Magnetic phases of two-component ultracold bosons in an optical lattice

We investigate spin-order of ultracold bosons in an optical lattice by means of Dynamical Mean-Field Theory. A rich phase diagram with anisotropic magnetic order is found, both for the ground state and at finite temperatures. Within the Mott insulator, a ferromagnetic to antiferromagnetic transition can be tuned using a spin-dependent optical lattice. In addition we find a supersolid phase, in which superfluidity coexists with antiferromagnetic spin order. We present detailed phase diagrams at finite temperature for the experimentally realized heteronuclear 87Rb - 41K mixture in a three-dimensional optical lattice.Comment: 6 pages, 4 figures, revised and published versio

Short Subjects: Sunshine State Showpieces: Alligator-Skin Bindings in the Florida Archives

Archivists are primarily concerned with the informational value of records. Sometimes, however, that emphasis on information is so great that other properties, such as intrinsic value, are ignored. Materials have intrinsic value if they possess qualities that make their original form the only archivally acceptable one for preservation. These qualities may be physical or intellectual; that is, they may relate to the material object itself or to the information contained in it. Books, for example, can have intrinsic value because of several unique or curious features: paper, imprints, watermarks, illustrations, or bindings

Floquet analysis of excitations in materials

Controlled excitation of materials can transiently induce changed or novel properties with many fundamental and technological implications. Especially, the concept of Floquet engineering and the manipulation of the electronic structure via dressing with external lasers have attracted some recent interest. Here we review the progress made in defining Floquet material properties and give a special focus on their signatures in experimental observables as well as considering recent experiments realizing Floquet phases in solid state materials. We discuss how a wide range of experiments with non-equilibrium electronic structure can be viewed by employing Floquet theory as an analysis tool providing a different view of excitations in solids

A first-principles time-dependent density functional theory framework for spin and time-resolved angular-resolved photoelectron spectroscopy in periodic systems

We present a novel theoretical approach to simulate spin, time, and angular-resolved photoelectron spectroscopy (ARPES) from first-principles that is applicable to surfaces, thin films, few layer systems, and low-dimensional nanostructures. The method is based on a general formulation in the framework of time-dependent density functional theory (TDDFT) to describe the real time-evolution of electrons escaping from a surface under the effect of any external (arbitrary) laser field. By extending the so-called t-SURFF method to periodic systems one can calculate the final photoelectron spectrum by collecting the flux of the ionization current trough an analyzing surface. The resulting approach, that we named t-SURFFP, allows us to describe a wide range of irradiation conditions without any assumption on the dynamics of the ionization process allowing for pump-probe simulations on an equal footing. To illustrate the wide scope of applicability of the method we present applications to graphene, monolayer, and bilayer WSe2, and hexagonal BN (hBN) under different laser configurations

Phonon Driven Floquet Matter

The effect of electron-phonon coupling in materials can be interpreted as a dressing of the electronic structure by the lattice vibration, leading to vibrational replicas and hybridization of electronic states. In solids, a resonantly excited coherent phonon leads to a periodic oscillation of the atomic lattice in a crystal structure bringing the material into a nonequilibrium electronic configuration. Periodically oscillating quantum systems can be understood in terms of Floquet theory, which has a long tradition in the study of semiclassical light-matter interaction. Here, we show that the concepts of Floquet analysis can be applied to coherent lattice vibrations. This coupling leads to phonon-dressed quasi-particles imprinting specific signatures in the spectrum of the electronic structure. Such dressed electronic states can be detected by time- and angular-resolved photoelectron spectroscopy (ARPES) manifesting as sidebands to the equilibrium band structure. Taking graphene as a paradigmatic material with strong electron-phonon interaction and nontrivial topology, we show how the phonon-dressed states display an intricate sideband structure revealing the electron-phonon coupling at the Brillouin zone center and topological ordering of the Dirac bands. We demonstrate that if time-reversal symmetry is broken by the coherent lattice perturbations a topological phase transition can be induced. This work establishes that the recently demonstrated concept of light-induced nonequilibrium Floquet phases can also be applied when using coherent phonon modes for the dynamical control of material properties

Monitoring Electron-Photon Dressing in WSe2

Optical pumping of solids creates a nonequilibrium electronic structure where electrons and photons combine to form quasiparticles of dressed electronic states. The resulting shift of electronic levels is known as the optical Stark effect, visible as a red shift in the optical spectrum. Here we show that in a pump-probe setup we can uniquely define a nonequilibrium quasiparticle bandstructure that can be directly measurable with photoelectron spectroscopy. The dynamical photon-dressing (and undressing) of the many-body electronic states can be monitored by pump-probe time and angular-resolved photoelectron spectroscopy (tr-ARPES) as the photon-dressed bandstructure evolves in time depending on the pump-probe pulse overlap. The computed tr-ARPES spectrum agrees perfectly with the quasi-energy spectrum of Floquet theory at maximum overlap and goes to the equilibrium bandstructure as the pump-probe overlap goes to zero. Additionally, we show how this time-dependent nonequilibrium quasiparticle structure can be understood to be the bandstructure underlying the optical Stark effect. The extension to spin-resolved ARPES can be used to predict asymmetric dichroic response linked to the valley selective optical excitations in monolayer transition metal dichalcogenides (TMDs). These results establish the photon dressed nonequilibrium bandstructures as the underlying quasiparticle structure of light-driven steady-state quantum phases of matter

Something in the way

The title of my thesis, Something in the Way, came to me only recently. It does address, however, my approach to photography in general, and my method for choosing subjects, as much as it addresses this particular body of work. Barriers of a literal and non-literal nature appear, often in the form of apathy or lassitude, impairing that subject's ability to achieve realization or actualization. People are depicted absorbed in thought or task, and a sense of ennui overshadows their existence. We cannot see into their thoughts, but we are informed of the subject's situation by the details of the setting: lying in a bed laden with suitcases, isolated in a motel room, a child in her room with a single overturned toy. Even as the images suggest an overshadowing or isolation, there is also present the possibility of transformation, and the grace of the subject itself is by no means suppressed. There is something in the way an expression reveals or conceals thoughts, in the way the light falls, or in the way a gesture expresses elegance. In large part, these images consist of portraits of my family and friends as well as the homes and interior spaces they occupy. Photographs of objects within the homes are significant for the meaning they hold for the owners as well as their implications for the viewer. Mundane human rituals interest me as well, and banal scenes like sitting around a table to eat, preparing food, smoking, or simply staring reflectively. There is an emotional distance between me and the subjects in many of the photographs. Within the framing and composition, there is often space around the subjects, allowing them to fill their environment and illustrate their absorption in a task or action. These images depict the subject apparently unaware of the presence of the camera and absorbed in a chore or thought. In most of the images the subjects aren't looking at the camera. I am not following a documentary subject or creating a documentary body of work. Rather, my approach is to visually connect images, themes and motifs through the process of accumulation and then editing with these connections in mind. Although I don't utilize tableau vivants or staged scenes, it is not uncommon for me to place subjects in a scene or direct their actions. My thesis will further examine these issues