Bhaumik Anagh, Narayan Jagdish
Department of Materials Science and Engineering, Centennial Campus, North Carolina State University, Raleigh, NC 27695-7907, USA.
Nanoscale. 2019 May 9;11(18):9141-9154. doi: 10.1039/c9nr00562e.
Here, we report the detailed structure-property correlations in phase-pure B-doped Q-carbon high-temperature superconductor having a superconducting transition temperature (Tc) of 55 K. This superconducting phase is a result of nanosecond laser melting and subsequent quenching of a highly super undercooled state of molten B-doped C. The temperature-dependent resistivity in different magnetic fields and magnetic susceptibility measurements indicate a type-II Bardeen-Cooper-Schrieffer superconductivity in B-doped Q-carbon thin films. The magnetic measurements indicate that the upper and lower critical fields follow Hc2(0)[1 - (T/Tc)1.77] and Hc1(0)[1 - (T/Tc)1.19] temperature dependence, respectively. The structure-property characterization of B-doped Q-carbon indicates a high density of electronic states near the Fermi-level and large electron-phonon coupling. These factors are responsible for s-wave bulk type superconductivity with enhanced Tc in B-doped Q-carbon. The time-dependent magnetic moment measurements indicate that B-doped Q-carbon thin films follow the Anderson-Kim logarithmic decay model having high values of pinning potential at low temperatures. The crossover from the two-dimensional to the three-dimensional nature of Cooper pair transport at T/Tc = 1.02 also indicates a high value of electron-phonon coupling which is also calculated using the McMillan formula. The superconducting region in B-doped Q-carbon is enclosed by Tc = 55.0 K, Jc = 5.0 × 108 A cm-2, and Hc2 = 9.75 T superconducting parameters. The high values of critical current density and pinning potential also indicate that B-doped Q-carbon can be used for persistent mode of operation in MRI and NMR applications. The Cooper pairs which are responsible for the high-temperature superconductivity are formed when B exists in the sp3 sites of C. The electron energy loss spectroscopy and Raman spectroscopy indicate a 75% sp3 bonded C and 70% sp3 bonded B in the superconducting phase of B-doped Q-carbon which has 27 at% B and rest C. The dimensional fluctuation and magnetic relaxation measurements in B-doped Q-carbon indicate its practical applications in frictionless motors and high-speed electronics. This discovery of high-temperature superconductivity in strongly-bonded and light-weight materials using non-equilibrium synthesis will provide the pathway to achieve room-temperature superconductivity.
在此，我们报告了具有55K超导转变温度（Tc）的纯相硼掺杂Q碳高温超导体中详细的结构-性质相关性。这种超导相是纳秒激光熔化并随后淬冷高度过冷的熔融硼掺杂碳状态的结果。在不同磁场下的温度依赖性电阻率和磁化率测量表明硼掺杂Q碳薄膜中存在II型巴丁-库珀-施里弗超导性。磁性测量表明，上临界场和下临界场分别遵循Hc2(0)[1 - (T/Tc)1.77]和Hc1(0)[1 - (T/Tc)1.19]的温度依赖性。硼掺杂Q碳的结构-性质表征表明在费米能级附近存在高密度的电子态以及较大的电子-声子耦合。这些因素导致硼掺杂Q碳中具有增强Tc的s波体超导性。随时间变化的磁矩测量表明硼掺杂Q碳薄膜遵循安德森-金对数衰减模型，在低温下具有高钉扎势值。在T/Tc = 1.02时从库珀对输运的二维性质到三维性质的转变也表明电子-声子耦合值很高，这也使用麦克米兰公式进行了计算。硼掺杂Q碳中的超导区域由Tc = 55.0K、Jc = 5.0×108 A cm-2和Hc2 = 9.75T的超导参数界定。临界电流密度和钉扎势的高值还表明硼掺杂Q碳可用于磁共振成像（MRI）和核磁共振（NMR）应用中的持续运行模式。当硼存在于碳sp3位点时形成负责高温超导性的库珀对。电子能量损失谱和拉曼光谱表明，在含27at%B且其余为碳的硼掺杂Q碳超导相中，75%的碳以sp3键合，70%的硼以sp3键合。硼掺杂Q碳中的维度涨落和磁弛豫测量表明其在无摩擦电机和高速电子学中的实际应用。利用非平衡合成在强键合和轻质材料中发现高温超导性将为实现室温超导提供途径。
