Heat Capacity of Na$_{0.3}$CoO$_{2}$$\cdot$1.3H$_{2}$O, a New Two-Gap Superconductor: Comparison with the Heat Capacity of MgB$_2$
Heat Capacity of Na$_{0.3}$CoO$_{2}$$\cdot$1.3H$_{2}$O, a New Two-Gap Superconductor: Comparison with the Heat Capacity of MgB$_2$
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新型二能隙超导体Na$_{0.3}$CoO$_{2}$$cdot$1.3H$_{2}$O的热容：与MgB$_2$热容的比较
DOI：
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
R. Cava
中科院分区：
文献类型：
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作者：
N. Oeschler;R. Fisher;N. Phillips;J. E. Gordon;M. Foo;R. Cava
在所有温度下，Na $_{0.3}$ CoO $_{2}$$\cdot$ 1.3H $_{2}$ O的超导态热容都与BCS理论有不同寻常的显著偏差。在低温下，热容量具有$T^2$依赖特性的线节点在能隙中，而不是指数温度依赖于一个全间隙，传统超导体。在临界温度的五分之一或更高的温度下，偏差与MgB $_2$惊人地相似，这是已知的费米表面不同薄片上存在本质上不同的能隙的结果。对Na $_{0.3}$ CoO $_{2}$$\cdot$ 1.3H ${_2}$ O数据的双间隙拟合得出的间隙振幅为45% and 125% of the BCS value, on parts of the Fermi surface that contribute, respectively, 45% and 55% to the normal-state density of states. The temperature of the onset of the transition to the vortex state is independent of magnetic field, which shows the presence of unusually strong fluctuations.
The superconducting-state heat capacity of Na$_{0.3}$CoO$_{2}$$\cdot$1.3H$_{2}$O shows unusual, marked deviations from BCS theory, at all temperatures. At low temperatures the heat capacity has the $T^2$ dependence characteristic of line nodes in the energy gap, rather than the exponential temperature dependence of a fully gapped, conventional superconductor. At temperatures of the order of one fifth of the critical temperature and above, the deviations are strikingly similar to those of MgB$_2$, which are known to be a consequence of the existence of substantially different energy gaps on different sheets of the Fermi surface. A two-gap fit to the Na$_{0.3}$CoO$_{2}$$\cdot$1.3H${_2}$O data gives gap amplitudes of 45% and 125% of the BCS value, on parts of the Fermi surface that contribute, respectively, 45% and 55% to the normal-state density of states. The temperature of the onset of the transition to the vortex state is independent of magnetic field, which shows the presence of unusually strong fluctuations.