Concept of a multichannel spin-resolving electron analyzer based on Mott scattering

Strocov, Vladimir N.; Petrov, V. N.; Dil, J. Hugo

doi:10.1107/s160057751500363x

Cited by 20 publications

(26 citation statements)

References 48 publications

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“…In this instrument, sequential acquisition of k ॥ -distributions at many energies yields the complete spin-resolved valence band structure. Targeting longterm stability, a theoretical study of multichannel Mott scattering at 40 keV has been performed recently [71]; it will be addressed in the outlook section.…”

Section: Space and Spin: Multichannel Spin Detectionmentioning

confidence: 99%

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Space-, time- and spin-resolved photoemission

Schoenhense

Medjanik

Elmers

2015

Journal of Electron Spectroscopy and Related Phenomena

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This article reviews photoemission experiments that simultaneously resolve at least two of the following degrees of freedom: space (real and momentum space), time (intrinsic time scale of a fast experiment or time-of-flight) and spin. In the spatiotemporal domain, imaging of fast processes by PEEM gives direct insight into plasmon dynamics or magnetization processes. In the category real space & spin the novel concept of imaging spin filters is discussed. In the time & spin chapter we address time-of-flight spin detectors and ultrafast spin processes that are accessible by pump-and-probe techniques. A main part of the paper is devoted to the resolution of momentum-space & time. This is implemented in form of the time-of-flight momentum microscope, a very recent development of which the first instrument has been in operation since 2014. In an extended outlook chapter, the potential of new developments and of a novel, highly parallelized delay-line type electron detector will be discussed. The combination of all three degrees of freedom k-space, time & spin is emerging through the combination of the ToF momentum microscope with imaging spin filter. Outline

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Section: Space and Spin: Multichannel Spin Detectionmentioning

confidence: 99%

“…For this case we refer to [70], where this case is treated in detail. For the normal-incidence geometry of a multichannel Mott detector [71] it is possible to simultaneously detect scattered electrons under different azimuthal angles, with strongly tilted image plane.…”

Section: Space and Spin: Multichannel Spin Detectionmentioning

confidence: 99%

Space-, time- and spin-resolved photoemission

Schoenhense

Medjanik

Elmers

2015

Journal of Electron Spectroscopy and Related Phenomena

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“…In order to make better quantitative comparisons and exhaustively study the dependence of spin polarization on several different parameters, however, a more systematic study is required, which will only become possible with the next generation of high-efficiency spin detectors [36,37] and with the development of a deeper theory of the relationship between spin polarization and time delay in photoemission from solid-state targets.…”

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confidence: 99%

Spin polarization in photoemission from the cuprate superconductor Bi2Sr2CaCu2O8+δ

et al. 2017

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Photoelectrons produced from the excitation of spin-degenerate states in solids can have a sizable spin polarization, which is related to the phase of interfering channels in the photoemission matrix elements. Such spin polarization can be measured by spin-resolved photoemission spectroscopy to gain information about the transitions and the Wigner time delay of the process. Incorporating strongly correlated electron systems into this paradigm could yield a novel means of extracting phase information crucial to understanding the mechanism of their emergent behavior. In this work, we present, as a case study, experimental measurements of the cuprate superconductor Bi 2 Sr 2 CaCu 2 O 8+δ by spin-resolved photoemission while maintaining full angular and energy resolution. A spin polarization of at least 10% is observed, which is related to the phase of the photoelectron wave function. DOI: 10.1103/PhysRevB.95.245125 The electronic properties of crystals are best understood when information on their band structure can be obtained. Angle-resolved photoemission spectroscopy (ARPES) provides a direct means of reconstructing the band structure by measuring the energies and momenta of electrons photoexcited from a solid [1]. Spin-and angle-resolved photoemission spectroscopy (SARPES), in addition, measures the spin polarization P of the photoelectron beam as a function of emission angle and kinetic energy. This can show a net polarization if the initial state is polarized as, for example, in ferromagnets [2,3] or spin-momentum-locked systems, such as Rashba-like materials [4][5][6] and topological insulators [7][8][9][10], but also as a result of the photoemission process as a whole [11]. If the incident light is circularly polarized, i.e., it carries angular momentum, the spin polarization of the photoelectron beam from solid-state targets can, in several different circumstances, be interpreted as a result of the selection rules for the considered transitions along the lines of the atomic Fano effect [12][13][14][15][16].Also, when the incident light is linearly polarized or unpolarized, i.e., it does not transfer a net angular momentum, the photoelectron beam can still present a sizable P. The origin of this effect lies in the symmetry reduction of angledependent photoemission and in the interference of different photoemission channels. The size of P is related to the phase shift of the complex matrix elements describing the transitions under consideration [17][18][19]. One can, therefore, access the phase information by measuring the spin polarization of the photoelectrons. In particular, a novel application of SARPES is the estimate of the Eisenbud-Wigner-Smith (EWS) time delay [20] τ EWS of photoemission, defined as the derivative of the phase shift with respect to the photoelectron kinetic energy, obtained from the measured P, as shown in Ref. [19] for the model system Cu(111). By expressing the spin polarization as a function of the radial parts and phase shifts of the matrix elements, along the lines of the ato...

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“…To assess the spin polarization of the individual bands caused by the Rashba effect, SARPES measurements were performed. However, until more efficient spin detection schemes become available [32] we are limited to the UV energy range, precluding the use of Te-capped surfaces. Therefore, all spectral features of the uncapped samples need to be disentangled according to their bulklike or surface-related character.…”

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confidence: 99%

Disentangling bulk and surface Rashba effects in ferroelectricα-GeTe

Volfová²,

et al. 2016

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Macroscopic ferroelectric order in α-GeTe with its noncentrosymmetric lattice structure leads to a giant Rashba spin splitting in the bulk bands due to strong spin-orbit interaction. Direct measurements of the bulk band structure using soft x-ray angle-resolved photoemission (ARPES) reveals the three-dimensional electronic structure with spindle torus shape. By combining high-resolution and spin-resolved ARPES as well as photoemission calculations, the bulk electronic structure is disentangled from the two-dimensional surface electronic structure by means of surface capping, which quenches the complex surface electronic structure. This unravels the bulk Rashba-split states in the ferroelectric Rashba α-GeTe(111) semiconductor exhibiting a giant spin splitting with Rashba parameter α R around 4.2 eVÅ, the highest of so-far known materials. DOI: 10.1103/PhysRevB.94.205111 In spintronics an important goal is to be able to control the spin of the electron in solids without applying magnetic fields [1,2]. The most promising mechanism is based on the Rashba effect [3] and the subsequent spin precession induced in such systems [4]. While most research has previously focused on 2D electron systems [5,6], recently a threedimensional (3D) form of such Rashba effect was found in a series of bismuth tellurohalides BiTeX (X = I, Br, or Cl) [7][8][9][10][11][12]. Although these materials exhibit a very large spin splitting, they lack an important property concerning functionalization, namely, the possibility to switch or tune the spin texture. This limitation can be overcome in a new class of functional materials displaying Rashba splitting coupled to ferroelectricity, the so-called ferroelectric Rashba semiconductors (FERS) [13,14].Recent photoemission experiments on α-GeTe-the stable rhombohedral room temperature configuration of the GeTe phase change material [15]-indicate that this system is a hallmark candidate for entanglement of the ferroelectric and spin-orbit order [16,17]. Due to the giant Rashba splitting spin injection from magnetic systems into GeTe appears viable in order to achieve spin-to-charge conversion [18]. Therefore, ferroelectric [13] or multiferroic [19] Rashba semiconductors bring new multifunctional assets for spintronic devices. A crucial issue for the understanding of FERS is to disentangle the Rashba effect in the bulk caused by the bulk ferroelectric lattice distortion and surface effects arising from particular surface terminations and/or possible band bendings. This represents a major challenge for surface sensitive techniques such as angle-resolved photoemission (ARPES). For this reason up to now ARPES measurements on α-GeTe surfaces performed in the surface-sensitive UV regime have been dominated by surface effects [16,17] and clear information of the three-dimensional bulk electronic structure and its spin texture has not been obtained.

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Concept of a multichannel spin-resolving electron analyzer based on Mott scattering

Cited by 20 publications

References 48 publications

Space-, time- and spin-resolved photoemission

Space-, time- and spin-resolved photoemission

Spin polarization in photoemission from the cuprate superconductor Bi2Sr2CaCu2O8+δ

Disentangling bulk and surface Rashba effects in ferroelectricα-GeTe

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