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## Spin stiffness of a Fermi liquid in the ν = 1 quantum Hall regime

Physical Review B: Condensed Matter and Materials Physics. 2020. Vol. 102. No. 23. P. 235424-1–235424-6.

Anomalous behavior of spin stiffness is revealed in ZnO-based two-dimensional electron systems (2DESs)

with strong Coulomb interaction and Wigner-Seitz parameter r_s > 6. The spin stiffness is extracted directly from

the quadratic k-dispersion of spin excitons at ν = 1 probed by inelastic light scattering. The resulting values are

found to be dramatically rescaled compared to the case of weakly interacting 2DESs—spin stiffness turned out

to be of the order of the cyclotron energy with the effective mass of Fermi-liquid quasiparticles. This result is

also confirmed by the exact diagonalization simulations.

Keywords: обменное взаимодействиеexchange interactionцелочисленный квантовый эффект ХоллаTwo-dimensional electron systemquantum Hall effectcollective excitationsколлективные возбужденияinelastic light scatteringнеупругое рассеяние светаДвумерные электронные системы

Publication based on the results of:

Vankov A., Кайсин Б. Д., Kukushkin I., Письма в Журнал экспериментальной и теоретической физики 2018 Т. 107 № 2 С. 110–114

In the two-dimensional electron systems with strong coupling in MgZnO/ZnO heterostructures, the thermal
behavior of Ising quantum Hall ferromagnets at the filling factor nu=2 has been studied. The spin polarization
of Hall ferromagnets has been detected by measuring the signal related to the inelastic light scattering by
intrasubband spin excitons. A stepwise change in the spin polarization at ...

Added: September 11, 2018

Vankov A., Kukushkin I., Письма в Журнал экспериментальной и теоретической физики 2020 Т. 112 № 1 С. 62–67

The Raman study of strongly interacting two-dimensional electron systems based on ZnO/MgZnO has revealed an anomalously intense spectral line of the anti-Stokes component of the spin exciton. This line is manifested near the filling factor v = 2 at the ferromagnetic ordering of the spin subsystem, whereas it is not observed at the paramagnetic ordering. ...

Added: January 25, 2021

Vankov A., Kaysin B. D., Volosheniuk S. et al., Physical Review B: Condensed Matter and Materials Physics 2019 Vol. 100 No. 4 P. 041407-1–041407-5

An unusual behavior of the exchange energy scale of a quantum Hall ferromagnet with ν=1 was found in strongly correlated two-dimensional electron systems based on MgZnO/ZnO heterostructures. The exchange contribution, entering the energy of a collective excitation, was probed by means of inelastic light scattering. It was established that, in a wide range of electron densities corresponding ...

Added: October 31, 2019

A. B. Van'kov, Koreyev A. S., P. S. Berezhnoy et al., Physical Review B: Condensed Matter and Materials Physics 2022 Vol. 106 No. 24 Article 245308

In strongly correlated quantum Hall ferromagnets with noninteger filling factors between ν = 1 and ν =
3/2, evidence of offbeat spin textures is obtained. The platforms for the study are two-dimensional electron
systems based on MgZnO/ZnO heterostructures, in which the parameters of Zeeman and exchange energies are
inconsistent with ordinary skyrmions. Experimental probing of magnetic order is ...

Added: December 29, 2022

Vankov A., Kukushkin I., Кулик Л. В. et al., JETP Letters 2017 Vol. 105 No. 6 P. 380–383

The magnetic field dynamics of intersubband collective excitations in two-dimensional electron systems
based on Mg Zn O/ZnO heterostructures is studied by the Raman scattering method. It is found that,
upon the change in the spin polarization under conditions of the transition from the filling factor to
, the energy of the intersubband magnetoplasmon changes considerably. The performed theoretical
analysis ...

Added: June 13, 2017

Vankov A., Kukushkin I., JETP Letters 2017 Vol. 105 No. 6 P. 380–383

The magnetic field dynamics of intersubband collective excitations in two-dimensional electron systems based on Mg_xZn_{1−x}O/ZnO heterostructures is studied by the Raman scattering method. It is found that, upon the change in the spin polarization under conditions of the transition from the filling factor ν=2 to ν=1, the energy of the intersubband magnetoplasmon changes considerably. The ...

Added: November 30, 2017

Vankov A., Kukushkin I., Physical Review B: Condensed Matter and Materials Physics 2021 Vol. 104 Article 165144

In ZnO-based two-dimensional electron systems with strong Coulomb interaction, the anomalous spin-exciton
branch is revealed. As probed by inelastic light scattering, in a ferromagnetic quantum-Hall state with the filling
factor ν = 2, a spin exciton has a negative momentum dispersion with steepness dependent on the electron
density. The negative dispersion of the spin exciton is associated with ...

Added: December 20, 2021

Vankov A., Solovyev V., Kaysin B. et al., Physical Review B: Condensed Matter and Materials Physics 2016 Vol. 94 P. 1552041–1552046

The neutral excitations in two-dimensional electron systems (2DES) confined at MgZnO/ZnO heterojunc- tions were studied by a resonant inelastic light scattering (ILS) technique. At zero magnetic field the ILS spectra of intra- and intersubband collective excitations are detected in the wavelength range close to the ZnO direct band gap. The intersubband spectrum is represented by ...

Added: October 21, 2016

Vankov A., Kaysin B. D., Kukushkin I., JETP Letters 2019 Vol. 110 No. 4 P. 296–300

The behavior of the degree of spin polarization and the specific exchange energy near the Hall ferromagnetic state with filling factor ν = 1 in strongly interacting two-dimensional electron systems in MgZnO/ZnO heterostructures is investigated. These characteristics have been determined by measuring the spectra of inelastic light scattering by the collective excitations of the electron ...

Added: October 31, 2019

Glushkov V. V., Demishev S. V., Samarin A. et al., Physica Status Solidi (B): Basic Research 2017 Vol. 254 No. 4 P. 1600571-1–1600571-5

Added: October 19, 2017

Khomskii D. I., K.I. Kugel, Sboychakov A. O. et al., Journal of Experimental and Theoretical Physics 2016 Vol. 122 No. 3 P. 484–498

We analyze the role of local geometry in the spin and orbital interaction in transition metal compounds with orbital degeneracy. We stress that the tendency observed in the most studied case (transition metals in O6 octahedra with one common oxygen—common corner of neighboring octahedra—and with ~180° metal–oxygen–metal bonds), that ferro-orbital ordering renders antiferro-spin coupling and, ...

Added: February 18, 2017

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

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 ...

Added: December 19, 2017

Vankov A., Бисти В. Е., Кулик Л. В. et al., Physics-Uspekhi 2015 Vol. 4 No. 58 P. 315–329

Experimental and theoretical research on neutral
excitations in a two-dimensional electron gas in a strong mag netic field is reviewed. Methods for calculating excitation en ergies in the strong-field limit for integer and noninteger filling
factors are considered. The effects of impurities and of the
nonideality of the two-dimensional system on the excitation
spectrum are examined. Experimental results that have been
obtained ...

Added: March 6, 2017

Igoshev P., Streltsov S., Kliment I. Kugel, Journal of Magnetism and Magnetic Materials 2023 Vol. 587 Article 171315

We present a detailed derivation of the effective Hamiltonian for a strongly correlated electron system involving
both orbital and spin degrees of freedom. This problem is relevant to a wide class of materials containing ions
with the orbitally degenerate ground state (Jahn–Teller ions). We treat in detail the case of double degenerate
orbitals, obtain the Kugel–Khomskii model, and ...

Added: February 1, 2024

Kulik L., Zhuravlev A. S., Musina L. I. et al., Nature Communications 2021 Vol. 12 Article 6477

Two-dimensional electron systems in a quantizing magnetic field are regarded as of
exceptional interest, considering the possible role of anyons—quasiparticles with non-boson
and non-fermion statistics—in applied physics. To this day, essentially none but the fractional
states of the quantum Hall effect (FQHE) have been experimentally realized as a system with
anyonic statistics. In determining the thermodynamic properties of anyon ...

Added: December 20, 2021

V.M. Pudalov, Reznikov M., Kuntsevich A. et al., Journal of Low Temperature Physics 2015 Vol. 181 No. 3-4 P. 99–112

This paper describes recent developments in experimental techniques for thermodynamic measurements. Particularly, we focus on the derivatives of the chemical potential with respect to magnetic field and temperature. The former enables to determine the spin magnetization per electron and the latter the entropy per electron. We briefly describe recent results obtained with these techniques and ...

Added: March 14, 2016

Горбунов А. В., Кулик Л. В., Kuznetsov V. et al., Письма в Журнал экспериментальной и теоретической физики 2017 Т. 106 № 10 С. 651–654

We demonstrate that non-equilibrium spin excitations drift to macroscopically large distances in a 2D electron gas (symmetrically doped GaAs/AlGaAs quantum well) in a quantizing magnetic field at filling factor $\nu $ = 2. The effect is induced by low-temperature photoexcitation of a dense ensemble of long-lived ($\sim 1 $ ms) spin excitations − cyclotron spin-flip magnetoexcitons. The spin excitation ...

Added: December 11, 2017

Dziom V., Shuvaev A. V., Shchepetilnikov A. et al., Physical Review B: Condensed Matter and Materials Physics 2019 Vol. 99 No. 4 Article 045305

The integer quantum Hall effect is a well-studied phenomenon at frequencies below about 100 Hz. The plateaus in high-frequency Hall conductivity were experimentally proven to retain up to 33 GHz, but the behavior at higher frequencies has remained largely unexplored. Using continuous-wave terahertz spectroscopy, the complex Hall conductivity of GaAs/AlGaAs heterojunctions was studied in the ...

Added: December 11, 2020

Pudalov V. M., Gershenson M. E., Kojima H., Physical Review B: Condensed Matter and Materials Physics 2014 Vol. 90 No. 7 P. 075147-1–075147-17

We have experimentally studied the renormalized effective mass m* and Dingle temperature TD in two spin subbands with essentially different electron populations. Firstly, we found that the product m*T_D that determines the damping of quantum oscillations, to the first approximation, is the same in the majority and minority subbands even at a spin polarization degree ...

Added: March 14, 2016

Chetverikov V., Вестник Московского университета. Серия 3: Физика и астрономия 2018 № 6 С. 28–33

A model for describing the distribution of magnetization over the thickness of a film of a ferromagnetic
semiconductor in an external constant electric field perpendicular to the film surface is considered. The
formulas obtained make it possible to determine the dependence of this distribution on the values of the
physical parameters of the film. ...

Added: March 1, 2019

Kulik L. V., Kuznetsov V. A., Gorbunov A. V. et al., Scientific Reports 2018 Vol. 8 No. 1 P. 1–6

We report on optical visualization of spin propagation more than 100 µm. We present an electronic system in a new state of aggregation, the magnetofermionic condensate, in which the lowest-energy spin excitations − photoexcited spin-triplet magnetoexcitons – freely propagate over long distances, in the order of a millimeter, which implies non-diffusion spin transport. Our results open ...

Added: September 3, 2018

Kozyrev N. V., Akhmadullin R. R., Namozov B. R. et al., Physical Review B: Condensed Matter and Materials Physics 2019 Vol. 99 No. 3 P. 1–7

Multiple Mn2+ spin-flip Raman scattering (SFRS) in Voigt geometry was observed in self-organized disk-shaped quantum dots (QDs) of CdSe/Zn0.99Mn0.01Se, where magnetic ions and QD carriers are spatially separated and therefore the exchange interaction between them is expected to be weak. Many lines (about ten) were observed in SFRS spectra, yet the overlapping of the hole wave function with Mn2+ ions ...

Added: May 31, 2021

Vankov A., Kaysin B. D., Kukushkin I., Physical Review B: Condensed Matter and Materials Physics 2018 Vol. 98 P. 121412–121412

We investigate the impact of Coulomb correlations on the low-energy collective excitations in two-dimensional electron systems in the quantum Hall state ν = 2. The collective excitations are studied using inelastic light scattering in the set of MgZnO/ZnO heterostructures with high-mobility two-dimensional electrons. The study focuses on the lowest-energy collective excitations in the paramagnetic state ...

Added: November 25, 2018

Chetverikov V., Journal of Physics: Conference Series 2019 Vol. 1163 No. 012077 P. 1–6

A theoretical model describing the spontaneous magnetization of a ferromagnetic semiconductor (InMn)As film in the presence of an external electric field directed across the film is considered. It is assumed that the ions of a manganese impurity with spin 5/2 are acceptors, have a uniform spatial distribution inside the semiconductor, and do not change their ...

Added: April 2, 2019