Fig. 1.
Specific heat measurements of the superconducting condensation energy and summary of neutron scattering results for PLCCO (Tc = 24 K). (a) (Upper) The two-dimensional CuO2 plane. (Lower) Schematic of typical constant-energy scans through reciprocal space. Spin excitations are centered at Q = (1/2, 1/2, 0). (b) Field dependence of the total electronic specific heat versus temperature. Data taken at 8 T were established to be above Hc2 (25) and were used to isolate and subtract background contributions from the normal-state phonon/electronic heat capacity. To obtain the normal-state electronic specific heat γT, 8-T data were fitted by C = γT +βT3, where βT3 is the phonon contribution. The resulting linear electronic contribution γT (γ = 5) was added back to the field-subtracted data to obtain the total electronic specific heat. (c) Field-subtracted measurements of the specific heat (CSC − CN)/T versus temperature. The resulting entropy loss SN(T) − SSC(T) = ∫0T (CN − CSC)dT′/T′ can then be calculated. (d) Condensation energy, Uc, determined from Eq. 1 and plotted as solid blue square symbols connected by a solid line. Intensity of the resonance mode plotted as a function of applied field. Red triangles denote peak intensity measurements at Q = (1/2, 1/2, 0), ℏω = 11 meV at T = 4 K with the normal state background at T = 30 K subtracted. For field strengths of >6 T, entire Q scans were performed to resolve the resonance excitation. The 5 K − 30 K peak intensities of Q scans at 6.8 T and 10 T taken from Gaussian fits on a linear background (whose raw data are shown in Fig. 2) are plotted as open green (6.8 T) and teal circles (10 T). (e) Schematic plots of the zero-field S(Q, ω) at Q = (1/2, 1/2, 0) below and above Tc. (f) For H > Hc2, the complete suppression of the resonance mode is observed along with the simultaneous appearance of a static AF order.