Creation and control of a two-dimensional electron liquid at the bare SrTiO3 surface

Abstract

Many-body interactions in transition-metal oxides give rise to a wide range of functional properties, such as high-temperature superconductivity, colossal magnetoresistance or multiferroicity . The seminal recent discovery of a two-dimensional electron gas (2DEG) at the interface of the insulating oxides LaAlO(3) and SrTiO(3) (ref. 4) represents an important milestone towards exploiting such properties in all-oxide devices. This conducting interface shows a number of appealing properties, including a high electron mobility, superconductivity and large magnetoresistance, and can be patterned on the few-nanometre length scale. However, the microscopic origin of the interface 2DEG is poorly understood. Here, we show that a similar 2DEG, with an electron density as large as 8×10(13) cm(-2), can be formed at the bare SrTiO(3) surface. Furthermore, we find that the 2DEG density can be controlled through exposure of the surface to intense ultraviolet light. Subsequent angle-resolved photoemission spectroscopy measurements reveal an unusual coexistence of a light quasiparticle mass and signatures of strong many-body interactions.

How Indium Nitride Senses Water

“…We observe circular electron pockets at the Γ-points, corresponding to a previously observed 2DEG in InN. 17,25 Cuts along the ΓK (k x ) and ΓM (k y ) high symmetry directions in Fig. 2 16 : a heavy-hole (HH), a light-hole (LH) and a split-off hole band (CH), with the valence band (VB) maximum at -1.36 eV.…”

Giant spin splitting of the two-dimensional electron gas at the surface of SrTiO3

“…On the other hand, contrary to P x , which does not change with photon energy or polarization, the out-of-plane component (P z ) of the spin polarization for the inner subband presents an anomaly (it gets inverted) at hν = 52 eV. This suggests that P z originates from extrinsic matrix elements of the SARPES process (Supplementary Note 3).The possibility that the two light subbands of the 2DEG in SrTiO 3 are oppositely spin polarized had been overlooked in previous works [12,13,15], mainly for two reasons mentioned earlier. First, the splitting of the spin polarized state, namely ∼ 0.1Å −1 , or about 100 meV at E F , is unexpectedly large.…”

“…Strontium titanate (SrTiO 3 ), the cornerstone of such oxide-based electronics, is a transparent, nonmagnetic, wide-band-gap insulator in the bulk, and has recently been found to host a surface 2DEG [12][13][14][15]. The most strongly confined carriers within this 2DEG comprise two sub-bands, separated by an energy gap of 90 meV and forming concentric circular Fermi surfaces [12,13,15].Using spin-and angle-resolved photoemission spectroscopy (SARPES), we show that the electron spins in these sub-bands have opposite chiralities. Although the Rashba effect might be expected to give rise to such spin textures, the giant splitting of almost 100 meV at the Fermi level is far larger than anticipated [16,17].…”

“…This degeneracy can be lifted by time-reversal symmetry breaking, implying the possible existence of magnetic order. These results show that confined electronic states at oxide surfaces can be endowed with novel, non-trivial properties that are both theoretically challenging to anticipate and promising for technological applications.The 2DEG at the surface of SrTiO 3 , formed by confined electrons of the t 2g conduction band with Ti-3d character, is universal in the sense that its constituent subbands, their fillings, and their Fermi surfaces are independent of the bulk sample doping and of whether the surfaces are prepared by cleaving [12,13] or by etching and in situ annealing [15]. This 2DEG consists on two light electron subbands dispersing down to about −180 meV and, respectively, −90 meV below the Fermi level (E F ), producing concentric Fermi surfaces around the Brillouin zone center, and heavy shallow subbands dispersing down to about −40 meV, forming ellipsoidal Fermi surfaces [12,13,15].…”

Two-dimensional electron gas at the LaAlO3/SrTiO3 inteface with a potential barrier

“…20 The third model, in turn, consists in the formation of bulk-like oxygen vacancies in the STO layers near the interface, which provide free charge carriers. [21][22][23][24][25][26] The polar catastrophe model is based on the argument that the alternating polarity of atomic layers in LaAlO 3 (LAO) along the [001] direction leads to a diverging electrostatic potential across the structure (hence the words polar catastrophe), unless the electric charges are reconstructed at the interface. Two possible choices for the connection of LAO and STO impose opposite electrostatic boundary conditions.…”