Evolution of low-energy magnetic excitations pair spectrum in SmMnO3+δ

Abstract

The identification of low-energy thermal excitations in SmMnO3+δ degenerate states of spin and superconducting quantum liquids in magnetic fields H ≤ 3.5 kOe is presented. In the temperature interval 4.2–12 K, the Landau quantization of the low-energy magnetic excitations pair spectrum of Z2 quantum spin liquid is found in the system spinon-gauge field. The formation of a broad continuum of spinon pair excitations in the “weak magnetic field” regime (H = 100 Oe, 1 kOe) in the FC regime is explained in the framework of the Landau quantization models of the compressible spinon gas with fractional values of the factor ν filling three overlapping bands. In the regime of “strong magnetic field” (H = 3.5 kOe), the quantum oscillations of temperature dependences of “supermagnetization” of the incompressible spinon liquid were observed. They have the form of three narrow steps (plateaus), corresponding to a complete filling of the non-overlapping Landau bands with integer values of the filling factor by spinons. These results are evidence for the existence of vortex gauge field fluctuations with a high density in the magnetic fields H ≥ 100 Oe. The strong growth of vortex fluctuations can be explained by a second-kind phase transition in SmMnO3+δ in the form of the vortices condensation. Growth of the external dc magnetic field strength in the SmMnO3+δ samples in the interval of fields 0 < H ≤ 3.5 kOe leads to a continuous decrease in the giant magnetization jump near the temperature TKT ≅ 12 K of the topological phase transition, Kosterlitz–Thouless dissociation of 2D vortex-antivortex pairs in a local superconducting state. The suppression of the magnetization jump near the TKT temperature with increasing H is explained by the polarization of vortex antivortex pairs at temperatures below TKT by an external dc magnetic field, which weakens the vortex interaction in pairs and leads to their dissociation.