arXiv subjects

T. Morinari

Publications and source records attributed to T. Morinari.

9 recordsLinked to original sources

arXiv2020

Quantum Phase Transition in Organic Massless Dirac Fermion System $α $-(BEDT-TTF)$_2$I$_3$ under pressure

We investigate the effect of strong electronic correlation on the massless Dirac fermion system, $α$-(BEDT-TTF)$_2$I$_3$, under pressure. In this organic salt, one can control the electronic correlation by changing pressure and access the quantum critical point between the massless Dirac fermion phase and the charge ordering phase. We theoretically study the electronic structure of this system by applying the slave-rotor theory and find that the Fermi velocity decreases without creating a mass gap upon approaching the quantum critical point from the massless Dirac fermion phase. We show that the pressure-dependence of the Fermi velocity is in good quantitative agreement with the results of the experiment where the Fermi velocity is determined by the analysis of the Shubnikov-de Haas oscillations in the doped samples. Our result implies that the massless Dirac fermion system exhibits a quantum phase transition without creating a mass gap even in the presence of strong electronic correlations.

cond-mat.str-el↗

arXiv2015

Anisotropic spin motive force in multi-layered Dirac fermion system, $α$-(BEDT-TTF)$_2$I$_3$

We investigate the anisotropic spin motive force in $α$-(BEDT-TTF)$_2$I$_3$, which is a multi-layered massless Dirac fermion system under pressure. Assuming the interlayer antiferromagnetic interaction and the interlayer anisotropic ferromagnetic interaction, we numerically examine the spin ordered state of the ground state using the steepest descent method. The anisotropic interaction leads to the anisotropic spin ordered state. We calculate the spin motive force produced by the anisotropic spin texture. The result quantitatively agrees with the experiment.

cond-mat.mes-hall↗

arXiv2009

Modeling Antiferromagnetic Phase in Iron Pnictides: Weakly Ordered State

We examine electronic states of antiferromagnetic phase in iron pnictides by mean-field calculations of the optical conductivity. We find that a five-band model exhibiting a small magnetic moment, inconsistent with the first-principles calculations, reproduces well the excitation spectra characterized by a multi-peak structure emerging below the Néel temperature at low energy, together with an almost temperature-independent structure at high energy. Investigating the interlayer magnetoresistance for this model, we also predict its characteristic field dependence reflecting the Fermi surface.

cond-mat.supr-con↗

arXiv2008

Fluctuation Effect in the π-flux State for Undoped High-Temperature Superconductors

The effect of fluctuations about the pi-flux mean field state for the undoped high-temperature superconductors is investigated. It is shown that fluctuations of the mean fields lead to a self-energy correction that doubles the band width of the fermion dispersion in the lowest order. The dynamical mass generation is associated with the self-energy effect due to the interaction mediated by the Lagrange multiplier field, which is introduced to impose the constraint on the fermions. A self-consistent picture about the mass generation and the prop- agation of the Lagrange multiplier field without damping is proposed. The antiferromagnetic long-range ordering is described without introducing an additional repulsive interaction. The theory suggests a natural framework to study spin disordered systems in which fermionic excitations are low-lying excitations.

cond-mat.str-el↗

arXiv2008

Phenomenological model for two gap states in underdoped high-temperature superconductors and short-range antiferromagnetic correlation effect

Assuming antiferromagnetic orbital correlations to model the pseudogap state in the underdoped high-temperature superconductors, we study how this correlation is distinguished from the d-wave superconductivity correlation with including the finite-range antiferromagnetic correlation effect. In spite of the fact that both correlations have the same d-wave symmetry, the contributions from each correlation is clearly distinguished in the spectral weight and the density of states.

cond-mat.str-el↗

arXiv2007

Strong coupling analysis of QED$_3$ for excitation spectrum broadening in undoped high-temperature superconductor

Theory of quantum electrodynamics in three spatial-time dimension is applied to the two-dimensional $S=1/2$ quantum Heisenberg antiferromagnet in order to investigate a doped hole in high-temperature superconductors. Strong coupling analysis of the U(1) gauge field interaction is carried out to describe spectral broadening observed in the undoped compounds. It is found that the fermionic quasiparticle spectrum is of Gaussian form with the width about 3J, with J being the superexchange interaction energy. The energy shift of the spectrum is on the order of the quasiparticle band width, which suggests that the system is in the strong coupling regime with respect to the gauge field interaction describing the phase fluctuations about the staggered flux state.

cond-mat.str-el↗

arXiv2005

Mechanism of d_{x^2-y^2}-wave superconductivity based on doped hole induced spin texture in high T_c cuprates

A mechanism of d_{x^2-y^2}-wave superconductivity is proposed for the high-T_c cuprates based on a spin texture with non-zero topological density induced by doped holes through Zhang-Rice singlet formation. The pairing interaction arises from the magnetic Lorentz force like interaction between the holes and the spin textures. The stability of the pairing state against the vortex-vortex interaction and the Coulomb repulsion is examined. The mechanism suggests appearance of a p-wave pairing component by introducing anisotropy in the CuO_2 plane.

cond-mat.supr-con↗

arXiv2005

Half-skyrmion picture of single hole doped CuO_2 plane

Based on the Zhang-Rice singlet picture, it is argued that the half-skyrmion is created by the doped hole in the single hole doped high-T_c cuprates with N'eel ordering. The spin configuration around the Zhang-Rice singlet, which has the form of superposition of the two different d-orbital hole spin states, is studied within the non-linear σmodel and the CP^1 model. The spin configurations associated with each hole spin state are obtained, and we find that the superposition of these spin configuration turns out to be the half-skyrmion that is characterized by a half of the topological charge. The excitation spectrum of the half-skyrmion is obtained by making use of Lorentz invariance of the effective theory and is qualitatively in good agreement with angle resolved photoemission spectroscopy on the parent compunds. Estimated values of the parameters contained in the excitation spectrum are in good agreement with experimentally obtained values. The half-skyrmion theory suggests a picture for the difference between the hole doped compounds and the electron doped compounds.

cond-mat.str-el↗

arXiv2005

Alternative formalism to the slave particle mean field theory of the t-J model without deconfinement

An alternative formalism that does not require the assumption of the deconfinement phase of a U(1) gauge field is proposed for the slave particle mean field theory. Starting form the spin-fermion model, a spinon field, which is either fermion or boson, is introduced to represent the localized spin moment. We find a d-wave superconductive state in the mean field theory in the case of the fermion representation of the localized spin moment that corresponds to the slave boson mean field theory of the t-J model, whereas the d-wave superconductive state is absent in case of the Schwinger boson representation of the localized spin moments.

cond-mat.str-el↗