Picoscale structural insight into superconductivity of monolayer FeSe/SrTiO3

Experiments reveal interfacial atomic-scale structure that may be critical for the interface enhanced high Tc in FeSe/SrTiO3. Remarkable enhancement of the superconducting transition temperature (Tc) has been observed for monolayer (ML) FeSe films grown on SrTiO3 substrates. The atomic-scale structure of the FeSe/SrTiO3 interface is an important determinant of both the magnetic and interfacial electron-phonon interactions and is a key ingredient to understanding its high-Tc superconductivity. We resolve the atomic-scale structure of the FeSe/SrTiO3 interface through a complementary analysis of scanning transmission electron microscopy and in situ surface x-ray diffraction. We find that the interface is more strongly bonded for a particular registration, which leads to a coherently strained ML. We also determine structural parameters, such as the distance between ML FeSe and the oxide, Se─Fe─Se bond angles, layer-resolved distances between Fe─Se, and registry of the FeSe lattice relative to the oxide. This picoscale structure determination provides an explicit structural framework and constraint for theoretical approaches addressing the high-Tc mechanism in FeSe/SrTiO3.

[1]  Qinghua Zhang,et al.  Oxygen vacancy modulated superconductivity in monolayer FeSe on SrTiO3−δ , 2019 .

[2]  I. Alexandrou,et al.  Visualization of Dopant Oxygen Atoms in a Bi2Sr2CaCu2O8+δ Superconductor , 2019, Advanced Functional Materials.

[3]  X. Lou,et al.  Evidence of cooperative effect on the enhanced superconducting transition temperature at the FeSe/SrTiO3 interface , 2019, Nature Communications.

[4]  W. Qin,et al.  Enhanced Superconducting State in FeSe/SrTiO_{3} by a Dynamic Interfacial Polaron Mechanism. , 2019, Physical review letters.

[5]  Q. Xue,et al.  Asymmetrically optimized structure in a high-Tc single unit-cell FeSe superconductor , 2018, Journal of physics. Condensed matter : an Institute of Physics journal.

[6]  W. Kaplan,et al.  Discerning interface atomistic structure by phase contrast in STEM: The equilibrated Ni-YSZ interface , 2018, Acta Materialia.

[7]  Ivan Lazić,et al.  Phase contrast scanning transmission electron microscopy imaging of light and heavy atoms at the limit of contrast and resolution , 2018, Scientific Reports.

[8]  D. Muller,et al.  Deep sub-Ångstrom imaging of 2D materials with a high dynamic range detector , 2018, 1801.04630.

[9]  G. Sawatzky,et al.  Electron Phonon Coupling versus Photoelectron Energy Loss at the Origin of Replica Bands in Photoemission of FeSe on SrTiO_{3}. , 2017, Physical review letters.

[10]  C. Ahn,et al.  Picoscale materials engineering , 2017 .

[11]  Q. Xue,et al.  Origin of charge transfer and enhanced electron–phonon coupling in single unit-cell FeSe films on SrTiO3 , 2017, Nature Communications.

[12]  P. Nellist,et al.  Electron ptychographic microscopy for three-dimensional imaging , 2017, Nature Communications.

[13]  J. Moodera,et al.  Direct imaging of electron transfer and its influence on superconducting pairing at FeSe/SrTiO3 interface , 2017, Science Advances.

[14]  O. Dolgov,et al.  The electron–phonon interaction with forward scattering peak is dominant in high Tc superconductors of FeSe films on SrTiO 3 (TiO2) , 2016, 1607.00843.

[15]  E. Altman,et al.  Surface phase, morphology, and charge distribution transitions on vacuum and ambient annealedSrTiO3(100) , 2016 .

[16]  S. Ismail-Beigi,et al.  Role of double Ti O 2 layers at the interface of FeSe/ SrTi O 3 superconductors , 2016, 1605.01312.

[17]  A. Millis,et al.  Charge transfer and electron-phonon coupling in monolayer FeSe on Nb-doped SrTiO 3 , 2016, 1603.02728.

[18]  M. Fang,et al.  A unifying phase diagram with correlation-driven superconductor-to-insulator transition for the 122 series of iron chalcogenides , 2016 .

[19]  Yan Wang,et al.  Ab initio study of cross-interface electron-phonon couplings in FeSe thin films on SrTiO 3 and BaTiO 3 , 2016, 1602.03288.

[20]  D. Feng,et al.  Direct evidence of superconductivity and determination of the superfluid density in buried ultrathin FeSe grown on SrTiO 3 , 2016, 1602.02580.

[21]  Dung-Hai Lee,et al.  What makes the Tc of monolayer FeSe on SrTiO3 so high: a sign-problem-free quantum Monte Carlo study , 2015, Science bulletin.

[22]  Qinghua Zhang,et al.  Atomically resolved FeSe/SrTiO3(001) interface structure by scanning transmission electron microscopy , 2015, 1512.05203.

[23]  Dung-Hai Lee.  What makes the Tc of FeSe/SrTiO3 so high? , 2015 .

[24]  X. H. Chen,et al.  Evolution of High-Temperature Superconductivity from a Low-T_{c} Phase Tuned by Carrier Concentration in FeSe Thin Flakes. , 2015, Physical review letters.

[25]  X. Lou,et al.  Anomalous correlation effects and unique phase diagram of electron-doped FeSe revealed by photoemission spectroscopy , 2015, Nature Communications.

[26]  Takashi Takahashi,et al.  High-temperature superconductivity in potassium-coated multilayer FeSe thin films. , 2015, Nature materials.

[27]  Yan Wang,et al.  Enhanced superconductivity due to forward scattering in FeSe thin films on SrTiO3 substrates , 2015, 1507.03967.

[28]  D. Feng,et al.  Onset of the Meissner effect at 65 K in FeSe thin film grown on Nb-doped SrTiO3 substrate , 2015, 1507.00129.

[29]  Wei Zhang,et al.  Plain s-wave superconductivity in single-layer FeSe on SrTiO3 probed by scanning tunnelling microscopy , 2015, Nature Physics.

[30]  Q. Xue,et al.  Superconductivity above 100 K in single-layer FeSe films on doped SrTiO3. , 2015, Nature materials.

[31]  C. Ahn,et al.  A new frontier for superconductivity , 2014, Nature Physics.

[32]  S. Louie,et al.  Large electron–phonon interactions from FeSe phonons in a monolayer , 2014, 1407.5657.

[33]  Q. Xue,et al.  Superconductivity in single-layer films of FeSe with a transition temperature above 100 K , 2014, 1406.3435.

[34]  Q. Xue,et al.  Molecular beam epitaxy growth and post-growth annealing of FeSe films on SrTiO3: a scanning tunneling microscopy study , 2014, Journal of physics. Condensed matter : an Institute of Physics journal.

[35]  D. Feng,et al.  Critical role of substrate in the high temperature superconductivity of single layer FeSe on Nb:BaTiO$_3$ , 2014, 1402.1357.

[36]  Z. K. Liu,et al.  Interfacial mode coupling as the origin of the enhancement of Tc in FeSe films on SrTiO3 , 2013, Nature.

[37]  Hongjun Xiang,et al.  Interfacial effects on the spin density wave in FeSe/SrTiO3thin films , 2013, 1310.4024.

[38]  Lin Zhao,et al.  Phase diagram and electronic indication of high-temperature superconductivity at 65 K in single-layer FeSe films. , 2012, Nature materials.

[39]  K. Mitsuhara,et al.  The structure of SrTiO3(001)-2 × 1 surface analyzed by high-resolution medium energy ion scattering coupled with ab initio calculations. , 2013, The Journal of chemical physics.

[40]  Lin Zhao,et al.  Phase Diagram and High Temperature Superconductivity at 65 K in Tuning Carrier Concentration of Single-Layer FeSe Films , 2012 .

[41]  Q. Xue,et al.  High temperature superconductivity in single unit-cell FeSe films on SrTiO$_{3}$ , 2014 .

[42]  L. Marks,et al.  Vacant-Site Octahedral Tilings on SrTiO 3 (001), the ( 13 × 13 ) R 33.7 ° Surface, and Related Structures , 2011 .

[43]  G. Kotliar,et al.  Kinetic frustration and the nature of the magnetic and paramagnetic states in iron pnictides and iron chalcogenides. , 2011, Nature materials.

[44]  T. Muranaka,et al.  Pressure-induced high- T c superconducting phase in FeSe: Correlation between anion height and T c , 2010, 1002.1832.

[45]  F. Hsu,et al.  Superconductivity in the PbO-type structure α-FeSe , 2008, Proceedings of the National Academy of Sciences.

[46]  H. Eisaki,et al.  Effect of Structural Parameters on Superconductivity in Fluorine-Free LnFeAsO1-y (Ln = La, Nd) , 2008, 0806.3821.

[47]  O. Bunk,et al.  Surface structure of SrTiO{sub 3}(001) , 2007 .

[48]  O. Bunk,et al.  Surface of strontium titanate. , 2007, Physical review letters.

[49]  N. Erdman,et al.  Surface structures of SrTiO3 (001): a TiO2-rich reconstruction with a c(4 x 2) unit cell. , 2003, Journal of the American Chemical Society.

[50]  N. Erdman,et al.  SrTiO3(0 0 1) surface structures under oxidizing conditions , 2003 .

[51]  Hisashi Sato,et al.  Reflection high-energy electron diffraction study on the SrTiO3 surface structure , 1994 .

[52]  I. Lazic,et al.  Chapter Three – Analytical Review of Direct Stem Imaging Techniques for Thin Samples , 2017 .

[53]  Ivan Lazić,et al.  Phase contrast STEM for thin samples: Integrated differential phase contrast. , 2016, Ultramicroscopy.

[54]  A. Hirata,et al.  Direct Observation of High-Temperature Superconductivity in One-Unit-Cell FeSe Films , 2014 .