Electronic Specific Heat of La_2-<i>x</i>Sr_<i>x</i>CuO₄: Pseudogap Formation and Reduction of the Superconducting Condensation Energy

Abstract

To examine the so-called small pseudogap and the superconducting (SC)\ncondensation energy U(0), the electronic specific heat Cel was measured on\nLa_{2-x}Sr_{x}CuO_{4} up to ~120K. In samples with doping level p (=x) less\nthan ~0.2, small pseudogap behavior appears in the \\gamma (=Cel/T) vs. T curve\naround the mean-field critical temperature for a d-wave superconductor Tco\n(=2*\\Delta_{0}/(4~5)k_B), where \\Delta_{0} is the maximum gap at T&lt;&lt;Tc. The\ncondensation energy U(0) is largely reduced in the pseudogap regime (p&lt; ~0.2).\nThe reduction of U(0) can be well reproduced by introducing an effective SC\nenergy scale \\Delta_{eff}=\\beta*p*\\Delta_{0} (\\beta=4.5) instead of \\Delta_{0}.\nThe effective SC energy scale is discussed in relation to the coherent pairing\ngap formed over the nodal Fermi arc.\n