Physics

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The ordered hexagonal perovskite Ba2CuTeO6 hosts weakly coupled S=12 spin ladders produced by an orbital ordering of Cu2+. The magnetic susceptibility $\chi$(T) of Ba2CuTeO6 is well described by that expected for isolated spin ladders with exchange coupling of J≈86K but shows a deviation from the expected thermally activated behavior at low temperatures below T∗≈25K. An anomaly in $\chi$(T), indicative of magnetic ordering, is observed at Tmag=16K. No clear signature of long-range ordering, however, is captured so far in NMR 1/T1, specific heat or neutron diffraction measurements at and below Tmag. The marginal magnetic transition, indicative of strong quantum fluctuations, is evidence that Ba2CuTeO6 is in very close proximity to a quantum critical point between magnetically ordered and spin-gapped phases controlled by interladder couplings.

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(SoNS) School of Natural Sciences

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Physical Review B

S= 12 quantum critical spin ladders produced by orbital ordering in Ba2CuTeO6

In order to understand, clarify and provide confirmations in the contexts of the prevalent confusions concerning Li-storage in graphenic carbon (viz. the reduced dimensional scale of graphitic carbon), electrochemical lithiation/delithiation has been performed with CVD-grown fairly pristine well-ordered few-layer graphene films (FLG; ∼7 layers; as a model material). Chronopotentiograms and cyclic voltammograms recorded with the FLG present distinct features corresponding to the transformation between different Li-GICs (i.e., 'staging') below 0.3 V against Li/Li+, thus confirming that 'classical' Li-intercalation does occur even at such reduced dimensional (nano)scale. Nevertheless, even in this lower potential window (our main focus here), Li-storage in FLG involves contributions from both diffusion- and surface-controlled mechanisms. The Li-capacities recorded with FLG just within this lower potential window, and also upon subtracting any possible contribution from the Cu current collector, were still ∼3-4 times greater than those obtained with similarly grown thicker bulk graphite films (TBG: ∼450 nm; Li-capacity recorded: ∼380 mA h g-1). Contrary to the usual belief, the excess Li-capacity of FLG cannot be explained by the presence of extrinsic/intrinsic defects, which are nearly negligible in the FLG films under consideration. Simulation of Li-storage in graphene via DFT indicated that the excess capacity (after formation of the LiC6 configuration) is associated with additional stable Li-storage on the outer graphene surfaces in the forms of more than one Li-layer (but different from Li-plating) and segregation close to the 'stepped' (exposed) edges of the inner graphene layers (but not exactly at the edge sites). Overall, such predicted Li-storage mechanisms are in agreement with the experimentally observed contributions from both 'classical' Li-intercalation and surface-controlled processes (even at potentials below 0.3 V), which primarily account for the excess Li-capacities recorded with graphenic carbon. © 2017 The Royal Society of Chemistry.

Journal of Materials Chemistry A

Understanding the Li-storage in few layers graphene with respect to bulk graphite: Experimental, analytical and computational study

It is proved the equivalence of the compatibility condition of Ramos (2011, 2012) with a condition found in Yadav et al. (2015). The link of Shape Invariance with the existence of a Potential Algebra is reinforced for the rationally extended Shape Invariant potentials. Some examples on X1 and Xℓ Jacobi and Laguerre cases are given. © 2017 Elsevier Inc.

Annals of Physics

A short note on “Group theoretic approach to rationally extended shape invariant potentials” [Ann. Phys. 359 (2015) 46–54]

Hamiltonians that are multivalued functions of momenta are of topical interest since they correspond to the Lagrangians containing higher-degree time derivatives. Incidentally, such classes of branched Hamiltonians lead to certain not too well understood ambiguities in the procedure of the quantization. Within this framework we pick up a model which samples the latter ambiguities and which, simultaneously, turns out to be amenable to a transparent analytic and perturbative treatment. © Published under licence by IOP Publishing Ltd.

Journal of Physics: Conference Series

Branched Hamiltonians for a Class of Velocity Dependent Potentials

Volume expansion and elastic softening of the Sn anode on lithiation result in mechanical degradation and pulverization of Sn, affecting the overall performance of Li-Sn batteries. It can, however, be overcome with the help of void space engineering by using a LixSn phase as the prelithiated anode, where an optimal value for x is desired. Currently, Li4.25Sn is known as the most lithiated Li-Sn compound, but recent studies have shown that at high pressure, several exotic and unusual stoichiometries can be obtained that may even survive decompression from high-to-ambient pressure with improved mechanical properties. With a belief that hydrostatic pressure may help in realizing Li-richer (x &gt; 4.25) Li-Sn compounds as well, we performed extensive calculations using an evolutionary algorithm and density functional theory to explore all stable and low-energy metastable Li-Sn compositions at pressures ranging from 1 atm to 20 GPa. This not only helped us in enriching the chemistry of a Li-Sn system, in general, but also in improving our understanding of the reaction mechanism in Li-Sn batteries, in particular, and guiding a route to improve the performance of Li-ion batteries through synthesis of Li-rich phases. Besides the experimentally known Li-Sn compounds, our study reveals the existence of five unreported stoichiometries (Li8Sn3, Li3Sn1, Li4Sn1, Li5Sn1, and Li7Sn1) and their associated crystal structures at ambient and high pressure. Although Li8Sn3 has been identified as one of the most stable Li-Sn compound in the entire pressure range (1 atm-20 GPa) with R3m symmetry, the Li-rich compounds like Li3Sn1-P2/m, Li4Sn1-R3m, Li5Sn1-C2/m, and Li7Sn1-C2/m are predicted to be metastable at ambient pressure and found to get thermodynamically stable at high pressure. Here, the discovery of Li5Sn1 and Li7Sn1 opens up the possibility to integrate them as a prelithiated anode for efficiently preventing electrochemical pulverization, as compared to the experimentally known highest lithiated compound, Li17Sn4. © 2017 American Chemical Society.

ACS Applied Materials and Interfaces

Understanding the Lithiation of the Sn Anode for High-Performance Li-Ion Batteries with Exploration of Novel Li-Sn Compounds at Ambient and Moderately High Pressure

We discuss the effects of the brane-localized mass terms on the fixed points of the toroidal orbifold T2/Z2 under the presence of background magnetic fluxes, where multiple lowest and higher-level Kaluza-Klein (KK) modes are realized before introducing the localized masses in general. Using linear algebra, we find that, in each KK level, one or more of the degenerate KK modes are almost inevitably perturbed, when single or multiple brane-localized mass terms are introduced. When the typical scale of the compactification is far above the electroweak scale or the TeV scale, we apply this mechanism for uplifting unwanted massless or light modes which are prone to appear in models on magnetized orbifolds. © 2017 American Physical Society.

Physical Review D

Brane-localized masses in magnetic compactifications

We analyze the flavor structure of composite vector bosons arising in a model of vectorlike technicolor — often called hypercolor (HC) — with eight flavors that form a one-family content of HC fermions. Dynamics of the composite vector bosons, referred to as HC ρ in this paper, are formulated together with HC pions by the hidden local symmetry (HLS), in a way analogous to QCD vector mesons. Then coupling properties to the standard model (SM) fermions, which respect the HLS gauge symmetry, are described in a way that couplings of the HC ρs to the left-handed SM quarks and leptons are given by a well-defined setup as taking the flavor mixing structures into account. Under the present scenario, we discuss significant bounds on the model from electroweak precision tests, flavor physics, and collider physics. We also try to address B anomalies in processes such as B → K(∗)μ+μ− and B→D(recently reported by LHCb, Belle, (ATLAS, and CMS in part). Then we find that the present model can account for the anomaly in B → K(∗)μ+μ− consistently with the other constraints while it predicts no significant deviations in B→D(∗) ν from the SM, which can be examined in the future Belle II experiment. The former is archived with the form C9 = −C10 of the Wilson coefficients for effective operators of b → sμ+μ−, which has been favored by the recent experimental data. We also investigate current and future experimental limits at the Large Hadron Collider (LHC) and see that possible collider signals come from dijet and ditau, or dimuon resonant searches for the present scenario with TeV mass range. To conclude, the present b → sμ+μ− anomaly is likely to imply discovery of new vector bosons in the ditau or dimuon channel in the context of the HC ρ model. Our model can be considered as a UV completion of conventional U(1)′ models. © 2017, The Author(s).

Journal of High Energy Physics

Phenomenology of flavorful composite vector bosons in light of B anomalies

We classify possible boundary conditions of a 6d Dirac fermion Ψ on a rectangle under the requirement that the 4d Lorentz structure is maintained, and derive the profiles and spectrum of the zero modes and nonzero KK modes under the two specific boundary conditions, (i) 4d-chirality positive components being zero at the boundaries and (ii) internal chirality positive components being zero at the boundaries. In the case of (i), twofold degenerated chiral zero modes appear which are localized towards specific directions of the rectangle pointed by an angle parameter θ. This leads to an implication for a new direction of pursuing the origin of three generations in the matter fields of the standard model, even though triple-degenerated zero modes are not realized in the six dimensions. When such 6d fermions couple with a 6d scalar with a vacuum expectation value, θ contributes to a mass matrix of zero-mode fermions consisting of Yukawa interactions. The emergence of the angle parameter θ originates from a rotational symmetry in the degenerated chiral zero modes on the rectangle extra dimensions since they do not feel the boundaries. In the case of (ii), this rotational symmetry is promoted to the two-dimensional conformal symmetry though no chiral massless zero mode appears. We also discuss the correspondence between our model on a rectangle and orbifold models in some details. © 2017 The Author(s)

Nuclear Physics B

6d Dirac fermion on a rectangle; scrutinizing boundary conditions, mode functions and spectrum

Evolution of a self-organized molecular packing at the microscopic scale in a bulk heterojunction active layer is critical for improving the performance of organic solar cells. We demonstrate that the molecular-shape-induced effects improve the morphology of the ternary thin films as PC61BM molecules were added to the host binary blend, PTB7-Th:PC71BM. Compared to the binary PTB7-Th:PC71BM devices, the ternary devices with 20\% PC61BM content (relative to PC71BM) exhibited an enhanced efficiency, from 6.4\% to 8.5\%. In particular, we find that the spherical PC61BM molecules with better precipitation kinetics than ellipsoidal PC71BM alter the morphology of ternary thin film and modulate interfaces to expedite charge transport and collection by reducing various recombination losses. (Figure Presented). © 2017 American Chemical Society.

Journal of Physical Chemistry C

Molecular-Shape-Induced Efficiency Enhancement in PC61BM and PC71BM Based Ternary Blend Organic Solar Cells

Temperature-dependent photoluminescence (PL) of titanium oxide (TiO2) shows an evolution of blue emission when exposed to 50 keV Ar+ ions. The origin of observed PL has been examined by X-ray absorption near-edge spectroscopy (XANES) at Ti-K,L and O-K edges, revealing the reduction of ligand field splitting owing to the formation of oxygen vacancies (OVs) by destroying TiO6 octahedral symmetry. Detailed PL and XANES analyses suggest that the fluence (ions/cm2) dependent increase in OVs not only boosts the conduction electrons but also increases the density of holes in localized self-trapped exciton (STE) states near the valence band. Based on these observations, we propose a model in which doped conduction electrons are recombining radiatively with the holes in STE states for blue light emission. © 2017 American Chemical Society.