Abstract:Several experimental groups have reported superconductivity in single unit cell layers of FeSe on SrTiO3 and a few other substrates, with critical temperature Tc reports ranging up to 100 K, and a variety of theoretical work has been done. Here we examine more closely the interaction of a single FeSe layer with a TiO2 terminated SrTiO3(001) (STO) substrate. Several situations are analyzed: the underlying ideal interface, the effect of z-polarized longitudinal optic [LO(ẑ)] phonons in STO, electron doping of th… Show more
“…E f of HS lies approximately 1eV above STO valance band maximum (VBM), which nearly at the middle of STO substrate energy gap. Thus, even if strong bonding takes place at the interface, the electronic states at the E f would deteriorate swiftly into STO layer, this supports the use of thin STO film as substrate 52 . Figure 4 Electronic band structure of Cubic STO with vacuum along c-axis.…”
A variety of theoretical and experimental works have reported several potential applications of MoS2 monolayer based heterostructures (HSs) such as light emitting diodes, photodetectors and field effect transistors etc. In the present work, we have theoretically performed as a model case study, MoS2 monolayer deposited over insulating SrTiO3 (001) to study the band alignment at TiO2 termination. The interfacial characteristics are found to be highly dependent on the interface termination. With an insulating oxide material, a significant band gap (0.85eV) is found in MoS2/TiO2 interface heterostructure (HS). A unique electronic band profile with an indirect band gap (0.67eV) is observed in MoS2 monolayer when confined in a cubic environment of SrTiO3 (STO). Adsorption analysis showed the chemisorption of MoS2 on the surface of STO substrate with TiO2 termination which is justified by the charge density calculations that shows the existence of covalent bonding at the interface. The fabrication of HS of such materials paves the path for developing the unprecedented 2D materials with exciting properties such as semiconducting devices, thermoelectric and optoelectronic applications.
“…E f of HS lies approximately 1eV above STO valance band maximum (VBM), which nearly at the middle of STO substrate energy gap. Thus, even if strong bonding takes place at the interface, the electronic states at the E f would deteriorate swiftly into STO layer, this supports the use of thin STO film as substrate 52 . Figure 4 Electronic band structure of Cubic STO with vacuum along c-axis.…”
A variety of theoretical and experimental works have reported several potential applications of MoS2 monolayer based heterostructures (HSs) such as light emitting diodes, photodetectors and field effect transistors etc. In the present work, we have theoretically performed as a model case study, MoS2 monolayer deposited over insulating SrTiO3 (001) to study the band alignment at TiO2 termination. The interfacial characteristics are found to be highly dependent on the interface termination. With an insulating oxide material, a significant band gap (0.85eV) is found in MoS2/TiO2 interface heterostructure (HS). A unique electronic band profile with an indirect band gap (0.67eV) is observed in MoS2 monolayer when confined in a cubic environment of SrTiO3 (STO). Adsorption analysis showed the chemisorption of MoS2 on the surface of STO substrate with TiO2 termination which is justified by the charge density calculations that shows the existence of covalent bonding at the interface. The fabrication of HS of such materials paves the path for developing the unprecedented 2D materials with exciting properties such as semiconducting devices, thermoelectric and optoelectronic applications.
“…In fact, enhancement of T c in the 2D limit (without doping or other extrinsic factors) is extremely rare, with a few prominent examples shown in Figure d. For the most notable example, monolayer FeSe grown on strontium titanate (STO), , the mechanism for enhancement is not yet understood but clearly requires strong substrate interaction, since the opposite trend is observed for FeSe on weakly interacting substrates . 2 H -TaS 2 shows increasing T c for thicknesses below the coherence length, with 4-fold enhancement in T c for the monolayer .…”
Crystalline
two-dimensional (2D) superconductors (SCs) with low
carrier density are an exciting new class of materials in which electrostatic
gating can tune superconductivity, electronic interactions play a
prominent role, and electrical transport properties may directly reflect
the topology of the Fermi surface. Here, we report the dramatic enhancement
of superconductivity with decreasing thickness in semimetallic T
d-MoTe2, with critical temperature
(T
c) increasing up to 7.6 K for monolayers,
a 60-fold increase with respect to the bulk T
c. We show that monolayers possess a similar electronic structure
and density of states (DOS) as the bulk, implying that electronic
interactions play a strong role in the enhanced superconductivity.
Reflecting the low carrier density, the critical temperature, magnetic
field, and current density are all tunable by an applied gate voltage.
The response to high in-plane magnetic fields is distinct from that
of other 2D SCs and reflects the canted spin texture of the electron
pockets.
“…Although ab initio calculations confirm the existence of small-q phonons as a strictly interfacial phenomenon in FeSe/STO [12,[21][22][23] and indicate the importance of the coupling between substrate phonons and FeSe electrons [24], the estimated low value of the electron-phonon coupling constant (λ ≤ 0.4) has been widely considered insufficient to explain the impressive T c enhancement unless another, dominant pairing mechanism is at play [6]. On the other hand, Eliashberg calculations within a single band model suggest that interfacial phonons may lead to the high T c with a coupling of merely half of that estimated by experiments [25].…”
We examine the impact of interfacial phonons on the superconducting state of FeSe/SrTiO3 developing a materials' specific multiband, full bandwidth, anisotropic Eliashberg theory for this system. Our selfconsistent calculations highlight the importance of the interfacial electron-phonon interaction, which is hidden behind the seemingly weak coupling constant λm=0.4, in mediating the high-Tc, and explain other puzzling experimental observations like the s-wave symmetry and replica bands. We discover that the formation of replica bands has a Tc decreasing effect that is nevertheless compensated by deep Fermi-sea Cooper pairing which has a Tc enhancing effect. We predict a strong coupling dip-hump signature in the tunneling spectra due to the interfacial coupling.Superconductivity in monolayer-thick FeSe on SrTiO 3 reaches amazingly high transition temperatures of typically T c =50-70 K [1-6] and up to 100 K [7], much higher than the 8-K value of bulk FeSe [8]. A coupling between SrTiO 3 phonons and FeSe electrons occurs at the FeSe/SrTiO 3 interface, which manifests itself as electron replica bands [6]. The value of this coupling is estimated by experiments to be around 0.4, thus it is commonly believed to moderately enhance T c but not be enough to explain it [6,9,10].The superconducting state in iron-based superconductors is customarily associated with residual spin fluctuations due to the remnant quasi-nesting between electron and hole Fermi sheets that give rise to a sign alternating gap [11]. However, for FeSe/STO the situation is markedly different. Charge transfer at the interface induces electron doping in FeSe [3,4], leading to a distinct Fermi surface consisting of only two electron sheets around the corners of the tetragonal Brillouin zone (M point) [12]. The observed anisotropic superconducting gap has a more conventional form with plain s-wave symmetry [13] and is thus nodeless in the entire Brillouin zone. Furthermore, angular resolved photoemission spectroscopy (ARPES) measurements [6] reveal an interfaceinduced electron-phonon interaction (EPI) between FeSe electrons and polar STO phonons that is strongly peaked at the q=0 phonon wavevector [6,[14][15][16][17][18]. There is growing experimental evidence for the pivotal role of such interfacial phonons in engineering high-T c heterostructures that involve FeSe [5,9,19] or even FeAs [20] monolayers.Although ab initio calculations confirm the existence of small-q phonons as a strictly interfacial phenomenon in FeSe/STO [12,[21][22][23] and indicate the importance of the coupling between substrate phonons and FeSe electrons [24], the estimated low value of the electron-phonon coupling constant (λ ≤ 0.4) has been widely considered insufficient to explain the impressive T c enhancement unless another, dominant pairing mechanism is at play [6]. On the other hand, Eliashberg calculations within a single band model suggest that interfacial phonons may lead to the high T c with a coupling of merely half of that estimated by experiments [25]. However, a mater...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
