Correlation of pseudogap, superconducting ordering and superconducting fluctuations with electron–phonon interactions in Bi2Sr2CaCu2O8+δ

Abstract

The relationship between anomalous pseudogap and superconducting states is a fascinating but controversial subject in high temperature superconductors. Here, we investigate the different quasiparticle dynamics with femtosecond transient optical spectroscopy in underdoped Bi _2 Sr _2 CaCu _2 O _8+ _δ at 3–250 K. Below T _c , these results reveal the coexistence of the anomalous pseudogap and superconducting states. On the basis of the Mattis–Bardeen formula for the Cooper-pairing superconducting gap and the Kabanov model for the pseudogap state, the measurements yield a temperature-dependent superconducting gaps and two temperature-independent pseudogaps below and above the superconducting transition T _c . Above the superconducting transition temperature, the pseudogap state can be explained as an incipient condensation of Cooper pairs with short coherence length. The quasiparticle dynamics in the superconducting and pseudogap states are correlated well with electron–phonon interaction characteristics.

Keywords

• pseudogap and superconducting state
• high temperature superconductors
• femtosecond transient optical spectroscopy
• electron–phonon interaction