Browsing by Author "Milovanović, Milica"
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- ItemDipole representation of half-filled Landau levelPredin, Sonja; Knežević, Ana; Milovanović, MilicaWe introduce a variant of a dipole representation for composite fermions in a half-filled Landau level, taking into account the symmetry under an exchange of particles and holes. This is implemented by a special constraint on a composite fermion and a composite hole degree of freedom (of an enlarged space), which makes the resulting composite particle (dipole) a symmetric object. We study an effective Hamiltonian that commutes with the constraint on the physical space and fulfills the requirement for boost invariance on the Fermi level. The calculated Fermi liquid parameter F2 is in good agreement with numerical investigations in Phys. Rev. Lett. 121, 147601 (2018)0031-900710.1103/PhysRevLett.121.147601.
- ItemExcitonic physics in a Dirac quantum dotRaca, Vigan; Milovanović, MilicaWe present a description of vacuum polarization in a circular Dirac quantum dot in two spatial dimensions assuming α - the relative strength of the Coulomb interaction small enough to render an approximation with a single electron (hole) lowest energy level relevant. Applying this approximation, we find that for αc≈1.05 the lowest level is half filled irrespective of the number of flavors that are present. The ground state can be represented as a superposition of particular (even number) excitonic states which constitute an excitonic cloud that evolves in a crossover manner. The ground state is degenerate with an intervalley excitonic state at αc≈1.05, a critical strength, that in our approximation marks a point with single electron and exciton resonances.
- ItemMicroscopic derivation of Dirac composite fermion theory: Aspects of noncommutativity and pairing instabilitiesGočanin, Dragoljub; Predin, Sonja; Dimitrijević Ćirić, Marija; Radovanović, Voja; Milovanović, MilicaBuilding 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.
- ItemMicroscopic derivation of Dirac composite fermion theory: Aspects of noncommutativity and pairing instabilitiesGočanin, Dragoljub; Predin, Sonja; Dimitrijević Ćirić, Marija; Radovanović, Voja; Milovanović, MilicaBuilding on previous work [N. Read, Phys. Rev. B58, 16262 (1998)10.1103/PhysRevB.58.16262; Z. Dong and T. Senthil, Phys. Rev. B102, 205126 (2020)10.1103/PhysRevB.102.205126] on the system of bosons at filling factor , 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 -wave pairing in the lowest Landau level, and strong coupling -wave pairing in the second Landau level that occurs in a band with nearly flat dispersion, a third power function of momentum.
- ItemModel interactions for Pfaffian paired states based on Chern-Simons field theory descriptionĐurđević, Stevan; Milovanović, MilicaOn the basis of a Chern-Simons field-theoretical description we propose a simple method for the derivation of model interactions for Pfaffian paired states. We verify the method in the case of the Pfaffian (i.e., Moore-Read) state and derive a general form of the model interaction in the case of the particle-hole (PH) Pfaffian. More than one Landau level is needed to establish the correlations of the PH Pfaffian, and we present the values of relevant three-body pseudopotentials for two Landau levels.
- ItemPaired states at 5/2: Particle-hole Pfaffian and particle-hole symmetry breakingAntonić, Luka; Vučičević, Jakša; Milovanović, MilicaWe study Cooper pairing in the Dirac composite fermion (CF) system. The presence of the mass term in the Dirac CF description (which may simulate Landau level mixing), i.e., breaking of particle-hole (PH) symmetry in this system, is a necessary condition for the existence of a PH Pfaffian-like topological state. In the scope of the random-phase approximation (RPA) and hydrodynamic approach, we find some signatures of pairing at finite frequencies. Motivated by this insight, we extend our analysis to the case of a different but still Dirac quasiparticle (CF) representation, appropriate in the presence of a mass term, and discuss the likelihood of PH Pfaffian and Pfaffian pairings in general. On the basis of gauge field effects, we find for a small Dirac mass, an anti-Pfaffian or Pfaffian instability depending on the sign of mass, while for large mass (Landau level mixing), irrespective of its sign, we find a PH Pfaffian-like instability.
- ItemQuantum Hall bilayer in dipole representationPredin, Sonja; Milovanović, MilicaThe Quantum Hall Bilayers (QHB) at filling factor ν=1 represents a competition between Bose-Einstein condensation (BEC) at small distances between layers and fermionic condensation, whose influence grows with distance and results in two separate Fermi liquid states for the underlying quasiparticles at very large (or infinite) distances. The question that can be raised is whether, at intermediate distances between layers, a distinct phase exists or if a singular transition occurs, with the possibility that this happens at infinite distances. Here, using a dipole representation for fermionic quasiparticles, we find support for the latter scenario: Within a large and relevant range of distances, BEC condensation, identified as Cooper s-wave pairing of dipole quasiparticles, prevails over both Cooper p-wave pairing and s-wave excitonic pairing of the same quasiparticles.