报告题目：MAGNETIC FIELD INDUCED SUPER-INSULATING STATE AND ENHANCEMENT OF SUPERCONDUCTIVITY IN ULTRATHIN Pb FILMS
报告人：Dr Peng Xiong （熊鹏 博士）
Department of Physics and Integrative NanoScience Institute, Florida State University
报告地点：强磁场中心磁体研制楼201会议室
报告时间：7月3日上午 10:00 （星期二）
报告人简介：熊鹏博士1987年中国科大物理系本科毕业，1993年获得美国布朗大学博士学位。 93-97年他在美国加州大学圣地牙哥分校从事博士后研究，于1997年11月获得美国Florida State University 教职，现任物理系教授。熊鹏博士长期从事低维和界观系统中的物理性质研究并取得系列有重大影响力的成果。他的研究包括磁场和无序诱导的超导-绝缘体转变、纳米磁性、金属和半导体纳米线、强关联电子系统的磁输运、超导/磁性及超导/半导体等复合结构中新效应、电子的自旋注入与输运等。近年来，熊鹏博士在生物和力学传感纳米器件等方面也进行了探索并取得系列成果。
报告内容简介：
We have carried out a systematic and detailed examination of the superconductivity and superconductor-insulator quantum phase transitions (SITs) in ultrathin amorphous Pb films as functions of disorder, magnetic field, and paramagnetic pair-breaking. The Pb films are grown via quench-condensation in a modified dilution refrigerator under ultrahigh vacuum at low temperature, and all the electrical measurements are performed in situ. Here we present two intriguing observations from these experiments:
1) A perpendicular magnetic field induces an SIT with transport behavior similar to those in the SIT of a granular film [1], such as reentrance and double-reentrance in R(T) and a peak in the magnetoresistance [2]. The observations are suggestive of mesoscale phase separation near Hc, and an insulating state with localized superconductivity.
2) In the same films, a parallel magnetic field is found to enhance superconductivity, increasing the mean-field Tc by as much as 13% at 8 T [3]. The Tc enhancement exhibits a non-monotonic dependence on the film thickness, initially increases and then decreases with increasing thickness, and vanishes in the 3D limit. Incremental deposition of paramagnetic impurity on a film progressively suppresses and eventually eliminates the effect of parallel field enhancement of superconductivity.
References:
1. K.A. Parendo, K.H.S.B. Tan, and A.M. Goldman, Phys. Rev. B 76, 100508 (2007).
2. J.S. Parker, D. Read, A. Kumar, and P. Xiong, Europhys. Lett. 75, 950 (2006).
3. H.J. Gardner, A.S. Kumar, L. Yu, P. Xiong, M. Warusawithana, L. Wang, O. Vafek, D.G. Schlom, Nature Physics 7, 895 (2011).
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