Epitaxial engineering of flat silver fluoride cuprate analogs

Abstract

As-grown AgF2 has a remarkably similar electronic structure as insulating cuprates, but it is extremely electronegative, which makes it hard to handle and dope. Furthermore, buckling of layers reduces magnetic interactions and enhances unwanted self-trapping lattice effects. We argue that epitaxial engineering can solve all these problems. By using a high throughput approach and first principle computations, we find a set of candidate substrates which can sustain the chemical aggressiveness of AgF2 and at the same time have good lattice parameter matching for heteroepitaxy, enhancing AgF2 magnetic and transport properties and opening the possibility of field-effect carrier injection to achieve a new generation of high-Tc superconductors. Assuming a magnetic mechanism and extrapolating from cuprates we predict that the superconducting critical temperature of a single layer can reach 195 K.

Separation‐Controlled Redox Reactions

“…[12] For a proof of concept we have picked a single layer of MgO as a reductor; this compound offers a good match of lattice constants (and thus negligible strain) with the RbMgF 3 spacer. Moreover, as shown before [13] it generates a strong charge transfer when in direct contact with the AgF 2 layer. The said charge reservoir, MgO, should sit on the appropriate redox-inert substrate.…”

“…7.76 eV for the 010 surface, and 7.21 eV for a single flat layer), [11] smooth charge transfer to AgF 2 could not be realized so far; [12] even Pt electrodes get oxidized when in touch with this voracious oxidizer. [12,13] Figure 1 demonstrates the principle of our setup which eliminates all these problems simultaneously.…”

“…Here, we have used RbMgF 3 which proved to provide the best match of lattice constants between the separator and AgF 2 . [13] RbMgF 3 is an ionic broad band gap insulator with the static dielectric constant close to unity. The spacer forms an interface also with the charge reservoir layer, which in our case should serve as reducing agent towards AgF 2 .…”

Fluorides of Silver Under Large Compression**

“…[20] The interest in spin-spin interactions in this system is motivated by recent discoveries of many similaritiesb etween AgF 2 and La 2 CuO 4 -aprecursor of copper oxide-based superconductors. [21][22][23][24] Here we present ad etailed computational exploration of the phase diagram of the binary Ag/F 2 system under large compression.I nc ontrastt or ecent work, [3] which considered only compounds with Ag in as ingle valence state (Ag I F, Ag II F 2 , Ag III F 3 ,A g IV F 4 ), we also lookeda tt he possibility of formation of as yet unknown mixed-valencec ompounds such as Ag 3 F 4 (= Ag I 2 Ag II F 4 ). The mixed-valence systems are of particular interest here since they formally correspond to electron-or holedoped AgF 2 .M oreover, either as ubstantial decrease or even closingo fthef undamentalb and gap (metallization) is expected to be obtainedu pon e À or h + doping in mixed-valenceo r intermediate valence fluorides of silver,a st ypical examples of Class Io rC lass III mixed-valence compounds, [25] respectively.…”

“…On the other hand, compression‐induced phase transitions of silver difluoride, AgF 2 (containing the 4d 9 Ag 2+ cation), [18, 19] are found to lead to both a dramatic increase in the antiferromagnetic (AFM) superexchange interaction between Ag 2+ centres, and a decrease of the magnetic dimensionality from 2D to 0D [20] . The interest in spin‐spin interactions in this system is motivated by recent discoveries of many similarities between AgF 2 and La 2 CuO 4 ‐ a precursor of copper oxide‐based superconductors [21–24] …”