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Institute of Physics Belgrade
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Stability of quantum degenerate Fermi gases of tilted polar molecules
Veljić, Vladimir; Pelster, Axel; Balaž, Antun
A recent experimental realization of a quantum degenerate gas of K-40 Rb-87 molecules opens up prospects of exploring strong dipolar Fermi gases and many-body phenomena arising in that regime. Here, we derive a mean-field variational approach based on the Wigner function for the description of the ground-state properties of such systems. We show that the stability of dipolar fermions in a general harmonic trap is universal as it only depends on the trap aspect ratios and the dipoles' orientation. We calculate the species-independent stability diagram and the deformation of the Fermi surface (FS) for polarized molecules, whose electric dipoles are oriented along a preferential direction. Compared to atomic magnetic species, the stability of a molecular electric system turns out to strongly depend on its geometry and the FS deformation significantly increases.
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Dva elementa pojma alternativnog investicionog fonda u srpskom pravu
Nikolić, Dušan
Legal regulations related to investment funds in the Republic of Serbia were reformed in 2019. In order to harmonize Serbian law with the European Union directives two new laws that regulate investment funds were enacted – one regulating open investment funds and the other alternative investment funds. This paper analyzes the current legal notion of the alternative investment fund, but the emphasis is placed on the two key elements of the said notion in a wider sense – the notion of the investment fund and the notion of the investor. The concepts are examined in the light of the above mentioned legislation, and the specific legal implications arising from them are described. In conclusion, the author proposes a lege ferenda solution with the ultimate objective of developing the market for alternative investment funds in the Republic of Serbia.
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Fragmentation in trader preferences among multiple markets: market coexistence versus single market dominance
Nicole, Robin; Alorić, Aleksandra; Sollich, Peter
Technological advancement has led to an increase in the number and type of trading venues and a diversification of goods traded. These changes have re-emphasized the importance of understanding the effects of market competition: does proliferation of trading venues and increased competition lead to dominance of a single market or coexistence of multiple markets? In this paper, we address these questions in a stylized model of zero-intelligence traders who make repeated decisions at which of three available markets to trade. We analyse the model numerically and analytically and find that the traders’ decision parameters—memory length and how strongly decisions are based on past success—make the key difference between consolidated and fragmented steady states of the population of traders. All three markets coexist with equal shares of traders only when either learning is too weak and traders choose randomly, or when markets are identical. In the latter case, the population of traders fragments across the markets. With different markets, we note that market dominance is the more typical scenario. Overall we show that, contrary to previous research emphasizing the role of traders’ heterogeneity, market coexistence can emerge simply as a consequence of co-adaptation of an initially homogeneous population of traders.
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Calculations of electron mobility in II-VI semiconductors
Vukmirović, Nenad
Electron mobility in the conduction band of II-VI semiconductors ZnSe, CdTe, ZnTe, and CdSe was studied. Temperature dependence of mobility was calculated using the methodology based on density functional theory calculations of the electronic states, phonon modes, and electron-phonon coupling constants, along with Fourier-Wannier procedure for interpolation to a dense grid in momentum space. The mobilities obtained from calculations within generalized gradient approximation of density functional theory overestimate the experimental mobility several times. The calculation that used improved electronic band structure and high-frequency dielectric constants obtained using a hybrid functional lead to a very good agreement with experimental mobilities for most of the materials studied. It was also found that the Frohlich model provides a reasonably good estimate of mobilities around room temperature where longitudinal optical phonons provide the dominant scattering mechanism, as expected for these direct gap materials where all relevant electronic states are in the vicinity of the Gamma point. The results indicate as well that the long-ranged part of electron-phonon interaction fully determines the electron mobility in the materials studied. For this reason, the approach where only this part of electron-phonon interaction is calculated using the relevant analytical formulas allows for accurate calculation of mobility without the use of the interpolation procedure for electron-phonon coupling constants.
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Microscopic derivation of Dirac composite fermion theory: Aspects of noncommutativity and pairing instabilities
Gočanin, Dragoljub; Predin, Sonja; Dimitrijević Ćirić, Marija; Radovanović, Voja; Milovanović, Milica
Building on previous work [N. Read, Phys. Rev. B 58, 16262 (1998); Z. Dong and T. Senthil, Phys. Rev. B 102, 205126 (2020)] on the system of bosons at filling factor nu = 1, we derive the Dirac composite fermion theory for a half-filled Landau level from first principles and apply the Hartree-Fock approach in a preferred representation. On the basis of the microscopic formulation, in the long-wavelength limit, we propose a noncommutative field-theoretical description, which in a commutative limit reproduces the Son's theory, with additional terms that may be expected on physical grounds. The microscopic representation of the problem is also used to discuss pairing instabilities of composite fermions. We find that a presence of a particle-hole symmetry breaking leads to a weak (BCS) coupling p-wave pairing in the lowest Landau level, and strong coupling p-wave pairing in the second Landau level that occurs in a band with nearly flat dispersion, a third power function of momentum.