Depth-resolved charge reconstruction at the LaNiO3/CaMnO3 interface

Abstract

Rational design of low-dimensional electronic phenomena at oxide interfaces is currently considered to be one of the most promising schemes for realizing new energy-efficient logic and memory devices. An atomically-abrupt interface between paramagnetic LaNiO 3 and antiferromagnetic CaMnO 3 exhibits interfacial ferromagnetism, which can be tuned via a thickness-dependent metal-insulator transition in LaNiO 3. Once fully understood, such emergent functionality could turn this archetypal Mott-interface system into a key building block for the above-mentioned future devices. Here, we use depth-resolved standing-wave photoemission spectroscopy in conjunction with scanning transmission electron microscopy and x-ray absorption spectroscopy, to demonstrate a depth-dependent charge reconstruction at the LaNiO 3 /CaMnO 3 interface. Our measurements reveal an increased concentration of Mn 3+ and Ni 2+ cations at the interface, which create an electronic environment favourable for the emergence of interfacial ferromagnetism mediated via the Mn 4+-Mn 3+ ferromagnetic double exchange and Ni 2+-O-Mn 4+ superexchange mechanisms. Our findings suggest a new strategy for designing functional Mott oxide heterostructures by tuning the interfacial cation characteristics via controlled manipulation of thickness, strain, and ionic defect states. by tuning the thickness of the LaNiO layer, which undergoes a metal-insulator transition in the ultrathin limit (<4 u.c.), resulting in the thickness-dependent controllability of the magnetic moment at the interface as demonstrated in a prior study [15].

Probing single-unit-cell resolved electronic structure modulations in oxide superlattices with standing-wave photoemission

“…It is immediately apparent that the three experimental rocking-curves are shifted with respect to each other in angular position (phase), 14 suggesting a different depth-of-origin (see Fig. 2c) [37,42], which is consistent with our prior analysis, as shown in Figs. 3c-g.…”

“…prior studies [19,20,35]. The thickness of the surface-adsorbed atmospheric contaminant (labelled "C/O") is 5 Å, also consistent with prior studies [35,37]. The blue-to-white color contrast in Fig.…”

“…b. 16 18 20 0.9 [26,35,37]. It is important to note that, although the entire superlattice, including the substrate and the surface-adsorbed atmospheric contaminant, must be considered by the model, only the topmost layers are actually relevant for our photoemission measurement due to the limited EAL of photoelectrons at 833 eV (~20 Å) [27,35,38,39].…”

Probing surfaces and interfaces in complex oxide films via in situ X-ray photoelectron spectroscopy

“…SrTiO 3 superlattices was reported [138]. Studies of LaNiO 3 -CaMnO 3 superlattices showed similar effects, with Ni 2+ states observed at the interface [139]. Likewise, changes in the interfacial Mn valence in (La,Sr) MnO 3 -SrTiO 3 superlattices were also observed [140].…”

Local polarization and valence distribution in LaNiO3/LaMnO3 heterostructures

“…The termination also affects the work function 17,18 , which is directly related to the band alignment. Even if we have a technique to arrange the atoms as designed, an interface or surface reconstruction of atomic [19][20][21][22] , valence [23][24][25] , and orbital arrangements [26][27][28] occur spontaneously, and the local field is altered. Therefore, experimental observation of the interfacial valence-and atomicarrangements is needed to understand and control the oxide interface properties.…”