La-139 NMR investigation of the interplay between lattice, charge, and spin dynamics in the charge-ordered high-T-c cuprate La1.875Ba0.125CuO4

摘要

We investigate the interplay between the lattice, charge, and spin dynamics in charge-ordered high T cuprate La1.875Ba0.125CuO4 (T-c = 4 K) based on the inverse Laplace transform (ILT) analysis of the La-139 nuclear spin-lattice relaxation rate 1/T-1 (dubbed ILTT1 analysis hereafter). A major thrust of the ILTT1 analysis is that one can deduce the probability density function P(1/T-1) of distributed 1/T-1. We demonstrate that 1/T-1(lm), defined as the log mean (i.e., the center of gravity on a logarithmic scale) of P(1/T-1), can be well approximated by 1/T-1(str) deduced from the phenomenological stretched fit; however, P(1/T-1) can provide much richer insight into how the lattice, charge, and spin fluctuations and their distribution develop near and below the long-range charge order at T-charge similar to 54 K. Upon entering the charge-ordered state, a divergent increase of 1/T-1(lm) toward the spin ordering at T-spin(mu SR) similar or equal to 35 K is accompanied by an asymmetric broadening of P(1/T-1). Even deep inside the charge-ordered state, 1/T-1 at a gradually diminishing fraction of La-139 sites continues to slow down as temperature is lowered, as expected for canonical superconducting CuO2 planes without enhanced spin fluctuations. The fraction of such canonical La-139 sites almost disappears by similar or equal to 40 K. In contrast, nearly half of the La-139 sites in La1.885Sr0.115CUO4 (T-charge similar or equal to 80 K) still exhibit the canonical behavior without enhanced spin fluctuations even near its T-c = 31 K. These contrasting behaviors explain why superconductivity in La1.875Ba0.125CuO4 is more strongly suppressed than in La1.885Sr0.115CuO4 despite the lower onset temperature of the charge order.