paper

Experimental observation of the crystallization of a paired holon state

arXiv:1004.1872 · doi:10.1103/PhysRevLett.105.026402

Abstract

A new excitation is observed at 201 meV in the doped-hole ladder cuprate Sr $_{14}$ Cu $_{24}$ O $_{41}$ , using ultraviolet resonance Raman scattering with incident light at 3.7 eV polarized along the direction of the rungs. The excitation is found to be of charge nature, with a temperature independent excitation energy, and can be understood via an intra-ladder pair-breaking process. The intensity tracks closely the order parameter of the charge density wave in the ladder (CDW $_{L}$ ), but persists above the CDW $_{L}$ transition temperature ( $T_{C D W_{L}}$ ), indicating a strong local pairing above $T_{C D W_{L}}$ . The 201 meV excitation vanishes in La $_{6}$ Ca $_{8}$ Cu $_{24}$ O $_{41 + I^´}$ , and La $_{5}$ Ca $_{9}$ Cu $_{24}$ O $_{41}$ 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 $T_{C D W}$ .

Accepted for publication in Physical Review Letters (4 figures)