Tunneling spectroscopy of layered superconductors: intercalated Li0.48(C4H8O)xHfNCl and De-intercalated HfNCl0.7
Tunneling spectroscopy of layered superconductors: intercalated Li0.48(C4H8O)xHfNCl and De-intercalated HfNCl0.7
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DOI：
10.1140/epjb/e2010-00035-4
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发表时间：
2010-01
期刊：
影响因子：
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通讯作者：
T. Takasaki;T. Ekino;A. Sugimoto;K. Shohara;S. Yamanaka;A. Gabovich
中科院分区：
文献类型：
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作者：
T. Takasaki;T. Ekino;A. Sugimoto;K. Shohara;S. Yamanaka;A. Gabovich
用断裂结谱和扫描隧道谱对β（SmSI）型层状超导体Li_（0.48）（THF）_xHfNCl（THF = C_4H_8O）和HfNCl_（0.7）进行了隧道测量。断裂结技术揭示了Bardeen-Cooper-Schrieffer（BCS）型带隙结构，其典型带隙值为2Δ（4.2 K）= 11-12 meV，最高Tc= 25.5 K。我们的一些测量揭示了多个能隙和dip-hump结构，最大的能隙2Δ（4.2 K）<$17 -20 meV在Tc处关闭。这是由断裂结和扫描隧道光谱显示。实验结果表明，最高能隙比2Δ/kBTc~ 8大大超过BCS弱耦合极限值：s波和d波序参量对称性分别为1.335和1.433。如此大的2Δ/kBT c比对于常规超导体是相当罕见的，但对于高Tc铜酸盐以及有机超导体是相当常见的。我们的研究收集了更多关于这些材料中巨大的对能的证据，并详细研究了它们的超导能隙谱的复杂性。观察到的现象的起源仍然有待澄清。
Tunneling measurements have been carried out on layered superconductors of the β(SmSI)-type – Li0.48(THF)xHfNCl (THF = C4H8O) and HfNCl0.7– by means of break-junction and scanning tunneling spectroscopy. Break-junction technique reveals Bardeen-Cooper-Schrieffer (BCS) – like gap structures with typical gap values of 2Δ (4.2 K) = 11–12 meV for Li0.48(THF)xHfNCl with the highest Tc= 25.5 K. Some of our measurements revealed multiple gaps and dip-hump structures, the largest gap 2Δ (4.2 K) ≈ 17–20 meV closing at Tc. This was shown both by break-junction and scanning-tunneling spectroscopy. From these experiments it stems that the highest obtained gap ratio 2Δ/kBTc~ 8 substantially exceeds the BCS weak-coupling limiting values: ≈3.5 and ≈4.3 for s-wave and d-wave order parameter symmetry, respectively. Such large 2Δ/kBTcratios are rather unusual for conventional superconductors but quite common to high-Tccuprates, as well as to organic superconductors. Our studies allowed to collect much more evidence concerning the huge pairing energy in those materials and to investigate in detail the complexity of their superconducting gap spectra. An origin of the observed phenomena still remains to be clarified.