$\mathit{c}$-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 ${\mathrm{La}}_{1.85-y}{\mathrm{Nd}}_y{\mathrm{Sr}}_{0.15}{\mathrm{CuO}}_4$. The Josephson plasma edge rapidly shifts towards lower frequency with increasing $y$, and almost disappears when $y$ exceeds a critical value $\left(y_c\approx 0.12\right)$ 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.