Biao Jin, Gang Su,* and Qing-Rong Zheng

College of Physical Sciences, Graduate School of the Chinese Academy of Sciences, P.O. Box 4588, Beijing 100049, China

(Received 10 December 2004; published 29 April 2005)

Abstract:

    First- and second-order phase transitions, Fulde-Ferrel sFFd inhomogeneous superconducting sSCd state, and quantum criticality in ferromagnet/superconductor/ferromagnet double-tunnel junctions are investigated. For the antiparallel alignment of magnetizations, it is shown that a first-order phase transition from the homogeneous BCS state to the inhomogeneous FF state occurs at a certain bias voltage V*, while the transitions from the BCS state and the FF state to the normal state at Vc are of the second-order. A phase diagram for the central superconductor is presented. In addition, a quantum critical point sQCPd, VQCP, is identified. It is uncovered that near the QCP, the SC gap, the chemical potential shift induced by the spin accumulation, and the difference of the free energies between the SC and the normal states vanish as uV−VQCPu zn with the quantum critical exponents zn= 1 2 , 1, and 2, respectively. The tunnel conductance and magnetoresistance are also discussed.

DOI: 10.1103/PhysRevB.71.144514                                                   PACS numberssd: 74.50.1r, 75.47.De, 73.40.Gk, 73.40.Rw