Submillimeter Wave ESR Measurement of a Finite Haldane Chain System Y2BaNi0.96Mg0.04O5

The edge states in the finite S=1 Haldane chain are expected to have different energy structures depending on the chain length due to the interaction through the finite chain. Electron spin resonance (ESR) signals coming from the finite chains with various chain length have been observed separately in Y
₂
BaNi
_0.96
Mg
_0.04
O
₅
, which is a famous Haldane system doped with non-magnetic ions, due to the high spectral resolution of our submillimeter wave ESR. From the analysis, the information about the correlation length in the Haldane system at low temperature has been obtained directly by the experiment for the first time.