Th-C4.4
Th-C4.4
Electron and spin structure of topological crystalline insulator
(Pb,Sn,Mn)Se
P. Dziawa‡, B.M. Wojek§, M.H. Berntsen§, B.J. Kowalski‡, A. Szczerbakow‡,
M. Leandersson†, J. Domagała‡, T. Wojciechowski‡, W. Knoff‡, T. Balasubramanian†,
O. Tjernberg§, and T. Story‡
‡
Institute of Physics, Polish Academy of Sciences, Lotników 32/46, 02-668 Warsaw, Poland
§
KTH Royal Institute of Technology, Electrum 229, 164 40 Kista, Sweden
†
MAX IV Laboratory, Lund University, 221 00 Lund, Sweden
In Pb1-xSnxSe topological crystalline insulator (TCI) the topological states are protected by
(110) mirror-plane symmetry of the rock-salt crystal structure [1]. This phase is manifested by
gapless Dirac-like surface states observed upon inversion of band symmetries and exhibits
specific helical spin texture [2, 3]. In these materials the topologically non-trivial state with
inverted band ordering is controlled by changing temperature [2], alloy chemical composition
[4] or crystal lattice distortion [5,6]. In this work, we experimentally examine the electron and
spin structure of surface topological states in Pb1-xSnxSe with magnetic ions of Mn. We
demonstrate the control of transition temperature from trivial to the TCI state by band gap
engineering as well as show the robustness of the helical spin texture of TCI states in the
presence of magnetic ions.
Bulk monocrystals of Pb1-x-ySnxMnySe with the rock-salt crystal structure and with
composition 0.28x0.385 and y0.022 were grown by the Bridgman method. Electron
paramagnetic resonance studies showed paramagnetic properties due to Mn2+ ions substituting
cations and carrying spin-only S=5/2 local magnetic moment. The (001) surface of crystals
cleaved in ultrahigh vacuum was studied by angle-resolved (ARPES) and spin-resolved
(SRPES) photoemission spectroscopy. Temperature evolution of the band structure for
samples with Mn ions shows the TCI transition strongly shifted to lower temperatures (by
about 100 K for 1 at. % of Mn) with respect to the reference Pb1-xSnxSe crystals. This can be
understood taking into account the shift of band inversion point due to experimentally
established composition (dEG/dy3 eV) and temperature (dEG/dT50 meV/K) dependence of
the band gap EG. We found that the temperature coefficient is independent of Mn content and
does not change in both trivial and TCI state. The SREPS studies of the wavevectordependent spin texture of the TCI states were carried out for the sample with very high Sn
content (x=0.385 and y=0.01) and the TCI transition expected at T=200 K. Spin resolved
spectra taken at T=65 K around Dirac cone located close to the X-bar point of the surface
Brillouin zone uncovered the expected change of the sign of spin polarization. This
observation is analogous to the spin texture obtained for Pb1-xSnxSe (001) crystals [3] and
provides clear evidence that magnetic ions in the crystal matrix of TCIs do not destroy the
topological state.
[1] L. Fu, Phys. Rev. Lett. 106, 106802 (2011)
[2] P. Dziawa, B.J. Kowalski, K. Dybko et al., Nat. Mat. 11, 1023 (2012)
[3] B.M. Wojek, R. Buczko, S. Safaei et al., Phys. Rev. B 87, 115106 (2013)
[4] B.M. Wojek, P. Dziawa, B.J. Kowalski et al., Phys. Rev. B 90, 161202(R) (2014)
[5] Y. Okada, M. Serbyn, H. Lin et al., Science 341, 1496 (2013)
[6] B.M. Wojek, M.H. Berntsen, V. Jonson et al., Nat. Commun. 6, 8463 (2015)