Comment on 'Anomalous capacitance response induced by the superconducting gap in an Au/BiFeO_3/La_(1.84)Sr_(0.16)CuO_4/LaSrAlO_4 heterostructure' [Appl. Phys. Lett. 103, 153507 (2013)]

摘要

Recently, Liu et al. have reported the capacitor characteristics of BiFeO_3/La_(1.84)Sr_(0.16)CuO_4 (BFO/LSCO) heterostructure. The authors observed a capacitance anomaly near the superconducting transition temperature T_c of LSCO and claimed that the so-called activation energy E_a fitted from the temperature dependence of the relaxation time τ(T) is closed to the superconducting gap of LSCO. They also claimed this method might give an easy and effective mean to detect the energy gap of high temperature superconductors. In this comment, we would like to point out that there are some errors about the central physical concepts and simulating equation in Liu et al. 's article. We found even if we try to use their "extended Arrhenius law" to fit the τ(T) data, we cannot get the values of E_a as reported by Liu et al. In fact, this anomalous capacitance response in BFO/LSCO heterostructure can be well understood by considering the inho-mogeneity of the heterojunction interface.