Frustration-driven C 4 symmetric order in a naturally-heterostructured superconductor Sr2VO3FeAs

Abstract

A subtle balance between competing interactions in iron-based superconductors (FeSCs) can be tipped by additional interfacial interactions in a heterostructure, often inducing exotic phases with unprecedented properties. Particularly when the proximity-coupled layer is magnetically active, rich phase diagrams are expected in FeSCs, but this has not been explored yet. Here, using high-accuracy 75As and 51V nuclear magnetic resonance measurements, we investigate an electronic phase that emerges in the FeAs layer below T 0 ~ 155 K of Sr2VO3FeAs, a naturally assembled heterostructure of an FeSC and a Mott-insulating vanadium oxide. We find that frustration of the otherwise dominant Fe stripe and V Neel fluctuations via interfacial coupling induces a charge/orbital order in the FeAs layers, without either static magnetism or broken C 4 symmetry, while suppressing the Neel antiferromagnetism in the SrVO3 layers. These findings demonstrate that the magnetic proximity coupling stabilizes a hidden order in FeSCs, which may also apply to other strongly correlated heterostructures.

Pressure dependence of the superconducting and magnetic transition temperatures in Sr2VO3FeAs

“…therefore imply V ordering. Reports on 51 V and 75 As nuclear magnetic resonance (NMR) are inconsistent since they either claim Fe magnetism [40,41] or argue in favor of V magnetism [27,38]. NMR measurements on our sample (Appendix D) are in agreement with the literature data to a large extent, but they cannot provide a conclusive answer as to which element carries the ordering moments.…”

Order on Command

“…S10]. We found that the C 4 order can be erased near 60 K, right above the Fe magnetic ordering temperature found in NMR measurement [29]. On the other hand, the application of a magnetic field up to 7 T does not induce any qualitative change in the C 4 (2 × 2) pattern in the Cr tip SPSTM topograph [ Fig.…”

“…At optimal doping, the FeAs layer usually prefers C 2 magnetism harboring superconductivity, while the VO 2 layer prefers C 4 magnetism [1][2][3]21]. Previous experimental studies of Sr 2 VO 3 FeAs [22][23][24][25][26][27][28], however, have reported inconsistent results about magnetic order; recent nuclear magnetic resonance (NMR) measurements on single crystals [29] and neutron diffraction [30] experiments show that there is no long-range magnetic order in the V lattice at any temperature, while in the Fe lattice a magnetic order with a small moment of ∼0.05μ B , possibly due to frustration, is developed below 50 K. Indeed, a theoretical generalized gradient approximation (GGA) calculation has suggested that there can be a number of competing metastable magnetic states composed of different symmetries in V and Fe layers [21]. This is a reasonable theoretical prediction considering the coupling and frustration between V and Fe layers (Supplemental Material Sec.…”

“…We grew single crystals of Sr 2 VO 3 FeAs with a self-flux method [29], which are then cleaved in situ at a temperature ∼15 K just before mounting on the STM head. Because of the weakly van der Waals-coupled SrO-SrO layers, the cleaved surface is almost always terminated with a symmetrically cleaved SrO layer.…”

“…3(e)] can be understood from the fact that the pristine state will probably have either C 2 single-stripe correlations or (in the presence of disorder) short-range C 2 single-stripe orders, both supporting superconducting pairing (Refs. [21,29], and Supplemental Material Sec. I [31]).…”