## 抄録

The quasi-onedimensional S = 1/2 antiferromagnet Yb_{4}As_{3} is studied by using low-temperature measurements of the specific heat C(T,B), thermal expansion α(T,B) and longitudinal elastic mode c_{11}(T,B). As has been previously shown [M. Köppen et al., Phys. Rev. Lett. 82, 4548 (1999)], finite magnetic fields perpendicular to the spin chains induce a gap in the spin-excitation spectrum (reminiscent of massive, soliton-like excitations) which manifests itself in distinct anomalies in the specific heat and thermal expansion. In this paper, we present an extension of the above work placing special emphasis on the lattice response and the evolution of the gap at higher fields. The main observations are: (i) the field-induced gap causes a minimum in the c_{11} elastic constant both as a function of temperature and field. Applying a simple two-level model allows for a determination of the gap value Delta;(B) as well as the constant G(B) = ∂Δ/∂ε introduced to account for the spin-lattice coupling. (ii) At B ≤ 9 T, the Δ(B) values derived from the various quantities are consistent with Δ(B) ∝ B^{2/3} as predicted by the quantum sine-Gordon model. (iii) Measurements of C(T,B = const) in dc-fields up to 18 T and of c_{11}(T = const, B) in pulsed fields up to 50 T, however, reveal deviations from this behavior at higher fields. (iv) Isothermal measurements of C_{11}(B) show a sharp increase above 35 T which is almost T-independent for T ≤ 10 K and whose origin is unknown.

本文言語 | English |
---|---|

ページ（範囲） | 3018-3023 |

ページ数 | 6 |

ジャーナル | International Journal of Modern Physics B |

巻 | 16 |

号 | 20-22 |

DOI | |

出版ステータス | Published - 2002 8月 30 |

外部発表 | はい |

## ASJC Scopus subject areas

- 統計物理学および非線形物理学
- 凝縮系物理学

## フィンガープリント

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