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Regular version of the site

Article

Optical manifestation of the Stoner ferromagnetic transition in two-dimensional electron systems

Physical Review B: Condensed Matter and Materials Physics. 2017. Vol. 96. P. 235401-1-235401-8.
Kukushkin I., Vankov A., Kaysin B.

We perform a magneto-optical study of a two-dimensional electron systems in the regime of the Stoner
ferromagnetic instability for even quantum Hall filling factors on MgxZn1−xO/ZnO heterostructures. Under
conditions of Landau-level crossing, caused by enhanced spin susceptibility in combination with the tilting of the
magnetic field, the transition between two rivaling phases, paramagnetic and ferromagnetic, is traced in terms of
optical spectra reconstruction. Synchronous sharp transformations are observed both in the photoluminescence
structure and parameters of collective excitations upon transition from paramagnetic to ferromagnetic ordering.
Based on these measurements, a phase diagram is constructed in terms of the two-dimensional electron density
and tilt angle of the magnetic field.Apart from stable paramagnetic and ferromagnetic phases, an instability region
is found at intermediate parameters with the Stoner transition occurring at ν ≈ 2. The spin configuration in all
cases is unambiguously determined by means of inelastic light scattering by spin-sensitive collective excitations.
One indicator of the spin ordering is the intra-Landau-level spin exciton, which acquires a large spectral weight
in the ferromagnetic phases. The other is an abrupt energy shift of the intersubband charge density excitation due
to reconstruction of the many-particle energy contribution. From our analysis of photoluminescence and light
scattering data, we estimate the ratio of surface areas occupied by the domains of the two phases in the vicinity
of a transition point. In addition, the thermal smearing of a phase transition is characterized.