arXiv subjects

Satoshi Fujimoto

Publications and source records attributed to Satoshi Fujimoto.

At least 91 records · Page 5Linked to original sources

arXiv2007

Fermi liquid theory for heavy fermion superconductors without inversion symmetry : Magnetism and transport coefficients

We present the microscopic Fermi liquid theory for magnetic properties and transport phenomena in interacting electron systems without inversion symmetry both in the normal state and in the superconducting state. Our argument is mainly focused on the application to noncentrosymmetric heavy fermion superconductors. The transport coefficients for the anomalous Hall effect, the thermal anomalous Hall effect, the spin Hall effect, and magnetoelectric effects, of which the existence is a remarkable feature of parity violation, are obtained by taking into account electron correlation effects in a formally exact way. Moreover, we demonstrate that the temperature dependence of the spin susceptibility which consists of the Pauli term and van-Vleck-like term seriously depends on the details of the electronic structure. We give a possible explanation for the recent experimental result obtained by the NMR measurement of CePt$_3$Si [Yogi et al., J. Phys. Soc. Jpn.{\bf 75}, 013709 (2006)], which indicates no change of the Knight shift below the superconducting transition temperature for any directions of a magnetic field.

cond-mat.str-el↗

arXiv2007

Electron Correlation and Pairing States in Superconductors without Inversion Symmetry

This article is a pedagogical review of theoretical studies of noncentrosymmetric superconductors with particular emphasis on the role played by electron correlation, which is important for heavy fermion systems. We survey unique properties of parity-violated superconductivity such as the admixture of spin singlet and triplet states, unusual paramagnetism, large Pauli limiting fields, magnetoelectric effects, the helical vortex phase, and the anomalous Hall effect. It is pointed out that these remarkable features are strengthened by a strong electron correlation effect, and thus are prominent in heavy fermion superconductors without inversion symmetry. We also discuss possible pairing states realized in the heavy fermion system CePt$_3$Si.

cond-mat.supr-con↗

arXiv2006

Emergent Nodal Excitations due to the Coexistence of Superconductivity and Antiferromagnetism: Cases with and without Inversion Symmetry

We argue the emergence of nodal excitations due to the coupling with static antiferromagnetic order in fully-gapped superconducting states in both cases with and without inversion symmetry. This line node structure is not accompanied with the sign change of the superconducting gap, in contrast to usual unconventional Cooper pairs with higher angular momenta. In the case without inversion symmetry, the stability of the nodal excitations crucially depends on the direction of the antiferromagnetic staggered magnetic moment. A possible realization of this phenomenon in CePt$_3$Si is discussed.

cond-mat.supr-con↗

arXiv2006

Low-energy properties of two-dimensional quantum triangular antiferromagnets: Non-perturbative renormalization group approach

We explore low temperature properties of quantum triangular Heisenberg antiferromagnets in two dimension in the vicinity of the quantum phase transition at zero temperature. Using the effective field theory described by the $SO(3)\times SO(2)/SO(2)$ matrix Ginzburg-Landau-Wilson model and the non-perturbative renormalization group method, we clarify how quantum and thermal fluctuations affect long-wavelength behaviors in the parameter region where the systems exhibit a fluctuation-driven first order transition to a long-range ordered state. We show that at finite temperatures the crossover from a quantum $ϕ^6$ theory to a renormalized two-dimensional classical nonlinear sigma model region appears, and in this crossover region, massless fluctuation modes with linear dispersion a la spin waves govern low-energy physics. Our results are in good agreement with the recent experimental observations for the two-dimensional triangular Heisenberg spin system, NiGa$_2$S$_4$.

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arXiv2005

Magnetoelectric effects in heavy-fermion superconductors without inversion symmetry

We investigate effects of strong electron correlation on magnetoelectric transport phenomena in noncentrosymmetric superconductors with particular emphasis on its application to the recently discovered heavy-fermion superconductor CePt$_3$Si. Taking into account electron correlation effects in a formally exact way, we obtain the expression of the magnetoelectric coefficient for the Zeeman-field-induced paramagnetic supercurrent, of which the existence was predicted more than a decade ago. It is found that in contrast to the usual Meissner current, which is much reduced by the mass renormalization factor in the heavy-fermion state, the paramagnetic supercurrent is not affected by the Fermi liquid effect. This result implies that the experimental observation of the magnetoelectric effect is more feasible in heavy-fermion systems than that in conventional metals with moderate effective mass.

cond-mat.supr-con↗

arXiv2005

Quantum Disordered Ground States in Frustrated Antiferromagnets with Multiple Ring Exchange Interactions

We present a certain class of two-dimensional frustrated quantum Heisenberg spin systems with multiple ring exchange interactions which are rigorously demonstrated to have quantum disordered ground states without magnetic long-range order. The systems considered in this paper are s=1/2 antiferromagnets on a honeycomb and square lattices, and an s=1 antiferromagnet on a triangular lattice. We find that for a particular set of parameter values, the ground state is a short-range resonating valence bond state or a valence bond crystal state. It is shown that these systems are closely related to the quantum dimer model introduced by Rokhsar and Kivelson as an effective low-energy theory for valence bond states.

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arXiv2004

Asymptotically Exact Solution for Superconductivity near Ferromagnetic Criticality

We analyze an asymptotically exact solution for the transition temperature of p-wave superconductivity near ferromagnetic criticality on the basis of the three-dimensional electron systems in which scattering processes are dominated by exchange interactions with small momentum transfers. Taking into account all Feynman diagrams in the gap equation, we show that vertex corrections neglected in the conventional Eliashberg's formalism enhance the dynamical retarded effect of the pairing interaction, and raise the superconducting transition temperature significantly, though they just give subleading corrections to properties of the normal state.

cond-mat.supr-con↗

arXiv2004

Kondo Problem and Related One-Dimensional Quantum Systems: Bethe Ansatz Solution and Boundary Conformal Field Theory

We review some exact results on Kondo impurity systems derived from Bethe-ansatz solutions and boundary conformal field theory with particular emphasis on universal aspects of the phenomenon. The finite-size spectra characterizing the low-energy fixed point are computed from the Bethe-ansatz solutions of various models related to the Kondo problem. Using the finite-size scaling argument, we investigate their exact critical properties. We also discuss that a universal relation between the Kondo effect and the impurity effect in one-dimensional quantum systems usefully expedites our understanding of these different phenomena.

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arXiv2004

Boundary susceptibility in the spin-1/2 chain: Curie like behavior without magnetic impurities

We investigate the low-temperature thermodynamics of the spin-1/2 Heisenberg chain with open ends. On the basis of boundary conformal field theory arguments and numerical density matrix renormalization group calculations, it is established that in the isotropic case the impurity susceptibility exhibits a Curie-like divergent behavior as the temperature decreases, even in the absence of magnetic impurities. A similar singular temperature dependence is also found in the boundary contributions of the specific heat coefficient. In the anisotropic case, for $1/2<Δ<1$, these boundary quantities still show singular temperature dependence obeying a power law with an anomalous dimension. Experimental consequences will be discussed.

cond-mat.str-el↗

arXiv2003

Low-temperature anomaly at the edge of the Heisenberg spin chains: a boundary conformal field theory approach

Asymptotically exact low temperature expansions for the $s=1/2$ Heisenberg XXZ chains with boundaries are implemented by using the boundary conformal field theory. It is found that for $1/2<Δ\leq 1$, ($Δ$, an anisotropic parameter) the boundary terms of the spin susceptibility and the specific heat coefficient show divergent behaviors, as temperature decreases. The degrees of the divergence coincide with those obtained by the Bethe ansatz method at zero temperature. Such low-temperature anomalous behaviors at boundaries are deeply related with finite-temperature corrections of the boundary entropy or the ground state degeneracy, the presence of which yields a very sensitive response of spin excitations.

cond-mat.str-el↗

arXiv2003

Drude Weight at Finite Temperatures for Some Non-Integrable Quantum Systems in One Dimension

Using conformal perturbation theory, we show that for some classes of the one-dimensional quantum liquids that possess the Luttinger liquid fixed point in the low energy limit, the Drude weight at finite temperatures is non-vanishing, even when the system is {\it non-integrable} and the total current is not conserved. We also obtain the asymptotically exact low-temperature formula of the Drude weight for Heisenberg XXZ spin chains, which agrees quite well with recent numerical data.

cond-mat.str-el↗

arXiv2003

Metal-to-Insulator Transition, Spin Gap Generation, and Charge Ordering in Geometrically Frustrated Electron Systems

We investigate a (semi-)metal to insulator transition (MIT) realized in geometrically frustrated electron systems on the basis of the Hubbard model on a three-dimensional pyrochlore lattice and a two-dimensional checkerboard lattice. Using the renormalization group method and mean field analysis, we show that in the half-filling case, MIT occurs as a result of the interplay between geometrical frustration and electron correlation. In the insulating phase, which has a spin gap, the spin rotational symmetry is not broken, while charge ordering exists. The charge ordered state is stabilized so as to relax the geometrical frustration in the spin degrees of freedom. We also discuss the distortion of the lattice structure caused by the charge ordering. The results are successfully applied to the description of the MIT observed in the pyrochlore system ${\rm Tl_2Ru_2O_7}$.

cond-mat.str-el↗

arXiv2002

Geometrical frustration induced (semi-)metal to insulator transition

We study the low-energy properties of the geometrically frustrated Hubbard model on a three-dimensional pyrochlore lattice and a two-dimensional checkerboard lattice on the basis of the renormalization group method and mean field analysis. It is found that in the half-filling case, a (semi-)metal to insulator transition (MIT) occurs. Also, in the insulating phase, which has a spin gap, the spin rotational symmetry is not broken, while charge ordering exists. The results are applied to the description of the MIT observed in the pyrochlore system ${\rm Tl_2Ru_2O_7}$.

cond-mat.str-el↗

arXiv2002

Pseudogap Phenomena in the BCS Pairing Model

We investigate pseudo-gap phenomena realized in the BCS pairing model with a long but finite interaction range. We calculate the single-particle self-energy in all order exactly in the temperature range where the superconducting fluctuation propagator is Gaussian-like. It is found that vertex corrections to the self-energy which are discarded in the previous studies are crucially important for the pseudo-gap of the single-particle density of states in higher order calculations.

cond-mat.supr-con↗

arXiv2002

Hubbard chains network on corner-sharing tetrahedra: origin of the heavy fermion state in LiV_2O_4

We investigate the Hubbard chains network model defined on corner-sharing tetrahedra (the pyrochlore lattice) which is a possible microscopic model for the heavy fermion state of LiV_2O_4. Based upon this model, we can explain transport, magnetic, and thermodynamic properties of LiV_2O_4. We calculate the spin susceptibility, and the specific heat coefficient, exploiting the Bethe ansatz exact solution of the 1D Hubbard model and bosonization method. The results are quite consistent with experimental observations. We obtain the large specific heat coefficient $γ\sim 222 {\rm mJ/mol K^2}$.

cond-mat.str-el↗

arXiv2001

Mott transition and heavy fermion state in the pyrochlore Hubbard model

We investigate the interplay between geometrical frustration and strong electron correlation based upon the pyrochlore Hubbard model. In the half-filling case, using the perturbative expansion in terms of electron correlation, we show that the self-energy shows a divergent behavior leading the system into the Mott insulating state, in which quantum disordered spin liquid without magnetic long-range order realizes. In the hole-doped case, we obtain heavy-fermion-like Fermi liquid state. We also calculate the neutron cross section which is well consistent with recent neutron scattering experiments for itinerant pyrochlore systems.

cond-mat.str-el↗

arXiv2000

Spinless impurities and Kondo-like behavior in strongly correlated electron systems

We investigate magnetic properties induced by a spinless impurity in strongly correlated electron systems, i.e. the Hubbard model in the spatial dimension $D=1,2,$ and 3. For the 1D system exploiting the Bethe ansatz exact solution we find that the spin susceptibility and the local density of states in the vicinity of a spinless impurity show divergent behaviors. The results imply that the induced local moment is not completely quenched at any finite temperatures. On the other hand, the spin lattice relaxation rate obtained by bosonization and boundary conformal field theory satisfies a relation analogous to the Korringa law, $1/T_1T \sim χ^2$. In the 2D and 3D systems, the analysis based upon the antiferromagnetically correlated Fermi liquid theory reveals that the antiferromagnetic spin fluctuation developed in the bulk is much suppressed in the vicinity of a spinless impurity, and thus magnetic properties are governed by the induced local moment, which leads to the Korringa law of $1/T_1$.

cond-mat.str-el↗

arXiv2000

Effects of Strong Correlation and Randomness in the Vicinity of the Mott Transition in the Quasi-One-Dimensional Hubbard Model

We study the strong correlation effects in the vicinity of the Mott metal-insulator transition using coupled clean or disordered Hubbard chains with a infinitely large coordinate number $D_{\perp}\to\infty$ in the direction perpendicular to the chains and with a long-range transverse hopping. Strong electron correlation effects are treated partially non-perturbatively with the use of the exact results for the 1D Hubbard model. In the case of clean systems, the thermodynamic and transport quantities which characterize the Mott transition from the Fermi liquid state, such as the specific heat coefficient, the Drude weight, and the compressibility, are obtained as functions of hole-doping $δ=1-n$ ($n$, electron density) by the systematic expansion in terms of the inverse of the transverse hopping range $l_{\perp}$. We find that the $δ$-dependence of these quantities shows non-universal behaviors with exponents depending on the strength of electron-electron interaction. In the presence of disorder, it is shown that the frequency-dependence of the dynamical conductivity obeys the Mott's law, implying the possibility of {\it Mott glass state} for $δ\to 0$, provided that there exists a finite range interaction.

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