Fizika Nizkikh Temperatur: Volume 47, Number 11 (November 2021), p. 1021-1033    ( to contents , go back )

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
E-mail: metatem@ukr.net
pos Анотація:2076

Received June 9, 2021, published online September 24, 2021

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 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.

Key words: spin liquid, spinon pairs, vortex pairs, magnetization oscillations, Landau quantization.

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