arXiv subjects

Daijiro Yoshioka

Publications and source records attributed to Daijiro Yoshioka.

At least 19 recordsLinked to original sources

arXiv2013

Meissner effect cannot be explained classically

The Meissner effect is an important characteristic of superconductivity and is critical to distinguishing superconductivity from simply the absence of electrical resistance (perfect conductivity). In a recent paper published in American Journal of Physics, Essén and Fiolhais claimed that the Meissner effect is explained by classical physics. [Am. J. Phys. {\textbf{80}} 164, (2012).] We claim it cannot be understood by classical mechanics and point out that their derivation of the Meissner effect by classical physics is based on an inadequate treatment of the magnetic field energy. A correct treatment of the magnetic field energy clarifies the need for quantum mechanics to understand the Meissner effect. We stress that Meissner effect is energetically favorable due to the energy of condensation of the Cooper pairs. The condensation of electrons into Cooper pairs is best understood as a quantum mechanical phenomenon.

cond-mat.supr-con↗

arXiv2012

Skyrme crystal in bilayer and multilayer graphene

The ground state of the two-dimensional electron systems in Bernal bilayer and ABC-stacked multilayer graphenes in the presence of a strong magnetic field is investigated with the Hartree-Fock approximation. Phase diagrams of the systems are obtained, focusing on charge density wave states including states with vortices of valley pseudospins (called a Skyrme crystal). The single-electron states in these stacked graphenes are given by two-component wave functions. That of the first excited Landau level has the same component as the lowest Landau level of the ordinary two-dimensional electrons. Because of this localized wave functions, the Skyrme crystal has low energy in this first excited level up to four layers of graphene, when the inter-layer distance is assumed to be infinitesimal. At the same time, bubble crystals are suppressed, so the phase diagram is different from that of a single-layer graphene.

cond-mat.mes-hall↗

arXiv2010

Stability of the Excitonic Phase in Bilayer Quantum Hall Systems at Total Filling One -- Effects of Finite Well Width and Pseudopotentials --

The ground state of a bilayer quantum Hall system at $ν_{\rm T}=1$ with model pseudopotential is investigated by the DMRG method. Firstly, pseudopotential parameters appropriate for the system with finite layer thickness are derived, and it is found that the finite thickness makes the excitonic phase more stable. Secondly, a model, where only a few pseudopotentials with small relative angular momentum have finite values, is studied, and it is clarified how the excitonic phase is destroyed as intra-layer pseudopotential becomes larger. The importance of the intra-layer repulsive interaction at distance twice of the magnetic length for the destruction of the excitonic phase is found.

cond-mat.str-el↗

arXiv2009

Uniform current in graphene strip with zigzag edges

Graphene exhibits zero-gap massless-Dirac fermion and zero density of states at E = 0. These particles form localized states called edge states on finite width strip with zigzag edges at E = 0. Naively thinking, one may expect that current is also concentrated at the edge, but Zarbo and Nikolic numerically obtained a result that the current density shows maximum at the center of the strip. We derive a rigorous relation for the current density, and clarify the reason why the current density of edge state has a maximum at the center.

cond-mat.mes-hall↗

arXiv2006

Local Density of States around an Impurity in a Strong Magnetic Field. I. a Two-Dimensional System with Parabolic Dispersion

Bound states around an impurity are investigated for a two dimensional electron system in a strong magnetic field. Long-range Coulomb potential and related potentials are considered. Schrödinger equation is solved numerically to obtain the bound states. The energy and wave function of these bound states are indirectly observed by the scanning tunneling spectroscopy as local density of states (LDOS). Theoretically obtained LDOS is compared with experiment. Reasonable agreement is obtained.

cond-mat.mes-hall↗

arXiv2006

Ground State of v=1 Bilayer Quantum Hall Systems

The ground-state wave function and the energy gap are calculated for various layer separations d and for up to 24 electrons by the density matrix renormalization group (DMRG) method. Two-particle distribution function and excitonic correlation function are calculated from the ground-state wave function, and the evolution of the ground state with increasing d is analyzed. The results indicate that the transition is continuous. A smooth crossover of the ground state is found at around d/l ~ 1.6 from the excitonic character at small d/l to the independent Fermi-liquid character at large d/l, where l is the magnetic length.

cond-mat.str-el↗

arXiv2004

Real Space Effective Interaction and Phase Transition in the Lowest Landau Level

The transition between the stripe state and the liquid state in a high magnetic field is studied by the density-matrix renormalization-group (DMRG) method. Systematic analysis on the ground state of two-dimensional electrons in the lowest Landau level shows that the transition from the stripe state to the liquid state at v=3/8 is caused by a reduction of repulsive interaction around r=3. The same reduction of the interaction also stabilizes the incompressible liquid states at v=1/3 and 2/5, which shows a similarity between the two liquid states at v=3/8 and 1/3. It is also shown that the strong short-range interaction around r=1 in the lowest Landau level makes qualitatively different stripe correlations compared with that in higher Landau levels.

cond-mat.mes-hall↗

arXiv2004

Theory of "charge" measured by the shot noise experiments in the fractional quantum Hall states

Shot noise at filling factor $ν=2/5$ is investigated theoretically. It is argued that the "charge" $e^*$ measured by the noise at zero temperature is not the quasiparticle charge but simply the filling factor times the electron charge $e$, namely $e^*=2e/5$. At higher temperature quasiparticles with charge $e^*=\pm e/5$ begin to contribute to the backscattering, and the shot noise gives charge $e^*=e/5$. This theory explains recent experiment by Chung et al. [Phys. Rev. Lett. \textbf{91} (2003) 216804.

cond-mat.mes-hall↗

arXiv2004

Ground state phase diagram of 2D electrons in high magnetic field

The ground state phase diagram of two-dimensional electrons in high magnetic field is studied by the density matrix renormalization group (DMRG) method. The low energy excitations and pair correlation functions in Landau levels of N=0,1,2 are calculated for wide range of fillings. The obtained results for systems with up to 25 electrons confirm the existence of various electronic states in quantum Hall systems. The ground state phase diagram for N=0,1,2 consisting of incompressible liquids, compressible liquids, charge density waves called stripe, bubble and Wigner crystal is determined.

cond-mat.mes-hall↗

arXiv2004

Stripe State in the Lowest Landau Level

The stripe state in the lowest Landau level is studied by the density matrix renormalization group (DMRG) method. The ground state energy and pair correlation functions are systematically calculated for various pseudopotentials in the lowest Landau level. We show that the stripe state in the lowest Landau level is realized only in a system whose width perpendicular to the two-dimensional electron layer is smaller than the order of magnetic length.

cond-mat.mes-hall↗

arXiv2003

Nontrivial behavior of the Fermi arc in the staggered-flux ordered phase

The doping and temperature dependences of the Fermi arc in the staggered-flux, or the d-density wave, ordered phase of the t-J model are analyzed by the U(1) slave boson theory. Nontrivial behavior is revealed by the self-consistent calculation. At low doped and finite-temperature region, both the length of the Fermi arc and the width of the Fermi pocket are proportional to $δ$ and the area of the Fermi pocket is proportional to $δ^2$. This behavior is completely different from that at the zero temperature, where the area of the Fermi pocket becomes $π^2 δ$. This behavior should be observed by detailed experiments of angle-resolved photoemission spectroscopy in the pseudogap phase of high-T_c cuprates if the pseudogap phase is the staggered-flux ordered phase.

cond-mat.str-el↗

arXiv2003

Gap evolution in nu=1/2 bilayer quantum Hall systems

Fractional quantum Hall states in bilayer system at total filling fraction $ν=1/2$ are examined numerically under some ranges of the layer separation and interlayer tunneling. It is shown that the ground state changes continuously from two-component state to one-component state as the interlayer tunneling rate is increased, while the lowest excited state changes discontinuously. This fact explains observed unusual behavior of the activation energy which reveals upward cusp as a function of interlayer tunneling. Some trial wave functions for the ground state and quasihole states are inspected.

cond-mat.mes-hall↗

arXiv2002

Relation between d-density wave of electron and staggered flux of spinon

A $d_{x^2-y^2}$-density wave (ddw) order of electron in two-dimensional t-J model is analyzed in saddle point level using the U(1) slave boson formalism. We considered not only the staggered flux (s-flux) order of spinon but also the s-flux order of holon. This analysis provides the relation between the s-flux order of spinon and the ddw order of electron. We discovered a new phase in the phase diagram. In this phase, there is a s-flux order of spinon, but no ddw order of electron.Our results are that 1) a region of electron ddw exists, 2) there is no coexistence of ddw and $d_{x^2-y^2}$-wave pairing (singlet-RVB) in all region of phase diagram, and that 3) the ground state is a purely $d_{x^2-y^2}$ wave superconducting state.

cond-mat.str-el↗

arXiv2002

Staggered flux state of electron in two-dimensional t-J model

The competition between the staggered flux state, or the d-density wave state, and the d-wave pairing state is analyzed in two-dimensional t-J model based on the U(1) slave boson mean-field theory. Not only staggered flux of spinon but also staggered flux of holon are considered. In this formalism, the hopping order parameter of $physical$ electron is described by the product of hopping order parameters of spinon and holon. The staggered flux amplitude of electron is the difference of staggered flux amplitude of spinon and that of holon. In $π$-flux phase of spinon, staggered fluxes of spinon and holon cancel completely and staggered flux order of electron does not exist. However, in staggered flux phase of spinon whose staggered flux amplitude is not $π$, fluxes does not cancel completely and staggered flux amplitude of electron remains. Thus, the phase transition between these two phases, $π$-flux phase and staggered flux phase of spinon, becomes a second order transition in $physical$ electron picture. The order parameter which characterizes this transition is staggered flux order parameter of electron. A mean-field phase diagram is shown. It is proved analytically that there is no coexisistence of staggered flux and d-wave pairing. The temperature dependences of Fermi surface and excitation gap at $(0,π)$ are shown. These behaviors are consistent with angle-resolved photoemission spectroscopy (ARPES) experiments.

cond-mat.str-el↗

arXiv2002

Evolution of $nu=1$ Bilayer Quantum Hall Ferromagnet

The natures of the ground state in a $ν_{\rm T}=1$ bilayer quantum Hall system at a variety of layer spacing are investigated. At small layer separations the system exhibits spontaneous interlayer phase coherence. It is claimed that the Halperin's (1,1,1) state is not relevant in the incompressible regime near the incompressible to compressible transition point in which the Josephson-like effect was observed. The two-particle correlation function shows the deflated correlation hole at this regime. An effective model that can give a good approximation to the ground state is proposed. A connection to the modified composite fermion theory is discussed.

cond-mat.mes-hall↗

arXiv2001

Pairing symmetry transitions in the even-denominator FQHE system

Transitions from a paired quantum Hall state to another quantum Hall state in bilayer systems are discussed in the framework of the edge theory. Starting from the edge theory for the Haldane-Rezayi state, it is shown that the charging effect of a bilayer system which breaks the SU(2) symmetry of the pseudo-spin shifts the central charge and the conformal dimensions of the fermionic fields which describe the pseudo-spin sector in the edge theory. This corresponds to the transition from Haldane-Rezayi state to Halperin's 331 state, or singlet d-wave to triplet p-wave ABM type paired state in the composite fermion picture. Considering interlayer tunneling, the tunneling rate-capacitance phase diagram for the $ν=5/2$ paired bilayer system is discussed.

cond-mat.mes-hall↗

arXiv2001

Orientation of the Stripe Formed by the Two-Dimensional Electrons in Higher Landau Levels

Effect of periodic potential on the stripe phase realized in the higher Landau levels is investigated by the Hartree-Fock approximation. The period of the potential is chosen to be two to six times of the fundamental period of the stripe phase. It is found that the stripe aligns perpendicularly to the external potential in contrast to a naive expectation and hydrodynamic theory. Charge modulation towards the Wigner crystallization along the stripe is essential for the present unexpected new result.

cond-mat.mes-hall↗

arXiv2001

DMRG Study of the Ground State at Higher Landau Levels - Stripes, Bubbles and the Wigner Crystal

Hartree-Fock theory predicted stripe or bubble phase in the third and higher Landau levels for two-dimensional electrons, and experimental evidences has been accumulated. In this paper theoretical confirmation of the stripe phase and bubble phase in higher Landau level is given by means of the density matrix renormalization group (DMRG) method, which can give essentially exact ground state for electron systems with up to 18 electrons. From the study of the pair correlation function, the stripe phase, bubble phase, and the Wigner crystal phase are identified, and phase diagram is obtained. The reentrant integer quantum Hall state is identified as the bubble state. The phase diagram of the fourth Landau level shows more diversity than the third level.

cond-mat.mes-hall↗