Orientational Tuning of the Fermi Sea of Confined Electrons at the ${\mathrm{SrTiO}}_{3}$ (110) and (111) Surfaces

Letter

Orientational Tuning of the Fermi Sea of Confined Electrons at the ${SrTiO}_{3}$ (110) and (111) Surfaces

T. C. Rödel, C. Bareille, F. Fortuna, C. Baumier, F. Bertran, P. Le Fèvre, M. Gabay, O. Hijano Cubelos, M. J. Rozenberg, T. Maroutian, P. Lecoeur, and A. F. Santander-Syro

Phys. Rev. Applied 1, 051002 – Published 18 June 2014

Abstract

We report the existence of confined electronic states at the (110) and (111) surfaces of ${SrTiO}_{3}$ . Using angle-resolved photoemission spectroscopy, we find that the corresponding Fermi surfaces, subband masses, and orbital ordering are different from the ones at the (001) surface of ${SrTiO}_{3}$ . This occurs because the crystallographic symmetries of the surface and subsurface planes and the effective electron masses along the confinement direction influence the symmetry of the electronic structure and the orbital ordering of the $t_{2 g}$ manifold. Remarkably, our analysis of the data also reveals that the carrier concentration and thickness are similar for all three surface orientations, despite their different polarities. The orientational tuning of the microscopic properties of two-dimensional electron states at the surface of ${SrTiO}_{3}$ echoes the tailoring of macroscopic (e.g., transport) properties reported recently in ${LaAlO}_{3} / {SrTiO}_{3}$ (110) and (111) interfaces, and is promising for searching new types of two-dimensional electronic states in correlated-electron oxides.

Received 1 March 2014

DOI:https://doi.org/10.1103/PhysRevApplied.1.051002

Authors & Affiliations

T. C. Rödel^1,2, C. Bareille¹, F. Fortuna¹, C. Baumier¹, F. Bertran², P. Le Fèvre², M. Gabay³, O. Hijano Cubelos³, M. J. Rozenberg^3,4, T. Maroutian⁵, P. Lecoeur⁵, and A. F. Santander-Syro^1,*

¹CSNSM, Université Paris-Sud and CNRS/IN2P3, Bâtiments 104 et 108, 91405 Orsay cedex, France
²Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin-BP48, 91192 Gif-sur-Yvette, France
³Laboratoire de Physique des Solides, Université Paris-Sud and CNRS, Bâtiment 510, 91405 Orsay, France
⁴Departamento de Física–IFIBA Conicet, FCEN, UBA, Ciudad Universitaria P.1, 1428, Buenos Aires, Argentina
⁵Institut d’Electronique Fondamentale, Université Paris-Sud and CNRS, Bâtiment 220, 91405 Orsay, France

^*andres.santander@csnsm.in2p3.fr

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Vol. 1, Iss. 5 — June 2014

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Figure 1
(a),(b) Unit cell of the cubic perovskite lattice of ${SrTiO}_{3}$ . The gray planes are the (110) and (111) planes, respectively. The yellow dots represent the $O^{2 -}$ anions, the black dot in the center the ${Sr}^{2 +}$ cation, and the red, green, and blue dots the ${Ti}^{4 +}$ cations in different (110) or (111) planes. Both orientations are highly polar, as the crystal is built of alternating layers of ${(SrTiO)}^{4 +}$ and $(O_{2})^{4 -}$ or ${Ti}^{4 +}$ and $({SrO}_{3})^{4 -}$ . (c),(d) ${Ti}^{4 +}$ cations of the crystal lattice at the (110) and (111) planes. The black arrows indicate the lattice vectors of the ${Ti}^{4 +}$ cations in one (110) or (111) plane. As indicated by the black lines in panel (d), a (111) bilayer of ${Ti}^{4 +}$ cations forms a honeycomb lattice. (e) Bulk Fermi surface, calculated using a tight-binding model with an unrealistically large value of $10^{21} {cm}^{- 3}$ for the bulk carrier density, intended to make the Fermi surface visible. Such a carrier density is at least 3 orders of magnitude higher than the bulk carrier density of the samples prepared for this study. (f),(g) Cross section of the bulk Fermi surface in (e) along the (110) and (111) planes, respectively. The gray lines show the cross section of the bulk 3D Brillouin zone through a $Γ$ point, while the black lines correspond to the surface Brillouin zone.
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Figure 2
(a) ARPES Fermi surface map (second derivative) at $h ν = 91 eV$ in the (110) plane of a fractured insulating ${SrTiO}_{3}$ sample. The map is a superposition of intensities measured in the bulk $Γ_{130}$ and $Γ_{131}$ Brillouin zones [22]. The red lines indicate the edges of the unreconstructed (110) Brillouin zones. (b) Energy-momentum intensity map at a $Γ$ point along the $k_{⟨ 001 ⟩}$ direction.
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Figure 3
(a) Fermi surface map measured at $h ν = 110 eV$ on a ${SrTiO}_{3} (111)$ surface prepared in situ. The black lines indicate the edges of the unreconstructed (111) Brillouin zones around $Γ_{222}$ . (b) Fermi surface map (second derivative of ARPES intensity, negative values) in the $k_{⟨ 111 ⟩} − k_{⟨ \bar{1} \bar{1} 2 ⟩}$ , or $(1 \bar{1} 0)$ plane, acquired by measuring at normal emission while varying the photon energy in 1 eV steps between $h ν_{1} = 67 eV$ and $h ν_{2} = 120 eV$ . The experimental Fermi momenta, represented by the black and red circles, are obtained by fitting the momentum distribution curves (MDCs) integrated over $E_{F} \pm 5 meV$ . The red rectangle is the bulk Brillouin zone in the $(1 \bar{1} 0)$ plane. (c) Energy-momentum map across the $Γ$ point along the $⟨ \bar{1} \bar{1} 2 ⟩$ direction. The dispersions of a heavy band and light bands are visible. (d) Raw energy distribution curves of the dispersions are shown in panel (c). In panels (a) and (c), the blue lines are simultaneous TB fits to the Fermi surface and dispersions.
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Physical Review Applied

Orientational Tuning of the Fermi Sea of Confined Electrons at the SrTiO3 (110) and (111) Surfaces

T. C. Rödel, C. Bareille, F. Fortuna, C. Baumier, F. Bertran, P. Le Fèvre, M. Gabay, O. Hijano Cubelos, M. J. Rozenberg, T. Maroutian, P. Lecoeur, and A. F. Santander-Syro

Phys. Rev. Applied 1, 051002 – Published 18 June 2014

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Orientational Tuning of the Fermi Sea of Confined Electrons at the ${SrTiO}_{3}$ (110) and (111) Surfaces