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Ryusuke Endo

Publications and source records attributed to Ryusuke Endo.

8 recordsLinked to original sources
arXiv2025

Theoretical investigation of interface atomic structure of graphene on NiFe alloy substrate

Two processes have been proposed to fabricate graphene/NiFe alloy interfaces for tunneling magnetoresistance devices. One is the transfer of graphene and the other is the evaporation of alloys onto graphene. The formation energy of a NiFe alloy substrate and the adsorption energy of graphene on the NiFe alloy substrate are investigated by a density functional theory calculations to reveal the difference in the atomic structure of the interface between the two processes. It is found that Ni-rich surfaces are preferable for the bare substrate, whereas Fe surfaces are stable for the graphene adsorbed on the substrate. This result indicates that the composition ratio of the surface layer depends on the interface fabrication process.

cond-mat.mtrl-sci↗
arXiv2025

Oxygen-induced Fe surface segregation at the $L1_0$-FePd(001)/graphene heterointerface for spintronics devices: a first-principles study

We theoretically investigate the atomic-scale structure of the heterointerface formed between the (001) surface of the $L1_0$-ordered iron palladium (FePd) intermetallic alloy and graphene (Gr), namely, $L1_0$-FePd(001)/Gr, which serves as an essential component in spintronic devices. Using density functional theory (DFT) calculations, we demonstrate that the topmost surface layer consisting of Pd (Pd-terminated surface) is energetically more stable than that consisting of Fe in vacuum, and that Pd-terminated surfaces are unfavorable for graphene adsorption. In contrast, under an oxygen atmosphere, the strong Fe--O bonding stabilizes Fe-terminated surfaces. The predicted Fe--O bonds on the oxidized surface are consistent with our X-ray photoelectron spectroscopy (XPS) measurements. These results reproduce the mechanism responsible for the graphene coverage observed in recent experiments. Similar oxygen-induced Fe surface segregation has been studied in heterogeneous catalysis on FePt and FePd alloys. In this work, we exploit this mechanism as a termination-engineering strategy to fabricate high-quality 2D-material/alloy heterointerfaces for nanoscale device applications.

cond-mat.mtrl-sci↗
arXiv2017

Gaugeon formalism for the two-form gauge fields

We present a BRST symmetric gaugeon formalism for the two-form gauge fields. A set of vector gaugeon fields is introduced as a quantum gauge freedom. One of the gaugeon fields satisfies a higher derivative field equation; this property is necessary to change the gauge-fixing parameter of the two-form gauge field. A naive Lagrangian for the vector gaugeon fields is itself invariant under a gauge transformation for the vector gaugeon field. The Lagrangian of our theory includes the gauge-fixing terms for the gaugeon fields and corresponding Faddeev--Popov ghosts terms.

hep-th↗
arXiv2017

Heat kernel approach to relations between covariant and consistent currents in chiral gauge theories

We apply the heat kernel method to relations between covariant and consistent currents in anomalous chiral gauge theories. Banerjee et al. have shown that the relation between these currents is expressed by a "functional curl" of the covariant current. Using the heat kernel method, we evaluate the functional curl explicitly in arbitrary even dimensions. We also apply the heat kernel method to evaluate Osabe and Suzuki's results of the difference between covariant and consistent currents in two and four dimensions. Applying the arguments of Banerjee et al. to gravitational anomalies, we investigate the relationship between the covariant and consistent energy-momentum tensors. The relation is found to be expressed by a functional curl of the covariant energy-momentum tensor.

hep-th↗
arXiv2015

Gauge Freedom in Path Integrals in Abelian Gauge Theory

We extend gauge symmetry of Abelian gauge field to incorporate quantum gauge degrees of freedom. We twice apply the Harada--Tsutsui gauge recovery procedure to gauge-fixed theories. First, starting from the Faddeev--Popov path integral in the Landau gauge, we recover the gauge symmetry by introducing an additional field as an extended gauge degree of freedom. Fixing the extended gauge symmetry by the usual Faddeev--Popov procedure, we obtain the theory of Type I gaugeon formalism. Next, applying the same procedure to the resulting gauge-fixed theory, we obtain a theory equivalent to the extended Type I gaugeon formalism.

hep-th↗
arXiv2007

BRST Symmetric Gaugeon Formalism for Higgs Model

We reinvestigate Yokoyama's gaugeon formalism for the spontaneously broken Abelian gauge theory. Within the framework of the covariant linear gauges, we give a general gauge-fixing Lagrangian which includes the gauge field, the Goldstone mode, the multiplier B-field and Yokoyama's gaugeon fields (as well as Faddeev-Popov ghosts). As special choices of the values of the gauge-fixing parameters, our theory includes the usual covariant gauges and R$_ξ$-like gauges. Although some of the gauge-fixing parameters can be shifted by the q-number gauge transformation, the $ξ$ parameter cannot be shifted in any of the R$_ξ$-like gauges.

hep-th↗
arXiv1994

Heat Kernel for Spin-3/2 Rarita-Schwinger Field in General Covariant Gauge

The heat kernel for the spin-3/2 Rarita-Schwinger gauge field on an arbitrary Ricci flat space-time ($d>2$) is investigated in a family of covariant gauges with one gauge parameter $α$. The $α$-dependent term of the kernel is expressed by the spin-1/2 heat kernel. It is shown that the axial anomaly and the one-loop divegence of the action are $α$-independent, and that the conformal anomaly has an $α$-dependent total derivative term in $d=2m\geq6$ dimensions.

hep-th↗