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Y. S. Kim

Publications and source records attributed to Y. S. Kim.

At least 19 recordsLinked to original sources
arXiv2021

A compact and stable incidence-plane-rotating second harmonics detector

We describe a compact and stable setup for detecting the optical second harmonics, in which the incident plane rotates with respect to the sample. The setup is composed of rotating Fresnel-rhomb optics and a femtosecond ytterbium-doped fiber-laser source operating at the repetition frequency of 10 MHz. The setup including the laser source occupies an area of 1 m2 and is stable so that the intensity fluctuation of the laser harmonics can be less than 0.2 % for 4 h. We present the isotropic harmonic signal of a gold mirror of 0.5 pW and demonstrate the integrity and sensitivity of the setup. We also show the polarization-dependent six-fold pattern of the harmonics of a few-layer WSe2, from which we infer the degree of local-field effects. Finally, we describe the extendibility of the setup to investigate the samples in various conditions such as cryogenic, strained, ultrafast non-equilibrium, and high magnetic fields.

physics.ins-det↗
arXiv2020

Kant and Hegel in Physics

Kant and Hegel are among the philosophers who are guiding the way in which we reason these days. It is thus of interest to see how physical theories have been developed along the line of Kant and Hegel. Einstein became interested in how things appear to moving observers. Quantum mechanics is also an observer-dependent science. The question then is whether quantum mechanics and relativity can be synthesized into one science. The present form of quantum field theory is a case in point. This theory however is based on the algorithm of the scattering matrix where all participating particles are free in the remote past and in the remote future. We thus need, in addition, a Lorentz-covariant theory of bound state which will address the question of how the hydrogen atom would look to moving observers. The question is then whether this Lorentz-covariant theory of bound states can be synthesized with the field theory into a Lorentz-covariant quantum mechanics. This article reviews the progress made along this line. This integrated Kant-Hegel process is illustrated in terms of the way in which Americans practice their democracy.

physics.hist-ph↗
arXiv2020

Work function seen with sub-meV precision through laser photoemission

Electron emission can be utilised to measure the work function of the surface. However, the number of significant digits in the values obtained through thermionic-, field- and photo-emission techniques is typically just two or three. Here, we show that the number can go up to five when angle-resolved photoemission spectroscopy (ARPES) is applied. This owes to the capability of ARPES to detect the slowest photoelectrons that are directed only along the surface normal. By using a laser-based source, we optimised our setup for the slow photoelectrons and resolved the slowest-end cutoff of Au(111) with the sharpness not deteriorated by the bandwidth of light nor by Fermi-Dirac distribution. The work function was leveled within $\pm$0.4 meV at least from 30 to 90 K and the surface aging was discerned as a meV shift of the work function. Our study opens the investigations into the fifth significant digit of the work function.

cond-mat.mtrl-sci↗
arXiv2020

Classification of the symmetry of photoelectron dichroism broken by light

We investigate how the direction of polarized light can affect the dichroism pattern seen in angle-resolved photoemission spectroscopy. To this end, we prepared a sample composed of highly-oriented Bi(111) micro-crystals that macroscopically has infinite rotational and mirror symmetry of the point group $\rm{C}_{\infty\rm{v}}$ and examined whether the dichroism pattern retains the $\rm{C}_{\infty\rm{v}}$ symmetry under the stationary configuration of the light and sample. The direction of the light was imprinted in the pattern. Thereby, we apply group theory and classify the pattern with the configuration of light taken into account. We complete the classification by discussing the cases when the out-of-plane component of the polarization can be neglected, when the incidence angle is either 0$^{\circ}$ or 90$^{\circ}$, when the polarization is either elliptic or linear, and also when the sample is a crystal.

cond-mat.str-el↗
arXiv2020

Momentum dependent $d_{xz/yz}$ band splitting in LaFeAsO

We performed angle-resolved photoemission spectroscopy (ARPES) studies of the electronic structure of the nematic phase in LaFeAsO. Degeneracy breaking between the dxz and dyz hole bands near the Γ and M point is observed in the nematic phase. Different temperature dependent band splitting behaviors are observed at the Γ and M points. The energy of the band splitting near the M point decreases as the temperature decreases while it has little temperature dependence near the Γ point. The nematic nature of the band shift near the M point is confirmed through a detwin experiment using a piezo device. Since a momentum dependent splitting behavior has been observed in other iron based superconductors, our observation confirms that the behavior is a universal one among iron based superconductors.

cond-mat.supr-con↗
arXiv2019

Role of Quantum Optics in Synthesizing Quantum Mechanics and Relativity

Two-photon states produce enough symmetry needed for Dirac's construction of the two-oscillator system which produces the Lie algebra for the O(3,2) space-time symmetry. This O(3,2) group can be contracted to the inhomogeneous Lorentz group which, according to Dirac, serves as the basic space-time symmetry for quantum mechanics in the Lorentz-covariant world. Since the harmonic oscillator serves as the language of Heisenberg's uncertainty relations, it is right to say that the symmetry of the Lorentz-covariant world, with Einstein's $E = mc^2$, is derivable from Heisenberg's uncertainty relations.

quant-ph↗
arXiv2017

On generalization of Bailey's identity involving product of generalized hypergeometric series

The aim of this research paper is to obtain explicit expressions of (i) $ {}_1F_1 \left[\begin{array}{c} α\\ 2α+ i \end{array} ; x \right]. {}_1F_1\left[ \begin{array}{c} β\\ 2β+ j \end{array} ; x \right]$ (ii) ${}_1F_1 \left[ \begin{array}{c} α\\ 2α- i \end{array} ; x \right] . {}_1F_1 \left[ \begin{array}{c} β\\ 2β- j \end{array} ; x \right]$ (iii) ${}_1F_1 \left[ \begin{array}{c} α\\ 2α+ i \end{array} ; x \right] . {}_1F_1 \left[\begin{array}{c} β\\ 2β- j \end{array} ; x \right]$ in the most general form for any $i,j=0,1,2,\ldots$ For $i=j=0$, we recover well known and useful identity due to Bailey. The results are derived with the help of a well known Bailey's formula involving products of generalized hypergeometric series and generalization of Kummer's second transformation formulas available in the literature. A few interesting new as well as known special cases have also been given.

math.CV↗
arXiv2016

Eugene Paul Wigner's Nobel Prize

In 1963, Eugene Paul Wigner was awarded the Nobel Prize in Physics for his contributions to the theory of the atomic nucleus and the elementary particles, particularly through the discovery and application of fundamental symmetry principles. There are no disputes about this statement. On the other hand, there still is a question of why the statement did not mention Wigner's 1939 paper on the Lorentz group, which was regarded by Wigner and many others as his most important contribution in physics. By many physicists, this paper was regarded as a mathematical exposition having nothing to do with physics. However, it has been more than one half century since 1963, and it is of interest to see what progress has been made toward understanding physical implications of this paper and its historical role in physics. Wigner in his 1963 paper defined the subgroups of the Lorentz group whose transformations do not change the four-momentum of a given particle, and he called them the little groups. Thus, Wigner's little groups are for internal space-time symmetries of particles in the Lorentz-covariant world. Indeed, this subgroup can explain the electron spin and spins of other massive particles. However, for massless particles, there was a gap between his little group and electromagnetic waves derivable Maxwell's equations. This gap was not completely removed until 1990. The purpose of this report is to review the stormy historical process in which this gap is cleared. It is concluded that Wigner's little groups indeed can be combined into one Lorentz-covariant formula which can dictate the symmetry of the internal space-time time symmetries of massive and massless particles in the Lorentz covariant world, just like Einstein's energy-momentum relation applicable to both slow and massless particles.

physics.hist-ph↗
arXiv2016

Symmetries of Massive and Massless Neutrinos

Wigner's little groups are subgroups of the Lorentz group dictating the internal space-time symmetries of massive and massless particles. These little groups are like O(3) and E(2) for massive and massless particles respectively. While the geometry of the O(3) symmetry is familiar to us, the geometry of the flat plane cannot explain the E(2)-like symmetry for massless particles. However, the geometry of a circular cylinder can explain the symmetry with the helicity and gauge degrees of freedom. It is shown further that the symmetry of the massless particle can be obtained as a zero-mass limit of O(3)-like symmetry for massive particles. It is shown further that the polarization of massless neutrinos is a consequence of gauge invariance, while the symmetry of massive neutrinos is still like O(3).

hep-ph↗
arXiv2016

Do Small-mass Neutrinos participate in Gauge Transformations?

Neutrino oscillation experiments presently suggest that neutrinos have a small but finite mass. If neutrinos are to have mass, there should be a Lorentz frame in which they can be brought to rest. This paper discusses how Wigner's little groups can be used to distinguish between massive and massless particles. We derive a representation of the SL(2,c) group which separates out the two sets of spinors contained therein. One set is gauge dependent. The other set is gauge-invariant and represents polarized neutrinos. We show that a similar calculation can be done for the Dirac equation. In the large-momentum/zero-mass limit, the Dirac spinors can be separated into large and small components. The large components are gauge invariant, while the small components are not. These small components represent spin-$\frac{1}{2}$ non-zero mass particles. If we renormalize the large components, these gauge invariant spinors again represent the polarization of neutrinos. Massive neutrinos cannot be invariant under gauge transformations.

physics.gen-ph↗
arXiv2015

The O(3,2) Symmetry derivable from the Poincaré Sphere

Henri Poincaré formulated the mathematics of the Lorentz transformations, known as the Poincaré group. He also formulated the Poincaré sphere for polarization optics. It is noted that his sphere contains the symmetry of the Lorentz group applicable to the momentum-energy four-vector of a particle in the Lorentz-covariant world. Since the particle mass is a Lorentz-invariant quantity, the Lorentz group does not allow its variations. However, the Poincaré sphere contains the symmetry corresponding to the mass variation, leading to the $O(3,2)$ symmetry. An illustrative calculation is given.

math-ph↗
arXiv2014

A note on a hypergeometric transformation formula due to Slater with an application

In this note we state (with minor corrections) and give an alternative proof of a very general hypergeometric transformation formula due to Slater. As an application, we obtain a new hypergeometric transformation formula for a ${}_5F_4(-1)$ series with one pair of parameters differing by unity expressed as a linear combination of two ${}_3F_2(1)$ series.

math.CA↗
arXiv2014

QCD. What else is needed for the Proton Structure Function?

While QCD can provide corrections to the parton distribution function, it cannot produce the distribution. Where is then the starting point for the proton structure function? The only known source is the quark-model wave function for the proton at rest. The harmonic oscillator is used for the trial wave function. When Lorentz-boosted, this wave function exhibits all the peculiarities of Feynman's parton picture. The time-separation between the quarks plays the key role in the boosting process. This variable is hidden in the present form of quantum mechanics, and the failure to measure it leads to an increase in entropy. This leads to a picture of boiling quarks which become partons in their plasma state.

hep-ph↗
arXiv2014

One analytic form for four branches of the ABCD matrix

It is not always possible to diagonalize the optical $ABCD$ matrix, but it can be brought into one of the four Wigner matrices by a similarity transformation. It is shown that the four Wigner matrices can be combined into one matrix with four branches. This result is illustrated in terms of optical activities, laser cavities, and multilayer optics.

math-ph↗
arXiv2014

Poincaré Sphere and a Unified Picture of Wigner's Little Groups

It is noted that the Poincaré sphere for polarization optics contains the symmetries of the Lorentz group. The sphere is thus capable of describing the internal space-time symmetries dictated by Wigner's little groups. For massive particles, the little group is like the three-dimensional rotation group, while it is like the two-dimensional Euclidean group for massless particles. It is shown that the Poincaré sphere, in addition, has a symmetry parameter corresponding to reducing the particle mass from a positive value to zero. The Poincaré sphere thus the gives one unified picture of Wigner's little groups for massive and massless particles.

math-ph↗
arXiv2014

On extensions of two results due to Ramanujan

The aim in this note is to provide a generalization of an interesting entry in Ramanujan's Notebooks that relate sums involving the derivatives of a function Phi(t) evaluated at 0 and 1. The generalization obtained is derived with the help of expressions for the sum of terminating 3F2 hypergeometric functions of argument equal to 2, recently obtained in Kim et al. [Two results for the terminating 3F2(2) with applications, Bull. Korean Math. Soc. 49 (2012) pp. 621{633]. Several special cases are given. In addition we generalize a summation formula to include integral parameter differences.

math.CV↗
arXiv2014

Lens optics and the continuity problems of the ABCD matrix

Paraxial lens optics is discussed to study the continuity properties of the $ABCD$ beam transfer matrix. The two-by-two matrix for the one-lens camera-like system can be converted to an equi-diagonal form by a scale transformation, leaving the off-diagonal elements invariant. It is shown that the matrix remains continuous during the focusing process, but this transition is not analytic. However, its first derivative is still continuous, which leads to the concept of "tangential continuity." It is then shown that this tangential continuity is applicable to $ABCD$ matrices pertinent to periodic optical systems, where the equi-diagonalization is achieved by a similarity transformation using rotations. It is also noted that both the scale transformations and the rotations can be unified within the framework of Hermitian transformations.

physics.optics↗