Strong coupling and double-gap density of states in superconducting MgB2
Strong coupling and double-gap density of states in superconducting MgB2
复制标题
超导MgB2中的强耦合和双能隙态密度
DOI：
10.1209/epl/i2002-00415-5
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发表时间：
2001
期刊：
影响因子：
--
通讯作者：
J. Klein
中科院分区：
文献类型：
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作者：
Filippo Giubileo;Filippo Giubileo;D. Roditchev;W. Sacks;R. Lamy;J. Klein
利用扫描隧道谱在T=4.2K的条件下，同时对颗粒状MgB_2进行了地形成像和准粒子态密度(DOS)映射。我们观察到一种新的光谱类型，表现出明显的双能隙，其量级为ΔS=3.9meV，ΔL=7.5meV，即远低于和远高于BCS极限。最大禁带宽度为2ΔL/kBTC=4.5，表明电子-声子耦合很强。其他超导区被发现具有特征的BCS形状的DOS。然而，光谱形状和低能隙宽度的变化，从2.0 meV到6.5 meV，表明了表面不均匀和邻近效应在以前发表的隧道效应数据中的重要性。我们的发现没有给出任何重要的带隙各向异性的证据。相反，它强烈支持在干净限制中的mgB2中的多间隙场景，以及在脏限制中的单间隙场景。
Using scanning tunneling spectroscopy at T = 4.2 K, we perform simultaneously the topographic imaging and the quasiparticle density of states (DOS) mapping in granular MgB2. We observe a new type of spectrum, showing a pronounced double gap, with the magnitudes of ΔS = 3.9 meV and ΔL = 7.5 meV, i.e. well below and well above the BCS limit. The largest gap value gives the ratio 2ΔL/kBTC = 4.5, which implies strong electron-phonon coupling. Other superconducting regions are found to have a characteristic BCS-shaped DOS. However, the variation of the spectral shape and lower gap widths, from 2.0 meV to 6.5 meV, indicate the importance of surface inhomogeneity and proximity effects in previously published tunneling data. Our finding gives no evidence for any important gap anisotropy. Instead, it strongly supports the multiple-gap scenario in MgB2 in the clean limit, and the single-gap scenario in the dirty limit.