Probing the SU(N) Fermi-Hubbard model with ytterbium atoms in an optical lattice

This thesis reports on the experimental realization of the 3D SU(N) Fermi-Hubbard model and the direct probing of the equation of state with an ultracold quantum gas of fermionic ytterbium in an optical lattice. Ultracold atoms in optical lattices constitute a flexible and highly tunable system to investigate Hamiltonians of condensed matter physics such as the Hubbard model. In particular, ytterbium atoms are ideal candidates for the realization of the Fermi-Hubbard model with SU(N)-symmetry due to a high decoupling of the nuclear spin from the electronic configuration. As a consequence of this enlarged symmetry, thermodynamic properties of the atomic sample depend on N, the number of spin components in the quantum gas, and novel, exotic phases are predicted to emerge at low temperatures. By locally probing a quantum gas of 173Yb in a 3D optical lattice, we determine the equation of state of the SU(6) and SU(3) Fermi-Hubbard model. The measurement of the equation of state allows us to obtain direct, model-independent access to the thermodynamic quantities of the lattice gas. In this way, we can characterize the crossover from a Fermi liquid to an SU(N) Mott insulator when tuning the interaction strength, and can probe the compressibility of the quantum gas in different interaction regimes. Moreover, we find a low specific entropy of the SU(6) gas below that of uncorrelated spins, indicating the presence of partial spin correlations in the atomic sample. The ability to access the equation of state of such high spin systems, as well as the low obtained entropy, represent an important step towards the realization of SU(N) spin Hamiltonians and the characterization of novel SU(N) phases.Diese Doktorarbeit beschreibt die experimentelle Umsetzung des 3D SU(N) Fermi-Hubbard Modells und die direkte Messung der Zustandsgleichung mit Hilfe eines ultrakalten Quantengases von fermionischen Ytterbium-Atomen in einem optischen Gitter. Ultrakalte, neutrale Atome in optischen Gittern stellen ein gut kontrollierbares und hochflexibles System dar um Modelle aus der Festkörperphysik, wie z.B. das Hubbard Modell, zu untersuchen. Insbesondere erlauben Ytterbium-Atome, diese Modelle mit SU(N) Symmetrie zu realisieren, da bei ihnen der Kernspin nahezu vollständig von der elektronischen Konfiguration der Atome entkoppelt ist. Als Folge dieser erweiterten Symmetrie hängen die thermodynamischen Größen von N – der Anzahl der Spinkomponenten im Quantengas – ab, und man erwartet neuartige Phasenzustände dieser Systeme bei niedrigen Temperaturen. Durch Messen der lokalen Eigenschaften eines 173Yb Quantengases, erhalten wir die Zustandsgleichung des SU(6) und SU(3) Fermi-Hubbard Modells. Die Zustandsgleichung erlaubt es uns, direkten, modellunabhängigen Zugang zu den thermodynamischen Größen des Gases im Gitter zu erlangen. Hiermit ist es möglich, durch Ändern der Wechselwirkungsstärke den Übergang von einer Fermi-Flüssigkeit zu einem SU(N) Mott-Isolator zu beobachten, sowie die Kompressibilität des Gases für unterschiedlich starke Wechselwirkungen zu ermitteln. In dem Experiment beobachten wir eine niedrige spezifische Entropie des SU(6) Gases, niedriger als die von unkorrelierten Spins, was auf partielle Spinkorrelationen im Quantengas hinweist. Die Möglichkeit, die Zustandsgleichung solcher Systeme mit hohem Spin direkt zu bestimmen, sowie die niedrige Entropie die erzielt wurde, stellen einen wichtigen Schritt für die Realisierung von SU(N) Spin-Hamiltonoperatoren dar, sowie für die Charakterisierung von neuartigen SU(N) Phasenzuständen

Probing the SU(N) Fermi-Hubbard model with ytterbium atoms in an optical lattice

This thesis reports on the experimental realization of the 3D SU(N) Fermi-Hubbard model and the direct probing of the equation of state with an ultracold quantum gas of fermionic ytterbium in an optical lattice. Ultracold atoms in optical lattices constitute a flexible and highly tunable system to investigate Hamiltonians of condensed matter physics such as the Hubbard model. In particular, ytterbium atoms are ideal candidates for the realization of the Fermi-Hubbard model with SU(N)-symmetry due to a high decoupling of the nuclear spin from the electronic configuration. As a consequence of this enlarged symmetry, thermodynamic properties of the atomic sample depend on N, the number of spin components in the quantum gas, and novel, exotic phases are predicted to emerge at low temperatures. By locally probing a quantum gas of 173Yb in a 3D optical lattice, we determine the equation of state of the SU(6) and SU(3) Fermi-Hubbard model. The measurement of the equation of state allows us to obtain direct, model-independent access to the thermodynamic quantities of the lattice gas. In this way, we can characterize the crossover from a Fermi liquid to an SU(N) Mott insulator when tuning the interaction strength, and can probe the compressibility of the quantum gas in different interaction regimes. Moreover, we find a low specific entropy of the SU(6) gas below that of uncorrelated spins, indicating the presence of partial spin correlations in the atomic sample. The ability to access the equation of state of such high spin systems, as well as the low obtained entropy, represent an important step towards the realization of SU(N) spin Hamiltonians and the characterization of novel SU(N) phases.Diese Doktorarbeit beschreibt die experimentelle Umsetzung des 3D SU(N) Fermi-Hubbard Modells und die direkte Messung der Zustandsgleichung mit Hilfe eines ultrakalten Quantengases von fermionischen Ytterbium-Atomen in einem optischen Gitter. Ultrakalte, neutrale Atome in optischen Gittern stellen ein gut kontrollierbares und hochflexibles System dar um Modelle aus der Festkörperphysik, wie z.B. das Hubbard Modell, zu untersuchen. Insbesondere erlauben Ytterbium-Atome, diese Modelle mit SU(N) Symmetrie zu realisieren, da bei ihnen der Kernspin nahezu vollständig von der elektronischen Konfiguration der Atome entkoppelt ist. Als Folge dieser erweiterten Symmetrie hängen die thermodynamischen Größen von N – der Anzahl der Spinkomponenten im Quantengas – ab, und man erwartet neuartige Phasenzustände dieser Systeme bei niedrigen Temperaturen. Durch Messen der lokalen Eigenschaften eines 173Yb Quantengases, erhalten wir die Zustandsgleichung des SU(6) und SU(3) Fermi-Hubbard Modells. Die Zustandsgleichung erlaubt es uns, direkten, modellunabhängigen Zugang zu den thermodynamischen Größen des Gases im Gitter zu erlangen. Hiermit ist es möglich, durch Ändern der Wechselwirkungsstärke den Übergang von einer Fermi-Flüssigkeit zu einem SU(N) Mott-Isolator zu beobachten, sowie die Kompressibilität des Gases für unterschiedlich starke Wechselwirkungen zu ermitteln. In dem Experiment beobachten wir eine niedrige spezifische Entropie des SU(6) Gases, niedriger als die von unkorrelierten Spins, was auf partielle Spinkorrelationen im Quantengas hinweist. Die Möglichkeit, die Zustandsgleichung solcher Systeme mit hohem Spin direkt zu bestimmen, sowie die niedrige Entropie die erzielt wurde, stellen einen wichtigen Schritt für die Realisierung von SU(N) Spin-Hamiltonoperatoren dar, sowie für die Charakterisierung von neuartigen SU(N) Phasenzuständen

Direct probing of the Mott crossover in the SU(NN) Fermi-Hubbard model

The Fermi-Hubbard model (FHM) is a cornerstone of modern condensed matter theory. Developed for interacting electrons in solids, which typically exhibit SU($2$) symmetry, it describes a wide range of phenomena, such as metal to insulator transitions and magnetic order. Its generalized SU($N$)-symmetric form, originally applied to multi-orbital materials such as transition-metal oxides, has recently attracted much interest owing to the availability of ultracold SU($N$)-symmetric atomic gases. Here we report on a detailed experimental investigation of the SU($N$)-symmetric FHM using local probing of an atomic gas of ytterbium in an optical lattice to determine the equation of state through different interaction regimes. We prepare a low-temperature SU($N$)-symmetric Mott insulator and characterize the Mott crossover, representing important steps towards probing predicted novel SU($N$)-magnetic phases

Conversion of self-assembled monolayers into nanocrystalline graphene: Structure and electric transport

Graphene-based materials have been suggested for applications ranging from nanoelectronics to nanobiotechnology. However, the realization of graphene-based technologies will require large quantities of free-standing two-dimensional (2D) carbon materials with tuneable physical and chemical properties. Bottom-up approaches via molecular self-assembly have great potential to fulfil this demand. Here, we report on the fabrication and characterization of graphene made by electron-radiation induced cross-linking of aromatic self-assembled monolayers (SAMs) and their subsequent annealing. In this process, the SAM is converted into a nanocrystalline graphene sheet with well defined thickness and arbitrary dimensions. Electric transport data demonstrate that this transformation is accompanied by an insulator to metal transition that can be utilized to control electrical properties such as conductivity, electron mobility and ambipolar electric field effect of the fabricated graphene sheets. The suggested route opens broad prospects towards the engineering of free-standing 2D carbon materials with tuneable properties on various solid substrates and on holey substrates as suspended membranes.Comment: 30 pages, 5 figure

Mycoremediation of petroleum contaminated soils: progress, prospects and perspectives

Mycoremediation, an aspect of bioremediation, has been investigated for some decades. However, there seems to be little progress on its commercial application to petroleum-contaminated soils despite some promising outcomes. In this review, mycoremediation is examined to identify development, limitations and perspectives for its optimal utilization on petroleum-contaminated soils. Mycoremediation agents and substrates that have been used for the treatment of petroleum contaminated soils have been identified, application methods discussed, recent advances highlighted and limitations for its applications accentuated. Possible solutions to the challenges in applying mycoremediation to petroleum-contaminated soils have also been discussed. From this review, we conclude that for optimal utilization of mycoremediation of petroleum-contaminated soils, ideal environmental, edaphic and climatic factors of a typical contaminated site must be incorporated into the approach from first principles. Development of application procedures that can easily translate laboratory results to field applications is also required

Shear bond strength of different retainer wires and bonding adhesives in consideration of the pretreatment process

Introduction: We aimed to compare the shear bond strength (SBS) of three different retainer wires and three different bonding adhesives in consideration of the pretreatment process of enamel surface sandblasting. Methods: 400 extracted bovine incisors were divided into 10 groups of 20 paired specimens each. 10 specimens of each group were pretreated by enamel sandblasting. The retainer wires Bond-A-Braid™, GAC-Wildcat®-Twistflex and everStick®ORTHO were bonded to the teeth with the adhesives Transbond™-LR, Tetric-EvoFlow™ and Stick®FLOW and then debonded measuring the SBS. Results: While sandblasting generally increased SBS for all tested combinations, the retainer wires bonded with Transbond™-LR showed the highest SBS both with and without prior sandblasting. Significantly lower SBS were found for Tetric-EvoFlow™ that were comparable to those for everStick®ORTHO. Conclusions: Pretreatment of enamel surfaces by sandblasting increased the SBS of all retainer-wires. Transbond™-LR showed the best results compared to Tetric-EvoFlow™ and everStick®ORTHO, while all combinations used provided sufficient bonding strengths for clinical use.<br

The kinetic behavior of insulin fibrillation is determined by heterogeneous nucleation pathways

When subjected to acidic conditions and high temperature, insulin is known to produce fibrils that display the common properties of disease amyloids. Thus, clarifying the mechanisms of insulin fibrillation can help the general understanding of amyloidal aggregation. Insulin fibrillation exhibits a very sharp time dependence, with a pronounced lag phase and subsequent explosive growth of amyloidal aggregates. Here we show that the initial stages of this process can be well described by exponential growth of the fibrillated proteins. This indicates that the process is mainly controlled by a secondary nucleation pathway

Singlet‐Oxygen Generation by Peroxidases and Peroxygenases for Chemoenzymatic Synthesis

Singlet oxygen is a reactive oxygen species undesired in living cells but a rare and valuable reagent in chemical synthesis. We present a fluorescence spectroscopic analysis of the singlet-oxygen formation activity of commercial peroxidases and novel peroxygenases. Singlet-oxygen sensor green (SOSG) is used as fluorogenic singlet oxygen trap. Establishing a kinetic model for the reaction cascade to the fluorescent SOSG endoperoxide permits a kinetic analysis of enzymatic singlet-oxygen formation. All peroxidases and peroxygenases show singlet-oxygen formation. No singlet oxygen activity could be found for any catalase under investigation. Substrate inhibition is observed for all reactive enzymes. The commercial dye-decolorizing peroxidase industrially used for dairy bleaching shows the highest singlet-oxygen activity and the lowest inhibition. This enzyme was immobilized on a textile carrier and successfully applied for a chemical synthesis. Here, ascaridole was synthesized via enzymatically produced singlet oxygen. © 2020 Wiley-VCH Gmb