c-Axis Optical Response in the Static Stripe Ordered Phase of the Cuprates

The c-axis far-infrared reflectivity spectra in the superconducting state were investigated for La_1.85-yNd_ySr_0.15CuO₄. The Josephson plasma edge rapidly shifts towards lower frequency with increasing y, and almost disappears when y exceeds a critical value \( y_c~0.12\) above which the low-temperature-tetragonal (LTT) deformation switches on, stabilizing the spin/charge ordered stripe phase. In the vicinity of y_c, a ``normal state'' reentrant behavior was observed with lowering temperature below T_c. This clearly demonstrates that the static stripe order pinned by the LTT distortion suppresses the interlayer phase coherence.