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Confined p-band Bose-Einstein condensates
Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
Stockholm University, Faculty of Science, Department of Physics. University of Cologne, Germany.
2012 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, no 3, 033638Article in journal (Refereed) Published
Abstract [en]

We study bosonic atoms on the p band of a two-dimensional optical square lattice in the presence of a confining trapping potential. Using a mean-field approach, we show how the anisotropic tunneling for p-band particles affects the cloud of condensed atoms by characterizing the ground-state density and the coherence properties of the atomic states both between sites and atomic flavors. In contrast to the usual results based on the local-density approximation, the atomic density can become anisotropic. This anisotropic effect is especially pronounced in the limit of weak atom-atom interactions and of weak lattice amplitudes, i.e., when the properties of the ground state are mainly driven by the kinetic energies. We also investigate how the trap influences known properties of the nontrapped case. In particular, we focus on the behavior of the antiferromagnetic vortex-antivortex order, which for the confined system is shown to disappear at the edges of the condensed cloud.

Place, publisher, year, edition, pages
2012. Vol. 85, no 3, 033638
National Category
Physical Sciences
Research subject
Theoretical Physics
Identifiers
URN: urn:nbn:se:su:diva-76124DOI: 10.1103/PhysRevA.85.033638ISI: 000301970900008OAI: oai:DiVA.org:su-76124DiVA: diva2:526174
Note

3

Available from: 2012-05-10 Created: 2012-05-09 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Multi-species systems in optical lattices: From orbital physics in excited bands to effects of disorder
Open this publication in new window or tab >>Multi-species systems in optical lattices: From orbital physics in excited bands to effects of disorder
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis we explore different aspects of the physics of multi-species atomic systems in optical lattices. In the first part we will study cold gases in the first and second excited bands of optical lattices - the p and d bands. The multi-species character of the physics in excited bands lies in the existence of an additional orbital degree of freedom, which gives rise to qualitative properties that are different from what is known for the systems in the ground band. We will introduce the orbital degree of freedom in the context of optical lattices and we will study the many-body systems both in the weakly interacting and in the strongly correlated regimes.

We start with the properties of single particles in excited bands, from where we investigate the weakly interacting regime of the many-body p- and d-orbital systems in Chapters 2 and 3. This presents part of the theoretical framework to be used throughout this thesis, and covers part of the content of Paper I and of Preprint II. In Chapter 4, we study Bose-Einstein condensates in the p band, confined by a harmonic trap. This includes the finite temperature study of the ideal gas and the characterization of the superfluid phase of the interacting system at zero temperature for both symmetric and asymmetric lattices. This material is the content of Paper I.

We continue with the strongly correlated regime in Chapter 5, where we investigate the Mott insulator phase of various systems in the p and d bands in terms of effective spin models. This covers the results of Paper II, of Preprint I and parts of Preprint II. More specifically, we show that the Mott phase with a unit filling of bosons in the p and in the d bands can be mapped, in two dimensions, to different types of XYZ Heisenberg models. In addition, we show that the effective Hamiltonian of the Mott phase with a unit filling in the p band of three-dimensional lattices has degrees of freedom that are the generators of the SU(3) group. Here we discuss both the bosonic and fermionic cases.

In the second part, consisting of Chapter 6, we will change gears and study effects of disorder in generic systems of two atomic species. This is the content of Preprint III, where we consider different systems of non-interacting but randomly coupled Bose-Einstein condensates in 2D, regardless of an orbital degree of freedom. We characterize spectral properties and discuss the occurrence of Anderson localization in different cases, belonging to the different chiral orthogonal, chiral unitary, Wigner-Dyson orthogonal and Wigner-Dyson unitary symmetry classes. We show that the different properties of localization in the low-lying excited states of the models in the chiral and the Wigner-Dyson classes can be understood in terms of an effective model, and we characterize the excitations in these systems. Furthermore, we discuss the experimental relevance of the Hamiltonians presented here in connection to the Anderson and the random-flux models.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2015. 117 p.
National Category
Condensed Matter Physics
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-116436 (URN)978-91-7649-188-1 (ISBN)
Public defence
2015-05-22, sal FB52, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Accepted. Paper 5: Submitted.

Available from: 2015-04-29 Created: 2015-04-20 Last updated: 2015-06-16Bibliographically approved

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