Browsing by Author "Predin, Sonja"

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    Dipole representation of half-filled Landau level
    Predin, Sonja; Knežević, Ana; Milovanović, Milica
    We 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.
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    Entanglement spectrum of the degenerative ground state of Heisenberg ladders in a time-dependent magnetic field
    Predin, Sonja
    We investigate the relationship between the entanglement and subsystem Hamiltonians in the perturbative regime of strong coupling between subsystems. One of the two conditions that guarantees the proportionality between these Hamiltonians obtained by using the nondegenerate perturbation theory within the first order is that the unperturbed ground state has a trivial entanglement Hamiltonian. Furthermore, we study the entanglement Hamiltonian of the Heisenberg ladders in a time-dependent magnetic field using the degenerate perturbation theory, where couplings between legs are considered as a perturbation. In this case, when the ground state is twofold degenerate, and the entanglement Hamiltonian is proportional to the Hamiltonian of a chain within first-order perturbation theory, even then also the unperturbed ground state has a nontrivial entanglement spectrum.
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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.
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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. 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.
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    Quantum Hall bilayer in dipole representation
    Predin, Sonja; Milovanović, Milica
    The 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.