Pure electronic metal-insulator transition at the interface of complex oxides

Abstract

In complex materials observed electronic phases and transitions between them often involve coupling between many degrees of freedom whose entanglement convolutes understanding of the instigating mechanism. Metal-insulator transitions are one such problem where coupling to the structural, orbital, charge, and magnetic order parameters frequently obscures the underlying physics. Here, we demonstrate a way to unravel this conundrum by heterostructuring a prototypical multi-ordered complex oxide NdNiO3 in ultra thin geometry, which preserves the metal-to-insulator transition and bulk-like magnetic order parameter, but entirely suppresses the symmetry lowering and long-range charge order parameter. These findings illustrate the utility of heterointerfaces as a powerful method for removing competing order parameters to gain greater insight into the nature of the transition, here revealing that the magnetic order generates the transition independently, leading to an exceptionally rare purely electronic metal-insulator transition with no symmetry change.

Charge order and antiferromagnetism in epitaxial ultrathin films ofEuNiO3

“…Previous studies by several groups, including our recent work on NNO, have shown the E -type AFM order in the nickelates is very robust and likely plays a significant role in the MIT transition in the less distorted nickelates 19,29,30,38 . In ENO, however, the separation of the MIT and the AFM transitions is nearly 300 K allowing independent investigation of each.…”

“…This class of materials has received significant attention recently due to the MIT 17 , E -type anti-ferromagnetic transition (AFM) 19 , structural transition 17 , predicted high T c superconductivity 20 , potential for device applications 6,7,21 , and the charge-ordering transition [22][23][24][25][26] . The charge ordering transition, in particular, a) Electronic mail: dmeyers@email.uark.edu has been a source of controversy and still requires further insight [27][28][29][30] . Indeed, devices utilizing less distorted NdNiO 3 (NNO) have already been realized, including electric field control, however the low transition temperature (∼ 150K) limits the practically of such systems 7,18,21 .…”

“…1(a). In the rare-earth nickelates, the CO transition is invariably present in the bulk, but, as in the manganites, has been shown to be suppressed in hetero-epitaxial ultra-thin film of NNO 24,[29][30][31] . Specifically, it was found that the interface is able to "pin" the symmetry in the non-CO Pbnm state, analogous to the effect of surface strain in La 0.5 Ca 0.5 MnO 3 and Sr 2 RuO 4 12,32 .…”

Ramp‐Reversal Memory and Phase‐Boundary Scarring in Transition Metal Oxides

“…Phase separation has been recently reported in ultrathin films. [25] Conflicting evidence for the presence of charge ordering [26][27][28][29] and the role of electronic vs. magnetic correlations [28,30] point to the intricate nature of this transition (see for example [31] and references therein).In typical T-driven MIT measurements, the temperature is ramped up from low to high temperatures, driving the system from an insulating to a metallic phase. To observe the memory effect, we perform a series of resistance vs. temperature (R-T) measurements, where we interrupt the usual temperature rise with a reversal of the ramp from heating to cooling at a specific temperature, TH, which lies within the transition region.…”

“…Phase separation has been recently reported in ultrathin films. [25] Conflicting evidence for the presence of charge ordering [26][27][28][29] and the role of electronic vs. magnetic correlations [28,30] point to the intricate nature of this transition (see for example [31] and references therein).…”