Sum Rules and Interlayer Conductivity of High- T _c Cuprates

Abstract

Analysis of the interlayer infrared conductivity of cuprate high-transition temperature superconductors reveals an anomalously large energy scale extending up to midinfrared frequencies that can be attributed to formation of the superconducting condensate. This unusual effect is observed in a va- riety of materials, including Tl2Ba2CuO6+x, La2-xSrxCuO4, and YBa2Cu3O6.6, which show an incoherent interlayer response in the normal state. Midinfrared range condensation was examined in the context of sum rules that can be formulated for the complex conductivity. One possible interpretation of these experiments is in terms of a kinetic energy change associated with the superconducting transition.

Temperature dependence of the superconductivity-induced collective mode in the c-axis infrared spectra of bilayer cuprate superconductors

“…The total optical SW exhibits a decrease below T c . This is consistent with the BCS theory and in contrast with the observed increase of the SW in the infrared [11,12,7]. A slightly different temperature dependence of the total SW would be obtained in case of a temperature dependent spin susceptibility v SF .…”

In-plane and out-of-plane plasma resonances in optimally doped La1.84Sr0.16CuO4

“…The ab-plane optical reflectivity data published by many groups shows the metallic reflectivity with a plasma edge at ~ 0.8 -1.0 eV for LSCO [4 -6], ~ 1.0 eV -1.2 eV for YBCO [7,8], ~ 1.0 eV for Bi 2 Sr 2 CaCu 2 O 8 (Bi-2212) [9], and ~ 1.2 eV Tl 2 Ba 2 Ca 2 Cu 3 O 8 [10,11].…”

“…However the c-axis plasma edge that emerges out of an insulator-like flat reflectivity only when T < T c was found at ~ 50 cm -1 (6 meV) -85 cm -1 (10 meV) for optimally doped LSCO [12 -14], ~ 65 cm -1 (8 meV) for YBCO 6.7 [15], ~ 250 cm -1 (30 meV) for YBCO 6.95 [16], ~ 220 cm -1 (27 meV) for Y 1 Ba 2 Cu 4 O 8 [17], ~ 40 cm -1 (5 meV) for Bi 1.6 Pb 0.6 Sr 1.8 CaCu 2 O y (T c = 65 K) [18], ~ 10 cm -1 (1.2 meV) for Bi-2212 (T c ~ 90 K) [19], and ~ 40 cm -1 (5 meV) for Tl 2 Ba 2 Ca 2 Cu 3 O 6+x (T c = 81 K) [11]. Since superconductivity is intrinsically a three-dimensional (3D) phenomenon, the screened ab-plane plasma frequency [20].…”

Conductivity sum rule, implication for in-plane dynamics, andc-axis response

“…Since the cuprates have layered structures, interlayer coupling between two adjacent CuO 2 planes plays an essential role, and its exact nature impacts on the recent experimental observation [2] of a significant violation of the conventional optical sum rule of Ferrel, Glove and Tinkham [3].…”