Korean Phys Research Articles

Bi-intercalated epitaxial graphene on SiC(0001)

Abstract The intercalation of graphene with suitable atomic species is one of the most frequently applied methods to decouple the graphene layer from the substrate in order to establish the classical electronic properties of graphene. In this context, we studied the bismuth (Bi) intercalation of the (6√3×6√3)R30° reconstructed so-called "zeroth layer graphene'' on SiC(0001). 
As reported earlier by Sohn et al. [J. Korean Phys. Soc. 78, 157 (2021)], two phases are formed depending on the amount of intercalated Bi, which in turn is controlled by the annealing temperature: The α phase, showing a 1×1 periodicity with respect to the substrate, and, at higher temperatures, the √3×√3 reconstructed β phase. We characterise both phases and the transformation from the α to the β phase by photoelectron spectroscopy, normal incidence x-ray standing waves, electron diffraction and electron microscopy. We clearly see an almost complete intercalation of the graphene layers in both phases, with strong (covalent) interaction between the topmost Si atoms of the substrate and the Bi intercalant, but only weak (van der Waals) interaction between Bi and the graphene layer. The n-doping of the graphene found for the α phase decreases continuously during the phase transformation, in agreement with a reduced density of the Bi intercalating layer. Missing core level shifts of the surface species as well as the normal incidence x-ray standing waves results indicate that all surface Si atoms remain saturated during the transition and no dangling bonds are formed. Low energy electron microscopy and diffraction reveal the coexistance of both phases after annealing to intermediate temperatures and allow a quantitative analysis of island sizes and numbers.

Reconfigurable screen-printed terahertz frequency selective surface based on metallic checkerboard pattern

We employed the screen-printing method to fabricate terahertz (THz) frequency selective surfaces (FSSs) featuring an inductive metallic checkerboard (i-MCB) pattern based on conductive silver ink onto a flexible polyethylene terephthalate substrate, chosen for its excellent THz transmission properties below 1 THz [Jin et al 2006 J. Korean Phys. Soc. 49 513–17]. Analytical studies, along with simulations and experiments, were conducted to investigate the filtering characteristics of the printed FSSs, confirming their functionality as a band-pass filter. Subsequently, we demonstrated the reconfigurability of a two-layer system by vertically stacking two layers. This was achieved by systematically shifting the position of the second layer in the x or y-direction relative to the first layer. Experimental verification revealed a significant variation in normalized transmission, ranging from 94% to 6% at 0.15 THz for type-I:i-MCBs and 90% to 5% at 0.20 THz for type-II:i-MCBs, respectively. This study presents a simple scheme for a reconfigurable screen-printed i-MCB-FSS operating in the THz range. Consequently, our findings demonstrate that screen printing method can effectively be employed for the large-scale production of THz FSSs.

Metaplectic operator approach to Gutzwiller’s trace formula

We derive the Gutzwiller’s trace formula by considering the time-evolution operator of the Hamiltonian which describes an N-dimensional time-dependent generalized harmonic oscillator with general force terms, where the time-evolution operator is composed of metaplectic and Weyl-Heisenberg operators. The Hamiltonian is constructed by expanding a wave packet quadratically in position and momentum operators around a reference trajectory. Using the explicit form of the metaplectic operator recently obtained in (2022, J. Korean Phys. Soc. 80, 95), we give the proof of the well known properties of the metaplectic operator, and using those properties, we derive Gutzwiller’s trace formula and investigate the Maslov index appearing in the formula.

Separation of Flux/Dose Contributions from Multiple Transport Pathways in Monte Carlo Shielding Analyses of a Consolidated Interim Spent Nuclear Fuel Storage Facility

The characteristics of the radiation field around a consolidated interim spent nuclear fuel storage facility were investigated comprehensively through Monte Carlo simulations. Neutron and gamma-ray flux/dose contributions from multiple transport pathways, including direct, streaming, skyshine, groundshine, and multishine, were isolated using a modified version of the method that was originally developed by Oh et al. [J. Korean Phys. Soc., Vol. 69, 1057 (2016)] for the evaluation of neutron skyshine from a high-energy electron accelerator. The application of the methodology was demonstrated in this paper, and the flux/dose contributions of individual pathways were examined and compared. The results provided additional insight into how the radiation propagated from the source to off-site locations. The modified method for separating five transport pathways can provide valuable information for shielding optimization during the design phase and is generally applicable to Monte Carlo shielding analyses of other nuclear facilities.

A Detailed Numerical Analysis for High-Tc Superconductivity and Physical Analysis of the High-Tc Phase Diagram Based on the U(1) Slave-Boson Approach to the t − J Hamiltonian

One of the major theoretical challenges in high-Tc superconductivity is to first reproduce the observed phase diagrams that display the monotonously decreasing pseudogap temperature T* and the dome-shaped superconducting phase transition temperature Tc in the plane of temperature vs. hole concentration. Earlier Lee and Salk [J. Korean Phys. Soc. 37, 545 (2000); Phys. Rev. B 64, 052501 (2001)] reported a successful reproduction of the phase diagram by providing a realistic gauge theoretic [SU(2)/U(1)] slave-boson approach to the t - J Hamiltonian. Most recently, we [S.-H. S. Salk, Quantum Studies: Mathematics and Foundations 5, 149 (2018)] presented a comprehensive discussion on both the SU(2) and the U(1) approaches from which one can readily understand the intimate relationship between the two formalisms and discussed that both approaches can lead to room-temperature superconductivity with suitably high values of the antiferromagnetic coupling constant J, owing to the demonstration of identical physical propensities, i.e., the higher the J is, the higher the superconducting phase transition temperature Tc is. Here, we discuss hither-to-unreported detailed numerical computations of the phase diagrams by varying the values of J by using the U(1) gauge slave-boson approach to the t − J Hamiltonian. For the sake of testing convergence, we vary the unit-cell lattice sizes from 10 × 10 to a sufficiently large size of 50 × 50. We find that even a small square lattice size of 20 × 20 is seen to show reliable agreement with the results for higher lattice sizes while the 50 × 50 lattice size displays complete convergence in both T*and Tc. In addition, we present a physical analysis of the structure of the high-Tc phase diagram, focusing on the role of the spin pairing order in association with the interplay between the pseudo-gap (spin gap) temperature and the bose-condensation temperature/dome-shaped superconducting phase transition temperature.

Study of the hyper-Rayleigh scattering first hyperpolarizability of a chalcone derivative in various solvent media

In this work we investigate the solvent media effects on the nonlinear optical properties of a chalcone derivative, (2E)-3-(3-methylphenyl)-1-(4-nitrophenyl) prop-2-en-1-one (3MPNP), using the polarizable continuum model (PCM) at DFT/B3LYP/6-311+G(d) level. The behavior of the hyper-Rayleigh scattering first hyperpolarizability and the average second hyperpolarizability, are studied as function of the dielectric constant of the solvent medium in both dynamic and static cases. Full Text: PDF ReferencesL. R. Almeida et al., "Synthesis, structural characterization and computational study of a novel amino chalcone: a potential nonlinear optical material", New J. Chem., vol. 41, no. 4, pp. 1744-1754, 2017. CrossRef P. K. Murthy et al., "An analysis of structural and spectroscopic signatures, the reactivity study of synthetized 4,6-dichloro-2-(methylsulfonyl)pyrimidine: A potential third-order nonlinear optical material", J. Mol. Struct., vol. 1186, pp. 263-275, Jun. 2019. CrossRef J. Kongsted, A. Osted, K. V Mikkelsen, and O. Christiansen, "“Second harmonic generation second hyperpolarizability of water calculated using the combined coupled cluster dielectric continuum or different molecular mechanics methods", J. Chem. Phys., vol. 120, no. 8, pp. 3787-98, Feb. 2004. CrossRef T. L. Fonseca, J. R. Sabino, M. A. Castro, and H. C. Georg, "A theoretical investigation of electric properties of L-arginine phosphate monohydrate including environment polarization effects", J. Chem. Phys., vol. 133, no. 14, pp. 1-8, 2010. CrossRef A. KARAKAŞ, Z. E. KOÇ, M. FRIDRICHOVÁ, P. NĚMEC, and J. KROUPA, "THE INVESTIGATION OF SECOND-ORDER NONLINEAR OPTICAL PROPERTIES OF P-NITROPHENYLAZOANILINE: SECOND HARMONIC GENERATION AND AB INITIO COMPUTATIONS", J. Theor. Comput. Chem., vol. 11, no. 01, pp. 209-221, Feb. 2012. CrossRef T. Seidler, K. Stadnicka, and B. Champagne, "Second‐order Nonlinear Optical Susceptibilities and Refractive Indices of Organic Crystals from a Multiscale Numerical Simulation Approach", Adv. Opt. Mater., vol. 2, no. 10, pp. 1000-1006, Oct. 2014. CrossRef L. M. G. Abegão et al., "Second- and third-order nonlinear optical properties of unsubstituted and mono-substituted chalcones", Chem. Phys. Lett., vol. 648, pp. 91-96, Mar. 2016. CrossRef W. F. Vaz et al., "Synthesis, characterization, and third-order nonlinear optical properties of a new neolignane analogue", RSC Adv., vol. 6, no. 82, pp. 79215-79227, 2016. CrossRef C. Valverde et al., "The solid state structure and environmental polarization effect of a novel asymmetric azine", New J. Chem., vol. 41, no. 19, pp. 11361-11371, 2017. CrossRef P. N. Prasad, D. J. Williams, and others, Introduction to nonlinear optical effects in molecules and polymers, vol. 1. Wiley New York etc., 1991. DirectLink P. Günter, Nonlinear Optical Effects and Materials, 4th ed. Berlin: Springer Berlin Heidelberg, 2000. CrossRef H. Inan et al., "Photonic crystals: emerging biosensors and their promise for point-of-care applications", Chem. Soc. Rev., vol. 46, no. 2, pp. 366-388, 2017. CrossRef H. J. Chang et al., "Chiral Nonlinear Optics in Oxides, Polymers and Liquid Crystals", J. Korean Phys. Soc., vol. 43, no. 4, p. 587, 2003. DirectLink R. Bersohn, Y. Pao, and H. L. Frisch, "Double‐Quantum Light Scattering by Molecules", J. Chem. Phys., vol. 45, no. 9, pp. 3184-3198, Nov. 1966. CrossRef K. Clays and A. Persoons, "Hyper-Rayleigh scattering in solution", Phys. Rev. Lett., vol. 66, no. 23, pp. 2980-2983, 1991. CrossRef J. Campo, F. Desmet, W. Wenseleers, and E. Goovaerts, "Highly sensitive setup for tunable wavelength hyper-Rayleigh scattering with parallel detection and calibration data for various solvents", Opt. Express, vol. 17, no. 6, p. 4587, Mar. 2009. CrossRef S. R. Prabhu, A. Jayarama, K. Chandrasekharan, V. Upadhyaya, and S. W. Ng, "Synthesis, growth, structural characterization, Hirshfeld analysis and nonlinear optical studies of a methyl substituted chalcone", J. Mol. Struct., vol. 1136, pp. 244-252, May 2017. CrossRef K. Clays and A. Persoons, "Hyper‐Rayleigh scattering in solution", Rev. Sci. Instrum., vol. 63, no. 6, pp. 3285-3289, Jun. 1992. CrossRef K. Clays et al., "Nonlinear Optical Properties of Proteins Measured by Hyper-Rayleigh Scattering in Solution", Science (80-. )., vol. 262, no. 5138, pp. 1419-1422, Nov. 1993. CrossRef M. Frisch et al., Gaussian, Inc., Wallingford CT, 2009. DirectLink J. M. F. Custodio et al., "Chalcone as Potential Nonlinear Optical Material: A Combined Theoretical, Structural, and Spectroscopic Study", J. Phys. Chem. C, vol. 123, no. 10, pp. 5931-5941, Mar. 2019. CrossRef

Autaptic Effects on Synchronization and Phase Response Curves of Neurons with a Chemical Synapse

Previously, we reported the effects of an autapse, a time-delayed self-feedback synapse, on synchronization of Morris-Lecar (ML) neurons with an electrical synapse [J. Korean Phys. Soc. 71, 63 (2017)]. Because communication between neurons via a chemical synapse is more common than that via a electrical synapse, the desire to study the autaptic effect on synchronization of neurons with a chemical synapse is natural. In this paper, we present the results for the autaptic effects on synchronization of neurons with a chemical synapse. We show that the phase response curves of a single neuron and a pair of neurons are useful for understanding the autaptic effects on synchronization. We introduce a model for a theoretical analysis of the autaptic effect on synchronization of parameter-mismatched neurons and find that the model qualitatively explains that effect well.

Five-dimensional spherical symmetric perfect fluid collapse in f(R, T) gravity

This paper contains the study of spherically symmetric perfect fluid collapse in the framework of f(R, T) modified theory of gravity using five-dimensional background. We consider the five-dimensional spherical symmetric metric as the interior region and a five-dimensional Schwarzschild metric as an exterior region. The Darmois junction conditions between exterior and interior regions are discussed. By taking the particular f(R, T) model, the corresponding field equations are evaluated for both marginally bound L(r) = 1 and non-marginally bound L(r) ≠ 1 cases. We find the gravitational mass of the collapsing system and discuss the apparent horizons and their time formation for different possible cases. Also, the cosmological and black hole horizons have been discussed. It has been concluded that the term involving λ plays a double role: it accelerates the collapse in the region where ρ0 < 4p0 and it slows down the collapsing of matter when ρ0 > 4p0. Further, it is noted that our results reduce to the results found by Sharif and Ahmad (J. Korean Phys. Soc. 52, 980 (2008). doi: 10.3938/jkps.52.980) in general relativity for λ = 0.

Neutron Transmission and Capture Measurements of 133Cs from 0.01 to 600 eV

Neutron capture and transmission measurements were carried out from 0.01 to 600 eV on both solid and liquid samples containing elemental cesium (133Cs). Only s-wave resonances were observed in these measurements. These data were analyzed for resonance parameters utilizing the SAMMY Bayesian analysis code to simultaneously fit both the capture and transmission data. Parameters were obtained for 31 cesium resonances up to 600 eV. The thermal capture cross section and capture resonance integral were determined. The thermal capture cross section is 10% larger than the ENDF, JENDL, and JEFF evaluated values but lies within the uncertainty of the most recent measurement by Yoon and Lee [New Phys.: Sae Mulli (Korean Phys. Soc.)., Vol. 61, p. 7 (2011)]. The capture resonance integral has a statistical 1σ error of 2% and lies 1.4σ above the JENDL value, 5.5σ above the ENDF value, and 3.9σ above the JEFF value. The s-wave strength function was determined.

Squeezing Effect on Entanglement Swapping: A Quantum Trajectory Approach

Using the results of our previous work (J. Korean Phys. Soc. 56, 10 (2010)), we calculate the negativity N and the geometric discord G of the final qubits of the entanglement swapping protocol through an amplitude-damping multi-qubit channel interacting with a squeezed thermal bath. Our numerical results confirm that the squeezing suppresses the decay rate of quantum coherence.

(Invited) Advanced Crystallization Using Blue Laser-Diode Annealing for Low Temperature Poly Si TFTs

Laser Crystallizations using Blue Laser-Diodes Annealing (BLDA) as well as conventional Excimer Laser Annealing (ELA) are discussed for mounting the TFTs on flexible panels. On glass, high crystallinity of Si films can be obtained by using multi-shots ELA as well as CW laser scanning [1, 2]. There are some issues for Si film after ELA, such as rough Si surface or shots MURA including the fabrication cost. As a result of scanning BLDA for thin Si films, remarkable crystallization occurs with keeping the surface smooth not only for CVD film but also for sputtered Si film [3]. By changing the laser power of 445 nm beam, the grain size can be controlled from micro-grains to large grains as well as to anisotropic long crystal grains [4]. For the Si films of heavily phosphorus doped condition, the resistivity decreased drastically due to the increase in the carrier mobility with high carrier concentration after BLDA of single beam scanning as well as after multi-shots ELA [5]. To realize high performance poly Si films directly not only on flexible glass [6] but also on flexible plastic sheet, effective laser annealing for high quality Si film by low temperature deposition is expected and a design for the thermal buffer layers on flexible sheet is effective [7]. To perform ultra-low temperature TFT process, metal source/drain structure without using ion implantation is also proposed. High performance poly Si TFTs with low fabrication cost on flexible panel should be possible not only for n-channel but also for p-channel [8, 9]. References M. Tai, M. Hatano, S. Yamaguchi, S. K. Park, T. Noda, M. Hongo, T. Shiba and M. Ohkura, Proc. of AM-LCD, TFT3-3, p.231 (2002)T. Noguchi, Mat. Res. Soc. Symp. Proc., 557, p.213 (1993),T. Okada, K, Sugihara, S. Chinen and T. Noguchi, J. Korean Phys. Soc., 66, No.8, pp.1266-1269 (2015). .T. Noguchi, J. Inf. Display, 11, No.1, p.12 (2010).T. Noguchi and T. Okada, J. of Inf. Display, 15, No.1, p.47 (2014).T. Harada, F. Gakiya, Y. Ishiki, T. Okada, T. Noguchi, K. Noda, A. Suwa and H. Ikenoue, Proc. of IDW, AMDp2-11L, p.444 (2016).T. Okada, J.D. Mugiraneza, K. Shirai, T. Suzuki, T. Noguchi, H. Matsushima, T. Hashimoto, Y. Ogino and E. Sahota, Jap. J. Appl. Phys. 51, 03CA02 (2012).K. Sugihara, K. Shimoda, T. Okada and T. Noguchi, J. Inf. Display, 18, No.4, 173-176 (2017).T. Ashitomi, T. Harada, T. Okada, T. Noguchi, O. Nishikata and A. Ota, J. Inf. Display, 18, No.4, 185-189 (2017).

Plausible room temperature superconductivity and physical properties of cuprate superconductors based on a rigorous slave-boson representation of the t–J Hamiltonian

We present newly clarified physical properties of cuprate superconductors based on careful examinations of our earlier studies and show plausibility of room temperature superconductivity. As well known, one of the major challenging problems in high-temperature superconductivity is to reproduce the observed phase diagrams (Chatterjee, PNAS 108:9346–9349, 2011; Oda, J Phys Soc Jpn 69:983–984, 2000; Nakano, J Phys Soc Jpn 67:2622–2625, 1998; Schmidt, New J Phys 13:065014, 2011, Cyr-Choiniere (Pseudogap temperature \({T}^{*}\) of cuprate from the Nernst effect, cond-mat.supr-con, 2017; Yoshida et al. Nature 454:1072, 2008) displaying both the monotonously decreasing pseudogap temperature \(T^{*}\) and the dome-shaped superconducting transition temperature \(T_\mathrm{c}\) in the plane of temperature vs. hole concentration. Earlier we Lee et al. (Phys Rev B 64:052501–052504, 2001), Lee and Salk (Phys Rev B 71:134518, 2005), (66:054427, 2002), (J Korean Phys Soc 37:545–551, 2000) reported successful reproductions of the phase diagrams using our slave-boson theory of U(1) and SU(2) symmetry for the t–J Hamiltonian. Later we further showed that predictions (Shin and Salk, Int J Mod Phys B 29:1542003–1542011, 2015; Shin et al. J Supercond Nov Magn 23:637–640, 2010; Eom et al. Int J Mod Phys B 21:3132, 2007) of both the temperature and doping dependence of magnetic susceptibility and the universal linear scaling behavior between the magnetic resonance energy, \(E_{{\mathrm{res}}}\) and \(T_\mathrm{c}\), are consistent with inelastic neutron scattering (INS) measurements (Dai et al. Science 284:1344, 1999; He et al. Phys Rev Lett 86:1610, 2001; Bourges et al. Phys C 424:45, 2005; Stock et al. Phys Rev B 75:172510, 2007; Wakimoto et al. Phys Rev Lett 98:247003, 2007; Yu et al. Nat Phys 5:873, 2009; Isonov et al. Phys Rev B 83:214520, 2011; Keimer et al. Nature 518:179, 2015). In this work we present further clarifications of physics involved with both the phase diagrams and the INS measurements. For this cause we explore the role of spin–charge coupling on both the universal behavior of \({T^{*}}/T_\mathrm{c}\) from the phase diagrams (Chatterjee, 2011) and the universal scaling ratio of \({E_{{\mathrm{res}}}}/{k_\mathrm{B} T_\mathrm{c}}\) from the INS measurements (He et al. Phys Rev Lett 86:1610, 2001; Bourges et al. Phys C 424:45, 2005; Yu et al. Nat Phys 5:873, 2009). Both of them are found to be independent of the Heisenberg exchange coupling constant J, involving the distinctive presence of spin pairing order in association with the two energy scales, the magnetic resonance energy and the pseudogap temperature. In addition, we also discuss the J independent universal behavior of the superfluid density vs. the superconducting transition temperature. We explain most specifically physics on how all of these universal behaviors are related to the presence of spin–charge coupling. The spin–charge coupling here refers to coupling between the spin (spinon) paring order and the charge (holon) paring order which is manifested in our rigorous derivation (Lee et al. 2001; Lee and Salk, 2005, 2002) of the slave-boson-based t–J Hamiltonian. In short, we plan to explain salient physics involved with the observed universal behaviors above. Noting that in association with the universal scaling behaviors of both \({T^{*}}/T_\mathrm{c}\) and \({E_{\mathrm{res}}}/{k_\mathrm{B} T_\mathrm{c}}\) the higher the J, the higher the \(T_\mathrm{c}\), we propose that room temperature superconductivity is plausible with proper chemical synthesis of cuprate oxides meeting a suitably high J value.

Effect of thermal expansion mismatch in grating material and host specimen on thermal sensitivity of FBG sensor

Authors have studied thermal sensitivity characteristics of FBG temperature sensor attached to the surface of targeted host specimen (Lee and Lee in J Korean Phys Soc 59(5):3188–3191, 2011; Yu-Lung and Han-Sheng in Meas Sci Technol 9:1543–1547, 1998; Reddy et al. in Opt Appl 40(3):685–692, 2010). In their mathematical analysis, the coefficient of thermal expansion of grating material is ignored due to its contribution to the shift in the wavelength is small as compared to shift because of CTE of host specimen. However, we find that the Bragg’s wavelength shift used for measuring temperature in FBG sensor is dependent on difference in thermal expansions of grating and targeted host specimen materials. We have investigated the effect of the expansion in the material of the grating as well as that of host material and have found that at low temperature the difference in the shift in wavelength is indeed very small of the order of 0.67 pm at \(26\,{^\circ }\hbox {C}\), but the difference in the shift in the wavelength at higher temperature say 350–\(400\,{^\circ }\hbox {C}\) is quite large of the order of 250 pm and cannot be neglected as it will result in error reading of the temperature for higher ranges.

Tomography of atomic number and density of materials using dual-energy imaging and the Alvarez and Macovski attenuation model

Dual-energy computed tomography and the Alvarez and Macovski [Phys. Med. Biol. 21, 733 (1976)] transmitted intensity (AMTI) model were used in this study to estimate the maps of density (ρ) and atomic number (Z) of mineralogical samples. In this method, the attenuation coefficients are represented [Alvarez and Macovski, Phys. Med. Biol. 21, 733 (1976)] in the form of the two most important interactions of X-rays with atoms that is, photoelectric absorption (PE) and Compton scattering (CS). This enables material discrimination as PE and CS are, respectively, dependent on the atomic number (Z) and density (ρ) of materials [Alvarez and Macovski, Phys. Med. Biol. 21, 733 (1976)]. Dual-energy imaging is able to identify sample materials even if the materials have similar attenuation coefficients at single-energy spectrum. We use the full model rather than applying one of several applied simplified forms [Alvarez and Macovski, Phys. Med. Biol. 21, 733 (1976); Siddiqui et al., SPE Annual Technical Conference and Exhibition (Society of Petroleum Engineers, 2004); Derzhi, U.S. patent application 13/527,660 (2012); Heismann et al., J. Appl. Phys. 94, 2073–2079 (2003); Park and Kim, J. Korean Phys. Soc. 59, 2709 (2011); Abudurexiti et al., Radiol. Phys. Technol. 3, 127–135 (2010); and Kaewkhao et al., J. Quant. Spectrosc. Radiat. Transfer 109, 1260–1265 (2008)]. This paper describes the tomographic reconstruction of ρ and Z maps of mineralogical samples using the AMTI model. The full model requires precise knowledge of the X-ray energy spectra and calibration of PE and CS constants and exponents of atomic number and energy that were estimated based on fits to simulations and calibration measurements. The estimated ρ and Z images of the samples used in this paper yield average relative errors of 2.62% and 1.19% and maximum relative errors of 2.64% and 7.85%, respectively. Furthermore, we demonstrate that the method accounts for the beam hardening effect in density (ρ) and atomic number (Z) reconstructions to a significant extent.

Theory of light scattering in subwavelength metallic slot antenna array fabricated on subwavelength thin film

We demonstrate an analytic model that describes the near-field electromagnetic field profile near a subwavelength-sized metallic slot antenna fabricated on a thin dielectric substrate having a subwavelength thickness reaching λ/1000 in the terahertz frequency region. We found two-dimensional light diffraction induced by the two-dimensional nature of the slot antenna, and back-reflected waves interfered with each other in a complicated manner, resulting in a coupling of the Fourierdecomposed field amplitudes between the diffraction orders along the x and the y directions. We applied these findings to our model by modifying a previously developed model [D. J. Park et al., J. Korean Phys. Soc. 65, 1390 (2014)], and we monitor the effect on far-field transmission. This coupling effect was found to contribute to removal of physically-meaningless spikes or divergences in the transmission spectra, especially for relatively thick substrates.

Critical decay exponent of the pair contact process with diffusion

We investigate the one-dimensional pair contact process with diffusion (PCPD) by extensive Monte Carlo simulations, mainly focusing on the critical density decay exponent δ. To obtain an accurate estimate of δ, we first find the strength of corrections to scaling using the recently introduced method [S.-C. Park. J. Korean Phys. Soc. 62, 469 (2013)KPSJAS0374-488410.3938/jkps.62.469]. For small diffusion rate (d≤0.5), the leading corrections-to-scaling term is found to be ∼t^{-0.15}, whereas for large diffusion rate (d=0.95) it is found to be ∼t^{-0.5}. After finding the strength of corrections to scaling, effective exponents are systematically analyzed to conclude that the value of critical decay exponent δ is 0.173(3) irrespective of d. This value should be compared with the critical decay exponent of the directed percolation, 0.1595. In addition, we study two types of crossover. At d=0, the phase boundary is discontinuous and the crossover from the pair contact process to the PCPD is found to be described by the crossover exponent ϕ=2.6(1). We claim that the discontinuity of the phase boundary cannot be consistent with the theoretical argument supporting the hypothesis that the PCPD should belong to the DP. At d=1, the crossover from the mean field PCPD to the PCPD is described by ϕ=2 which is argued to be exact.

Derivation of the linear optical conductivity for electron-phonon interactions in solids by using the revised combined projection technique

A revised version of the combined projection technique introduced earlier by the present authors [J. Korean Phys. Soc. 59, 3372 (2011)] is introduecd and is applied to deriving the linear optical conductivity containing the linewidth function for optical transitions of electrons interacting with phonons in solids. The result is shown to satisfy the population criterion which claims that the Fermi distribution functions for electrons and the Planck distribution functions for phonons should be combined in multiplicative forms in the many-body formalism. The main part of the result is further shown to be indentical with that obtained by using the projection-reduction method [Progr. Theor. Phys. 96, 307 (1996)].

Cryptanalysis of a multi-user quantum network system and quantum communication using χ-type entangled states

A quantum secure direct communication and quantum key distribution(QSDC-QKD) protocol based on χ-type entangled states was recently proposed by Hong et al. [J. Korean Phys. Soc. 61, 1 (2012)]. By analyzing the protocol, we find that it is not secure; that is, the eavesdropper can eavesdrop on half of Bob’s secret messages and half of Alice’s secret keys without introducing any error.

Cryptanalysis and Improvement of a Multi-User Quantum Communication Network Using χ-Type Entangled States

The security of a multi-user quantum communication network protocol using χ-type entangled states (Chang et al., J. Korean Phys. Soc. 61:1–5, 2012) is analyzed. We find that, by using one χ-type state in this protocol, two participants can only share 2 bits of information, not 4 bits as the authors stated. In addition, we give a special attack strategy by which an eavesdropper can elicit half of the secret information without being detected. Finally, we improve the protocol to be secure against all the present attacks.

Three-particle entanglement swapping in an imperfect channel

Extending our previous work [J. Korean Phys. Soc. 58, 1708 (2011)], we analyze the noise effects of an imperfect channel on three-particle entanglement swapping by calculating the fidelity F of a three-qubit state after a GHZ measurement. In contrast to other kinds of noise, the bit flip noise and the phase flip noise do not cause the fidelity to decay exponentially to 0.25 but to 0.5, which shows the presence of genuine entanglement.