arXiv subjects

H. Fehrmann

Publications and source records attributed to H. Fehrmann.

24 records · Page 2Linked to original sources

arXiv2005

Quantum gases in trimerized kagomé lattices

We study low temperature properties of atomic gases in trimerized optical kagomé lattices. The laser arrangements that can be used to create these lattices are briefly described. We also present explicit results for the coupling constants of the generalized Hubbard models that can be realized in such lattices. In the case of a single component Bose gas the existence of a Mott insulator phase with fractional numbers of particles per trimer is verified in a mean field approach. The main emphasis of the paper is on an atomic spinless interacting Fermi gas in the trimerized kagomé lattice with two fermions per site. This system is shown to be described by a quantum spin 1/2 model on the triangular lattice with couplings that depend on the bond directions. We investigate this model by means of exact diagonalization. Our key finding is that the system exhibits non-standard properties of a quantum spin-liquid crystal: it combines planar antiferromagnetic order in the ground state with an exceptionally large number of low energy excitations. The possibilities of experimental verification of our theoretical results are critically discussed.

cond-mat.other↗

arXiv2005

Atomic Fermi gas in the trimerized Kagomé lattice at the filling 2/3

We study low temperature properties of an atomic spinless interacting Fermi gas in the trimerized Kagomé lattice for the case of two fermions per trimer. The system is described by a quantum spin 1/2 model on the triangular lattice with couplings depending on bonds directions. Using exact diagonalizations we show that the system exhibits non-standard properties of a {\it quantum spin-liquid crystal}, combining a planar antiferromagnetic order with an exceptionally large number of low energy excitations.

cond-mat.other↗

arXiv2004

Mean-field theory of Bose-Fermi mixtures in optical lattices

We determine the phase diagram of a mixture of ultracold bosons and polarized fermions placed in an optical lattice using mean field theory. In the limit of strong atom-atom interactions, there exist quantum phases that involve pairing of fermions with one or more bosons, or bosonic holes, respectively. We obtain the analytic form of the phase boundaries separating these composite fermion phases from the bosonic superfluid coexisting with Fermi liquid. We compare the results with numerical simulations and discuss their validity and relevance for current experiments.

cond-mat.other↗

arXiv2004

Atomic Bose-Fermi mixtures in an optical lattice

A mixture of ultracold bosons and fermions placed in an optical lattice constitutes a novel kind of quantum gas, and leads to phenomena, which so far have been discussed neither in atomic physics, nor in condensed matter physics. We discuss the phase diagram at low temperatures, and in the limit of strong atom-atom interactions, and predict the existence of quantum phases that involve pairing of fermions with one or more bosons, or, respectively, bosonic holes. The resulting composite fermions may form, depending on the system parameters, a normal Fermi liquid, a density wave, a superfluid liquid, or an insulator with fermionic domains. We discuss the feasibility for observing such phases in current experiments.

cond-mat.other↗

arXiv2004

Atomic quantum gases in Kagomé lattices

We demonstrate the possibility of creating and controlling an ideal and \textit{trimerized} optical Kagomé lattice, and study the low temperature physics of various atomic gases in such lattices. In the trimerized Kagomé lattice, a Bose gas exhibits a Mott transition with fractional filling factors, whereas a spinless interacting Fermi gas at 2/3 filling behaves as a quantum magnet on a triangular lattice. Finally, a Fermi-Fermi mixture at half filling for both components represents a frustrated quantum antiferromagnet with a resonating-valence-bond ground state and quantum spin liquid behavior dominated by continuous spectrum of singlet and triplet excitations. We discuss the method of preparing and observing such quantum spin liquid employing molecular Bose condensates.

cond-mat.other↗

arXiv2001

A Hartree-Fock Study of Charge Redistribution in a 2D Mesoscopic Structure

In this paper, we investigate the ground state of two-dimensional disordered cylinders which contain spinless, interacting electrons using the Hartree-Fock approximation. Calculations of the deviation of the polarization from uniformity reveal a tendency of the charge to rearrange towards the ends of the system. The presence of disorder results in fluctuations of the deviation around its mean value, which are more pronounced when the disorder strength is of the order of the interaction between the electrons.

cond-mat↗