arXiv subjects

K. Niemela

Publications and source records attributed to K. Niemela.

3 recordsLinked to original sources

arXiv2003

Broken Symmetry in Density-Functional Theory: Analysis and Cure

We present a detailed analysis of the broken-symmetry mean-field solutions using a four-electron rectangular quantum dot as a model system. Comparisons of the density-functional theory predictions with the exact ones show that the symmetry breaking results from the single-configuration wave function used in the mean-field approach. As a general cure we present a scheme that systematically incorporates several configurations into the density-functional theory and restores the symmetry. This cure is easily applicable to any density-functional approach.

cond-mat↗

arXiv2000

Theory of the Half-Polarized Quantum Hall States

We report a theoretical analysis of the half-polarized quantum Hall states observed in a recent experiment. Our numerical results indicate that the ground state energy of the quantum Hall $ν= 2/3$ and $ν= 2/5$ states versus spin polarization has a downward cusp at half the maximal spin polarization. We map the two-component fermion system onto a system of excitons and describe the ground state as a liquid state of excitons with non-zero values of exciton angular momentum.

cond-mat.mes-hall↗

arXiv2000

Comment on ``Composite Fermion Hofstadter Problem: Partially Polarized Density Wave States in the $ν=2/5$ ...''

In a recent paper [Phys.Rev.Lett. 82, 3665 (1999)], magnetic field driven spin transitions in fractional quantum Hall (FQH) states were reported, and in particular, at filling factors 2/3 and 2/5, weak features were observed at half polarization. This would imply that the ground state energy is non-monotonic at half polarization. It was proposed in Ref.[Phys. Rev. Lett. 84, 350 (2000)] that the system is then a charge density wave (CDW) state of composite fermions with a subband gap that could explain the observed plateaus at half polarization. Similar CDW state is also expected at filling factor 2/3. Here we show that the proposed CDW state is not the half polirized ground state at these two filling factors.

cond-mat.mes-hall↗