Staggered field effect on the one-dimensional S = 1/2 antiferromagnet Yb₄As₃

Inelastic neutron scattering measurements of magnetic excitations in the charge-ordered state of Yb₄As₃ were performed under magnetic field up to about 6 T. The experimental results show that the change of the spectrum in applied magnetic field occurs only around q = 1, being in contrast to the theoretical discussion for the Cu benzoate case. Taking account of the fact that the neutron scattering technique covers almost the whole energy scale of this system. Yb₄As₃ can be regarded as an ideal system to investigate the new quantum spin state under magnetic field apart from the 'heavy electron' problem in this material.