arXiv subjects

Naokazu Shibata

Publications and source records attributed to Naokazu Shibata.

44 records · Page 3Linked to original sources

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

Application of the density matrix renormalization group method to finite temperatures and two-dimensional systems

The density matrix renormalization group (DMRG) method and its applications to finite temperatures and two-dimensional systems are reviewed. The basic idea of the original DMRG method, which allows precise study of the ground state properties and low-energy excitations, is presented for models which include long-range interactions. The DMRG scheme is then applied to the diagonalization of the quantum transfer matrix for one-dimensional systems, and a reliable algorithm at finite temperatures is formulated. Dynamic correlation functions at finite temperatures are calculated from the eigenvectors of the quantum transfer matrix with analytical continuation to the real frequency axis. An application of the DMRG method to two-dimensional quantum systems in a magnetic field is demonstrated and reliable results for quantum Hall systems are presented.

cond-mat.str-el↗

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↗

arXiv1999

Numerical Study of the One-Dimensional Spin-Orbit Coupled System with SU(2)$\otimes$SU(2) Symmetry

We numerically study the SU(2)$\otimes$SU(2) symmetric spin-orbit coupled model as a lower symmetric generalization of the SU(4) exchange model. On the symmetric line with respect to the spin and orbit, our result shows the essentially singular gap formation in consistent with the analytic approach, which is different from the previous numerical calculation. Furthermore, we find new critical phases around the SU(4) point, surrounding the previously known gapless symmetric line. In these novel phases either spin or orbital excitations around momentum $q=π$ form massless continua which split from the excitations belonging to the $[2^2]$ irreducible representation at the SU(4) point. On the critical symmetric line, the additional coupled spin-orbit excitations around $q=π/2$ originating from [$2^11^2$] become critical, too.

cond-mat.str-el↗

arXiv1999

Crossover Phenomena in the One-Dimensional SU(4) Spin-Orbit Model under Magnetic Fields

We study the one-dimensional SU(4) exchange model under magnetic fields, which is the simplest effective Hamiltonian in order to investigate the quantum fluctuations concerned with the orbital degrees of freedom in coupled spin-orbit systems. The Bethe ansatz approaches and numerical calculations using the density matrix renormalization group method are employed. The main concern of the paper is how the system changes from the SU(4) to the SU(2) symmetric limit as the magnetic field is increased. For this model the conformal field theory predicts an usual behavior: there is a jump of the critical exponents just before the SU(2) limit. For a finite-size system, however, the orbital-orbital correlation functions approach continuously to the SU(2) limit after interesting crossover phenomena. The crossover takes place in the magnetization range of 1/3 $\sim$ 1/2 for the system with 72 sites studied in this paper.

cond-mat.str-el↗

arXiv1998

SU(4) spin-orbit critical state in one dimension

Effect of quantum fluctuations concerned with the orbital degrees of freedom is discussed for the model with SU(4) symmetry in one dimension. An effective Hamiltonian is derived from the orbitally degenerate Hubbard model at quarter filling. This model is equivalent to the Bethe soluble SU(4) exchange model. Quantum numbers of the ground state and the lowest branch of excitations are determined. The spin-spin correlation functions are obtained numerically by the density matrix renormalization group method. It shows a power-law decay with oscillations of the period of four sites. The period originates from the interference between the spin and orbital degrees of freedom. The exponent of the power-law decay estimated from the finite size data is consistent with the prediction by the conformal field theory.

cond-mat.str-el↗

arXiv1998

Temperature-induced gap formation in dynamic correlation functions of the one-dimensional Kondo insulator --- Finite-temperature density-matrix renormalization-group study ---

Combination of the finite-temperature density-matrix renormalization-group and the maximum entropy presents a new method to calculate dynamic quantities of one-dimensional many-body systems. In the present paper, density of states, local dynamic spin and charge correlation functions of the one-dimensional Kondo insulator are discussed. Excitation gaps open with decreasing temperature and the gaps take different values depending on channels. The excitation spectra change qualitatively around the characteristic temperature corresponding to the spin gap which is the lowest energy scale of the Kondo insulator.

cond-mat.str-el↗

arXiv1998

Metal-Insulator Transition Accompanied with a Charge Ordering in the One-dimensional t-J' Model

We study the metal-insulator transition accompanied with a charge ordering in the one-dimensional (1D) t-J' model at quarter filling by the density matrix renormalization group method. In this model the nearest-neighbor hopping energy t competes with the next-nearest-neighbor exchange energy J'. We have found that a metal-insulator transition occurs at a finite value of t/J'; (t/J')_C = 0.18 and the transition is of first order. In the insulating phase for small t/J', there is an alternating charge ordering and the system behaves as a 1D quantum Heisenberg antiferromagnet. The metallic side belongs to the universality class of the Tomonaga-Luttinger liquids. The quantum phase transition is an example of melting of the 1D quantum Heisenberg antiferromagnet.

cond-mat.str-el↗