Europhys. Lett.
Volume 75, Number 6, September 2006
Page(s) 950 - 956
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 09 August 2006
Europhys. Lett., 75 (6), pp. 950-956 (2006)
DOI: 10.1209/epl/i2006-10198-1

Superconducting quantum phase transitions tuned by magnetic impurity and magnetic field in ultrathin $\mth{a}$-$\chem{Pb}$ films

J. S. Parker, D. E. Read, A. Kumar and P. Xiong

Department of Physics and Center for Materials Research and Technology Florida State University - Tallahassee, FL 32306, USA

received 3 July 2006; accepted in final form 21 July 2006
published online 9 August 2006

Superconducting quantum phase transitions tuned by disorder (d), paramagnetic impurity (MI) and perpendicular magnetic field (B) have been studied in homogeneously disordered ultrathin a-Pb films. The MI-tuned transition is characterized by progressive suppression of the critical temperature to zero and a continuous transition to a weakly insulating normal state with increasing MI density. In all important aspects, the d-tuned transition closely resembles the MI-tuned transition and both appear to be fermionic in nature. The B-tuned transition is qualitatively different and probably bosonic. In the critical region it exhibits transport behavior that suggests a B-induced mesoscale phase separation and presence of Cooper pairing in the insulating state.

74.78.-w - Superconducting films and low-dimensional structures.
74.25.Fy - Transport properties (electric and thermal conductivity, thermoelectric effects, etc.).
73.50.-h - Electronic transport phenomena in thin films.

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