Angular dependence of the specific heat of La sub(1.85)Sr sub(0.15)CuO sub(4) in superconducting mixed state

• Published in: Physica. C, Superconductivity Superconductivity, 2000-01, Vol.334 (1), p.25-32
• Main Authors: Panova, G Kh, Shikov, A A, Khlopkin, M N, Chernoplekov, N A, Shulyatev, D A
• Format: Article
• Language: English
• ISSN: 0921-4534

The specific heat of single crystals La sub(1.85)Sr sub(0.15)CuO sub(4) has been studied as a function of the relative orientation of the crystal axes and a magnetic field rotating in the Cu-O plane and normal to this plane. Measurements were carried out in the temperature range 2-50 K in magnetic fields up to 8 T and with four directions of the magnetic fields: in the a-b plane (along the [100] and [010] directions) and at angles of 45 degree and 90 degree with respect to the a-b plane (along [001] and [103] directions). For all orientations of the magnetic field the specific heat of the mixed state at low temperatures is a nonlinear function of the magnetic field. The dependence of the specific heat on the magnetic field H shows the feature predicted for d-wave pairing: H super(1/2)T term. A fourfold symmetry characteristic of the electronic density of states in the crystalline a-b plane and a twofold symmetry in a-c plane was resolved in the magnetic field. The results show unambiguously that the in-plane and out-of-plane electronic density of states in the magnetic field is highly anisotropic and has a minimum when the field is along the a-axis and a maximum when the field makes an angle of 45 degree with the a and c axes. Using these results, we present an angular mapping of the electronic density of states and the upper critical field H sub(c2)(T) estimated from the heat capacity measurements. These results are consistent with d sub(x(2)-y(2))-symmetry of the bulk order parameter.