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Abstract:
We report low-temperature specific heat, C(T), measurements on
(Yb1-xLux)(4)As-3, with x = 0.01 and x = 0.03, where nonmagnetic Lu
atoms are randomly distributed on antiferromagnetic S = 1/2 Heisenberg
chains with J/k(B) = 28 K. The observed reduction of C below 15 K with
increasing x is accurately described by quantum transfer matrix
simulations without any adjustable parameter, implying that the system
is an excellent experimental realization of segmented quantum spin
chains. Finite-size effects consistent with conformal-field theory
predictions are leading to the formation of an effective low-energy gap.
The size of the gap increases with Lu content and accounts for the
impurity-driven reduction of the specific heat. For both concentrations
our results verify experimentally the low-temperature scaling behavior
established theoretically and also confirm the value of J determined
from pure Yb4As3.
