Electronic Specific Heat of La _2-x-zNd_zSr_xCu _1-yZn_yO ₄ up to Room Temperature

Abstract

Behavior of the electronic specific heat C el of La 2- x - z Nd z Sr x Cu 1- y Zn y O 4 has been investigated over the wide temperature ( T ) range between 2 K and 300 K. For samples with z =0.4 and 0.0≦ x ≦0.25, by carefully subtracting the phonon contribution from the total specific heat, the electronic specific heat coefficient γ≡ C el / T has been extracted, where anomalous x - and T -dependence related to the so-called 1/8 problem or the “stripe” order is observed. Zn-doping effects on the behavior of γ( T ) of La 2- x Sr x Cu 1- y Zn y O 4 ( x =0.10 and 0.08) and La 1.88- z Nd z Sr 0.12 Cu 1- y Zn y O 4 ( z =0.2 and 0.4) suggest that not only the long range “stripe” order but also the fluctuating “stripe” suppress both the pseudo gap and the singlet pair formation.