اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدAnisotropy effects on Rashba and topological insulator spin polarized surface states: a unified phenomenological description
204
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Spin polarized two-dimensional electronic states have been previously observed on metallic surface alloys with giant Rashba splitting and on the surface of topological insulators. We study the surface band structure of these systems, in a unified manner, by exploiting recent results of k.p theory. The model suggests a different way to address the effect of anisotropy in Rashba systems. Changes in the surface band structure of various Rashba compounds can be captured by a single effective parameter which quantifies the competition between the Rashba effect and the hexagonal warping of the constant energy contours. The same model provides a unified phenomenological description of the surface states belonging to materials with topologically trivial and non-trivial band structures.
قيم البحث
اقرأ أيضاً
We study the nature of (001) surface states in Pb_{0.73}Sn_{0.27}Se in the newly discovered topological-crystalline-insulator (TCI) phase as well as the corresponding topologically trivial state above the band-gap-inversion temperature. Our calculati
ons predict not only metallic surface states with a nontrivial chiral spin structure for the TCI case, but also nonmetallic (gapped) surface states with nonzero spin polarization when the system is a normal insulator. For both phases, angle- and spin-resolved photoelectron spectroscopy measurements provide conclusive evidence for the formation of these (001) surface states in Pb_{0.73}Sn_{0.27}Se, as well as for their chiral spin structure.
Several recent experiments on three-dimensional topological insulators claim to observe a large charge current-induced non-equilibrium ensemble spin polarization of electrons in the helical surface state. We present a comprehensive criticism of such
claims, using both theory and experiment: First, we clarify the interpretation of quantities extracted from these measurements by deriving standard expressions from a Boltzmann transport equation approach in the relaxation-time approximation at zero and finite temperature to emphasize our assertion that, despite high in-plane spin projection, obtainable current-induced ensemble spin polarization is minuscule. Second, we use a simple experiment to demonstrate that magnetic field-dependent open-circuit voltage hysteresis (identical to those attributed to current-induced spin polarization in topological insulator surface states) can be generated in analogous devices where current is driven through thin films of a topologically-trivial metal. This result *ipso facto* discredits the naive interpretation of previous experiments with TIs, which were used to claim observation of helicity, i.e. spin-momentum locking in the topologically-protected surface state.
We present a theoretical study of surface states close to 3d transition metal adatoms (Cr, Mn, Fe, Co, Ni and Cu) on a Cu(111) surface in terms of an embedding technique using the fully relativistic Korringa-Kohn-Rostoker method. For each of the adat
oms we found resonances in the s-like states to be attributed to a localization of the surface states in the presence of an impurity. We studied the change of the s-like densities of states in the vicinity of the surface state band-edge due to scattering effects mediated via the adatoms d-orbitals. The obtained results show that a magnetic impurity causes spin-polarization of the surface states. In particular, the long-range oscillations of the spin-polarized s-like density of states around an Fe adatom are demonstrated.
The protected surface conductivity of topological insulators, carried by ultra-relativistic Dirac fermions, is in high demand for the next generation of electronic devices. Progress in the unambiguous identification of this surface contribution and,
in a second step, its control are needed to move forward. Here we demonstrate both, with a combined transport and spectroscopy study of high-quality single crystals and mesoscopic devices of the topological insulator TlBiSe2. We show how various external stimuli-from thermal radiation, via low-intensity light, to high-intensity laser pumping and current driving-can boost the surface contribution, thereby making it both unambiguously detectable and potentially exploitable for applications. Once switched on, the extra surface contribution is persistent, with lifetimes of hundreds of years at low temperatures. We understand this effect in terms of the well-known concept of surface charge accumulation via a Schottky barrier formation, and propose that the same mechanism underlies also the slow relaxations seen with spectroscopic probes in our and other materials, which might thus also be persistent. We expect our technique to be readily transferable to other materials and probes, thereby shedding light on unexplained slow relaxations in transport and beyond.
A comprehensive mapping of the spin polarization of the electronic bands in ferroelectric a-GeTe(111) films has been performed using a time-of-flight momentum microscope equipped with an imaging spin filter that enables a simultaneous measurement of
more than 10.000 data points (voxels). A Rashba type splitting of both surface and bulk bands with opposite spin helicity of the inner and outer Rashba bands is found revealing a complex spin texture at the Fermi energy. The switchable inner electric field of GeTe implies new functionalities for spintronic devices.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
