New High-Field Phenomena in Spin-Peierls Systems

Abstract

The spin-Peierls (SP) transition in zero field is a spin-lattice dimeri-zation phenomenon which occurs in a quasi-1-D Heisenberg S= 1/2 antiferromag-netic chains. The chains are coupled to the 3-D phonon field of the lattice, and a magneto-elastic transition results which is the insulating analogue of the well-known Peierls transition in a quasi-1-D conductor. For T<Tsp, the magnetic chains have a dimerized (alternating) character, resulting from an underlying progressive lattice distortion, with a nonmagnetic singlet ground state and an excitation energy gap to magnetic excited states. The character of an alternating as opposed to uniform chain lattice, together with the corresponding magnetic excitations, is shown schematically in Fig. 1.