Giant Magnetoresistance Oscillations Induced by Microwave Radiation and a Zero-Resistance State in a 2D Electron System with a Moderate Mobility

The effect of a microwave field in the frequency range from 54 to 140 $\mathrm{GHz}$ on the magnetotransport in a GaAs quantum well with AlAs/GaAs superlattice barriers and with an electron mobility no higher than $10^6$ $\mathrm{cm^2/Vs}$ is investigated. In the given two-dimensional system under the effect of microwave radiation, giant resistance oscillations are observed with their positions in magnetic field being determined by the ratio of the radiation frequency to the cyclotron frequency. Earlier, such oscillations had only been observed in GaAs/AlGaAs heterostructures with much higher mobilities. When the samples under study are irradiated with a 140-$\mathrm{GHz}$ microwave field, the resistance corresponding to the main oscillation minimum, which occurs near the cyclotron resonance, appears to be close to zero. The results of the study suggest that a mobility value lower than $10^6$ $\mathrm{cm^2/Vs}$ does not prevent the formation of zero-resistance states in magnetic field in a two-dimensional system under the effect of microwave radiation.Comment: 4 pages, 2 figur

Anisotropic positive magnetoresistance of a nonplanar 2D electron gas in a parallel magnetic field

We study the transport properties of a 2D electron gas in narrow GaAs quantum wells with AlAs/GaAs superlattice barriers. It is shown that the anisotropic positive magnetoresistance observed in selectively doped semiconductor structures in a parallel magnetic field is caused by the spatial modulation of the 2D electron gas.Comment: 4 pages, 3 figure

On surface plasmon polariton wavepacket dynamics in metal-dielectric heterostructures

The WKB equations for dynamics of the surface plasmon polariton (SPP) wavepacket are studied. The dispersion law for the SPP in the metal-dielectric heterostructure with varying thickness of a perforated dielectric layer is rigorously calculated and investigated using the scattering matrix method. Two channels of the SPP wavepacket optical losses related to the absorption in a metal and to the SPP leakage are analyzed. It is shown that change of the dielectric layer thickness acts on the SPP as an external force leading to evolution of its quasimomentum and to the wavepacket reversal or even to the optical Bloch oscillations (BO). Properties of these phenomena are investigated and discussed. Typical values of the BO amplitude are about tens of microns and the period is around tens or hundreds of femtoseconds.Comment: 12 pages, 5 figure

SRG/eROSITA Survey in the Lockman Hole: Classification of X-ray Sources

We have classified the point-like X-ray sources detected by the SRG/eROSITA telescope in the deep Lockman Hole survey. The goal was to separate the sources into Galactic and extragalactic objects. In this work have used the results of our previous cross-match of X-ray sources with optical catalogs. To classify SRG/eROSITA sources we have used the flux ratio $F_{x}/F_{o}$ and information about the source optical extent. As a result, of the 6885 X-ray sources in the eROSITA catalog 357 sources have been classified as Galactic and 5929 and as extragalactic. 539 out of 6885 have been treated as hostless, i.e., having no optical counterparts in the optical catalogs under consideration. 60 have remained unclassified due to the insufficient reliability of optical photometry. Recall and precision for the extragalactic sources are 99.9 and 98.9% (respectively) and 91.6 and 99.7% for the Galactic sources. Using this classification, we have constructed the curves of cumulative number counts for the Galactic and extragalactic sources in the Lockman Hole field. The code that accompanies this paper is available at https://github.com/mbelveder/ero-lh-class.git.Comment: Published in Astronomy Letter

Cosmic ray acceleration and non-thermal emission from fast luminous optical transient sources

Fast blue optical transients (FBOTs) represent a new class of highly energetic sources observed from radio to X-rays. High luminosity, light curves and spectra of the sources can be understood if they are associated with supernova-like or tidal disruption events. Radio observations of the transient sources revealed a mildly relativistic expansion of some of the remnants. The high power and mildly relativistic shock velocities are providing favorable conditions for very high energy particle acceleration. In this paper we present a model of particle acceleration in mildly relativistic magnetohydrodynamic (MHD) outflow of the transient source. To construct the non-thermal radiation and cosmic ray spectra in a broad range of energies we combined the microscopic particle-in-cell (PIC) simulations of electron and proton injection at mildly relativistic shock with Monte Carlo technique for high energy particle transport and acceleration. The kinetic PIC simulations provided the energy partition parameter $\epsilon_{e}$ used to fit the observed non-thermal radio emission using the magnetic field amplification mechanisms modelled with Monte Carlo simulations. The model allowed to describe the radio-spectrum of CSS161010 and it's X-ray luminosity. The high X-ray luminosity of AT2018 and AT2020mrf detected during the first weeks can be connected to the jet interaction with the stellar companion in a binary system. The model predicts that FBOTs can accelerate cosmic rays to energies above 10 PeV with a possible upper limit of maximum energy of 100 PeV. With the expected event rate of FBOTs they can contribute to the very high energy cosmic rays population in galaxies.Comment: 11 pages, 8 figure

Photocurrent, Rectification, and Magnetic Field Symmetry of Induced Current Through Quantum Dots

We report mesoscopic dc current generation in an open chaotic quantum dot with ac excitation applied to one of the shape-defining gates. For excitation frequencies large compared to the inverse dwell time of electrons in the dot (i.e., GHz), we find mesoscopic fluctuations of induced current that are fully asymmetric in the applied perpendicular magnetic field, as predicted by recent theory. Conductance, measured simultaneously, is found to be symmetric in field. In the adiabatic (i.e., MHz) regime, in contrast, the induced current is always symmetric in field, suggesting its origin is mesoscopic rectification.Comment: related papers at http://marcuslab.harvard.ed

Studies of h/e Aharonov-Bohm Photovoltaic Oscillations in Mesoscopic Au Rings

We have investigated a mesoscopic photovoltaic (PV) effect in micron-size Au rings in which a dc voltage Vdc is generated in response to microwave radiation. The effect is due to the lack of inversion symmetry in a disordered system. Aharonov-Bohm PV oscillations with flux period h/e have been observed at low microwave intensities for temperatures ranging from 1.4 to 13 K. For moderate microwave intensities the h/e PV oscillations are completely quenched providing evidence that the microwaves act to randomize the phase of the electrons. Studies of the temperature dependence of Vdc also provide evidence of the dephasing nature of the microwave field. A complete theoretical explanation of the observed behavior seems to require a theory for the PV effect in a ring geometry.Comment: 10 pages (RevTex twocolumn style), 8 figures-2 pages (one postscript file) To be published in Phys. Rev.

Making Good Lawyers

Today, the criticism of law schools has become an industry. Detractors argue that legal education fails to effectively prepare students for the practice of law, that it is too theoretical and detached from the profession, that it dehumanizes and alienates students, too expensive and inapt in helping students develop a sense of professional identity, professional values, and professionalism. In this sea of criticisms it is hard to see the forest from the trees. “There is so much wrong with legal education today,” writes one commentator, “that it is hard to know where to begin.” This article argues that any reform agenda will fall short if it does not start by recognizing the dominant influence of the culture of autonomous self-interest in legal education. Law schools engage in a project of professional formation and instill a very particular brand of professional identity. They educate students to become autonomously self-interested lawyers who see their clients and themselves as pursuing self-interest as atomistic actors. As a result, they understand that their primary role is to serve as neutral partisans who promote the narrow self-interest of clients without regard to the interests of their families, neighbors, colleagues, or communities and to the exclusion of counseling clients on the implications of those interests. They view as marginal their roles as an officer of the legal system and as a public citizen and accordingly place a low priority on traditional professional values, such as the commitment to the public good, that conflict with their primary allegiance to autonomous self-interest. In this work of professional formation, law schools are reflecting the values and commitments of the autonomously self-interested culture that is dominant in the legal profession. Therefore, even if law schools sought to form a professional identity outside of the mold of autonomous self-interest, such a commitment would require much more than curricular reform. It would, at minimum, require the construction of a persuasive alternative understanding of the lawyer’s role. The article seeks to offer such an understanding grounded in a relational perspective on lawyers and clients. Part I offers workable definitions of professionalism and professional identity that enable an informed discussion of the formation of professional identity in and by law schools. Part II explores what and how legal education teaches students showing that both institutionally (at the law school level) and individually (at the law professor level) legal education is proactively engaged in the formation of a professional identity of autonomous self-interest. Part II further explains that its dominance in legal education notwithstanding, autonomous self-interest is but one, often unpersuasive, account of professionalism and professional identity. Part III turns to the competing vision of relationally self-interested professionalism and professional identity and develops an outline for legal education grounded in these conceptions. Because legal education reflects a deep commitment to the dominant culture of autonomous self-interest, it is unlikely that reform proposals that are inconsistent with that culture are likely to succeed in the near future. Yet proposing an alternative account of professional identity that exposes the assumptions of the dominant culture, explains their limitations, and develops a more persuasive understanding is a necessary step toward providing a workable framework for reformers committed to promoting professional values in the long term

Non-linear magnetotransport in microwave-illuminated two-dimensional electron systems

We study magnetoresistivity oscillations in a high-mobility two-dimensional electron system subject to both microwave and dc electric fields. First, we observe that the oscillation amplitude is a periodic function of the inverse magnetic field and is strongly suppressed at microwave frequencies near half-integers of the cyclotron frequency. Second, we obtain a complete set of conditions for the differential resistivity extrema and saddle points. These findings indicate the importance of scattering without microwave absorption and a special role played by microwave-induced scattering events antiparallel to the electric field.Comment: 4 pages, 4 figure

Electron spin resonance investigation of Mn^{2+} ions and their dynamics in manganese doped SrTiO_3

Using electron spin resonance, lattice position and dynamic properties of Mn2+ ions were studied in 0.5 and 2 % manganese doped SrTiO3 ceramics prepared by conventional mixed oxide method. The measurements showed that Mn2+ ions substitute preferably up to 97 % for Sr if the ceramics is prepared with a deficit of Sr ions. Motional narrowing of the Mn2+ ESR spectrum was observed when temperature increases from 120 K to 240-250 K that was explained as a manifestation of off-center position of this ion at the Sr site. From the analysis of the ESR spectra the activation energy Ea = 86 mV and frequency factor 1/?0 ? (2-10)x10^(-14) 1/s for jumping of the impurity between symmetrical off-center positions were determined. Both values are in agreement with those derived previously from dielectric relaxation. This proves the origin of dielectric anomalies in SrTiO3:Mn as those produced by the reorientation dynamics of Mn2+ dipoles.Comment: 16 pages, 6 figure