Coexistence of superconductivity and spin density wave in underdoped YBa2Cu4O8

Abstract

We have measured the magnetic torque of YBa2Cu4O 8 in the a-axis and b-axis rotation for revealing the intrinsic physics in the underdoped cuprates. So far, we have shown that the first peak below 40 K in b-axis rotation appears at θca∼90°±10°, where θca is the angle between the c-axis and the field direction towards the a-axis. We consider that the origin of first peak is the spiral spin density wave along a-axis with a long period. We have also measured the magnetic torque of YBa 2Cu4O8 around the [110] axis. The first peaks are again confirmed to appear in the torque curve. The NMR spectra are systematically investigated by using the field-aligned powder sample. The NMR line width shows an appreciable broadening at temperatures below 30 K when H⊥c axis. We consider that this might be subsequent evidence for the occurrence of the spin density wave in YBa2Cu4O 8. © 2004 Elsevier B.V. All rights reserved.