Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCircular dichroism in angle-resolved photoemission spectroscopy of topological insulators
148
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Topological insulators are a new phase of matter that exhibits exotic surface electronic properties. Determining the spin texture of this class of material is of paramount importance for both fundamental understanding of its topological order and future spin-based applications. In this article, we review the recent experimental and theoretical studies on the differential coupling of left- versus right-circularly polarized light to the topological surface states in angle-resolved photoemission spectroscopy. These studies have shown that the polarization of light and the experimental geometry plays a very important role in both photocurrent intensity and spin polarization of photoelectrons emitted from the topological surface states. A general photoemission matrix element calculation with spin-orbit coupling can quantitatively explain the observations and is also applicable to topologically trivial systems. These experimental and theoretical investigations suggest that optical excitation with circularly polarized light is a promising route towards mapping the spin-orbit texture and manipulating the spin orientation in topological and other spin-orbit coupled materials.
rate research
Read More
A differential coupling of topological surface states to left- versus right-circularly polarized light is the basis of many opto-spintronics applications of topological insulators. Here we report direct evidence of circular dichroism from the surface states of Bi$_2$Se$_3$ using a laser-based time-of-flight angle-resolved photoemission spectroscopy. By employing a novel sample rotational analysis, we resolve unusual modulations in the circular dichroism photoemission pattern as a function of both energy and momentum, which perfectly mimic the predicted but hitherto un-observed three-dimensional warped spin-texture of the surface states. By developing a microscopic theory of photoemission from topological surface states, we show that this correlation is a natural consequence of spin-orbit coupling. These results suggest that our technique may be a powerful probe of the spin-texture of spin-orbit coupled materials in general.
The helical Dirac fermions at the surface of topological insulators show a strong circular dichroism which has been explained as being due to either the initial-state spin angular momentum, the initial-state orbital angular momentum, or the handedness of the experimental setup. All of these interpretations conflict with our data from Bi2Te3 which depend on the photon energy and show several sign changes. Our one-step photoemission calculations coupled to ab initio theory confirm the sign change and assign the dichroism to a final-state effect. The spin polarization of the photoelectrons, instead, remains a reliable probe for the spin in the initial state.
We use angle-resolved photoemission with circularly polarized excitation to demonstrate that in the 5x1 superstructure-free Pb-Bi2212 material there are no signatures of time-reversal symmetry breaking in the sense of the criteria developed earlier (Kaminski et al. Nature {bf 416}, 610 (2002)). In addition to the existing technique, we suggest and apply an independent experimental approach to prove the absence of the effect in the studied compounds. The dichroic signal retains reflection antisymmetry as a function of temperature and doping and in all mirror planes, precisely defined by the experimental dispersion at low energies. The obtained results demonstrate that the signatures of time-reversal symmetry violation in pristine Bi2212, as determined by ARPES, are not a universal feature of all cuprate superconductors.
Pumping graphene with circularly polarized light is the archetype of light-tailoring topological bands. Realizing the induced Floquet-Chern insulator state and tracing clear experimental manifestions has been a challenge, and it has become clear that scattering effects play a crucial role. We tackle this gap between theory and experiment by employing microscopic quantum kinetic calculations including realistic electron-electron and electron-phonon scattering. Our theory provides a direct link to the build-up of the Floquet-Chern insulator state in light-driven graphene and its detection in time- and angle-resolved photoemission spectroscopy (ARPES). This allows us to study the stability of the Floquet features due to dephasing and thermalization effects. We also discuss the ultrafast Hall response in the laser-heated state. Furthermore, the induced pseudospin texture and the associated Berry curvature gives rise to momentum-dependent orbital magnetization, which is reflected in circular dichroism in ARPES (CD-ARPES). Combining our nonequilibrium calculations with an accurate one-step theory of photoemission allows us to establish a direct link between the build-up of the topological state and the dichroic pump-probe photoemission signal. The characteristic features in CD-ARPES are further corroborated to be stable against heating and dephasing effects. Thus, tracing circular dichroism in time-resolve photoemission provides new insights into transient topological properties.
Quantum gas microscopes are a promising tool to study interacting quantum many-body systems and bridge the gap between theoretical models and real materials. So far they were limited to measurements of instantaneous correlation functions of the form $langle hat{O}(t) rangle$, even though extensions to frequency-resolved response functions $langle hat{O}(t) hat{O}(0) rangle$ would provide important information about the elementary excitations in a many-body system. For example, single particle spectral functions, which are usually measured using photoemission experiments in electron systems, contain direct information about fractionalization and the quasiparticle excitation spectrum. Here, we propose a measurement scheme to experimentally access the momentum and energy resolved spectral function in a quantum gas microscope with currently available techniques. As an example for possible applications, we numerically calculate the spectrum of a single hole excitation in one-dimensional $t-J$ models with isotropic and anisotropic antiferromagnetic couplings. A sharp asymmetry in the distribution of spectral weight appears when a hole is created in an isotropic Heisenberg spin chain. This effect slowly vanishes for anisotropic spin interactions and disappears completely in the case of pure Ising interactions. The asymmetry strongly depends on the total magnetization of the spin chain, which can be tuned in experiments with quantum gas microscopes. An intuitive picture for the observed behavior is provided by a slave-fermion mean field theory. The key properties of the spectra are visible at currently accessible temperatures.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
