arXiv subjects

S. Theil

Publications and source records attributed to S. Theil.

5 recordsLinked to original sources

arXiv2022

Volkov-Pankratov states in a 2d material: excited states of a structural soliton

We show that partial dislocations, defects that naturally arise in bilayer graphene, host an analogue of the mass inversion Volkov-Pankratov (VP) states, the spectrum of excited states at a topologically non-trivial interface. In contrast to the dislocation states arising from the change in valley Chern index, such states (i) exist both with and without an interlayer bias, i.e. for metallic as well as insulating bulk and (ii) have distinct electron and hole bound states, whose number is proportional to the dislocation width. Recently discovered at heterojunctions of 3d topological insulators, their existence at the partial dislocations of a 2d material opens a rich structural playground for their investigation, and we demonstrate that the dislocation type, i.e. screw or edge, as well as the dislocation width, both play a decisive role in the creation of a topological spectrum of exited states.

cond-mat.mes-hall↗

arXiv2020

A general relation between stacking order and Chern index: a topological map of minimally twisted bilayer graphene

We derive a general relation between the stacking vector ${\bf u}$ describing the relative shift of two layers of bilayer graphene and the Chern index. We find $C = ν- \text{sign}\left(|V_{AB}|-|V_{BA}|\right)$, where $ν$ is a valley index and $|V_{αβ}|$ the absolute value of stacking potentials that depend on ${\bf u}$ and that uniquely determine the interlayer interaction; AA stacking plays no role in the topological character. With this expression we show that while ideal and relaxed minimally twisted bilayer graphene appear so distinct as to be almost different materials, their Chern index maps are, remarkably, identical. The topological physics of this material is thus strongly robust to lattice relaxations.

cond-mat.mes-hall↗

arXiv2008

Odyssey: a Solar System Mission

The Solar System Odyssey mission uses modern-day high-precision experimental techniques to test the laws of fundamental physics which determine dynamics in the solar system. It could lead to major discoveries by using demonstrated technologies. The mission proposes to perform a set of precision gravitation experiments from the vicinity of Earth to the outer Solar System. Its scientific objectives can be summarized as follows: i) test of the gravity force law in the Solar System up to and beyond the orbit of Saturn; ii) precise investigation of navigation anomalies at the fly-bys; iii) measurement of Eddington's parameter at occultations; iv) mapping of gravity field in the outer solar system and study of the Kuiper belt. To this aim, the Odyssey mission is built up on a main spacecraft, designed to fly up to 13 AU, with the following components: a) a high-precision accelerometer, with bias-rejection system, measuring the deviation of the trajectory from the geodesics; b) Ka-band transponders, as for Cassini, for a precise range and Doppler measurement up to 13 AU, with additional VLBI equipment; c) optional laser equipment, which would allow one to improve the range and Doppler measurement. In this baseline concept, the main spacecraft is designed to operate beyond the Saturn orbit, up to 13 AU. It experiences multiple planetary fly-bys at Earth, Mars or Venus, and Jupiter. The cruise and fly-by phases allow the mission to achieve its baseline scientific objectives (i) to iii) in the above list). In addition to this baseline concept, the Odyssey mission proposes the release of the Enigma radio-beacon at Saturn, allowing one to extend the deep space gravity test up to at least 50 AU, while achieving the scientific objective of a mapping of gravity field in the outer Solar System.

gr-qc↗

arXiv2005

Fundamental Physics with the Laser Astrometric Test Of Relativity

The Laser Astrometric Test Of Relativity (LATOR) is a joint European-U.S. Michelson-Morley-type experiment designed to test the pure tensor metric nature of gravitation - a fundamental postulate of Einstein's theory of general relativity. By using a combination of independent time-series of highly accurate gravitational deflection of light in the immediate proximity to the Sun, along with measurements of the Shapiro time delay on interplanetary scales (to a precision respectively better than 0.1 picoradians and 1 cm), LATOR will significantly improve our knowledge of relativistic gravity. The primary mission objective is to i) measure the key post-Newtonian Eddington parameter γwith accuracy of a part in 10^9. (1-γ) is a direct measure for presence of a new interaction in gravitational theory, and, in its search, LATOR goes a factor 30,000 beyond the present best result, Cassini's 2003 test. The mission will also provide: ii) first measurement of gravity's non-linear effects on light to ~0.01% accuracy; including both the Eddington βparameter and also the spatial metric's 2nd order potential contribution (never measured before); iii) direct measurement of the solar quadrupole moment J2 (currently unavailable) to accuracy of a part in 200 of its expected size; iv) direct measurement of the "frame-dragging" effect on light by the Sun's gravitomagnetic field, to 1% accuracy. LATOR's primary measurement pushes to unprecedented accuracy the search for cosmologically relevant scalar-tensor theories of gravity by looking for a remnant scalar field in today's solar system. We discuss the mission design of this proposed experiment.

gr-qc↗

arXiv2005

A Mission to Explore the Pioneer Anomaly

The Pioneer 10 and 11 spacecraft yielded the most precise navigation in deep space to date. These spacecraft had exceptional acceleration sensitivity. However, analysis of their radio-metric tracking data has consistently indicated that at heliocentric distances of $\sim 20-70$ astronomical units, the orbit determinations indicated the presence of a small, anomalous, Doppler frequency drift. The drift is a blue-shift, uniformly changing with a rate of $\sim(5.99 \pm 0.01)\times 10^{-9}$ Hz/s, which can be interpreted as a constant sunward acceleration of each particular spacecraft of $a_P = (8.74 \pm 1.33)\times 10^{-10} {\rm m/s^2}$. This signal has become known as the Pioneer anomaly. The inability to explain the anomalous behavior of the Pioneers with conventional physics has contributed to growing discussion about its origin. There is now an increasing number of proposals that attempt to explain the anomaly outside conventional physics. This progress emphasizes the need for a new experiment to explore the detected signal. Furthermore, the recent extensive efforts led to the conclusion that only a dedicated experiment could ultimately determine the nature of the found signal. We discuss the Pioneer anomaly and present the next steps towards an understanding of its origin. We specifically focus on the development of a mission to explore the Pioneer Anomaly in a dedicated experiment conducted in deep space.

gr-qc↗