Kavli Affiliate: Long Zhang
| First 5 Authors: Ying Chen, Ying Chen, , ,
| Summary:
The $S=1/2$ antiferromagnetic Heisenberg chain is a paradigmatic quantum
system hosting exotic excitations such as spinons and solitons, and forming
random singlet state in the presence of quenched disorder. Realizing and
distinguishing these excitations in a single material remains a significant
challenge. Using nuclear magnetic resonance (NMR) on a high-quality single
crystal of copper benzoate, we identify and characterize all three excitation
types by tuning the magnetic field at ultra-low temperatures. At a low field of
0.2 T, a temperature-independent spin-lattice relaxation rate ($1/T_1$) over
more than a decade confirms the presence of spinons. Below 0.4 K, an additional
relaxation channel emerges, characterized by $1/T_1 propto T$ and a spectral
weight growing as $-ln(T/T_0)$, signaling a random-singlet ground state
induced by weak quenched disorder. At fields above 0.5 T, a field-induced spin
gap $Delta propto H^2/3$ observed in both $1/T_1$ and the Knight shift
signifies soliton excitations. Our results establish copper benzoate as a
unique experimental platform for studying one-dimensional quantum integrability
and the interplay of disorder and correlations.
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