Pseudogaps and Emergence of Coherence in Two-Dimensional Electron Liquids inSrTiO3

Quasistatic antiferromagnetism in the quantum wells of SmTiO3/SrTiO3 heterostructures

“…A 2 nm (4 nm) STO quantum well is composed of 5 SrO (10 SrO) planes alternating with 6 (11) planes of TiO 2 , and all quantum well thicknesses are hereafter referenced by their number of SrO planes. Previous tunneling spectra show that in a 5 SrO quantum well a pseudogap opens at~20 K, while a 10 SrO well does not display a gap opening above 2 K. 22 Excellent sample quality consistent with previous reports, [23][24][25] including uniform layer thicknesses and sharp interfaces, was verified by measuring a reference 5 SrO quantum well heterostructure embedded between thick SmTiO 3 spacer layers via x-ray reflectometry measurements (Fig. 1a).…”

“…Our data demonstrate the onset of quasistatic antiferromagnetic correlations coincident with the T * state inside the SrTiO 3 quantum wells and suggest that incipient antiferromagnetic order drives the formation of the pseudogap state in this oxide heterostructure. 22 More broadly, our results suggest that high density quantum wells driven towards a metal-insulator transition emulate the essential physics underlying bulk antiferromagnetic Mott states as they are destabilized via carrier substitution.…”

“…20,21 Chief among these is the appearance of a low temperature pseudogap state whose onset temperature T * is enhanced with increasing carrier density (thinner wells). 22 The proximity of antiferromagnetism in the Mott insulating SmTiO 3 host matrix of this heterostructure is hypothesized to be endemic to this behavior and suggests parallels to the pseudogap states observed near the antiferromagnetic Mott states of bulk transition metal oxides.…”

“…For 5 SrO thick wells, a pseudogap appears below~20 K consistent with the T * freezing transition resolved in our wTF µSR data. 22 This connects the quasistatic spin freezing to the free carriers in the wells as the origin for pseudogap formation. Furthermore, the proximity of the antiferromagnetic SmTiO 3 host is key to stabilizing this behavior.…”

Oxide Heterostructures from a Realistic Many-Body Perspective

“…Further investigations hint towards competing AFM-FM fluctuations in the Mott-critical zone as a possible cause for NFL behavior (Lechermann 2017b). A pseudogap(-like) structure in the theoretical spectral function subject to such fluctuations has indeed been identified in experimental studies (Marshall et al 2016). In an extension of this study, it was shown that the addition of further SrO layers establishes an extra band-insulating regime in the formed SrTiO 3 -like region, with a stronger inplane xy-polarized metallic layer at the boundary (Lechermann 2017a).…”