Disentangling bulk and surface Rashba effects in ferroelectric<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>α</mml:mi></mml:math>-GeTe

Krempaský, J.; Volfová, Henrieta; Muff, Stefanie; Pilet, N.; Landolt, G.; Radović, Miroslav; Shi, M.; Kriegner, Dominik; Holý, V.; Braun, Jürgen; Ebert, H.; Bisti, F.; Rogalev, V. A.; Strocov, Vladimir N.; Springholz, G.; Minář, J.; Dil, J. Hugo

doi:10.1103/physrevb.94.205111

Cited by 89 publications

(140 citation statements)

References 37 publications

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“…Spin polarization for the inner bands are of opposite direction and only slightly smaller. These results confirm previously published data [13,14].…”

supporting

confidence: 93%

“…3(a,b). The P x component for the larger absolute k || of the Rashba splitted band is also parallel to that of the surface band with larger k || value, which is in agreement with the Rashba-type spin orientation, respective the theoretical predictions for the equilibrium ferroelectric polarization of GeTe [14,15].…”

supporting

confidence: 85%

“…A considerably larger splitting has been predicted theoretically [12] and was recently found experimentally for the surface states of GeTe(111) [13,14].…”

mentioning

confidence: 52%

“…This can be explained by the smaller Rashba splitting and the corresponding partial overlap of the intensity of inner and outer band. A large perpendicular spin component cannot be excluded from the experiment but seems unlikely in respect to the theoretical predictions [13,14]. The spin direction is mostly perpendicular to the E(k y )-cut shown in Figs.…”

mentioning

confidence: 75%

“…A recent experimental and theoretical study revealed that at the Fermi level the hybridization of surface and bulk states causes surface-bulk resonant states resulting in unconventional spin topologies with chiral symmetry [14].…”

mentioning

confidence: 99%

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Spin mapping of surface and bulk Rashba states in ferroelectric α -GeTe(111) films

Elmers¹,

Wallauer²,

Liebmann³

et al. 2016

Phys. Rev. B

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A comprehensive mapping of the spin polarization of the electronic bands in ferroelectric α-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.The strong coupling of electron momentum and spin in low-dimensional structures allows an electrically controlled spin manipulation in spintronic devices [1][2][3][4], e.g. via the Rashba effect [5].The Rashba effect has first been experimentally demonstrated in semiconductor heterostructures, where an electrical field perpendicular to the layered structure, i.e. perpendicular to the electron momentum, determines the electron spin orientation relative to its momentum [6][7][8]. An asymmetric interface structure causes the necessary inversion symmetry breaking and accounts for the special spin-splitting of electron states, the Rashba effect [5], the size of which can be tuned by the strength of the electrical field.For most semiconducting materials the Rashba effect causes only a quite small splitting of the order of 10 −2Å−1 and thus requires experiments at very low temperatures [9][10][11] and also implies large lateral dimensions for potential spintronic applications. A considerably larger splitting has been predicted theoretically [12] and was recently found experimentally for the surface states of GeTe(111) [13,14].GeTe is a ferroelectric semiconductor with a Curie temperature of 700 K. Thus, besides the interface induced Rashba splitting, the ferroelectric properties also imply a broken inversion symmetry within the bulk and thus would allow for the electrical tuning of the bulk Rashba splitting via switching the ferroelectric polarization [12,15,16]. This effect is of great interest for nonvolatile spin orbitronics [10].For GeTe a bulk Rashba splitting of 0.19Å −1 has been predicted theoretically [12]. Experimentally, bulkRashba bands are rare and have only been found in the layered polar semiconductors BiTeCl and BiTeI [17][18][19][20] that, however, are not switchable.A characterization of the ferroelectric properties and a measurement of the spin polarization of the surface states of GeTe(111) at selected k-points has been performed previously by force microscopy [21,22] and spinresolved angular resolved photoemission spectroscopy, respectively [13]. A recent experimental and theoretical study revealed that at the Fermi level the hybridization of surface and bulk states causes surface-bulk resonant states resulting in unconventional spin topologies with chiral symmetry [14].Here, we demonstrate the spin structure of surface and bulk bands of the GeTe(111) surface using the novel photoemission technique of spin-resolved time-of-flight momentum micro...

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“…Spin polarization for the inner bands are of opposite direction and only slightly smaller. These results confirm previously published data [13,14].…”

supporting

confidence: 93%

supporting

confidence: 85%

“…A considerably larger splitting has been predicted theoretically [12] and was recently found experimentally for the surface states of GeTe(111) [13,14].…”

mentioning

confidence: 52%

mentioning

confidence: 75%

mentioning

confidence: 99%

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Spin mapping of surface and bulk Rashba states in ferroelectric α -GeTe(111) films

Elmers¹,

Wallauer²,

Liebmann³

et al. 2016

Phys. Rev. B

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Giant Rashba Splitting in Pb_1–_xSn_xTe (111) Topological Crystalline Insulator Films Controlled by Bi Doping in the Bulk

et al. 2016

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to external perturbations. [10,15,16] Therefore, the trivial to nontrivial topological phase transition can be controlled by many different means, such as by varying temperature, [1,6] pressure, [2] hybridization in ultrathin film geometries, [17][18][19] magnetic interactions, [20] or by breaking of mirror symmetries by strain, [16,[21][22][23] electrostatic fields, [18] or ferroelectric (FE) lattice distortions. [24,25] This provides ample degrees of freedom for topology control not available in conventional Z 2 TIs. For this reason, TCIs offer an ideal template for observation of exotic phenomena such as partially flat band helical snake states and interfacial superconductivity, [16] large-Chern-number quantum anomalous Hall effect, [26] as well as for realization of novel topology-based devices such as topological photodetectors, [23] spin transistors, [18] and spin torque devices. [27] For most of such applications, thin film structures with precisely controlled composition and Fermi level are required. Up to now, most work has been performed on highly p-type bulk crystals exploiting the natural (001) cleavage plane of the IV-VI compounds, [3,4,6] whereas for other surface orientations and practical devices epitaxial TCI film structures are required. [18,[28][29][30][31][32] The (111) orientation is particularly interesting due to the polar nature of its surface [12] as well as the ease of lifting the fourfold valley degeneracy at the L-points of the Brillouin zone (BZ) [33] by opening a gap at particular Dirac points by strain [16] and quantum confinement [17][18][19] to induce a transition from a TCI to a normal Z 2 -TI material. [25]

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Ultrafast Thermalization Pathways of Excited Bulk and Surface States in the Ferroelectric Rashba Semiconductor GeTe

et al. 2022

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A large Rashba effect is essential for future applications in spintronics. Particularly attractive is understanding and controlling nonequilibrium properties of ferroelectric Rashba semiconductors. Here, time‐ and angle‐resolved photoemission is utilized to access the ultrafast dynamics of bulk and surface transient Rashba states after femtosecond optical excitation of GeTe. A complex thermalization pathway is observed, wherein three different timescales can be clearly distinguished: intraband thermalization, interband equilibration, and electronic cooling. These dynamics exhibit an unconventional temperature dependence: while the cooling phase speeds up with increasing sample temperature, the opposite happens for interband thermalization. It is demonstrated how, due to the Rashba effect, an interdependence of these timescales on the relative strength of both electron–electron and electron–phonon interactions is responsible for the counterintuitive temperature dependence, with spin‐selection constrained interband electron–electron scatterings found both to dominate dynamics away from the Fermi level, and to weaken with increasing temperature. These findings are supported by theoretical calculations within the Boltzmann approach explicitly showing the opposite behavior of all relevant electron–electron and electron–phonon scattering channels with temperature, thus confirming the microscopic mechanism of the experimental findings. The present results are important for future applications of ferroelectric Rashba semiconductors and their excitations in ultrafast spintronics.

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Disentangling bulk and surface Rashba effects in ferroelectricα-GeTe

Cited by 89 publications

References 37 publications

Spin mapping of surface and bulk Rashba states in ferroelectric α -GeTe(111) films

Spin mapping of surface and bulk Rashba states in ferroelectric α -GeTe(111) films

Giant Rashba Splitting in Pb_1–_xSn_xTe (111) Topological Crystalline Insulator Films Controlled by Bi Doping in the Bulk

Ultrafast Thermalization Pathways of Excited Bulk and Surface States in the Ferroelectric Rashba Semiconductor GeTe

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Disentangling bulk and surface Rashba effects in ferroelectricα-GeTe

Cited by 89 publications

References 37 publications

Spin mapping of surface and bulk Rashba states in ferroelectric α -GeTe(111) films

Spin mapping of surface and bulk Rashba states in ferroelectric α -GeTe(111) films

Giant Rashba Splitting in Pb1–xSnxTe (111) Topological Crystalline Insulator Films Controlled by Bi Doping in the Bulk

Ultrafast Thermalization Pathways of Excited Bulk and Surface States in the Ferroelectric Rashba Semiconductor GeTe

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Giant Rashba Splitting in Pb_1–_xSn_xTe (111) Topological Crystalline Insulator Films Controlled by Bi Doping in the Bulk