Quasiparticle spectrum of the cuprateBi2Sr2CaCu2O8+δ

Abstract

We previously introduced [T. Cren et al., Europhys. Lett. 52, 203 (2000)] an energy-dependant gap function, ∆(E), that fits the unusual shape of the quasiparticle (QP) spectrum for both BiSrCaCuO and YBaCuO. A simple anti-resonance in ∆(E) accounts for the pronounced QP peaks in the density of states, at an energy ∆p, and the dip feature at a higher energy, E dip . Here we go a step further : our gap function is consistent with the (T, p) phase diagram, where p is the carrier density. For large QP energies (E ≫ ∆p), the total spectral gap is ∆(E) ≃ ∆p + ∆ϕ, where ∆ϕ is tied to the condensation energy. From the available data, a simple p-dependance of ∆p and ∆ϕ is found, in particular ∆ϕ(p) ≃ 2.3 kB Tc(p). These two distinct energy scales of the superconducting state are interpreted by comparing with the normal and pseudogap states. The various forms of the QP density of states, as well as the spectral function A(k, E), are discussed.

Pair–pair interactions as a mechanism for high-Tcsuperconductivity

“…Although phenomenological, the static model describes very well the particular signatures of the spectral function, the SC density of states (DOS), and the transition to the pseudogap state [22]. Still, the origin of these signatures remains to be clarified.…”

“…Very different interpretations have been proposed : the two-energy scale gap function, implying a non-retarded pairing interaction [22,41,42], and the coupling to a spin collective mode [11][12][13][14][15][16][17][18][43][44][45][46]. Although phenomenological, the static model describes very well the particular signatures of the spectral function, the SC density of states (DOS), and the transition to the pseudogap state [22].…”

“…In addition to many theoretical ideas [4][5][6][7][8][9] the experiments reveal an inherent complexity : a complex quasiparticle self-energy [10][11][12], coupling to a spin collective mode [13][14][15][16][17][18], anomalous specific heat [19], multiple energy scales [20][21][22][23], spatial inhomogeneities [24][25][26][27][28][29], checkerboard oscillations [30,31], pseudogap phenomena above T c [7,19,[32][33][34][35], etc. The SC state of cuprates is indeed far from the desired lex parsimoniae.…”

c-axis coupling in underdopedBi2Sr2CaCu2Spathis1, Colson2, Yang3 et al. 2008Phys. Rev. B4010View full textAdd to dashboardCite

“…This value not only means that ⌫ s Ͼ 30 K, comforting our interpretation of the decrease of j c c ϰ T c in terms of unitary scatterers induced in the CuO 2 planes, but it is also remarkably close to characteristic energy scales found in recent Raman scattering 2,53 and scanning tunneling microscopy experiments. 54 The first study finds that in underdoped HgBa 2 CuO 4 , the B 2g Raman mode, which directly couples to the same low-energy nodal quasiparticle excitations that are responsible for the reduction of the c-axis superfluid density in the IAH model, is characterized by an energy scale ϳ2k B T c ͑related to the nodal slope of the gap function͒. 53 We surmise that ⌬ 0 is a closely related parameter.…”

“…The second study finds that the total tunneling gap amplitude is determined by two energy scales, the smaller of which, ⌬ Ϸ 2.8k B T c , is related to superconductivity. 54 It is interesting that the existence of a second small energy scale describing nodal quasiparticle excitations may well be responsible for the observed suppression of j c c as a function of doping ͑de-creasing p or ␦͒. 16 The proportionality of this decrease to the ratio of the gap maximum ͑at the antinode͒ and T c finds a logical explanation if the smaller energy scale ͓ϳ͑2 -2.5͒k B T c ͔ is what determines the magnitude of the c-axis critical current density.…”