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arXiv 0812.4806cond-mat.supr-con
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球形铌单晶的峰值效应、表面超导电性和顺磁迈斯纳效应

Peak effect phenomena, surface superconductivity and paramagnetic Meissner effect in a spherical single crystal of niobium

Pradip Das, C. V. Tomy, H. Takeya, S. Ramakrishnan, A. K. Grover

摘要:

本文通过等温和变温的直流磁化强度和交流磁化率的测量,研究了球形铌单晶(T ~ 9.3K)中的涡旋相图。该晶体具有极弱的钉扎,这可以从T_c以下的环的可逆性推断。然而,在T = 8 K之前,我们可以看到等温M-H环中的峰值效应(PE)特征。在H > 750 Oe的等温交流磁化率数据中,PE也是突出的。在本研究中,一个有趣的观察是表面超导性的突出指纹,开始于PE峰值位置处的钉扎崩溃上方,结束于表面临界场(H_c3)。我们还观察到了顺磁迈斯纳效应的场冷磁化数据记录在相对较大的领域在这种晶体。通过标记PE(H_p)、上临界场(H_c2)和表面临界场(H_c3)的峰值位置,绘制了涡旋相图。与以往报道的Nb晶体相图中H_p、H_c2和H_c3线相交处存在多临界点不同,我们在弱钉扎晶体中没有观察到多临界点。

英文摘要:

We have explored the vortex phase diagram in a spherical single crystal of niobium (T ~ 9.3 K) via isothermal and temperature dependent dc magnetization and ac-susceptibility measurements. The crystal has extremely weak pinning that can be inferred from the reversibility of loops below T_c. However, one can visualize the peak effect (PE) feature in the isothermal M-H loops up to T = 8 K. The PE is also prominent in isothermal ac-susceptibility data for H > 750 Oe. An interesting observation in the present study is the prominent fingerprints of surface superconductivity, starting just above the collapse of pinning at the peak position of the PE and ending at the surface critical field (H_c3). We have also observed the paramagnetic Meissner effect in field-cooled magnetization data recorded at relatively large fields in this crystal. A vortex phase diagram is constructed by marking the peak positions of the PE (H_p), the upper critical field (H_c2) and the surface critical field (H_c3). Unlike a previous report which shows the existence of a multi-critical point in the phase dia-gram of a Nb crystal, where H_p, H_c2 and H_c3 lines meet, we do not observe a multi-critical point in our weak pinning crystal.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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