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PHYSICS REPORTS OF KUMAMOTO UNIVERSITY Vol. 13, No. 2

## CONTENTS

Satoshi Yajima, Makoto Fukuda, Tomonori Oka, Shinji Yamashita, Takuo Yamamoto and Ko-hei Eguchi @.....@137
@An Irreducible Form of Gamma Matrices for the Heat Kernel in 10 Dimensions
abstract

Takashi Kai, Tamon Baba, Kenzo Arai and Shin-ichiro Fujimoto @.....@163
@The Influence of the Viscosity Prescription on Self-Gravitating Accretion Disk
abstract

Tamon Baba, Takashi Kai and Kenzo Arai @.....@171
@Two-Temperature Model of Advection Dominated Accretion Flow
abstract

Hitoshi Itoh, Tamon Baba, Takashi Kai, Masahiro Hirakawa and Kenzo Arai @.....@183
@On the Warped Disk in NGC 4258
abstract

Shin-ichiro Fujimoto, Ryuichi Matsuba and Kenzo Arai @.....@191
@Lithium Production and Soft X-ray Emission in Neutron Star Soft X-Ray Transients Cen X-4 and Aql X-1
abstract

Riou Nakamura, Masa-aki Hashimoto, Katsuhiko Sato and Kenzo Arai @.....@201
@Big Bang Nucleosynthesis
abstract

E. P. B. A. Thushari, Riou Nakamura, Masa-aki Hashimoto and Kenzo Arai @.....@217
@Observational Constraints on Brans-Dicke Theory with a Variable Cosmological Term
abstract

Masaomi Ono, Masa-aki Hashimoto, Yukihiro Kikuchi, Shin-ichiro Fujimoto and Kenzo Arai @.....@227
@Synthesis of Heavy Elements in a Helium Star of 32 Msun inside a Jet of Supernova Explosion
abstract

Motoaki Saruwatari, Masa-aki Hashimoto and Kenzo Arai @.....@235
@Effects of Neutrino Transport on the r-Process Nucleosynthesis for the Explosion of a 3.3 Msun Helium Star
abstract

Yasuhide Matsuo, Masa-aki Hashimoto and Kenzo Arai @.....@247
@Abundance Distribution in Supernova Remnant Cas A
abstract

Motoaki Saruwatari, Masa-aki Hashimoto and Kenzo Arai @.....@255
@Effects of a New Triple- Reaction Rate on the Helium Ignition of Accreting White Dwarfs
abstract

Shosuke Ikeda and Masaru Aniya @.....@261
@Nonlinear Optical Constants of Fluoride Ion Conductors --Analysis by the Sheik-Bahae Equation --
abstract

Haruhito Sadakuni and Masaru Aniya @.....@267
@Temperature Dependence of the Second-order Elastic Constants of AgB
abstract

Sahara and Masaru Aniya @.....@273
@Theoretical Analysis of the Viscosity of Disaccharide Solutions
abstract

Satoshi Ohmura and Fuyuki Shimojo @.....@279
@Ab initio Molecular-Dynamics Study of Atomic Diffusion in Liquid GeO3 and SrGeO3 under Pressure
abstract

Akihide Koura, Satoshi Ohmura and Fuyuki Shimojo @.....@287
@Pressure Dependence of Structural and Electronic Properties of Liquid ZnCl2 -- An Ab initio Molecular-Dynamics Study --
abstract

Ryo Yoshimura, Satoshi Ohmura and Fuyuki Shimojo @.....@293
@Ab initio Molecular-Dynamics Study of of Structural and Electronic Properties of Liquid MgSiO3 under Pressure
abstract

Kikuo Itoh, Mitsutoshi Tomita, Shuhei Takahashi, Keita Akasaki, Fusao Ichikawa and Yoshie Noguchi @.....@301
@Effect of Pd Seed Layer on Magnetic Anisotropy in Co Films Evaporated at Oblique Incidence
abstract

Shingo Komaki, Shohei Maeda, Takuya Tsuneoka, Taiki Murano, Yoshiharu Sawada, Bunshiro Saya, Fusao Ichikawa and Kikuo Itoh @.....@309
@Effect of Ion-doping for Transport Properties in Bi2Sr2CaCu2Oy+ Single Crystals
abstract

Kenichi Koga, Muneaki Fujii and Kunihide Okada @.....@317
@X-ray Diffraction on CsMn1-xZnxBr3
abstract

Chomsin Sulistya Widodo and Muneaki Fujii @.....@325
@Spontaneous Magnetization of K2CuF4 at Millikelvin Temperature
abstract

Ichiro Akai, Kuniaki Miyanari, Tomoshige Shimamoto, Atsuhiro Fujii and Mutsumi Kimura @.....@333
@Dexter Type Energy Transfer in Meta-Linked Branching Dendrimers
abstract

Tomoshige Shimamoto, Kuniaki Miyanari, Atsuhiro Fujii, Ichiro Akai and Mutsumi Kimura @.....@341
@Length Dependence of Rapid Energy Transfer in -Conjugated Dendrimers Having Oligo Phenylenevinylene Antennas
abstract

Makoto Hidegara, Masahiro Hara and Takashi Kimura @.....@349
@Ballistic Magnetic Sensor with a Collimated Electron Beam
abstract

Errata
Satoshi Yajima, Makoto Fukuda, Yoji Higashida, Shin-Ichiro Kubota, Shoshi Tokuo, Yuki Kamo, Shinji Yamashita and Tomonori Oka (Vol. 13, p. 1) @.....@355
An Irreducible Form of Gamma Matrices for the Heat Kernel in 8 Dimensions

Satoshi Yajima, Makoto Fukuda, Tomonori Oka, Shinji Yamashita, Takuo Yamamoto and Ko-hei Eguchi
An Irreducible Form of Gamma Matrices for the Heat Kernel in 10 Dimensions

In order to apply the asymptotic expansion coefficients $[a_q]$ of the heat kernel for the fermion interacting with bosonic background fields to calculation of quantum effects, it is useful to decompose the coefficients into tensorial components with irreducible matrices which are the totally antisymmetric products of $\gamma$ matrices. In 10 dimensional curved space, we present the formulae to give a tensorial form of the $\gamma$ matrix-valued quantities $X$, $\tilde{\Lambda}_{\mu\nu}$ and their products and covariant derivatives, with the irreducible matrices. The fifth coefficient $[a_5]$ obtained by repeating the application of the formulae simplifies the trace calculation on the $\gamma$ matrix and the derivation of the tensorial form of loop corrections.

Takashi Kai, Tamon Baba, Kenzo Arai and Shin-ichiro Fujimoto
The Influence of the Viscosity Prescription on Self-Gravitating Accretion Disk

We investigate the difference between the accretion disk models based on two kinds of $\alpha$-prescription of viscosity. The models are constructed with self-gravity in the vertical direction of the disk around a supermassive black hole. It is found that the structures are completely different in the self-gravity dominant region, though they are almost the same for the standard disk model. We should be careful in treating viscosity, if self-gravity is taken into account for a disk model of an emitting region of H$_2$O masers in an active galactic nucleus (AGN).

Tamon Baba, Takashi Kai and Kenzo Arai
Two-Temperature Model of Advection Dominated Accretion Flow

We investigate the two-temperature model of the Advection Dominated Accretion Flow (ADAF) around a supermassive black hole. Electron temperature is determined from the local balance between energy transfer from ions through Coulomb collisions and radiative cooling via bremsstrahlung, synchrotron radiation and inverse Compton scattering. Appling our model to Sgr A$^*$, we evaluate the corresponding spectrum emitted from the whole disk. It is found that the resulting spectrum is well fitted to the observed one when the mass accretion rate is in the range $(3.6-7.2) \times 10^{-8}$ $M_{\odot}$ yr$^{-1}$, which is in agreement with the value derived from polarized emission at radio wavelength.

Hitoshi Itoh, Tamon Baba, Takashi Kai, Masahiro Hirakawa and Kenzo Arai
On the Warped Disk in NGC 4258

We investigate evolution of the warped disk induced by torque due to radiation pressure from the central object. The warp is treated as a small perturbation on to a standard disk model around a supermassive black hole. We derive simultaneous differential equations which govern the development of the warp. Applying our procedure to NGC 4258, we specify the mass of the black hole $M = 3.9 \times 10^{7} M_\odot$, the accretion rate $\dot{M} = 8.6 \times 10^{-4} M_\odot$ yr$^{-1}$ and the luminosity $L = 1.0 \times 10^{44}$ erg s$^{-1}$. The initial small tilt angle of the disk grows by a factor of 54 during 10 Gyr. It is found that the resulting warped disk can be well superposed on the observed map of water maser emitting clouds.

Shin-ichiro Fujimoto, Ryuichi Matsuba and Kenzo Arai
Lithium Production and Soft X-ray Emission in Neutron Star Soft X-Ray Transients Cen X-4 and Aql X-1

We investigate production of Li in soft X-ray transients (NSSXTs) during quiescence. Lithium is abundantly synthesized in a hot accretion flow and is transfered to the surface of a secondary star. Almost all charged nuclei in the accretion flow are outflowed by the magneto-centrifugal forces, so that the accretion flow is mainly composed of neutrons. Accretion energies of neutrons liberated on the surface of the neutron star naturally explain the origin of blackbody-like soft X-rays from a quiescent NSSXT. It is found that for reasonable values of the mass accretion rate $\dot{M} = 2-4 \times 10^{-11} \Ms$ yr$^{-1}$ from the secondary and the magnetic field $B_{\rm NS} = 2-3 \times 10^8 \G$ of the neutron star, the abundance of Li on the secondary is LI/H$\simeq 10^{-9}$ and the soft X-ray luminosity is $L_X = 2-3 \times 10^{32} \ergps$, which are comparable to the observed values in Cen X-4 during quiescence. Moreover, the isotopic ratio $^6$Li/ $^7$Li is found to be comparable to the observed value. The scenario for the Li production and the emission mechanism of the soft X-ray in terms of neutron accretion explains the non-detection of Li in Aql X-1 due to strong magnetic fields. %%and are consistent with soft X-ray luminosities in other NSSXTs during quiescence. These facts strongly suggest the existence of a hot accretion flow in an NSSXT during quiescence.

Riou Nakamura, Masa-aki Hashimoto, Katsuhiko Sato and Kenzo Arai
Big Bang Nucleosynthesis

Big bang nucleosynthesis is reviewed with taking into account the observed abundance of light elements. We examine the standard big bang nucleosynthesis (SBBN) and confirm that helium abundance is not enough to fix the baryon to photon ratio $\eta$. As for deuterium, observational constraint on $\eta$ agrees well with the value determined from WMAP. It is, however, difficult to reconcile the observations of $^7$Li with the WMAP constraint. Furthermore, we investigate a simple two-zone model of inhomogeneous big bang nucleosynthesis (IBBN), where we review a series of our recent studies. In a high density region, heavy elements are produced up to the mass number 160. We present several interesting results that may become an important milestone for the origin of the elements in the universe.

E. P. B. A. Thushari, Riou Nakamura, Masa-aki Hashimoto and Kenzo Arai
Observational Constraints on Brans-Dicke Theory with a Variable Cosmological Term

We investigate Big-Bang nucleosynthesis in the Brans-Dicke model with a variable cosmological term ($BD\Lambda$) for the coupling constant $\omega=10^4$. The model parameters are constrained from comparison between the resulting abundance of $^4$He, D and $^7$Li and the observed ones. Furthermore, we examine the magnitude redshift ($m-z$) relation for the $BD\Lambda$ with and without another constant cosmological term in a flat universe. Observational data of Type Ia Supernovae (SNIa) are used in the redshift range $0.01 < z <2$. It is found that $BD\Lambda$ is inconsistent with the present accelerating universe but the model with a constant cosmological term with the value 0.7 can explain the SNIa data. The model parameters are insensitive to the $m-z$ relation.

Masaomi Ono, Masa-aki Hashimoto, Yukihiro Kikuchi, Shin-ichiro Fujimoto and Kenzo Arai
Synthesis of Heavy Elements in a Helium Star of 32 Msun inside a Jet of Supernova Explosion

We investigate synthesis of heavy elements in a helium star of $32 \,M_{\odot}$. Numerical calculations of nucleosynthesis have been performed during the stage of hydrostatic stellar evolution. A collapsar model is adopted whose jets are driven by magneto-hydrodynamical effects of differentially rotating core. Nucleosynthesis inside the jets is followed along the trajectories of tracer particles. Both results of hydrostatic and explosive nucleosyntheses are combined to be the yields after supernoca explosion. Comparing with the solar system abundances, we find appreciable overproduction for nuclei of the mass number $60 ڎ֖߂ Motoaki Saruwatari, Masa-aki Hashimoto and Kenzo Arai Effects of Neutrino Transport on the r-Process Nucleosynthesis for the Explosion of a 3.3 Msun Helium Star We investigate$r$-process during the magnetohydrodynamical (MHD) explosion of supernova in a helium star of 3.3\,$M_{\odot}$with including the neutrino effects. Contrary to the case of the spherical explosion, jet-like explosion due to the combined effects of differential rotation and magnetic field reduces the electron fraction significantly inside the layers. It is found that the ejected material of low electron fraction responsible for the$r$-process comes out from just outside the neutrino sphere deep inside the Fe-core. This leads to the production of the second to third peaks in the solar$r$-process elements. We suggest that there are variations in synthesis of heavy elements according to the initial conditions of rotation and magnetic field. In particular, the third peak elements are significantly over-produced, indicating a possible new site of MHD jets in supernovae. We can infer that the third peak is originated from supernova explosions associated to the jet-like explosion such as$\gamma$-ray bursts. Yasuhide Matsuo, Masa-aki Hashimoto and Kenzo Arai Abundance Distribution in Supernova Remnant Cas A Two dimensional hydrodynamical simulations of supernova remnant Cas A are performed starting from the onset of explosion to the present phase. Before the explosion, distributions of circumstellar medium is constructed, where the medium is assumed to be ejected from a progenitor. A supernova simulation is carried out by two dimensional hydrodynamical calculation. It is found that the Rayleigh-Taylor instability is advanced from the boundary between hydrogen and helium layers. The instability from silicon and iron layers is not grown enough to induce the observed mixing of materials. It is suggested that mixing before the explosion and/or instability at the boundary of silicon and iron layers due to different distributions of circumstellar medium is needed to explain the observations. Motoaki Saruwatari, Masa-aki Hashimoto and Kenzo Arai Effects of a New Triple- Reaction Rate on the Helium Ignition of Accreting White Dwarfs Effects of a new rate of the triple-$\alpha$reaction on the ignition of a carbon-oxygen white dwarf accreting helium in a binary system have been investigated. The ignition points determine the properties of a thermonuclear explosion of a Type Ia supernova (SNIa). We examine the evolutionary tracks of white dwarfs with various accretion rates and initial masses. It is found that for all cases from slow to intermediate accretion rates, nuclear burnings are ignited at the helium layers. As a consequence, carbon deflagration would be triggered for the lower accretion rate than$dM/dt\simeq 4\times10^{-8} M_{\odot}~\rm yr^{-1}$which has been believed to the lower limit of the accretion rate for the deflagration supernova. Furthermore, the off-center helium detonation dominates the mechanism of SNIa for intermediate and slow accretion rates. Shosuke Ikeda and Masaru Aniya Nonlinear Optical Constants of Fluoride Ion Conductors --Analysis by the Sheik-Bahae Equation -- Study on the correlation between ionic conduction and nonlinear optical (NLO) constants has been extended to fluoride materials. It is found that the activation energy of ion transport decreases with the increase of the NLO constants. To understand the origin of the relationship, the NLO constants of fluoride ion conductors are investigated by using the Sheik-Bahae equation, which has been used successfully in the study of nonlinear refractive indexes of semiconductors. The analysis reveals that the bond fluctuation model of superionic conductors provides a basis to understand the observed behavior. Haruhito Sadakuni and Masaru Aniya Temperature Dependence of the Second-order Elastic Constants of AgB The temperature dependence of the second-order elastic constants of AgBr is calculated by using a thermodynamic relation. It is shown that the model reproduces the experimental values of the elastic constant$C_{44}$from room temperature to near the melting point. However, the calculated values of$C_{11}$and$C_{12}$are estimated over the experimental data by large amonts above 550 K. The result indicates that in the case of AgBr, the material parameters evaluated at the reference temperature (room temperature) can not be extrapolated above 550 K and that the model for the elastic constant used widely in the literature should be used carefully. Sahara and Masaru Aniya Theoretical Analysis of the Viscosity of Disaccharide Solutions The temperature dependence of the viscosity of disaccharide solutions such as trehalose, maltose and sucrose has been investigated by means of the Bond Strength-Coordination Number Fluctuation (BSCNF) model. The result indicates that the fragilities of these systems are almost the same and that the values of the materials parameters are determined to be consistent with those of the trehalose-water-lithium iodide system which were observed in a previous study. Satoshi Ohmura and Fuyuki Shimojo Ab initio Molecular-Dynamics Study of Atomic Diffusion in Liquid GeO3 and SrGeO3 under Pressure The dyanamic properties of liquids GeO$_2$and SrGeO$_3$are studied by {\em ab initio} molecular-dynamics simulations. We clarify the microscopic diffusion mechanisms in liquids GeO$_2$and SrGeO$_3$. In both liquids, at ambient pressure, non-bridging oxygen double bonded to only one germanium plays a key role in the atomic diffusion mechanism. It is found that, in liquid SrGeO$_3$, which has non-bridging oxygen in the equilibrium state, atomic diffusion is possible without generating overcoordinated atoms at ambient pressure, in contrast to the fact that the overcoordinated atoms are always needed for the formation of non-bridging oxygens in liquid GeO$_2$. When pressure increases, only liquid GeO$_2$has a diffusion maximum, because the atomic diffusion occurs with a concerted reaction under higher pressures, while the diffusion coefficients decrease monotonically with pressure in liquid SrGeO$_3$Akihide Koura, Satoshi Ohmura and Fuyuki Shimojo Pressure Dependence of Structural and Electronic Properties of Liquid ZnCl2 -- An Ab initio Molecular-Dynamics Study -- The structural and bonding properties of liquid ZnCl$_2$under pressure are investigated from first-principles molecular-dynamics simulations in the isobaric-isothermal ensemble. % calculated quantum mechanically in the framework of the density functional theory. The pressure range covers from 0 to 80 GPa. It is shown that the ZnCl$_4^{2-}$tetrahedra are considerably deformed under pressure with keeping the nearest-neighbor distance between Zn and Cl atoms almost constant. The average coordination number of Cl atoms around Zn atoms changes from 4 at 0 GPa to about 5 at about 10 GPa, and increases monotonically with pressure. The Zn-Zn distance is nearly unchanged up to 10 GPa, and begins to decrease under further compression. On the other hand, the Cl-Cl distance decreases with increasing pressure from ambient conditions. Ryo Yoshimura, Satoshi Ohmura and Fuyuki Shimojo Ab initio Molecular-Dynamics Study of of Structural and Electronic Properties of Liquid MgSiO3 under Pressure The structural and electronic properties of liquid MgSiO$_3$under pressure are investigated by {\em ab initio} molecular-dynamics simulations. At ambient pressure, most Si atoms have the same coordination even in the liquid state as in the crystalline phase, i.e., each Si atom is bonded to two bridging oxygens twofold-coordinated to Si, and two nonbridging oxygens onefold-coordinated to Si. It is found that the structural defects, such as fivefold- or threefold-coordinated Si atoms, are always formed with the rearrangement of Si-O covalent bonds in the atomic diffusion processes. The population analysis clarifies that maximum of the diffusivity in the pressure dependence is originated from the increasing of the number of defects under compression. Kikuo Itoh, Mitsutoshi Tomita, Shuhei Takahashi, Keita Akasaki, Fusao Ichikawa and Yoshie Noguchi Effect of Pd Seed Layer on Magnetic Anisotropy in Co Films Evaporated The effect of Pd seed layer on the magnetic anisotropy in Co films evaporated at oblique incidence was investigated. The thickness of Pd was 500 {\AA} and that of Co was varied from 100 to 600 \AA. The substrate temperatures were$- 60$,$- 30$and 20$^\circ$C. Negatively large anisotropy of the squareness ratio appeared in the films prepared at low substrate temperatures$- 60$and$- 30^\circ$C though the anisotropy of the reflection coefficient and the magnetic anisotropy field were positive. The degree of the$c$-axis orientation perpendicular to the incidence plane seems to be a little larger than that of parallel one. From these results, it is considered that the positive in-plane magnetic anisotropy may originate from the shape anisotropy of the columnar grains and/or magnetocrystalline anisotropy, and the anisotropy of the squareness ratio does not reflect the in-plane magnetic anisotropy. In the films with negatively large anisotropy of the squareness ratio, large coercive force perpendicular to the film plane appeared. The$MH$loop in those films can be explained to be superposition of two loops with small and large coercive forces. We consider that the coercive force of under Co layer is small and that of over Co layer large. Shingo Komaki, Shohei Maeda, Takuya Tsuneoka, Taiki Murano, Yoshiharu Sawada, Bunshiro Saya, Fusao Ichikawa and Kikuo Itoh Effect of Ion-doping for Transport Properties in Bi2Sr2CaCu2Oy+ Single Crystals For a systematic study of the superconducting-insulator transition in high-temperature superconductors, single crystals in the Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$system with replacement of Pb for Bi and Y for Ca were grown, cleaved, and characterized. Several fabrication conditions were attempted to growth much larger crystals. Chemical composition was estimated by the electron probe microanalysis. The measured Y content in crystals is much higher than the nominal one. The ratio of Bi/Sr is almost constant with varying Y content. No relation between the growth condition and the transport properties was found. Kenichi Koga, Muneaki Fujii and Kunihide Okada X-ray Diffraction on CsMn1-xZnxBr3 Magnetic diluted crystal with CsMn$_{1-x}$Zn$_x$Br$_3$is synthesized using Bridgeman furnace. On its powdered substance, the X-ray diffraction experiment is made. The experimental data on the 2$\theta$-pattern are in good agreement with the theoretically calculated ones. Chomsin Sulistya Widodo and Muneaki Fujii Spontaneous Magnetization of K2CuF4 at Millikelvin Temperature The spontaneous magnetization of the crystal structure of K$_{2}$NiF$_{4}$type has been investigated using Cu-NMR in temperature below 1 K at zero external magnetic field. In the range of millikelvin temperature, the spontaneous magnetization of ferromagnetic depends on temperature. The experiments have been performed using a single crystal of K$_{2}$CuF$_{4}$. It is well known that the compounds K$_{2}$CuF$_{4}$are typical of the nearly two-dimensional ferromagnet. We obtain two peaks in the Cu-NMR spectrum at temperature of 470 mK. The NMR frequencies are 158 and 167.5 MHz due to$^{63}$Cu and$^{65}$Cu nuclear spins, respectively. The results indicate that the spontaneous magnetization depends on temperature. It is in accordance with the spin wave theory by Holstein-Primakoff's and Green's function formalism. Ichiro Akai, Kuniaki Miyanari, Tomoshige Shimamoto, Atsuhiro Fujii and Mutsumi Kimura Dexter Type Energy Transfer in Meta-Linked Branching Dendrimers We investigated rapid energy transfer (ET) processes in dendrimers having \textit{meta}-linked branching light harvesting antennas. It was found that, at room temperature (RT), the rapid ET occurs efficiently from the antennas to the core and gives rise to intense core-PL bands under the selective excitation on the antenna. However, the ET efficiency impairs at lower temperatures than$\sim$100~K. For understanding these experimental results, we analyzed molecular vibrations and molecular orbitals of a simple model molecule. From these analyses, it was demonstrated that the torsional vibration of the entire antenna subunit is excited sufficiently at RT and the rapid ET in phDG$n$dendrimer is realized via the$\pi^\ast$-conjugated network mediated by thermal activation of this torsional vibration. Tomoshige Shimamoto, Kuniaki Miyanari, Atsuhiro Fujii, Ichiro Akai and Mutsumi Kimura Length Dependence of Rapid Energy Transfer in -Conjugated Dendrimers Having Oligo Phenylenevinylene Antennas From analyses of molecular vibrations, we have studied rapid energy transfer (ET) process in a series of star-shaped stilbenoid phthalocyanines (SSS$n$Pc;$n=1, 2$) having$\pi$-conjugated light harvesting antennas. In SSS$n$Pc, the highly efficient ET occurs through a$\pi$-conjugation network between the core and the antenna. However, a different temperature dependence of the ET efficiencies were found between SSS1Pc and SSS2Pc. Molecular structures and torsional vibrations of the antenna subunits were analyzed in model molecules for SSS$n\$Pc. Consequently, it was found that the co-planarities between the core and the antenna subunit are different between SSS1Pc and SSS2Pc, and the variance in the temperature dependence of the ET efficiency in these dendrimers is originated from such difference of the co-planarity.

Makoto Hidegara, Masahiro Hara and Takashi Kimura
Ballistic Magnetic Sensor with a Collimated Electron Beam

We have proposed a highly sensitive magnetic sensor using ballistically transporting electrons. The magnetic sensor consists of a pair of closely located quantum point contacts (QPCs) formed in a two dimensional conductor. A collimated electron beam through one QPC is deflected only by the external magnetic field and is sensitively detected by the other QPC. The device performance optimized by adjusting the relative position of the QPCs is much higher than those of other magnetic sensors reported so far.

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Email: arai@sci.kumamoto-u.ac.jp

Last updated: January 4, 2011