Phase transition of quantum spin liquid in La-=SUB=-0.15-=/SUB=-Sm-=SUB=-0.85-=/SUB=-MnO-=SUB=-3+delta-=/SUB=- in weak magnetic field tochiral state with topological order during sample magnetization reversal

Abstract

In this work, a detailed study of the nature of phase transitions in the Z2 quantum spin liquid in La La0.15Sm0.85MnO3+delta manganites induced at a temperature of 4.2 K by a weak external dc magnetic field in the ZFC and FC regimesof measuring the field dependences of the magnetization in the field range of ± 5 kOe is carried out. It is shown that during the magnetization reversal of the sample in the ZFC-regime near the external magnetic field H=0, a second-order phase transition Z2 quantum spin liquid occurs in the state of a chiral gap quantum spin liquid with a topological order. The transition is accompanied by an unusual hump-like increase in the number of magnetic excitations in the form of Majorana fermions and local gauge Z2 magnetic fluxes in the range of fields ± 500 Oe near zero field. A characteristic feature of the magnetization features is their strong dependence on the direction of growth of the external magnetic field, which is accompanied by the breakingof the mirror symmetry of the sample magnetization upon reversal of the sign of the external magnetic field, which is typical for the Z2 chiral state of a quantum spin liquid. In the FC-measurementregime, characteristic signs of excitation-destruction of 1D-fragments of gapless charge/spin density waves were found near H=0 during sample magnetization reversal due to confinement-deconfinement of spinon pairs in a system of spin chains. Keywords: chiral quantum spin liquid, Majorana fermions, confinement-deconfinement of spinon pairs, 1D-charge/spin density waves.