Abstract
We investigate frustrated antiferromagnetic Heisenberg quantum spin chains at $T=0$ for $S=\frac{3}{2}$ and $S=2$ using the DMRG method. We localize disorder and Lifshitz points, confirming that quantum disorder points can be seen as quantum remnants of classical phase transitions. Both in the $S=\frac{3}{2}$ and the $S=2$ chain, we observe the disappearance of effectively free $S=\frac{1}{2}$ and $S=1$ end spins, respectively. The frustrated spin chain is therefore a suitable system for clearly showing the existence of free end spins ${S}^{\ensuremath{'}}=[S/2]$ also in half-integer antiferromagnetic spin chains with $S>\frac{1}{2}.$ We suggest that the first-order transition found for $S=1$ in our previous work [A. K. Kolezhuk, R. Roth, and U. Schollw\"ock, Phys. Rev. Lett. 77, 5142 (1996); Phys. Rev. B 55, 8928 (1997)] is present in all frustrated spin chains with $S>\frac{1}{2},$ characterized by the disappearance of effectively free end spins with ${S}^{\ensuremath{'}}=[S/2].$
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