Quantization of the spectrum of spinon pairs in a magnetic field and formation of bosons in the form of fragments of 1D-waves of charge/spin density in SmMnO-=SUB=-3+delta-=/SUB=-

Abstract

Quantum oscillations of the temperature dependences of magnetization of SmMnO3+delta in magnetic fields H=100 and 350 Oe, 1 and 3.5 kOe are studied within a temperature interval of 4.2-12 K. The continuum of thermal excitations of spinon pairs in magnetic field H=100 Oe is divided into three overlapping Landau bands with energies En (n=1,2,3) and fractional band filling factors ν. The symmetric intense "supermagnetization" doublet consisting of two overlapping peaks around mean excitation temperature Tspinon=~8 K produces the primary contribution to magnetization. As the field increases to H=1 kOe, the spinon excitation spectrum transforms into a broad sinusoid peak with its apex around Tspinon=~8 K, which is typical of the excitation continuum of spinon pairs with strong dispersion in the regime of their confinement. The thermal excitation spectrum of spinons changes significantly in magnetic field H=3.5 kOe: a new type of quantization of the spinon spectrum in the form of magnetization features shaped like narrow steps (plateaus), which correspond to integer filling with spinons of three Landau bands with a finite gap, emerges in Landau bands with n=1,2, and 3. The evolution of the boson spectrum in the form of thermal excitations of gapless quasi-one-dimensional waves of charge/spin density in the Luttinger liquid at temperatures below 60 K is examined. A continuous quantum phase transition of the quantum spin liquid into the Luttinger liquid state induced by an increase in the magnetic field intensity is found at temperatures around T=0. This transition has features typical of the formation of 1D-waves of charge/spin density induced by the confinement of spinon pairs and is accompanied by strong field hysteresis. Keywords: quantum spin liquid, Luttinger liquid, confinement of spinon pairs, spinon --- gauge field system, landau quantization, 1D-waves of charge/spin density, quantum oscillations.