Crossover in charge transport from one-dimensional copper-oxygen chains to two-dimensional ladders in(La,Y)y(Sr,Ca)14−yCu24O41

The charge transport in the copper-oxygen chain/ladder layers of ${(\text{La},\text{Y})}_{y}{(\text{Sr},\text{Ca})}_{14\ensuremath{-}y}{\text{Cu}}_{24}{\text{O}}_{41}$ is investigated along two crystallographic directions in the temperature range from 50 to 700 K and for doping levels from $y\ensuremath{\approx}6$ (number of holes ${n}_{h}l1$) to $y=0$ (number of holes ${n}_{h}=6$). A crossover from a one-dimensional hopping transport along the chains for $y\ensuremath{\ge}3$ to a quasi-two-dimensional charge conduction in the ladder planes for $y\ensuremath{\lesssim}2$ is observed. This is attributed to a partial hole transfer from chains to ladders when the hole doping exceeds ${n}_{h}\ensuremath{\approx}4$ and approaches fully doped value ${n}_{h}=6$. For $y\ensuremath{\lesssim}2$ a weak dielectric relaxation at radio frequencies and a microwave mode are detected, which might be recognized as signatures of a charge-density wave phase developed at short length scales in the ladder planes.