Post-growth Fe deposition on the superconductivity of monolayer FeSe films on 
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Jiao, Xiaotong; Gong, Guanghua; Zhang, Zhe; Dong, Wenfeng; Ding, Cui; Pan, Minghu; Wang, Lili; Xue, Qunji

doi:10.1103/physrevmaterials.6.064803

“…We cannot make any quantitative statements on the size of l max S at this time -however, we would like to stress that free-standing iron-based monolayers are unstable. As such, they are necessarily epitaxially grown on a substrate, such as SrTiO 3 [96,97]. The bonding between FeSe and SrTiO 3 is not weak, involves a sharing of electrons (doping of FeSe [40]), and is known to strain the iron atoms [40,95] -leading to a small difference in lattice constant relative to the bulk [40].…”

Section: Discussionmentioning

confidence: 99%

“…The purpose of this manuscript is two fold: lay down the general theoretical framework necessary for future investigations into a new class of moire heterostructures, as well as provide a clear proposal for immediate experimental exploration of a specific device composed of either FeSe/SrTiO 3 [26,[95][96][97] or FeTe/SrTiO 3 [52,55] monolayers. To this end we have organized this paper in such a way as to prioritize the experimental proposal laid out in this Intro, starting first with details specific to moire bands at Γ .…”

Section: Introductionmentioning

confidence: 99%

Twisted-bilayer FeSe and the Fe-based superlattices

Eugenio,

Vafek

2023

SciPost Phys.

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We derive BM-like continuum models for the bands of superlattice heterostructures formed out of Fe-chalcogenide monolayers: (I) a single monolayer experiencing an external periodic potential, and (II) twisted bilayers with long-range moire tunneling. A symmetry derivation for the inter-layer moire tunnelling is provided for both the \GammaΓ and MM high-symmetry points. In this paper, we focus on moire bands formed from hole-band maxima centered on \GammaΓ, and show the possibility of moire bands with C=0C=0 or ±1±1 topological quantum numbers without breaking time-reversal symmetry. In the C=0C=0 region for \theta→0θ→0 (and similarly in the limit of large superlattice period for I), the system becomes a square lattice of 2D harmonic oscillators. We fit our model to FeSe and argue that it is a viable platform for the simulation of the square Hubbard model with tunable interaction strength.

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“…Under the strong interface coupling limit, the 1 UC FeSe film consists of domains with diameters below hundred nanometers separated by unidirectional line defects, wherein the outer gap reaches at 20 meV in maximum. However, the gap magnitude decreases with reduced domain size and even vanishes in isolated domains with diameter below ~20 nm 25 . Besides the random and drastic variation of pairing gaps in the sub-micron scale, the pairing gaps exhibit lateral gradient reduction of ~2 meV per millimeter, resulting from the lateral oxygen gradient accumulation due to their spontaneous flow under the electric field 23 .…”

Section: Introductionmentioning

confidence: 97%

Electronic inhomogeneity and phase fluctuation in one-unit-cell FeSe films

Zhao,

Cui,

Liu

et al. 2024

Nat Commun

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One-unit-cell FeSe films on SrTiO3 substrates are of great interest owing to significantly enlarged pairing gaps characterized by two coherence peaks at ±10 meV and ±20 meV. In-situ transport measurement is desired to reveal novel properties. Here, we performed in-situ microscale electrical transport and combined scanning tunneling microscopy measurements on continuous one-unit-cell FeSe films with twin boundaries. We observed two spatially coexisting superconducting phases in domains and on boundaries, characterized by distinct superconducting gaps ($${\Delta }_{1}$$ Δ 1 ~15 meV vs. $${\Delta }_{2}$$ Δ 2 ~10 meV) and pairing temperatures (Tp1~52.0 K vs. Tp2~37.3 K), and correspondingly two-step nonlinear $$V \sim {I}^{\alpha }$$ V ~ I α behavior but a concurrent Berezinskii–Kosterlitz–Thouless (BKT)-like transition occurring at $${T}_{{{{{{\rm{BKT}}}}}}}$$ T BKT ~28.7 K. Moreover, the onset transition temperature $${T}_{{{{{{\rm{c}}}}}}}^{{{{{{\rm{onset}}}}}}}$$ T c onset ~54 K and zero-resistivity temperature $${T}_{{{{{{\rm{c}}}}}}}^{{{{{{\rm{zero}}}}}}}$$ T c zero ~31 K are consistent with Tp1 and $${T}_{{{{{{\rm{BKT}}}}}}}$$ T BKT , respectively. Our results indicate the broadened superconducting transition in FeSe/SrTiO3 is related to intrinsic electronic inhomogeneity due to distinct two-gap features and phase fluctuations of two-dimensional superconductivity.

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“…The latter is evidenced by the varied gap magnitude from 12 to 17 meV in a couple of millimeters with the gradient distribution of oxygen vacancies (O v ) spontaneously formed under an electric field [ 10 ]. Third, the lattice mismatch and coherent FeSe/TiO 2 coupling lead to tens-of-nanometer-scaled domains in monolayer FeSe separated by line defects of Fe vacancies [ 8 , 21 ], introducing in-plane electronic confinement in turn. Consequently, the electronic structure and paring strength in the monolayer FeSe vary on the nanometer scale [ 10 , 21 ].…”

Section: Introductionmentioning

confidence: 99%

“…Third, the lattice mismatch and coherent FeSe/TiO 2 coupling lead to tens-of-nanometer-scaled domains in monolayer FeSe separated by line defects of Fe vacancies [ 8 , 21 ], introducing in-plane electronic confinement in turn. Consequently, the electronic structure and paring strength in the monolayer FeSe vary on the nanometer scale [ 10 , 21 ].…”

Section: Introductionmentioning

confidence: 99%

Significantly enhanced superconductivity in monolayer FeSe films on SrTiO3(001) via metallic δ-doping

Jiao

¹

,

Dong

²

,

Shi

³

et al. 2023

National Science Review

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Superconductivity transition temperature (Tc) marks the inception of a macroscopic quantum phase-coherent paired state in fermionic systems. For two-dimension superconductivity, the paired electrons condense into a coherent superfluid state at Tc, which is usually lower than the pairing temperature, between which intrinsic physics including Berezinskii-Kosterlitz-Thouless transition and pseudogap state are hotly debated. In the case of monolayer FeSe superconducting films on SrTiO3(001), although the pairing temperature (Tp) is revealed to be 65–83 K by spectroscopy characterization, the measured zero-resistance temperature (${T}_{c}^0$) is limited to 20 K. Here, we report significantly enhanced superconductivity in monolayer FeSe films by δ-doping of Eu or Al on SrTiO3(001) surface, in which ${T}_{c}^0$ is enhanced by 12 K with narrowed transition width ΔTc ∼ 8 K, compared with non-doped samples. Using scanning tunneling microscopy/spectroscopy measurements, we demonstrate lowered work function of the δ-doped-SrTiO3(001) surface and enlarged superconducting gaps in the monolayer FeSe with improved morphology/electronic homogeneity. Our work provides a practical route to enhance 2D superconductivity by interface engineering.

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Post-growth Fe deposition on the superconductivity of monolayer FeSe films on SrTiO3−δ

Cited by 6 publications

References 36 publications

Twisted-bilayer FeSe and the Fe-based superlattices

Twisted-bilayer FeSe and the Fe-based superlattices

Electronic inhomogeneity and phase fluctuation in one-unit-cell FeSe films

Significantly enhanced superconductivity in monolayer FeSe films on SrTiO3(001) via metallic δ-doping

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