Anomalous orbital structure in a spinel–perovskite interface

Abstract

In all archetypical reported (001)-oriented perovskite heterostructures, it has been deduced that the preferential occupation of two-dimensional electron gases is in-plane dxy state. In sharp contrast to this, the investigated electronic structure of a spinel-perovskite heterostructure γ-Al2O3/SrTiO3 by resonant soft X-ray linear dichroism, demonstrates that the preferential occupation is out-of-plane dxz/dyz states for interfacial electrons. Moreover, the impact of strain further corroborates that this anomalous orbital structure can be linked to the altered crystal field at the interface and symmetry breaking of the interfacial structural units. Our findings provide another interesting route to engineer emergent quantum states with deterministic orbital symmetry.

Suppressed carrier density for the patterned high mobility two-dimensional electron gas at γ-Al2O3/SrTiO3 heterointerfaces

“…Nevertheless, although extensive research has been carried out on this system, the typical mobility remains ~ 1,000 cm 2 V -1 s -1 or less (at low temperatures). Recently, a new 2DEG was discovered at the non-isostructural interface between perovskite STO and spinel -Al2O3 (GAO) with compatible oxygen sublattices [6][7][8][9][10] . Remarkably, the GAO/STO heterostructure shows much higher electron mobility (greater than 140, 000 cm 2 V -1 s -1 ) as well as extremely high carrier densities of more than 10 15 cm -2 .…”

Stimulating Oxide Heterostructures: A Review on Controlling SrTiO3‐Based Heterointerfaces with External Stimuli

“…It was also demonstrated using resonant soft X‐ray linear dichroism that the out‐of‐plane d xz / d yz bands have a lower energy state than the in‐plane d xy bands in the GAO/STO heterostructure (see Figure ) . This is in sharp contrast to the heterostructure where LAO is deposited on the (001) surface of STO and the in‐plane d xy state is the lowest energy subband.…”

“…This typically leads to a biaxial strain where the thin film is elongated (compressed) in the plane of the film and compressed (elongated) perpendicular to the plane. By using appropriate substrates, the value of the strain can be varied and large biaxial strain of several percent can typically be achieved . Biaxial strain was used, e.g., to increase the transition temperature in high‐Tc superconductors and ferroelectric materials as well as the superconducting transition temperature in STO .…”

“…This is in sharp contrast to the heterostructure where LAO is deposited on the (001) surface of STO and the in‐plane d xy state is the lowest energy subband. In the study by Cao et al, GAO/STO was deposited epitaxially on NdGaO 3 and TbScO 3 substrates, which caused a 1.16% compressive and 1.29% tensile strain to the heterostructure, respectively . The splitting between the in‐plane and out‐of‐plane bands were found to be highly tunable with compressive strain leading to an enlargement of the splitting while practically degenerate bands were observed with tensile strain.…”

Strain Engineering of Epitaxial Oxide Heterostructures Beyond Substrate Limitations

“…Strong coupling and complex interplay between strain and spin, charge, orbital and lattice degrees of freedom provide a fertile new ground for creating exotic phases and realizing novel functionalities in complex oxide thin films and heterostructures [1][2][3][4][5][6][7][8] . This has enabled epitaxial strain as a powerful tool for the creation of new ground states (associated with phase transitions) [9][10][11][12][13] , the improvement of catalytic activity [14][15][16] , and the manipulation of electric and magnetic properties [17][18][19][20][21][22][23][24] including greatly enhanced superconducting, 26,27 ferroelectric 28,29 and ferromagnetic 31,32 transition temperatures. To realize these emergent phenomena, the availability of appropriate single-crystal substrates for the growth of high-quality epitaxial oxide films with a desired strain state cannot be overemphasized 4,33 .…”