Origin of the Anomalous Mass Renormalization in Metallic Quantum Well States of Strongly Correlated OxideSrVO3

Abstract

In situ angle-resolved photoemission spectroscopy (ARPES) has been performed on SrVO3 ultrathin films, which show metallic quantum well (QW) states, to unveil the origin of the anomalous mass enhancement in the QW subbands. The line-shape analysis of the ARPES spectra reveals that the strength of the electron correlation increases as the subband bottom energy approaches the Fermi level. These results indicate that the anomalous subband-dependent mass enhancement mainly arises from the quasi-one-dimensional character of confined V 3d states as a result of their orbital-selective quantization.PACS numbers: 73.21. Fg, 71.27.+a, Quantum confinement of strongly correlated electrons in oxide heterostructures has attracted considerable interest not only for its potential for technological applications in future oxide electronics, but also for the opportunity it presents to better understand the fundamental low-dimensional physics of strongly correlated electron systems [1]. The reduction of the dimensionality changes the complex interaction among the spin, charge, and orbital degrees of freedom of the correlated electrons, resulting in the emergence of unusual quantum phenomena [2,3]. Recently, metallic quantum well (QW) states have been clearly observed by using angle-resolved photoemission spectroscopy (ARPES) for strongly correlated electrons in SrVO 3 (SVO) ultrathin films grown on SrTiO 3 (STO) substrates, where the high-density strongly correlated electrons of the order of ∼ 10 22 cm −3 are confined in a narrow space on the scale of a few nanometers [4]. This situation is distinct from the two-dimensional electron gas (2DEG) states in oxide semiconductors [5][6][7][8][9][10][11]. Thus, such a use of quantum confinement to form twodimensional electron liquid (2DEL) states will provide a foundation for studying the behavior of strongly correlated electrons under reduced dimensions and for controlling the extraordinary physical properties of strongly correlated oxides.The observed metallic QW states in SVO ultrathin films exhibit two distinctive features [4]. The first is the orbital-selective quantization originating from the anisotropic orbital character of the V 3d t 2g (d xy , d yz , and d zx ) band states. In bulk crystals, each band essentially has a two-dimensional (2D) character in the xy, yz, and zx planes, respectively. In thin films, the * Author to whom correspondence should be addressed; masakik@post.kek.jp † Present address: Department of Applied Chemistry, Tokyo Institute of Technology, Tokyo 152-8522, Japan 2D nature of each band causes the further reduction of dimensionality to one dimension that is determined by the quantization direction: When the SVO film has become sufficiently thin in the z direction to realize quantum confinement, the bands derived from the d yz /d zx orbitals are subject to quantization (changing from 2D to 1D (one-dimensional)), while the d xy band states remain unchanged (maintaining their 2D nature). The other distinctive feature is the anomalous mass enhancement, which de...

Hubbard band versus oxygen vacancy states in the correlated electron metal SrVO3

“…The coherent growth of these SrVO 3 thin film was confirmed by four-circle X-ray diffraction measurements. The characterization results are essentially identical to those reported in previous studies [41,43,44], and indicate that there are no detectable structural disorders in the prepared SrVO 3 thin films grown on Nb:SrTiO 3 (001) substrates.…”

Correlated electronic states of SrVO 3 revealed by angle-resolved photoemission spectroscopy

“…As the bottom of the subband approaches E F , anomalous enhancement of the effective electron mass, which is a few times larger than that in the bulk band, has been observed [15]. Since such a strong mass enhancement has not been observed in typical QW states in metal thin films, this can be viewed as a characteristic phenomenon originating from strong electron correlation between d electrons which are confined in quasi-one-dimensional space [18]. Fundamental understanding of the QW states with correlated electrons in SrVO 3 would provide a new way to material design in functional oxide devices by using the QW states.…”

High Carrier Mobility, Electrical Conductivity, and Optical Transmittance in Epitaxial SrVO3 Thin Films

“…These findings indicate that TCO films such as SVO, and probably other materials requiring ultralow oxygen pressure deposition conditions, can be grown with optimal properties by PLD or other more scalable techniques, as required for large scale applications. From a different perspective and beyond the scope of TCOs, SVO films have been explored in search of quantum confinement effects; indeed, orbital selective quantization and anomalous mass enhancement effects have been reported in PLD‐grown films, and SVO is considered to be the drosophila model for strongly correlated physics . Moreover, as emphasized by Backes et al, the role of defects is pivotal for a microscopic description of the spectroscopic features.…”