Two Pseudogap Behavior in La_2-xSr_xCuO₄: Thermoelectric Power at High Temperature

Abstract

Thermoelectric power (TEP) of high-T C superconductors has been investigated in a wide range of temperature (T C < T < 700 K) for La 2−x Sr x CuO 4 . TEP of La 2−x Sr x CuO 4 shows different temperature dependences in three temperature regions. In the low-temperature region, a positive broad TEP peak is observed near T p , which shifts to lower temperature upon doping. As temperature increases, TEP decreases linearly at intermediate temperature.In the high-temperature region, TEP deviates from the linear temperature dependence at a certain temperature, T h showing a saturation behavior. As the doping concentration increases, the characteristic temperatures, T C , T p , and T h , show systematic changes. In comparison with pseudogap temperature estimated from other experiments, the large pseudogap behavior in TEP at high temperature has been discussed and distinguished from the small pseudogap observed at lower temperature. A possibility of bound pairs formation in the normal state opening the pseudogap at high temperature is discussed briefly. The coexistence of bound pairs and the normal independent carriers for T C < T < T h could be the origin of the intrinsic inhomogeneity.

Quantized Repetitions of the Cuprate Pseudogap Line

“…lation to high T c . 2,42,44,83,97 This transition manifests clearly in neutron scattering, X-ray diffraction, resistance, and TEP measurements. The green lines (third from the top, four data sets) mark the pseudogap temperature T * , where ARPES shows that a pseudogap opens in the density of states.…”

“…(c) Kim, 2004. 44 Thermoelectric power. The temperature reported here marks a break from the linear signal seen at high temperatures.…”

“…The topmost red lines (four data sets) show T max , visible both as a peak in the magnetic susceptibility and as kinks in the resistance and thermoelectric power (TEP). 44,64,99 The yellow lines (second from the top, five data sets) show the temperature T LT O of the wellknown transition from the high symmetry tetragonal phase to a lower symmetry orthorhombic phase, which has generally though not unanimously 83…”

Indications for Topological Physics in High-$T_c$ Materials

“…77 • dT /dρ 2D = 0.35 and 0.21 for the beginning and end of a linear regime in the thermoelectric power. 78 • dT /dρ 2D = 0.13 for a Weiss temperature measured using nuclear quadrupole resonance. 79 • dT /dρ 2D = 0.64 for a pairing temperature detected using hysteresis in the low field magnetization.…”

“…Five of these, measured with ARPES, the thermoelectric power, and the magnetic susceptibility, seem to be direct manifestations of the density of mobile holes because they intercept T = 0 near the low doping edge of the superconducting dome. [76][77][78][79] The sixth data set, a pairing temperature measured using magnetic hysteresis, extrapolates to T = 0 at a lower doping p = 0.023, presumably because of a sensitivity to pinned holes. In summary, in the bad metal regime above T c there are linear relations between hole sheet density, magnetic field, temperature as a thermodynamic quantity, and the several characteristic temperatures found above T c including the pseudogap temperature.…”