Modulations in the CuO Chain Layer ofYBa2Cu3O7−δ: Charge Density Waves?

Abstract

We have performed reversed-bias scanning tunneling microscopy at 20 K on the CuO chain layer of cold-cleaved single crystals of $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$. We find 1.3-nm corrugations which change sign under bias polarity reversal. This behavior and the 1.3-nm wavelength are in agreement with the hypothesis that the one-dimensional CuO chains undergo a charge density wave transition. This is the first real-space evidence of such a transition in $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$. We also explore the possibility that the corrugations are caused by Friedel oscillations or bipolaron scattering. Several-nm depressions along the CuO chains transform into broad swells and depressions as the bias voltage is increased.