Conduction Band Structure of SrTiO₃

Abstract

Shubnikov de Haas(SdH) oscillations have been measured for the semiconducting single domain SrTiO3 with Carrier concentration of 3.4×1018 cm-3 and 5.9×1018 cm-3. From the temperature dependence of the SdH amplitude, the cyclotron mass values are determined for the [001] and [110] magnetic field directions. We have found, from the angular dependence of the SdH oscillation, that there exist several branches of the frequencies among which the highest and lowest branches originate from the Fermi spheres at the Brillouin zone center, and the other ones from the extremal area which is interconnected through the magnetic breakdown tunneling paths. Energy band parameters based on the k p perturbation method are determined.

Structure and correlation effects in semiconductingSrTiO3

“…The elliptic bands, with an aspect ratio of about 2.4, represent cuts through the in-plane-oriented d yz and d zx ellipsoidal pockets. The elongation of the ellipsoids is much stronger than the findings of the Shubnikov-de Haas oscillations, 17,18 in which the crystals with small values of n͑ϳ5 ϫ 10 18 cm −3 ͒ are used. However, the strong elongation is in agreement with the theoretical band model ͑n =10 19 -10 20 cm −3 ͒.…”

“…The thermoelectricity is directly related to the effective mass, which has been measured by different experimental methods 5,17,18,32 and rarely compared with calculations. 6,33 Differences between our observed value of effective mass and the calculated values suggest the need for improved electronic-structure calculations and further investigation of STO with different doping.…”

“…While earlier transport 17,18 and angle-resolved photoemission spectroscopy ͑ARPES͒ ͑Refs. 19-22͒ measurements provided some information, important details such as the Fermi-surface size and band offsets are in disagreement with theory 15,16 and furthermore the effects of the structural change and electron correlation on the band structure have not been determined.…”

Enhancing the electron mobility of SrTiO3 with strain

“…Previous estimates of the conduction band splitting 7,8 due to the tetragonal distortion suggest that the Fermi energy for the two samples studied may well be below that needed to solely occupy the lower band when the films are under compressive stress, transport occurs in a single band. The highly enhanced mobility implies that under compressive stress the lower, solely occupied state has a light mass along the strain ͑com-pressive͒ and transport direction.…”

“…1͑b͔͒. 7,8 The manifold of states resembles in many ways the states in conventional semiconductors, such as Si, Ge, or GaAs, at the top of the valence band. In these semiconductors, a compressive, uniaxial stress along the transport direction results in valence band splitting and warping, reducing the effective mass and causing dramatic gains in the hole mobility.…”