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Rashba coupling amplification by a staggered crystal field

Transferring information in quantum computation and spintronic devices by using the electron’s spin instead of electron’s charge is novel technology that has pushed the growing interest in materials possessing strong spin-orbit coupling, leading to spin-polarized quantum states. This can be achieved by the so-called Rashba-Dresselhaus effect, where states with opposite spin chirality split in energy in the presence of an electric field. Sizable spin splitting of states can be expected in layered compounds of heavy elements with no inversion symmetry, or at surfaces of layered polar compounds possessing strong crystal fields.
We investigated the giant Rashba-Dresselhaus spin-splitting of the electronic band structure of the centrosymmetric bulk BaNiS2 crystal by means of angle-resolved photoemission spectroscopy (ARPES) supported by ab initio calculations. The system is composed by light elements so the spin-orbit coupling could not account for the measured band splitting of ΔE ≈ 150 meV. As illustrated in Figure 1a, this striking finding is explained by a huge ~ 1.4 V/ staggered electric crystal field created between Ni ions along the NiS5 pyramids, and due to a local inversion asymmetry arising from non-symmorphic P4/nmm symmetry.


 

Figure 1. a) Schematic illustration of the staggered electric field E created between Ni ions along the NiS5 pyramids. b) Brillouin zone and calculated Fermi surface including spin-orbit coupling.

Figure 2 shows the ARPES measured at the BaDElPh beamline from vacuum cleaved BaNiS2 single crystals along the ГM (ZA) and ГX (ZR) high symmetry directions (Figure 1b) obtained with a photon energy of 26 eV. Solid lines represent the ab initio calculated band structure at kz = π/c without spin-orbit splitting (dark blue line) and with spin-orbit splitting (light blue line). One can easily see that spin-orbit splitting is necessary to open a gap at the Г/Z symmetry point. The slight discrepancy between the experimental band structure and the calculated one concerns the position of the Fermi level with respect to the electron-like bands along U and T directions near R.
 

Figure 2. ARPES spectra along the ГM (ZA) and ГX (ZR) high symmetry directions of Brillouin zone, compared to first principles calculated band structure at kz = π/c without (dark blue lines) and with (light blue lines) spin-orbit coupling.

Finally, it is worth noting that contrary to the usual case of Rashba-Dresselhaus effect occurring in non-centrosymmetric systems, the current effect concerns electronic states with inversion symmetry where no external fields or heavy elements were present. This observation suggests a novel route to tailor the topological properties of electronic phases in solids by using staggered crystal fields.



This research was conducted by the following research team:

David Santos-Cottin1,  Michele Casula1, Gabriel Lantz2, Yannick Klein1, Luca Petaccia3, Patrick Le Fèvre4, François Bertran4, Evangelos Papalazarou2, Marino Marsi2, and Andrea Gauzzi1
 

1 IMPMC, Sorbonne Universités, Université Pierre et Marie Curie, CNRS, IRD, MNHN, Paris, France
Laboratoire de Physique des Solides, CNRS, Université Paris-Sud, Université Paris-Saclay, Orsay, France
Elettra Sincrotrone Trieste, Trieste, Italy
Synchrotron SOLEIL, L'Orme des Merisiers, Cedex, France


Contact person:

Evangelos Papalazarou, email: evangelos.papalazarou@u-psud.fr
Luca Petaccia, email: luca.petaccia@elettra.eu
Andrea Gauzzi, email: andrea.gauzzi@impmc.upmc.fr

 

Reference

D. Santos-Cottin,  M. Casula, G. Lantz, Y. Klein, L. Petaccia, P. Le Fèvre, F. Bertran, E. Papalazarou, M. Marsi, and A. Gauzzi, Rashba coupling amplification by a staggered crystal field, Nat. Commun. 7, 11258 (2016); DOI: 10.1038/ncomms11258

Last Updated on Tuesday, 17 May 2016 14:39