20.500.12556/RUL-134624 Phantom Bethe excitations and spin helix eigenstates in integrable periodic and open spin chains We demonstrate the existence of a special chiral “phantom” mode with some analogy to a Goldstone mode in the anisotropic quantum XXZ Heisenberg spin chain. The phantom excitations contribute zero energy to the eigenstate, but a finite fixed quantum of momentum $k_0$. The mode exists not due to symmetry principles, but results from nontrivial scattering properties of magnons with momentum $k_0$ given by the anisotropy via $\cos{k_0}=\Delta$. Different occupations of the phantom mode lead to energetical degeneracies between different magnetization sectors in the periodic case. This mode originates from special string-type solutions of the Bethe ansatz equations with unbounded rapidities, the phantom Bethe roots (PBRs). We derive criteria under which the spectrum contains eigenstates with PBRs, both in open and periodically closed integrable systems, for spin-1/2 and higher spins, and discuss the respective chiral eigenstates. The simplest of such eigenstates, the spin helix state, which is a periodically modulated state of chiral nature, is built up from the phantom excitations exclusively. Implications of our results for experiments are discussed. quantum mechanics kvantna mehanika true false true Angleški jezik Slovenski jezik Neznano 2022-01-21 11:56:55 2022-01-21 11:56:56 2022-09-13 03:56:11 0000-00-00 00:00:00 2021 0 0 Str. L081410-1-L081410-6 iss. 8 Vol. 104 2021 0000-00-00 PostprintKoncna Objavljeno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 530.145 2469-9950 10.1103/PhysRevB.104.L081410 94433027 RAZ_Popkov_Vladislav_2021.pdf RAZ_Popkov_Vladislav_2021.pdf 1 1B051AAFD97B50AD925B61AD9BC383EA 061426aae81c6a9f0ebdf1e194789e3fba43fb4e17107ca34852b482228635d4 3e859c89-7aa9-11ec-abdb-00155dcfd717 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=153149 https://doi.org/10.1103/PhysRevB.104.L081410 0 4ca6606e-7aa9-11ec-abdb-00155dcfd717 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=153150 Fakulteta za matematiko in fiziko 0 0 0