Spin-triplet Channel Research Articles

Influence of oscillatory quantum shielding on scattering-induced spin-asymmetry and spin-channel preference in quantum plasmas

This paper is devoted to the oscillatory screening effect on the electron scattering spin-asymmetry and spin-channel preference in quantum plasmas. It is found that the oscillatory quantum screening effects enhance the spin-singlet electron-scattering channel, but suppress the spin-triplet electron-scattering channel for the forward and backward scattering directions with increasing wave number for small quantum wave numbers. It is also found that the preference of the spin-singlet scattering, including the influence of oscillatory quantum shielding, has been reduced with increasing quantum wave number. The variation of the angular averaged scattering spin-asymmetry phenomenon is also discussed.

Spin–orbit force from lattice QCD

We present a first attempt to determine nucleon–nucleon potentials in the parity-odd sector, which appear in the P11, P03, P13, P23–F23 channels, in Nf=2 lattice QCD simulations. These potentials are constructed from the Nambu–Bethe–Salpeter wave functions for JP=0−,1− and 2−, which correspond to the A1−, T1− and T2−⊕E− representation of the cubic group, respectively. We have found a large and attractive spin–orbit potential VLS(r) in the isospin-triplet channel, which is qualitatively consistent with the phenomenological determination from the experimental scattering phase shifts. The potentials obtained from lattice QCD are used to calculate the scattering phase shifts in the P11, P03, P13 and P23–F23 channels. The strong attractive spin–orbit force and a weak repulsive central force in spin-triplet P-wave channels lead to an attraction in the P23 channel, which is related to the P-wave neutron paring in neutron stars.

ΛΛ4H in halo effective field theory

The ${}_{\ensuremath{\Lambda}\ensuremath{\Lambda}}^{\phantom{\rule{0.28em}{0ex}}\phantom{\rule{0.28em}{0ex}}\phantom{\rule{0.28em}{0ex}}\phantom{\rule{1.0pt}{0ex}}4}$H bound state and the $S$-wave hypertriton(${}_{\ensuremath{\Lambda}}^{\phantom{\rule{0.16em}{0ex}}3}$H)-$\ensuremath{\Lambda}$ scattering in spin singlet and triplet channels below the hypertriton breakup momentum scale are studied in halo/cluster effective field theory at leading order by treating the ${}_{\ensuremath{\Lambda}\ensuremath{\Lambda}}^{\phantom{\rule{0.28em}{0ex}}\phantom{\rule{0.28em}{0ex}}\phantom{\rule{0.28em}{0ex}}\phantom{\rule{1.0pt}{0ex}}4}$H system as a three-cluster ($\ensuremath{\Lambda}$-$\ensuremath{\Lambda}$-deuteron) system. In the spin singlet channel, the amplitude is insensitive to the cutoff parameter ${\ensuremath{\Lambda}}_{c}$ introduced in the integral equation, and we find that there is no bound state. In this case, the scattering length of the hypertriton-$\ensuremath{\Lambda}$ scattering is found to be ${a}_{0}^{}=16.0\ifmmode\pm\else\textpm\fi{}3.0$ fm. In the spin triplet channel, however, the amplitude obtained by the coupled integral equations is sensitive to ${\ensuremath{\Lambda}}_{c}$, and we introduce the three-body contact interaction ${g}_{1}^{}({\ensuremath{\Lambda}}_{c})$. After phenomenologically fixing ${g}_{1}^{}({\ensuremath{\Lambda}}_{c})$, we find that the correlation between the two-$\ensuremath{\Lambda}$ separation energy ${B}_{\ensuremath{\Lambda}\ensuremath{\Lambda}}$ from the ${}_{\ensuremath{\Lambda}\ensuremath{\Lambda}}^{\phantom{\rule{0.28em}{0ex}}\phantom{\rule{0.28em}{0ex}}\phantom{\rule{0.28em}{0ex}}\phantom{\rule{1.0pt}{0ex}}4}$H bound state and the scattering length ${a}_{\ensuremath{\Lambda}\ensuremath{\Lambda}}^{}$ of the $S$-wave $\ensuremath{\Lambda}$-$\ensuremath{\Lambda}$ scattering is significantly sensitive to the value of ${\ensuremath{\Lambda}}_{c}$.

Parity-Mixed Superconductivity in Locally Non-centrosymmetric System

We study the parity-mixed superconductivity in locally non-centrosymmetric systems. In multilayer systems an inhomogeneous Rashba spin-orbit coupling is induced by the local violation of inversion symmetry. Our previous study revealed that a pair-density wave (PDW) phase, with a sign-modulated order parameter, is stabilized in the spin-singlet multilayer superconductors owing to the spin-orbit coupling. In this letter, we show that the uniform spin-triplet superconductivity emerges through parity mixing in the PDW phase, taking into account a weak interaction in the spin-triplet channel, which was neglected in our previous study. The spin-triplet superconducting phase is nonunitary owing to field-induced parity mixing. The critical magnetic field is markedly increased by the emergence of spin-triplet superconductivity. We calculate the density of states and analyze the signature specific to this phase.

ΛN and ΣN Interactions from Lattice QCD

We present our recent study on ΛN and ΣN (isospin I = 3/2) interactions by measuring Nambu–Bethe–Salpeter wave functions on the Lattice QCD. The lattice QCD calculation is performed by using the Nf = 2 + 1 gauge configurations generated by PACS-CS collaboration together with employing an improved method to obtain potentials in lattice QCD simulations. For the 1S0 channel, the central ΣN (I = 3/2) potential and the central ΛN (1S0) potential are found to be very similar. For the spin triplet (3S1−3D1) channels, the central ΛN(3S1−3D1) potential is attractive while the central ΣN(I = 3/2, 3S1−3D1) potentials is repulsive. Tensor potentials, on the other hand, are rather weak in both ΛN and ΣN(I = 3/2) systems.

Effective soft-mode theory of strongly interacting fermions

An effective field theory for clean electron systems is developed in analogy to the generalized nonlinear $\ensuremath{\sigma}$ model for disordered interacting electrons. The physical goal is to separate the soft or massless electronic degrees of freedom from the massive ones and integrate out the latter to obtain a field theory in terms of the soft degrees of freedom only. The resulting theory is not perturbative with respect to the electron-electron interaction. It is controlled by means of a systematic loop expansion and allows for a renormalization-group analysis in a natural way. It is applicable to universal phenomena within phases, and to transitions between phases, with order parameters in arbitrary angular-momentum channels, and in the spin-singlet, spin-triplet, particle-hole, and particle-particle channels. Applications include ferromagnetic and ferrimagnetic ordering, non-$s$-wave ferromagnetic order (magnetic nematics), Fermi-liquid to non-Fermi-liquid transitions, and universal phenomena within a Fermi-liquid phase.

Nucleon-nucleon potential in holographic QCD

We derive the nucleon-nucleon potential in the D4-D8 model of holographic QCD. The nucleon-nucleon potential emerges from one-boson exchange picture with massless pseudo-scalars and an infinite tower of spin one mesons. We observe in particular that the tensor coupling of the ρ meson with nucleon comes out naturally larger than the vector coupling, whereas for ω mesons and axial mesons, such tensor couplings are completely absent. The potential is universally repulsive ∼ 1 / r 2 at short distance, and has the usual long-distance attractive behavior ∼ − 1 / r 3 along a isospin singlet and spin triplet channel. Both the large N c form and the finite N c form are given. In the former, a shallow classical minimum of depth ∼ 0.1 M K K N c / λ forms at about r M K K ≃ 5.5 . We discuss shallow bound states of nucleons with the holographic potential.

ΛNandΞ NInteractions Studied with Lattice QCD

We present our recent studies of Lambda-Nucleon (�N) as well as Cascade-Nucleon (�N) interac- tions by using lattice QCD. The equal-time Bethe-Salpeter (BS) amplitude of the lowest energy scattering state of baryon number B = 2 system (proton-� and proton-� 0 ) is calculated from lattice QCD. For the calculation of the �N potential, two different types of gauge configurations are employed: (i) 2 +1 flavor full QCD configurations generated by the PACS-CS collaboration at � = 1.9 (a = 0.0907(13) fm) on a 32 3 × 64 lattice, whose spatial vol- ume is (2.90 fm) 3 . (ii) Quenched QCD configurations at � = 5.7 (a = 0.1416(9) fm) on a 32 3 × 48 lattice, whose spatial volume is (4.5 fm) 3 . The spin-singlet central potential is calculated from the BS wave function for the spin J = 0 state, whereas the spin-triplet central potential as well as the tensor potential are deduced simultaneously from the BS wave function for the spin J = 1 state by dividing it into the S -wave and the D-wave components. For the calculation of theN potential, we employ quenched QCD configurations, at � = 5.7 (a = 0.1416(9) fm) on a 32 3 × 32 lattice, whose spatial volume is (4.5 fm) 3 . The effective central potential in the spin triplet channel as well as the central potential in the spin singlet channel are calculated for theN. The scattering lengths are obtained from the asymptotic behavior of the BS wave function by using the Luscher's formula.

Holographic deuteron and nucleon-nucleon potential

We compute the potential between a pair of nucleons in the D4-D8 holographic QCD. In the large 't Hooft coupling limit, $\lambda \gg 1$, the hadronic size of the baryon is small $\sim 1/\sqrt{\lambda}M_{KK}$, and their interaction with mesons are well approximated by a set of dimension four and five operators. The nucleon-nucleon potential emerges from one-boson exchange picture involving massless pseudo-scalars and an infinite tower of spin one mesons. We find in particular that $\rho$ meson exchanges are dominated by a dimension five derivative coupling of tensor type, whereas for $\omega$ mesons and axial mesons, such tensor couplings are completely absent. The potential is universally repulsive $\sim 1/r^2$ at short distance, and has the usual long-distance attractive behavior $\sim -1/r^3$ along a isosinglet and spin triplet channel. Both the large $N_c$ form and the finite $N_c$ form are given. In the former, a shallow classical minimum of depth $\sim 0.1M_{KK}{N_c/\lambda}$ forms at around $rM_{KK}\simeq 5.5$.

Isotropic s-wave pairing symmetry in non-centrosymmetricRe3W revealed by point-contact spectroscopy

We use point-contact spectroscopy to study the temperature and magnetic fielddependence of the superconducting gap of a non-centrosymmetric superconductorRe3W for the first time. The spectra can be fitted very well to the isotropic s-wave BTK theory.The superconducting gap determined depends on the temperature and magnetic field in thesame way as expected for the weak-coupling s-wave BCS superconductors. These resultssuggest that the contribution of the spin-triplet pairing channel can be negligible in theRe3W system.

Spin-Triplet Pairing Instability of the Spinon Fermi Surface in aU(1)Spin Liquid

Recent experiments on the organic compound kappa-(ET)2Cu2(CN)3 have provided a promising example of a two-dimensional spin liquid state. This phase is described by a two-dimensional spinon Fermi sea coupled to a U(1) gauge field. We study Kohn-Luttinger-like pairing instabilities of the spinon Fermi surface due to singular interaction processes with twice-the-Fermi-momentum transfer. We find that under certain circumstances the pairing instability occurs in odd-orbital-angular momentum or spin-triplet channels. Implications to experiments are discussed.

Deconstructing triplet nucleon-nucleon scattering

Nucleon-nucleon scattering in spin-triplet channels is analyzed within an effective field theory where one-pion exchange is treated nonperturbatively. Justifying this requires the identification of an additional low-energy scale in the strength of that potential. Short-range interactions are organized according to the resulting power counting, in which the leading term is promoted to significantly lower order than in the usual perturbative counting. In each channel there is a critical momentum above which the waves probe the singular core of the tensor potential and the new counting is necessary. When the effects of one- and two-pion exchange have been removed using a distorted-wave Born approximation, the residual scattering in waves with L{ =}3 is consistent with the perturbative counting, at least for energies up to 300 MeV. This pattern is in agreement with estimates of the critical momenta in these channels.

Spin-triplet f-wave pairing in the one-dimensional triangular-lattice Hubbard model: Possible relevance to superconductivity in Bechgaard salts

The density-matrix renormalization group method is used to study the Hubbard model at quarter filling defined on the one-dimensional (1D) triangular lattice. We in particular calculate the pair correlation function in order to clarify the symmetry of the Cooper-pair wave function of our proposed spin-triplet superconductivity induced by the ring-exchange mechanism. We thereby show that the pairing occurs predominantly in the spin-triplet f-wave channel. Experimental relevance to superconductivity observed in Bechgaard salts is discussed.

Fermi liquid instabilities in the spin channel

We study the Fermi-surface instabilities of the Pomeranchuk type [Sov. Phys. JETP 8, 361 (1959)] in the spin-triplet channel with high orbital partial waves $[{F}_{l}^{a}(l>0)]$. The ordered phases are classified into two classes, dubbed the $\ensuremath{\alpha}$ and $\ensuremath{\beta}$ phases by analogy to the superfluid $^{3}\mathrm{He}$ A and B phases. The Fermi surfaces in the $\ensuremath{\alpha}$ phases exhibit spontaneous anisotropic distortions, while those in the $\ensuremath{\beta}$ phases remain circular or spherical with topologically nontrivial spin configurations in momentum space. In the $\ensuremath{\alpha}$ phase, the Goldstone modes in the density channel exhibit anisotropic overdamping. The Goldstone modes in the spin channel have a nearly isotropic underdamped dispersion relation at small propagating wave vectors. Due to the coupling to the Goldstone modes, the spin-wave spectrum develops resonance peaks in both the $\ensuremath{\alpha}$ and $\ensuremath{\beta}$ phases, which can be detected in inelastic neutron-scattering experiments. In the $p$-wave channel $\ensuremath{\beta}$ phase, a chiral ground-state inhomogeneity is spontaneously generated due to a Lifshitz-like instability in the originally nonchiral systems. Possible experiments to detect these phases are discussed.

Spin-triplet f-wave superconductivity in one-dimensional triangular-lattice Hubbard models

The Hubbard model at quarter filling defined on the one-dimensional (1D) triangular lattice (i.e., three chains coupled with interchain zigzag bonds) is studied by the density-matrix renormalization group method in order to clarify the symmetry of the Cooper-pair wave function of our proposed spin-triplet superconductivity induced by the ring-exchange mechanism. We calculate the rotational symmetry of the pair correlation function and show that the pairing occurs predominantly in the spin-triplet f-wave channel. Possible experimental relevance is discussed.

Ring exchange mechanism for triplet superconductivity in a two-chain Hubbard model

The density–matrix renormalization group (DMRG) method is used to calculate the binding energy of electrons and pair correlation functions in the two-chain zigzag-bond Hubbard model at quarter filling. We show that the ground state of the model can be superconducting in the spin-triplet channel when we make an appropriate choice of the signs of hopping integrals for the ferromagnetic ring-exchange mechanism to work. Possible relevance of our mechanism to the triplet superconductivity observed in ( TMTSF ) 2 X is discussed.

Ring-exchange mechanism for triplet superconductivity in a two-chain Hubbard model: Possible relevance to Bechgaard salts

The density-matrix renormalization group method is used to study the ground state of the two-chain zigzag-bond Hubbard model at quarter filling. We show that, with a proper choice of the signs of hopping integrals, the ring exchange mechanism yields ferromagnetic spin correlations between interchain neighboring sites, and produces the attractive interaction between electrons as well as the long-range pair correlations in the spin-triplet channel, thereby leading the system to triplet superconductivity. We argue that this novel mechanism may have possible relevance to observed superconductivity in Bechgaard salts.

Ordering instability of weakly interacting electrons in a dirty metal

In a dirty metal, electron-electron interactions in the spin-triplet channel lead to singular corrections to a variety of physical quantities. We show that these singularities herald the emergence of ferromagnetism. We calculate the effective action for the magnetic moment of weakly-interacting electrons in a dirty metal and show that a state with finite ferromagnetic moment minimizes this effective action. The saddle-point approximation is exact in an appropriate large-N limit. We discuss the physics of the ferromagnetic state with particular regard to thermal fluctuations and localization effects.

Superconductivity in doped nondegenerate insulators

An analysis of experimental data on the change in the electronic structure and the position of the chemical potential depending on the doping level in superconducting tungsten bronze NaxWO3 and cuprates La2−xSrxCuO4 and Nd2−xCexCuO4 demonstrates the importance of the general problem of superconductivity in the impurity bands of doped nondegenerate insulators. The theory of superconductivity in the impurity bands of doped nondegenerate insulators is formulated. The approach to a description of a doped insulator is substantiated on the basis of Holstein-Anderson (Frohlich-Anderson) model with electron correlations at impurity sites distributed at random in the initial lattice. An insulator-metal transition observed in the normal phase is caused by attenuation of spin fluctuations in the doped system upon an increase in the doping level and/or temperature. This transition is characterized by the presence of narrow allowed bands in the initial insulator. In contrast to the BCS theory, the equation for the superconducting gap does not arise in the description of such a peculiar superconductivity. Instead, a nontrivial solution to the equation for singlet bosons localized at lattice sites must exist for a superconducting transition. The formation of such bosons is a precursor to the emergence of charged extended bosons in the doped system. In the general case, both singlet and triplet pairing channels are possible in the superconducting state. The spin-triplet channel exists only in the case of a finite spectral density of spin fluctuations in a doped compound. In this case, single-particle Green functions are nondiagonal in the spin index. The results of analysis of the phonon mechanism of superconductivity with a spin-singlet pairing channel are considered. The superconductor-metal transition in a doped compound, which is induced by changes in the temperature and/or the doping level, as well as the isotopic effect, is studied using numerical methods. The results are compared with the available data for HTSC materials.

Renormalizing the Lippmann-Schwinger equation for the one-pion exchange potential

We address the question whether the cut-off dependence, which has to be introduced in order to properly define the Lippmann-Schwinger equation for the one pion exchange potential plus local (delta-function) potentials, can be removed (up to inverse powers of it) by a suitable tuning of the various (bare) coupling constants. We prove that this is indeed so both for the spin singlet and for the spin triplet channels. However, the latter requires such a strong cut-off dependence of the coupling constant associated to the non-local term which breaks orbital angular momentum conservation, that the renormalized amplitude lacks from partial wave mixing. We argue that this is an indication that this term must be treated perturbatively.