Spin texture of generic helical edge states

We study the spin texture of a generic helical liquid, the edge modes of a two-dimensional topological insulator with broken axial spin-symmetry. By considering honeycomb and square lattice realizations of topological insulators, we show that in all cases the generic behavior of a momentum-dependent rotation of the spin quantization axis is realized. Here we establish this mechanism also for disk geometries with continuous rotational symmetry. Finally, we demonstrate that the rotation of spin-quantization axis remains intact for arbitrary geometries, i.e. in the absence of any continuous symmetry. We also calculate the dependence of this rotation on the model and material parameters. Finally we propose a spectroscopy measurement which should directly reveal the rotation of the spin-quantization axis of the helical edge states.Comment: 16 pages, 17 figure

Spider\u27s Lace

My current work is about identical lessons learned by separate people from different personal experiences. Interviews with friends and family are conducted to identify a lesson both me and the subject of the interview have learned and combine the separate experiences into one story. Because the story exists in a place beyond any one human character, they are transformed into animal fables, which are then illustrated with print based installations. The stories are built around what the interviewee would most like to teach to someone younger. The fables exist in a world where these lessons become established as rules in nature. I’m looking at artists like Joanna Mueller, who uses animal and ancient North American myth symbolism to achieve a narrative-like effect, and Anne Hamilton who uses installation and print multiples to create immersive experiences. The media and style of each print installation is entirely dependent on the fable. The prints range from black and white linoleum cuts, to soft and colorful lithographs, and the installations range from to little wooden boxes filled with dozens of small monoprints, to wearable books on live models. Design elements are incorporated to give the show cohesiveness by unifying the different stylistic aspects of the separate works with a common visual narrative. A series of posters accompany the works of the show, identifying the title of each story and installation and matching it with a unique icon displayed near each piece in vinyl. In addition to the posters there are small hand-bound books identified by each fable’s icon; each book contains a written fable laid out with experimental type and minimal graphics. The show gives the viewer a sense of discovery as they move through the fables via illustrative prints, books, and installations.https://digitalcommons.murraystate.edu/art498/1012/thumbnail.jp

Transport through a quantum spin Hall antidot as a spectroscopic probe of spin textures

We investigate electron transport through an antidot embedded in a narrow strip of two-dimensional topological insulator. We focus on the most generic and experimentally relevant case with broken axial spin symmetry. Spin-non-conservation allows additional scattering processes which change the transport properties profoundly. We start from an analytical model for noninteracting transport, which we also compare with a numerical tight-binding simulation. We then extend this model by including Coulomb repulsion on the antidot, and we study the transport in the Coulomb-blockade limit. We investigate sequential tunneling and cotunneling regimes, and we find that the current-voltage characteristic allows a spectroscopic measurement of the edge-state spin textures.Comment: 11 pages, 7 figure

Inelastic electron backscattering in a generic helical edge channel

We evaluate the low-temperature conductance of a weakly interacting one-dimensional helical liquid without axial spin symmetry. The lack of that symmetry allows for inelastic backscattering of a single electron, accompanied by forward-scattering of another. This joint effect of weak interactions and potential scattering off impurities results in a temperature-dependent deviation from the quantized conductance, $\delta G \propto T^4$. In addition, $\delta G$ is sensitive to the position of the Fermi level. We determine numerically the parameters entering our generic model for the Bernevig-Hughes-Zhang Hamiltonian of a HgTe/CdTe quantum well in the presence of Rashba spin-orbit coupling.Comment: 4+ pages, 3 figures, published versio

Can the Universe escape eternal acceleration?

Recent astronomical observations of distant supernovae light-curves suggest that the expansion of the universe has recently begun to accelerate. Acceleration is created by an anti-gravitational repulsive stress, like that produced by a positive cosmological constant, or universal vacuum energy. It creates a rather bleak eschatological picture. An ever-expanding universe's future appears to be increasingly dominated by its constant vacuum energy. A universe doomed to accelerate forever will produce a state of growing uniformity and cosmic loneliness. Structures participating in the cosmological expansion will ultimately leave each others' horizons and information-processing must eventually die out. Here, we examine whether this picture is the only interpretation of the observations. We find that in many well-motivated scenarios the observed spell of vacuum domination is only a transient phenomenon. Soon after acceleration starts, the vacuum energy's anti-gravitational properties are reversed, and a matter-dominated decelerating cosmic expansion resumes. Thus, contrary to general expectations, once an accelerating universe does not mean always an accelerating universe.Comment: 6 pages, 2 figure

Unconventional superconductivity in the extended Hubbard model: Weak-coupling renormalization group

We employ the weak-coupling renormalization group approach to study unconventional superconducting phases emerging in the extended, repulsive Hubbard model on paradigmatic two-dimensional lattices. Repulsive interactions usually lead to higher-angular momentum Cooper pairing. By considering not only longer-ranged hoppings, but also non-local electron-electron interactions, we are able to find superconducting solutions for all irreducible representations on the square and hexagonal lattices, including extended regions of chiral topological superconductivity. For the square, triangular and honeycomb lattices, we provide detailed superconducting phase diagrams as well as the coupling strengths which quantify the corresponding critical temperatures depending on the bandstructure parameters, band filling, and interaction parameters. We discuss the sensitivity of the method with respect to the numerical resolution of the integration grid and the patching scheme. Eventually we show how to efficiently reach a high numerical accuracy.Comment: 18 pages, 15 figure

La praxis y la parodia del discurso del ars moriendi en el Quijote de 1615

This article examine the use of tropes related to the religious, moralizing discourse of the good death in Part II of Don Quijote (1615), published at a time in Spain when the social practice of dying underwent increased clerical control. By analyzing the sociohistorical context of the ars moriendi discourse along with the way Cervantes’s characters use it pragmatically in conversation, one can glimpse ironic and even parodic tonalities that reveal the tensions inherent in a transitional moment as the Medieval vision of death cedes before emergent modern perspectives.En este artículo se examina el uso de los tópicos del bien morir, discurso religioso y moralizante que se transformaba en la España del siglo XVI debido a la mayor clericalización de la muerte, en la segunda parte del Quijote (1615). A través del análisis del contexto sociohistórico del ars moriendi junto con el estudio del uso pragmático de refranes, axiomas e imágenes relacionadas con la muerte en la conversación de los personajes cervantinos, es posible iluminar matices irónicos y aún paródicos que ponen de manifiesto las tensiones inherentes en la transición desde una óptica medieval sobre la muerte hacia una perspectiva más moderna

Weighing a galaxy bar in the lens Q2237+0305

In the gravitational lens system Q2237+0305 the cruciform quasar image geometry is twisted by ten degrees by the lens effect of a bar in the lensing galaxy. This effect can be used to measure the mass of the bar. We construct a new lensing model for this system with a power-law elliptical bulge and a Ferrers bar. The observed ellipticity of the optical isophotes of the galaxy leads to a nearly isothermal elliptical profile for the bulge with a total quasar magnification of 16^{+5}_{-4}. We measure a bar mass of 7.5\pm1.5 \times 10^8 h^{-1}_{75} M_{\sun} in the region inside the quasar images.Comment: 9 pages, 5 Postscript figures, uses mn.sty and eps.sty, submitted to MNRA