Depression of quasiparticle density of states at zero energy in La1.9Sr0.1Cu1-xZnxO4

Abstract

We have measured low-temperature specific hear C(T, H) of La1.9Sr0.1Cu1-xZnxO4 (x = 0, 0.01, and 0.02) in both zero and applied magnetic fields. A pronounced dip of C/T below 2 K was observed in Zn-doped samples, which is absent in the nominally clean one. If the origin of the dip in CIT is electronic, the quasiparticle density of states N(E) in Zn-doped samples may be depressed below a small energy scale Eo. The present data can be well described by the model N(E) = N(0) + alpha E-1/2, with a nonzero N(0) and positive alpha. Magnetic fields depress N(0) and lead to an increase in E-0, while leaving the energy dependence of N(E) unchanged. This novel depression of N(E) below Eo in impurity-doped cuprates cannot be reconciled with the semiclassical self-consistent approximation model. Discussions in the framework based on the nonlinear sigma model field theory and other possible explanations are presented.