We report a novel aspect of the competition and coexistence between magnetism and superconductivity in the high-$T_{ c}$ cuprate La$_{ 2-x}$Sr$_{ x}$CuO$_{ 4}$ (La214). With a modest magnetic field applied $H \parallel c$-axis, we monitored the infrared signature of pair tunneling between the CuO$_2$ planes and discovered the complete suppression of interlayer coupling in a series of underdoped La214 single crystals. We find that the in-plane superconducting properties remain intact, in spite of enhanced magnetism in the planes.
Categories: cond-mat.supr-con cond-mat.str-el