In-situ angle-resolved photoemission spectroscopy of copper-oxide thin films synthesized by molecular beam epitaxy

ACS Appl. Mater. Interfaces

Valla

2021

Self Cite

The presence of inherently strong spin-orbit coupling in bismuth, its unique layer-dependent band topology and high carrier mobility make it an interesting system for both fundamental studies and applications. Theoretically, it has been suggested that strong quantum size effects should be present in the Bi(110) films, with the possibility of Dirac fermion states in the odd-bilayer (BL) films, originating from dangling pz orbitals and quantum-spin hall (QSH) states in the even-bilayer films. However, the experimental verification of these claims has been lacking. Here, we study the electronic structure of Bi(110) films grown on a high-Tc superconductor, Bi2Sr2CaCu2O 8+δ (Bi2212) using angle-resolved photoemission spectroscopy (ARPES). We observe an oscillatory behavior of electronic structure with the film thickness and identify the Dirac-states in the odd-bilayer films, consistent with the theoretical predictions. In the even-bilayer films, we find another Dirac state that was predicted to play a crucial role in the QSH effect. In the low thickness limit, we observe several extremely one-dimensional states, probably originating from the edge-states of Bi(110) islands. Our results provide a much needed experimental insight into the electronic and structural properties of Bi(110) films.

Section: Methodsmentioning

confidence: 99%

Quantum Size Effects, Multiple Dirac Cones, and Edge States in Ultrathin Bi(110) Films

ACS Appl. Mater. Interfaces

Valla

2021

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“…The experiments within this study were performed in an experimental facility that integrates oxide-molecular beam epitaxy (OMBE), ARPES, and scanning tunneling microscopy (STM) in a common ultra-high vacuum (UHV) system 57 . Bulk CrI and VI single crystals were grown by the chemical vapor transport method (CVT).…”

Section: Methodsmentioning

confidence: 99%

Valence band electronic structure of the van der Waals ferromagnetic insulators: VI$$_3$$ and CrI$$_3$$

Liu²,

Petrović³

et al. 2020

Sci Rep

Ferromagnetic van der Waals (vdW) insulators are of great scientific interest for their promising applications in spintronics. It has been indicated that in the two materials within this class, CrI$$_3$$ 3 and VI$$_3$$ 3 , the magnetic ground state, the band gap, and the Fermi level could be manipulated by varying the layer thickness, strain or doping. To understand how these factors impact the properties, a detailed understanding of the electronic structure would be required. However, the experimental studies of the electronic structure of these materials are still very sparse. Here, we present the detailed electronic structure of CrI$$_3$$ 3 and VI$$_3$$ 3 measured by angle-resolved photoemission spectroscopy (ARPES). Our results show a band-gap of the order of 1 eV, sharply contrasting some theoretical predictions such as Dirac half-metallicity and metallic phases, indicating that the intra-atomic interaction parameter (U) and spin-orbit coupling (SOC) were not properly accounted for in the calculations. We also find significant differences in the electronic properties of these two materials, in spite of similarities in their crystal structure. In CrI$$_3$$ 3 , the valence band maximum is dominated by the I 5p, whereas in VI$$_3$$ 3 it is dominated by the V 3d derived states. Our results represent valuable input for further improvements in the theoretical modeling of these systems.

“…The experiments within this study were performed in an experimental facility that integrates oxide-molecular beam epitaxy (OMBE), ARPES, and STM in a common ultra high vacuum (UHV) system. [33] Bi films were grown in-situ on as-grown and overdoped Bi2212 substrates. The starting, as-grown Bi2212 crystals were synthesized by the traveling floating zone method, clamped to the sample holder and cleaved with Kapton tape in the ARPES preparation chamber.…”

Section: Methodsmentioning

confidence: 99%

Origin of Suppression of Proximity‐Induced Superconductivity in Bi/Bi₂Sr₂CaCu₂O8+δ Heterostructures

Drozdov

et al. 2020

Adv Quantum Tech

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Mixing of topological states with superconductivity could result in topological superconductivity with the elusive Majorana fermions potentially applicable in fault‐tolerant quantum computing. One possible candidate considered for realization of topological superconductivity is thin bismuth films on Bi2Sr2CaCu2O8+δ (Bi2212). Here, angle‐resolved and core‐level photoemission spectroscopy studies of thin Bi films grown in‐situ on as‐grown Bi2212 showing the absence of proximity effect are presented. It is found that the electron transfer from the film to the substrate and the resulting severe underdoping of Bi2212 at the interface is a likely origin for the absence of proximity effect. A possible way of preventing a total loss of proximity effect in this system is also proposed. These results offer a better and more universal understanding of the film/cuprate interface and resolve many issues related to the proximity effect.