Spin resolved bandstructure imaging with a high resolution momentum microscope

Tusche, Christian; Krasyuk, A.; Kirschner, J.

doi:10.1016/j.ultramic.2015.03.020

Cited by 183 publications

(171 citation statements)

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“…In recent years it has been successfully applied to a variety of materials [14][15][16]. At the same time, the efficiency of stateof-the-art photoelectron spin detectors has been improved tremendously [11,16,17], making it now possible to measure the photoelectron spin polarization over wide regions of momentum space with varying energy and polarization of the exciting light. Despite these encouraging developments fundamental issues remain debated, namely to which degree, under which conditions, and in which way the measured photoelectron spin polarization actually reflects the intrinsic spin properties of spin-orbit split states [11,[18][19][20][21][22][23][24][25][26].…”

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Strong Linear Dichroism in Spin-Polarized Photoemission from Spin-Orbit-Coupled Surface States

et al. 2017

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A comprehensive understanding of spin-polarized photoemission is crucial for accessing the electronic structure of spin-orbit coupled materials. Yet, the impact of the final state in the photoemission process on the photoelectron spin has been difficult to assess in these systems. We present experiments for the spin-orbit split states in a Bi-Ag surface alloy showing that the alteration of the final state with energy may cause a complete reversal of the photoelectron spin polarization. We explain the effect on the basis of ab initio one-step photoemission theory and describe how it originates from linear dichroism in the angular distribution of photoelectrons. Our analysis shows that the modulated photoelectron spin polarization reflects the intrinsic spin density of the surface state being sampled differently depending on the final state, and it indicates linear dichroism as a natural probe of spin-orbit coupling at surfaces.The creation and manipulation of spin-polarized electronic states in crystalline solids, low-dimensional systems, and heterostructures through strong spin-orbit interaction is a central topic in contemporary condensed matter physics [1][2][3][4][5]. Among the most vivid examples are the surface states of topological insulators in which the coupling of the spin and momentum degrees of freedom gives rise to helical spin textures in momentum space [6]. Moreover, spin-orbit split band structures, in general, attract attention in a broad range of materials, including Weyl semimetals [7], with unconventional spin-polarized states in the bulk and at the surface, stronglycorrelated topological Kondo insulators [8,9], as well as twodimensional systems, such as metallic oxide interfaces [5] and transition-metal dichalcogenide layers [3]. Thus, given the tremendous interest in spin-orbit coupled materials, it is of critical importance to probe their electronic structure with spin sensitivity and to reliably verify the anticipated spin dependences, see, e.g., Refs. [10-13].The most versatile tool to spectroscopically address the momentum-dependent spin polarization of electronic band structures in condensed matter physics has been spin-and angle-resolved photoemission spectroscopy (spin-ARPES). In recent years it has been successfully applied to a variety of materials [14][15][16]. At the same time, the efficiency of stateof-the-art photoelectron spin detectors has been improved tremendously [11,16,17], making it now possible to measure the photoelectron spin polarization over wide regions of momentum space with varying energy and polarization of the exciting light. Despite these encouraging developments fundamental issues remain debated, namely to which degree, under which conditions, and in which way the measured photoelectron spin polarization actually reflects the intrinsic spin properties of spin-orbit split states [11,[18][19][20][21][22][23][24][25][26].Within the one-step theory of photoemission the spindependent photocurrent is determined by the photoemission matrix element which involves the ...

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Strong Linear Dichroism in Spin-Polarized Photoemission from Spin-Orbit-Coupled Surface States

et al. 2017

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“…Figures 2(a)-(d) show SARPES spectra obtained by using p and s for BiAg 2 and BiCu 2 . The corresponding spin-polarization and intensity maps [32] are shown in Figs. 2(e)-(h). For p , the inner and outer sp z -bands aroundΓ point in the both materials show negative and positive spin-polarization, respectively, displaying a conventional Rashba-type spin-texture [22,23].…”

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Direct mapping of spin and orbital entangled wave functions under interband spin-orbit coupling of giant Rashba spin-split surface states

et al. 2017

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We use spin-and angle-resolved photoemission spectroscopy (SARPES) combined with polarization-variable laser and investigate the spin-orbit coupling effect under interband hybridization of Rashba spin-split states for the surface alloys Bi/Ag(111) and Bi/Cu(111). In addition to the conventional band mapping of photoemission for Rashba spin-splitting, the different orbital and spin parts of the surface wavefucntion are directly imaged into energy-momentum space. It is unambiguously revealed that the interband spin-orbit coupling modifies the spin and orbital character of the Rashba surface states leading to the enriched spin-orbital entanglement and the pronounced momentum dependence of the spin-polarization. The hybridization thus strongly deviates the spin and orbital characters from the standard Rashba model. The complex spin texture under interband spin-orbit hybridyzation proposed by first-principles calculation is experimentally unraveled by SARPES with a combination of p-and s-polarized light. PACS numbers:A realization of functional capabilities to generate spinsplitting of electronic states without any external magnetic field is a key subject in the research of spintronics [1]. A promising strategy exploits the influence of spin-orbit (SO) interaction that can give rise to the lifting of spin degeneracy under broken space inversion symmetry, the so-called Rashba effect [2]. In the conventional Rashba model, an eigenstate of the SO-induced spin-splitting is treated with an assumption of a pure spin state fully chiral spin-polarized which protects electrons from backscattering [2][3][4][5]. However, in real materials, the assumption can be usually broken because the SO coupling mixes different states with different orbitals and orthogonal spinors in a quasiparticle eigenstate [6][7][8]. The SO entanglement can permit the spin-flip electron backscattering [9] and moreover orbital mixing in the eigenstate can play a significant role in an emergence of the large spin-splitting [10][11][12][13][14]. Therefore, it is essentially important to experimentally explore the SO coupling not only in the lifting spin degeneracy but also in the spin and orbital wavefunction as eigenstates.Beyond the conventional Rashba model, a well-ordered surface alloy BiAg 2 grown on Ag(111) provides an ideal case to study the SO entanglement in Rashba surface states. In the surface alloy, an occupied sp z -like band and a mostly unoccupied p xy -like band show significant Rashba spin splitting [15,16] and cross each other at the specific k || [17][18][19] as shown in Fig. 1 (b). In particular, density functional theory (DFT) calculations showed the strong SO entanglement [8,9] and predicted the complex spin texture that is significantly different from the conventional Rashba model; the sp z band switches spinpolarization at the crossing through SO-induced interband hybridization [19] which is in contrast to the similar system BiCu 2 /Cu(111) as shown in Fig. 1 (b) [14,20,21]. While the presence of the spin-polarized electronic bands ...

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“…This becomes feasible by a new generation of two-dimensional spin polarimeters [18,19]. The combination of momentum microscopy with a two-dimensional spin polarimeter yields a view into the spin-polarized electronic structure with unprecedented detail [62].…”

Section: A Scientific Backgroundmentioning

confidence: 99%

New Developments in Spin-Dependent Photoemission

Schneider¹

2018

e-J. Surf. Sci. Nanotech.

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The electron spin governs many phenomena in modern condensed matter physics, such as magnetism, superconductivity, etc. Often, minute details in the electronic structure determine the physical behavior of a material. Photoelectron emission-being the most established approach to explore electronic structures-is currently entering a new era thanks to a breathtaking development in light sources, spectrometer concepts, and spin detectors. In particular, the evolution in novel highly efficient electron spin polarimeters opens up new experimental opportunities and permits unequaled insights into the electronic structure. This contribution will discuss several examples in this field of spin-dependent interactions and spin-based phenomena. A prominent one refers to the class of topological insulators, where strong spin-orbit coupling (SOC) causes a unique spin-momentum locking around the Dirac cone. Transition metal dichalcogenides consist of quasi-2D layers coupled by v. d. Waals interactions. Here, strong SOC leads to pronounced hybridization effects. We also address fundamental issues in ferromagnetism, e.g., the complex interplay of SOC and exchange interaction, causing characteristic k-, spin-and symmetry-dependent band mixing. Using spin-and time-resolved photoemission we explore ultrafast spin dynamics in ferromagnets driven by strong ultrashort laser pulses. We find the changes in both majority and minority spin states to take place on a 100 fs time scale and to be compatible with band mirroring.In this contribution, we will discuss several new aspects of spin-dependent and spin-resolved photoemission covering both static and dynamic issues of electronic states.

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Spin resolved bandstructure imaging with a high resolution momentum microscope

Cited by 183 publications

References 58 publications

Strong Linear Dichroism in Spin-Polarized Photoemission from Spin-Orbit-Coupled Surface States

Strong Linear Dichroism in Spin-Polarized Photoemission from Spin-Orbit-Coupled Surface States

Direct mapping of spin and orbital entangled wave functions under interband spin-orbit coupling of giant Rashba spin-split surface states

New Developments in Spin-Dependent Photoemission

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