arXiv subjects

Takao Morinari

Publications and source records attributed to Takao Morinari.

49 records · Page 3Linked to original sources

arXiv2007

Formation of a sonic horizon in isotropically expanding Bose-Einstein condensates

We propose a simple experiment to create a sonic horizon in isotropically trapped cold atoms within currently available experimental techniques. Numerical simulation of the Gross-Pitaevskii equation shows that the sonic horizon should appear by making the condensate expand. The expansion is triggered by changing the interaction which can be controlled by the Feshbach resonance in real experiments. The sonic horizon is shown to be quasi-static for sufficiently strong interaction or large number of atoms. The characteristic temperature that is associated with particle emission from the horizon, which corresponds to the Hawking temperature in an ideal situation, is estimated to be a few nK.

cond-mat.other↗

arXiv2005

Half-skyrmion picture of single hole doped high-T_c cuprate

The single hole doped CuO_2 plane is studied by the O(3) non-linear σmodel and its CP^1 representation. It is argued that the spin configuration around a Zhang-Rice singlet is described by a half-skyrmion. The form of the excitation spectrum of the half-skyrmion is the same as that in the π-flux phase.

cond-mat.str-el↗

arXiv2003

Evolution of Neel order and localized spin moment in the doped two-dimensional Hubbard model

We investigate effects of doped holes' hopping on Neel order in the two-dimensional Hubbard model. Semiclassical staggered moments are computed by solving saddle point equations derived from a path-integral formalism. Effects of quantum fluctuations are taken into account by the Schwinger boson mean field theory. We argue that hopping of doped holes is ineffective in suppressing Neel order compared to rapid supprestion of Neel order in high-temperature superconductors. After destruction of Neel order, the quantum disordered phase sets in. Taking the strong coupling limit in the quantum disordered phase leads to a model of spinless fermions and bosons but no gauge field interaction.

cond-mat.str-el↗

arXiv2002

Strongly coupled quantum criticality with a Fermi surface in two dimensions: fractionalization of spin and charge collective modes

We describe two dimensional models with a metallic Fermi surface which display quantum phase transitions controlled by strongly interacting critical field theories below their upper critical dimension. The primary examples involve transitions with a topological order parameter associated with dislocations in collinear spin density wave ("stripe") correlations: the gapping of the order parameter fluctuations leads to a fractionalization of spin and charge collective modes, and this transition has been proposed as a candidate for the cuprates near optimal doping. The coupling between the order parameter and long-wavelength volume and shape deformations of the Fermi surface is analyzed by the renormalization group, and a runaway flow to a non-perturbative regime is found in most cases. A phenomenological scaling analysis of simple observable properties of possible second order quantum critical points is presented, with results quite similar to those near quantum spin glass transitions and to phenomenological forms proposed by Schroeder et al. (cond-mat/0011002).

cond-mat.str-el↗

arXiv2002

Reexamination of d-wave superconductivity in the two-dimensional Hubbard model

We reexamine the possibility of d-wave superconductivity in the hole-doped two-dimensional Hubbard model. In terms of the gauge field description of the spin fluctuations, we show that d-wave superconductivity is unstable in the perturbative region with respect to the on-site Coulomb repulsion, U. Whereas in the region where d-wave superconductivity is possible, there is a strong constraint on the gap of superconductivity. Analysis of the localized spin moments suggests that there is another d-wave (d_{x^2-y^2}-wave) pairing due to the short-range antiferromagnetic correlation.

cond-mat.str-el↗

arXiv2001

Tunneling effect on composite fermion pairing state in bilayer quantum Hall system

We discuss the composite fermion pairing state in bilayer quantum Hall systems. After the evaluation of the range of the inter-layer separation in which the quantum Hall state is stabilized, we discuss the effect of inter-layer tunneling on the composite fermion pairing state at ν=1/2. We show that there is a cusp at the transition point between the Halperin (3,3,1) state and the Pfaffian state.

cond-mat.mes-hall↗

arXiv2001

Mechanism of unconventional superconductivity induced by skyrmion excitations in two-dimensional strongly-correlated electron systems

We propose a mechanism of unconventional superconductivity in two-dimensional strongly-correlated electron systems. We consider a two-dimensional Kondo lattice system or double-exchange system with spin-orbit coupling arising from buckling of the plane. We show that a Chern-Simons term is induced for a gauge field describing the phase fluctuations of the localized spins. Through the induced Chern-Simons term, carriers behave like skyrmion excitations that lead to a destruction mechanism of magnetic long-range order by carrier doping. After magnetic long-range order is destroyed by carrier doping, the Chern-Simons term plays a dominant role and the attractive interaction between skyrmions leads to unconventional superconductivity. For the case of the ferromagnetic interaction between the localized spins, the symmetry of the Cooper pair is p-wave ($p_x \pm ip_y$). For the case of the antiferromagnetic interaction between the localized spins, the symmetry of the Cooper pair is d-wave ($d_{x^2-y^2}$). Applications to various systems are discussed, in particular to the high-$T_c$ cuprates.

cond-mat.str-el↗

arXiv2001

d-Wave Superconductivity Induced by Chern-Simons Term in High-$T_c$ Cuprates

We show that a Chern-Simons term for a gauge field describing a fluctuation of spins is induced by integrating out hole fields in the presence of spin-orbit coupling which originates from a buckling of the CuO$_2$ plane. Through the Chern-Simons term, holes behave like skyrmion excitations in a spin system and become a superconducting state with $d_{x^2-y^2}$ symmetry after the antiferromagnetic long-range order is destroyed.

cond-mat.supr-con↗

arXiv2000

The influence of chiral surface states on the London penetration depth in Sr$_2$RuO$_4$

The London penetration depth for the unconventional superconductor Sr$_2$RuO$_4$ is analyzed assuming an order parameter which breaks time reversal symmetry and parity simultaneously. Such a superconducting state possesses chiral quasiparticle states with subgap energies at the surface. We show that these subgap states can give a significant contribution to the low-temperature behavior of the London penetration depth yielding a $ T^2 $ power-law even though bulk quasiparticle spectrum is gapped. The presence of several electron bands gives rise to interband transition among the subgap surface states and influences the properties of the surface impedance. Furthermore, the surface states lead also to a non-linear Meissner effect.

cond-mat.supr-con↗

arXiv1999

The role of imaginary vector potential in composite fermion pairing theory

We show that the imaginary vector potential causes a pair-breaking effect in the composite fermion theory, and discuss its irrelevance in the pairing state. The Hamiltonian for pairing states of composite fermions is proposed. The advantage of non-unitary transformations and the meaning of the non-Hermitian term are discussed.

cond-mat.mes-hall↗

arXiv1998

Quantum Hall effect at half-filled Landau level: Pairing of composite fermions

We discuss the possibility of the quantum Hall effect at half-filled Landau level in terms of the pairing of the composite fermions. In the absence of Coulomb energy, we show that the ground state of the system is described by the {\it p}-wave BCS pairing state of composite fermions. When the ratio $α\equiv (e^2/ε\ell_B)/ε_F$ ($\ell_B$ : the magnetic length, $ε_F$ : Fermi energy of the composite fermions) is larger than a critical value $α_c \sim 8.2$ the gap of the pairing state vanishes. However, $α$ remains less than $α_c$ if $\hbar ω_c \gg e^2/ε\ell_B$ holds. Then in this situation it is possible that the pairing state which results in the quantum Hall effect occurs. The effect of the real spin degrees of freedom and the Zeeman energy is also discussed.

cond-mat.mes-hall↗

arXiv1998

Composite Fermion Pairing in Bilayer Quantum Hall Systems

We derive the effective Hamiltonian for the composite fermion in double-layer quantum Hall systems with inter-layer tunneling at total Landau-level filling factor $ν=1/m$, where $m$ is an integer. We find that the ground state is the triplet p-wave BCS pairing state of the composite fermions. At $ν=1/2$, the ground state of the system evolves from the Halperin $(3,3,1)$-state toward the Pfaffian-state with increasing the tunneling amplitude. On the other hand, at $ν=1$, the pairing state is uniquely determined independent of tunneling amplitude.

cond-mat.mes-hall↗

arXiv1996

Edge Modes in the Hierarchical Fractional Quantum Hall Liquids with Coulomb Interaction

Edge modes are studied for the hierarchical fractional quantum Hall liquids (FQHL) by treating the edge and bulk in a unified fashion. Within the RPA treatment of the composite boson effective theory with Coulomb interaction, one edge magneto-plasmon is shown to be the eigen-mode of the system. This mode decays algebraically perpendicular to the edge. All the other modes decay faster than power-law, and correspond to the neutral modes. However these neutral modes generally couple with the electromagnetic field within the magnetic length from the edge. The time-of-flight experiment in the $ν=2/3$ FQHL is discussed in terms of these results.

cond-mat↗