Experimental observation of the crystallization of a paired holon state

Abstract

An excitation at 201 meV is observed in the doped-hole ladder cuprate Sr14Cu24O41, using ultraviolet resonance Raman scattering with incident light at 3.7 eV polarized along the rungs. The excitation is of charge nature, with a temperature independent excitation energy, and can be understood via an intraladder pair-breaking process. The intensity tracks closely the order parameter of the charge density wave in the ladder CDWL, but persists above its transition temperature TCDWL, indicating a strong local pairing above the TCDWL. The 201 meV excitation vanishes in La6Ca8Cu24O41+δ, and La5Ca9Cu24O41 which are samples with no holes in the ladders. Our results suggest that the doped holes in the ladder are composite bosons consisting of paired holons that order below TCDW. © 2010 The American Physical Society.