_BT_c=2.7-3.8 and 6.6-8.4, respectively. The former is within the value of conventional superconductors, while the latter is extremely large in comparison with that of the conventional strong-coupling superconductors. The larger ratio is similar to the value of high-T_c cuprates. The origins of such two kinds of gaps are discussed.
社団法人日本物理学会の論文
2005-09-15