Superconductivity over 30 K of Nd2CuO4 Films on CaF2 Substrates

Nd2CuO4 has a crystal structure called the Nd2CuO4 (T’) structure in which fluorite-like Nd2O2 slabs and CuO2 planes stack alternately. Nd2CuO4 is known to show superconductivity by carrier doping via anion/cation substitution, or making the oxygen sublattice highly ordered via a stringent control of thermodynamic conditions during crystal growth. In this study, CaF2 is used for growing Nd2CuO4 films, as a substrate material which contains fluorine atoms. The films show superconducting onset (Tonc) beyond 30 K. Furthermore, in contrast to reported superconductivity in this system, the emergence of superconductivity is found to be insensitive to post annealing procedures.PostprintPeer reviewe

Epitaxial growth of AgCrSe2 thin films by molecular beam epitaxy

Funding: The authors gratefully acknowledge the European Research Council (through the QUESTDO project, 714193) and The Leverhulme Trust (Grant No. RL-2016-006) for support. The MBE growth facility was funded through an EPSRC strategic equipment grant: EP/M023958/1. The research leading to this result has been supported by the project CALIPSO under Grant Agreement 312284 from the EU Seventh Framework Programme (FP7/2007-2013).AgCrSe2 exhibits remarkably high ionic conduction, an inversion symmetry-breaking structural transition, and is host to complex non-colinear magnetic orders. Despite its attractive physical and chemical properties, and its potential for technological applications, studies of this compound to date are focused almost exclusively on bulk samples. Here, we report the growth of AgCrSe2 thin films via molecular beam epitaxy. Single-orientated epitaxial growth was confirmed by X-ray diffraction, while resonant photoemission spectroscopy measurements indicate a consistent electronic structure as compared to bulk single crystals. We further demonstrate significant flexibility of the grain morphology and cation stoichiometry of this compound via control of the growth parameters, paving the way for the targeted engineering of the electronic and chemical properties of AgCrSe2 in thin-film form.Publisher PDFPeer reviewe

Bose glass and Fermi glass

It is known that two-dimensional superconducting materials undergo a quantum phase transition from a localized state to superconductivity. When the disordered samples are cooled, bosons (Cooper pairs) are generated from Fermi glass and reach superconductivity through Bose glass. However, there has been no universal expression representing the transition from Fermi glass to Bose glass. Here, we discovered an experimental renormalization group flow from Fermi glass to Bose glass in terms of simple β-function analysis. To discuss the universality of this flow, we analyzed manifestly different systems, namely a Nd-based two-dimensional layered perovskite and an ultrathin Pb film. We find that all our experimental data for Fermi glass fall beautifully into the conventional self-consistent β-function. Surprisingly, however, flows perpendicular to the conventional β-function are observed in the weakly localized regime of both systems, where localization becomes even weaker. Consequently, we propose a universal transition from Bose glass to Fermi glass with the new two-dimensional critical sheet resistance close to R□=h/e2.Publisher PDFPeer reviewe

The role of ion dissolution in metal and metal oxide surface inactivation of SARS CoV-2

Funding: This work was funded by UKRI-NIHR (MRC MR/V028464/1) COVID-19 Rapid Response Initiative.Anti-viral surface coatings are under development to prevent viral fomite transmission from high-traffic touch surfaces in public spaces. Copper’s anti-viral properties have been widely documented, but the anti-viral mechanism of copper surfaces is not fully understood. We screened a series of metal and metal oxide surfaces for anti-viral activity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease (COVID-19). Copper and copper oxide surfaces exhibited superior anti-SARS-CoV-2 activity; however, the level of anti-viral activity was dependent on the composition of the carrier solution used to deliver virus inoculum. We demonstrate that copper ions released into solution from test surfaces can mediate virus inactivation, indicating a copper ion dissolution-dependent anti-viral mechanism. The level of anti-viral activity is, however, not dependent on the amount of copper ions released into solution per se. Instead, our findings suggest that degree of virus inactivation is dependent on copper ion complexation with other biomolecules (e.g., proteins/metabolites) in the virus carrier solution that compete with viral components. Although using tissue culture-derived virus inoculum is experimentally convenient to evaluate the anti-viral activity of copper-derived test surfaces, we propose that the high organic content of tissue culture medium reduces the availability of “uncomplexed” copper ions to interact with the virus, negatively affecting virus inactivation and hence surface anti-viral performance. We propose that laboratory anti-viral surface testing should include virus delivered in a physiologically relevant carrier solution (saliva or nasal secretions when testing respiratory viruses) to accurately predict real-life surface anti-viral performance when deployed in public spaces.PostprintPeer reviewe

Interplay of ferromagnetism and spin-orbit coupling in Sr4Ru3O10

Funding: IB acknowledges funding through the International Max Planck Research School for Chemistry and Physics of Quantum Materials, MN, CT and PW through EP/R031924/1 and EP/T031441/1 and LCR from the Royal Commission of the Exhibition of 1851. TEM measurements were supported through grants EP/R023751/1, EP/L017008/1 and EP/T019298/1. YN acknowledges support through the ERC grant ERC-714193-QUESTDO held by Phil King.The ground state of metamagnetic materials can be controlled by magnetic field, promising new functionalities for spintronics applications. Yet, a microscopic understanding of the interplay of the electronic structure with the susceptibility to emergent orders is often missing, but would greatly facilitate optimization of the properties of metamagnetic materials. Here, we use low temperature scanning tunneling microscopy (STM) and spectroscopy to study the metamagnetism in the trilayer ruthenate Sr4Ru3O10, combining STM-based magnetostriction measurements with quasiparticle-interference imaging (QPI) to elucidate the role of the microscopic electronic structure in the macroscopic metamagnetic properties. Our results highlight the importance of the orthorhombicity of the material for its metamagnetic properties, confirmed by magnetization measurements. Our QPI results show clear signatures of the minority spin bands crossing the Fermi energy, and provide a link between the ferromagnetic properties, spin-orbit coupling and the orthorhombicity of the crystal structure.PostprintPeer reviewe

Epitaxial growth of large-area monolayers and van der Waals heterostructures of transition-metal chalcogenides via assisted nucleation

Funding: We gratefully acknowledge support from the Leverhulme Trust (Grant No. RL-2016-006) and the Engineering and Physical Sciences Research Council (Grant Nos. EP/X015556/1 and EP/M023958/1). S.B. and A.Z. gratefully acknowledge studentship support from the International Max-Planck Research School for Chemistry and Physics of Quantum Materials.The transition-metal chalcogenides include some of the most important and ubiquitous families of 2D materials. They host an exceptional variety of electronic and collective states, which can in principle be readily tuned by combining different compounds in van der Waals heterostructures. Achieving this, however, presents a significant materials challenge. The highest quality heterostructures are usually fabricated by stacking layers exfoliated from bulk crystals, which – while producing excellent prototype devices – is time consuming, cannot be easily scaled, and can lead to significant complications for materials stability and contamination. Growth via the ultra-high vacuum deposition technique of molecular-beam epitaxy (MBE) should be a premier route for 2D heterostructure fabrication, but efforts to achieve this are complicated by non-uniform layer coverage, unfavorable growth morphologies, and the presence of significant rotational disorder of the grown epilayer. This work demonstrates a dramatic enhancement in the quality of MBE grown 2D materials by exploiting simultaneous deposition of a sacrificial species from an electron-beam evaporator during the growth. This approach dramatically enhances the nucleation of the desired epi-layer, in turn enabling the synthesis of large-area, uniform monolayers with enhanced quasiparticle lifetimes, and facilitating the growth of epitaxial van der Waals heterostructures.Peer reviewe

2ジゲンPdO2ネットワークニオケルデンキデンドウ

博士（工学）東京農工大

Bose glass and Fermi glass

It is known that two-dimensional superconducting materials undergo a quantum phase transition from a localized state to superconductivity. When the disordered samples are cooled, bosons (Cooper pairs) are generated from Fermi glass and reach superconductivity through Bose glass. However, there has been no universal expression representing the transition from Fermi glass to Bose glass. Here, we discovered an experimental renormalization group flow from Fermi glass to Bose glass in terms of simple β-function analysis. To discuss the universality of this flow, we analyzed manifestly different systems, namely a Nd-based two-dimensional layered perovskite and an ultrathin Pb film. We find that all our experimental data for Fermi glass fall beautifully into the conventional self-consistent β-function. Surprisingly, however, flows perpendicular to the conventional β-function are observed in the weakly localized regime of both systems, where localization becomes even weaker. Consequently, we propose a universal transition from Bose glass to Fermi glass with the new two-dimensional critical sheet resistance close to R□=h/e2

The role of ion dissolution in metal and metal oxide surface inactivation of SARS-CoV-2

Antiviral surface coatings are under development to prevent viral fomite transmission from high-traffic touch surfaces in public spaces. Copper's antiviral properties have been widely documented; but the antiviral mechanism of copper surfaces is not fully understood. We screened a series of metal and metal oxide surfaces for antiviral activity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease (COVID-19). Copper and copper oxide surfaces exhibited superior anti-SARS-CoV-2 activity; however, level of antiviral activity was dependent upon the composition of the carrier solution used to deliver virus inoculum. We demonstrate that copper ions released into solution from test surfaces can mediate virus inactivation, indicating a copper ion dissolution-dependent antiviral mechanism. Level of antiviral activity is, however, not dependent on the amount of copper ions released into solution per se. Instead, our findings suggest that degree of virus inactivation is dependent upon copper ion complexation with other biomolecules (e.g., proteins/metabolites) in the virus carrier solution that compete with viral components. Although using tissue culture-derived virus inoculum is experimentally convenient to evaluate the antiviral activity of copper-derived test surfaces, we propose that the high organic content of tissue culture medium reduces the availability of "uncomplexed" copper ions to interact with the virus, negatively affecting virus inactivation and hence surface antiviral performance. We propose that laboratory antiviral surface testing should include virus delivered in a physiologically relevant carrier solution (saliva or nasal secretions when testing respiratory viruses) to accurately predict real-life surface antiviral performance when deployed in public spaces