В спектре фотолюминесценции двумерного электронного газа в квантующем магнитном поле, при факторе заполнения электронов ν=2, в условиях фотовозбуждения неравновесного ансамбля циклотронных магнитоэкситонов, обнаружены новые линии. Их энергия лежит в области, запрещенной для одночастичных оптических переходов: в диапазоне переходов из возбужденных состояний трехчастичных трансляционно-инвариантных комплексов - магнитотрионов. Предполагается, что новые линии связаны со сложным спектром внутреннего движения магнитотриона, состоящего из электрона на первом и двух тождественных дырок на нулевом уровнях Ландау.
We study the entanglement entropy and particle number cumulants for a system of disordered noninteracting fermions in d dimensions. We show, both analytically and numerically, that for a weak disorder the entanglement entropy and the second cumulant (particle number variance) are proportional to each other with a universal coefficient. The corresponding expressions are analogous to those in the clean case but with a logarithmic factor regularized by the mean free path rather than by the system size. We also determine the scaling of higher cumulants by analytical (weak disorder) and numerical means. Finally, we predict that the particle number variance and the entanglement entropy are nonanalytic functions of disorder at the Anderson transition.
We have measured antiferromagnetic resonance (AFMR) frequency-field dependences for aluminum–manganese garnet Mn3Al2Ge3O12 at frequencies from 1 to 125 GHz and fields up to 6 T. There are three AFMR modes for all orientations, their zero field gaps are about 40 and 70 GHz. Andreev–Marchenko hydrodynamic theory  well describes experimental frequency–field dependences. We have observed hysteresis of resonance absorption as well as history dependence of resonance absorption near gap frequencies below 10 kOe in all three measured field orientations, which are supposedly due to the sample domain structure. Observation of the AFMR signal at the frequencies from 1 to 5 GHz allows to estimate repulsion of nuclear and electron modes of spin precession in the vicinity of spin-reorientation transition at H || .
A method is proposed for the creation of an entangled metastable (subradiance) excited state in a system of two closely spaced identical atoms. The system of unexcited atoms is first placed in a magnetic field that is directed at a magic angle of α0=arccos(1/3–√)≈54.7∘α0=arccos(1/3)≈54.7∘ to the line connecting the atoms and has a transverse gradient. The gradient of the field results in the detuning of frequencies of an optical transition of the atoms. Then, the resonant laser excitation of an atom with a higher transition frequency is performed with the subsequent adiabatic switching-off of the gradient of the magnetic field. It is shown that the excited atomic system in this case transits with overwhelming probability to an entangled subradiance state. Requirements on the spectroscopic parameters of the transitions and on the rate of varying the gradient of the magnetic field necessary for the implementation of this effect are analyzed.
Original Russian Text © A.A. Makarov, V.I. Yudson, 2017, published in Pis’ma v Zhurnal Eksperimental’noi i Teoreticheskoi Fiziki, 2017, Vol. 105, No. 3, pp. 193–197.
We discuss the emergence of p-wave superfluidity of identical atomic fermions in a two-dimensional optical lattice. The optical lattice potential manifests itself in an interplay between an increase in the density of states on the Fermi surface and the modification of the fermion-fermion interaction (scattering) amplitude. The density of states is enhanced due to an increase of the effective mass of atoms. In deep lattices the scattering amplitude is strongly reduced compared to free space due to a small overlap of wave functions of fermions sitting in the neighboring lattice sites, which suppresses the p-wave superfluidity. However, for moderate lattice depths the enhancement of the density of states can compensate the decrease of the scattering amplitude. Moreover, the lattice setup significantly reduces inelastic collisional losses, which allows one to get closer to a p-wave Feshbach resonance. This opens possibilities to obtain the topological px+ipy superfluid phase, especially in the recently proposed subwavelength lattices. We demonstrate this for the two-dimensional version of the Kronig-Penney model allowing a transparent physical analysis.
We consider a problem of persistent magnetization precession in a single-domain ferromagnetic nanoparticle under the driving by the spin-transfer torque. We find that the adjustment of the electronic distribution function in the particle renders this state unstable. Instead, abrupt switching of the spin orientation is predicted upon increase of the spin-transfer torque current. On the technical level, we derive an effective action of the type of Ambegaokar-Eckern-Schön action for the coupled dynamics of magnetization [gauge group SU(2)] and voltage [gauge group U(1)].