Surface properties of SmB6 from x-ray photoelectron spectroscopy

We have investigated the properties of cleaved SmB$_6$ single crystals by x-ray photoelectron spectroscopy. At low temperatures and freshly cleaved samples a surface core level shift is observed which vanishes when the temperature is increased. A Sm valence between 2.5 - 2.6 is derived from the relative intensities of the Sm$^{2+}$ and Sm$^{3+}$ multiplets. The B/Sm intensity ratio obtained from the core levels is always larger than the stoichiometric value. Possible reasons for this deviation are discussed. The B $1s$ signal shows an unexpected complexity: an anomalous low energy component appears with increasing temperature and is assigned to the formation of a suboxide at the surface. While several interesting intrinsic and extrinsic properties of the SmB$_6$ surface are elucidated in this manuscript no clear indication of a trivial mechanism for the prominent surface conductivity is found

Ternary algebras and groups

We construct explicitly groups associated to specific ternary algebras which extend the Lie (super)algebras (called Lie algebras of order three). It turns out that the natural variables which appear in this construction are variables which generate the three-exterior algebra. An explicit matrix representation of a group associated to a peculiar Lie algebra of order three is constructed considering matrices with entry which belong to the three exterior algebra.Comment: 11 pages contribution to the 5th International Symposium on Quantum Theory and Symmetries (QTS5

Biomolecular Release from Alginate-modified Electrode Triggered by Chemical Inputs Processed through a Biocatalytic Cascade – Integration of Biomolecular Computing and Actuation

Biocatalytic cascades involving more than one or two enzyme-catalyzed step are inefficient inside alginate hydrogel prepared on an electrode surface. The problem originates from slow diffusion of intermediate products through the hydrogel from one enzyme to another. However, enzyme activity can be improved by surface immobilization. We demonstrate that a complex cascade of four consecutive biocatalytic reactions can be designed, with the enzymes immobilized in an LBL-assembled polymeric layer at the alginate-modified electrode surface. The product, hydrogen peroxide, then induces dissolution of iron-cross-linked alginate, which results in release process of entrapped biomolecular species, here fluorescently marked oligonucleotides, denoted F-DNA. The enzymatic cascade can be viewed as a biocomputing network of concatenated AND gates, activated by combinations of four chemical input signals, which trigger the release of F-DNA. The reactions, and diffusion/release processes were investigated by means of theoretical modeling. A bottleneck reaction step associated with one of the enzymes was observed. The developed system provides a model for biochemical actuation triggered by a biocomputing network of reactions. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, WeinheimNational Science Foundation, NSF: CBET-1403208Russian Science Foundation, RSF: 17-13-01096This work was supported by National Science Foundation, USA, (award CBET-1403208) and by Russian Science Foundation (project no. 17-13-01096)

Nesting-driven multipolar order in CeB6 from photoemission tomography

Some heavy fermion materials show so-called hidden-order phases which are invisible to many characterization techniques and whose microscopic origin remained controversial for decades. Among such hidden-order compounds, CeB6 is of model character due to its simple electronic configuration and crystal structure. Apart from more conventional antiferromagnetism, it shows an elusive phase at low temperatures, which is commonly associated with multipolar order. Here we show that this phase roots in a Fermi surface instability. This conclusion is based on a full 3D tomographic sampling of the electronic structure by angle-resolved photoemission and comparison with inelastic neutron scattering data. The hidden order is mediated by itinerant electrons. Our measurements will serve as a paradigm for the investigation of hidden-order phases in f-electron systems, but also generally for situations where the itinerant electrons drive orbital or spin order

Magnetic field dependence of the neutron spin resonance in CeB6

In zero magnetic field, the famous neutron spin resonance in the f-electron superconductor CeCoIn5 is similar to the recently discovered exciton peak in the non-superconducting CeB6. Magnetic field splits the resonance in CeCoIn5 into two components, indicating that it is a doublet. Here we employ inelastic neutron scattering (INS) to scrutinize the field dependence of spin fluctuations in CeB6. The exciton shows a markedly different behavior without any field splitting. Instead, we observe a second field-induced magnon whose energy increases with field. At the ferromagnetic zone center, however, we find only a single mode with a non-monotonic field dependence. At low fields, it is initially suppressed to zero together with the antiferromagnetic order parameter, but then reappears at higher fields inside the hidden-order phase, following the energy of an electron spin resonance (ESR). This is a unique example of a ferromagnetic resonance in a heavy-fermion metal seen by both ESR and INS consistently over a broad range of magnetic fields.Comment: 7 pages, 6 figures including one animation, accepted to Phys. Rev.