Evolution of low-energy magnetic excitations pair spectrum in SmMnO3+δ
F. N. Bukhanko and A. F. Bukhanko
Donetsk Institute of Physics and Technology named after A. A. Galkin NASU, Kyiv 03028, Ukraine
Received June 9, 2021, published online September 24, 2021
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 de-crease 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.