Magnetic-Field-Induced Localization of Quasiparticles in Underdoped La${}_{2-x}$Sr${}_x$CuO${}_4$ Single Crystals

Magnetic-field-induced ordering of electrons around vortices is a striking phenomenon recently found in high-$T_c$ cuprates. To identify its consequence in the quasiparticle dynamics, the magnetic-field ($H$) dependence of the low-temperature thermal conductivity $\kappa$ of La${}_{2-x}$Sr${}_x$CuO${}_4$ crystals is studied for a wide doping range. It is found that the behavior of $\kappa (H)$ in the sub-Kelvin region changes drastically across optimum doping, and the data for underdoped samples are indicative of unusual magnetic-field-induced localization of quasiparticles; this localization phenomenon is probably responsible for the unusual “insulating normal state” under high magnetic fields.