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We investigate the stability of the multipolar orderings in $f$-electron material CeCoSi based on a self-consistent mean-field calculation for the effective localized model. This material has two ordered phases in the temperature-pressure phase diagram: the antiferromagnetic phase and the nonmagnetic phase, the latter of which has been suggested to be an antiferroquadrupolar phase. Meanwhile, the origin of the antiferroquadrupolar phase has been unclear, since a quadrupole degree of freedom is present only between the ground-state level and highly separated excited-state level under a tetragonal crystalline electric field (CEF), whose energy scale is much larger than the transition temperature. To understand the sequence of the phase transition from the paramagnetic phase, antiferroquadrupolar phase, and antiferromagnetic phase when decreasing the temperature, we examine the important interaction parameters in the effective localized model. We clarify that the $3z^2-r^2$-type of the antiferroquadrupolar interactions can renormalize the CEF level splitting, which assists a quadrupolar ordering even in a tetragonal system without orbital degeneracy. Moreover, the stability of the antiferroquadrupolar and antiferromagnetic states in a magnetic field and the behavior of the magnetic/quadrupolar susceptibility are also presented for the information to identify the unknown order parameter in the nonmagnetic ordered phase., Comment: 9 pages, 4 figures, 1 table

The relationship between crystal structures and superconducting critical temperatures has attracted considerable attention as a clue to designing higher-$T_{\rm c}$ superconductors. In particular, the relationship between the number $n$ of CuO$_2$ layers in a unit cell of cuprate superconductors and the optimum superconducting transition temperature $T_{\rm c}^{\rm opt}$ is intriguing. As experimentally observed in layered cuprates, $T_{\rm c}^{\rm opt}$ increases when $n$ is increased, up to $n=3$, and, then, decreases for larger $n$. However, the mechanism behind the $n$ dependence of $T_{\rm c}^{\rm opt}$ remains elusive although there have been many studies on the $n$ dependence. In this paper, we studied a bilayer $t$-$t'$ Hubbard model to clarify the effects of the adjacent CuO$_2$ layers on the stability of the superconductivity by using a many-variable variational Monte Carlo method. We calculate the superconducting correlation at long distance and zero temperature, and the amplitude of the superconducting gap functions estimated from the momentum distribution as the observables correlated with $T_{\rm c}^{\rm opt}$. It is found that the in-plane superconducting correlation is not enhanced in comparison with that in the single-layer $t$-$t'$ Hubbard model. The superconducting correlations of the bilayer Hamiltonian are significantly small in the overdoped region in comparison with those of single-layer Hamiltonian, which is attributed to the van Hove singularity. In addition, we found that the amplitude of the superconducting gap functions is also similar in both the single-layer and bilayer $t$-$t'$ Hubbard model at the optimal doping. Therefore, we conclude that the adjacent Hubbard layers are not relevant to the enhancement of $T_{\rm c}^{\rm opt}$ in the bilayer cuprates. Possible origins of the enhanced $T_{\rm c}^{\rm opt}$ other than the adjacent layers are also discussed., 18 pages, 10 figures

We investigate magnetic orderings on kagome lattice numerically from the tight-binding Hamiltonian of electrons, governed by the filling factor and spin-orbit coupling (SOC) of electrons. We find that even a simple kagome lattice model can host both ferromagnetic and noncollinear antiferromagnetic orderings depending on the electron filling, reflecting gap structures in the Dirac and flat bands characteristic to the kagome lattice. Kane--Mele- or Rashba-type SOC tends to stabilize noncollinear orderings, such as magnetic spirals and 120-degree antiferromagnetic orderings, due to the effective Dzyaloshinskii--Moriya interaction from SOC. The obtained phase structure helps qualitative understanding of magnetic orderings in various kagome-layered materials with Weyl or Dirac electrons., 5 pages, 5 figures + Supplemental Material (3 pages, 5 figures)

We investigate the superconductivity of carbon compounds with a sodalite structure, which are similar to hydrogen compounds showing the high-temperature superconductivity. A systematic analysis by first-principles calculations is carried out, including examination of mechanical and dynamic instabilities under external pressure $P$. These instabilities are classified on the phase diagram for the effective doping charge versus the lattice constant of the system. We also present the superconducting transition temperature $T_{\rm c}$ as a function of $P$ for many carbon compounds and a pure carbon system with the sodalite structure. Some of them have $T_{\rm c}$ of up to about 100 K at $P > \sim 30$ GPa, and the results suggest that the sodalite structure of carbon may be a key to producing phonon-mediated high-$T_{\rm c}$ superconductivity., 5 pages, 10 figures, Modified version

We investigated the interlayer magnetoresistance in an organic massless Dirac electron system $\alpha$-(BEDT-TTF)$_2$I$_3$ under pressure. We experimentally demonstrate that the width of the zero mode owing to carrier scattering is much narrower than that of the other Landau levels., Comment: 6 pages, 1 figures

Spin Hall effect at finite wave vector in a ferromagnetic conductor is theoretically studied by calculating the spin density as the linear response to an applied electric field. The cases of a spin-orbit interaction due to random impurities and a localized Rashba interaction are considered. It is shown that the spin Hall effect has a broad response for the wave vector $q\lesssim 2\kf$ where $\kf $ is the Fermi wave vector. This fact confirms the local nature of the spin-charge conversion effects.

A skyrmion crystal (SkX) expressed as a multiple number of spiral modulations manifests itself not only in its peculiar magnetic texture but also in nontrivial transport properties originating from an emergent magnetic field. We here report our numerical results for multiple SkXs in a centrosymmetric tetragonal crystal system. By performing simulated annealing for an effective spin model for itinerant magnets, we find that three types of the SkXs with the skyrmion numbers of one and two, which are characterized by different superpositions of helices, are stabilized in the ground state, and are transformed by an external magnetic field. The essence of the emergent multiple SkXs is lied in itinerant frustration where exchange interactions are competed in momentum space due to the nature of itinerant electrons., 6 pages, 4 figures

A magnetic monopole in spin ice is a novel quasiparticle excitation in condensed matter physics, and we found that the ac frequency dependent magnetic susceptibility $\chi(\omega)$ in the two-dimensional (2D) spin ice (so-called kagom\'{e} ice) of Dy$_2$Ti$_2$O$_7$ shows a single scaling form. This behavior can be understood in terms of the dynamical scaling law for 2D Coulomb gas (CG) systems [Phys. Rev. B 90, 144428 (2014)], characterized by the charge correlation length $\xi (\propto1/\sqrt{\omega_1})$, where $\omega_{1}$ is a characteristic frequency proportional to the peak position of the imaginary part of $\chi(\omega)$. It is a generic behavior among a wide variety of models such as the vortex dynamics of 2D superconductors, 2D superfluids, classical XY magnets, and dynamics of melting of Wigner crystals., Comment: 5 pages, 4 figures, Supplemental Material

Numerical experiments on the Heisenberg model of headless spins are performed for the two-dimensional triangular lattice. The assumed model is with the two-body interaction preferring twisted align...

An underscreened Kondo model for the impurity spin S = 7/2 in a weak crystal field is studied to elucidate the Kondo effect in the Eu compounds. By utilizing the numerical renormalization group met...

Single crystal and polycrystalline samples of MoP$_4$ with a black-phosphorus-derived structure have been successfully synthesized by a high-pressure technique. The polycrystalline samples show a large positive magnetoresistance and a small negative Seebeck coefficient at low temperatures, reflecting a semi-metallic nature with high-mobility electrons. Consistent with the transport properties, the band structure calculation reveals a semi-metallic state with the presence of two types of Dirac nodes slightly below the Fermi level. The Dirac node along the $\Gamma$-X direction normal to the phosphorus layers is gapped out in the presence of spin-orbit coupling (SOC), whereas the band crossing at the Z-point is immune to SOC because of the non-symmorphic symmetry. This work demonstrates a great potential of phosphorus-based layered Zintl compounds for topological semimetal candidates allowing chemical band engineering., Comment: 14 pages, 4 figures, 2 tables

Effect of spin-orbit coupling (SOC) on Dirac electrons in the organic conductor $\alpha$-(BETS)$_2$I$_3$ [BETS = bis(ethylenedithio)tetraselenafulvalene] has been examined by calculating electric conductivity and spin magnetic susceptibility. A tight-binding (TB) model with real and imaginary transfer energies is derived using first-principles density-functional theory method. The conductivity without the SOC depends on both anisotropies of the velocity of the Dirac cone and the tiling of the cone. Such conductivity is suppressed by the SOC, which gives rise to the imaginary part of the transfer energy. Due to the SOC, we find at low temperatures that the reduction of the conductivity becomes large and that the anisotropy of the conductivity is reduced. A nearly constant conductivity at high temperatures is obtained by an electron--phonon (e--p) scattering. Further, the property of the Dirac cone is examined for the spin susceptibility, which is mainly determined by the density of states (DOS). The result is compared with the case of the organic conductor $\alpha$-(BEDT-TTF)$_2$I$_3$ [BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene], which provides the Dirac cone without the SOC. The relevance to experiments is discussed., Comment: arXiv admin note: text overlap with arXiv:2009.14594

We analytically derive the dependence of the current of the spin-down minority electrons on the magnon at zero temperature for a tunnel junction composed of ferromagnetic and normal metals using th...

Magnetic susceptibility and torque measurements have been performed for neutral BEDT-TTF crystals to investigate the diamagnetic properties. The diamagnetic susceptibility is found to be anisotropi...

We developed a framework for directly calculating the spin susceptibility of anisotropic itinerant ferromagnets in the full temperature range within the coherent potential approximation in the disordered local moment picture. As a test of our formulation, we demonstrate the computation for the temperature ($T$) dependence of the spin susceptibility for Rashba-type ferromagnets with the Curie temperature $T_\mathrm{C}$. In a certain parameter, we found that the inverse transverse susceptibility $1/\chi_\perp\simeq\mathrm{const.}$ for $TT_\mathrm{C}$, which reflects characteristics of itinerant ferromagnets including a spin-orbit interaction.

A line shape change in the V 1s core level photoemission spectrum (CPES) across the metal–insulator transition (MIT) in VO2 is simulated using a two-band Hubbard model with a core–hole potential an...

The one-dimensional Heisenberg antiferromagnet of S = 1 spins is studied by numerical diagonalization method based on the Lanczos algorithm. The Haldane gap of this system is numerically estimated from finite-size clusters under the twisted boundary condition up to the 30-site system. The finite-size results are analyzed by a convergence-acceleration technique; the multistep procedure of the convergence acceleration is successfully carried out. The present estimate for the gap magnitude is more precisely than the previously reported value from a Lanczos-diagonalization study. It also agrees well with the result reported in a study based on the density matrix renormalization group calculation. The present study clarifies that Lanczos-diagonalization calculations can sufficiently contribute for precisely estimating an energy gap although this method can treat only small clusters.

We performed $^{59}$Co nuclear magnetic and quadrupole resonance (NMR and NQR) measurements under pressure on a single-crystalline CeCoSi, which undergoes an unresolved phase transition at $T_0$. The NQR spectra clearly showed that the phase transition at $T_0$ is nonmagnetic, but any symmetry lowering at the Co site was not seen irrespective of the feature of second-order phase transition. By contrast, the NMR spectra were split by the induced magnetic field perpendicular to the external magnetic field. These results show that the phase below $T_0$ is not a simple paramagnetic state but is most likely electric multipolar ordered state of Ce $4f$ electrons. The development of the Kondo effect by applying pressure is thought to be crucial to stabilize this state and to show novel features beyond commonality of tetragonal Ce-based systems., 6 pages, 4 figures

We discuss the mechanism and the conditions for the appearance of synchronized charge oscillations which have been observed experimentally and theoretically after strong photoexcitation of dimerized systems. In the Hubbard model with on-site repulsion, the Bloch equations for a wave-number-dependent pseudospin -- whose components describe the charge-density difference, current density, and bond density between the two sublattices -- involve an alternatingly tilted pseudomagnetic field, which assists the synchronization of pseudospins with different wave numbers, irrespective of the initial condition. This fact is numerically confirmed by the dynamics in finite lattices based on the exact diagonalization method. In the presence of nearest-neighbor repulsion, however, the synchronization can be hindered by excitons. Therefore, the excitation of a sufficiently large density of free electron-hole pairs, but low density of excitons, is needed to achieve synchronization., Comment: 9 pages, 8 figures

Trilayer films consisting of ferromagnetic NiFe, nonmagnetic Cu or Ru, and antiferromagnetic FeMn layers were prepared by sputtering technique. The long-range exchange bias properties were investigated with magnetization curve measurements for the trilayer films with various nonmagnetic layer thicknesses tNM between 0 and 12 Å. Both the exchange bias and coercive fields were observed in the magnetic hysteresis curves (M–H curves) of all trilayer films. When tNM was increased, the exchange and coercive fields determined from the M–H curves showed exponential decrease [exp(−tNM/λ)] with almost the same attenuation length λ. The cause of the observed behavior was discussed on the basis of numerical calculations using an extended Meiklejohn and Bean model in which distribution of the magnetic anisotropy in the antiferromagnetic layer was introduced.

In most Dirac semimetals, time-reversal and inversion symmetries are believed to play a crucial role in their stability. We demonstrate that these symmetries are broken in Dirac fermions in the organic conductor α-(BEDT-TTF)₂I₃ due to the bond correlation created by the strong inter-site electronic correlation. The system is a three-dimensional type-II Dirac semimetal in the coherent inter-layer tunneling regime. A chiral anomaly is predicted to be observed in the magnetoresistance when the magnetic field is tuned to the inter-layer tunneling direction. Our result suggests that α-(BEDT-TTF)₂I₃ is a useful platform to explore interplay between the chiral anomaly and the strong correlation and/or dimensionality.

Motivated by the recent quasi-elastic neutron scattering experiment, we extend the spin-dynamics simulation on the triangular-lattice Heisenberg antiferromagnet, to observe a sharp central peak of its energy width $\sim 0.001J$ ($J$ the exchange coupling) of the $Z_2$-vortex origin, consistently with the experiment.

We illustrate the emergence of the three-channel Kondo effect in a seven-orbital impurity Anderson model hybridized with $\Gamma_7$ and $\Gamma_8$ conduction electron bands employing a numerical renormalization group method. In particular, we focus on the case with ten local $f$ electrons corresponding to a Ho$^{3+}$ ion. By investigating the dependence of the low-temperature behavior of the $f$-electron entropy on the crystalline electric field potential and hybridization, we found a residual entropy of $\log \phi$ with the golden ratio $\phi=(1+\sqrt{5})/2$, characteristic of the three-channel Kondo effect, for the wide range of parameters of the local $\Gamma_5$ triplet ground state. To improve our insight of local impurity spin, we explored a quantum critical point between three-channel Kondo and Fermi-liquid phases. Finally, we briefly discussed the cubic Ho compound as a candidate to observe experimentally the three-channel Kondo effect., Comment: 4 pages, 3 figures. To appear in J. Phys. Soc. Jpn

Charge density wave (CDW) in high-TC cuprates has drawn a lot of attention in the field. In this article, we review some of our recent x-ray studies about the ground state and the excitation spectr...

In this article, we focus on the charge degree of freedom in cuprate superconductors and review theoretical insights into the electronic nematic order, bond-charge orders, and plasmons. The low-energy charge dynamics is controlled by the spin-spin interaction J, which generates various bond-charge ordering tendencies including the electronic nematic order. The nematic order is driven by a d-wave Pomeranchuk instability and is pronounced in the underdoped region as well as around van Hove filling in the hole-doped case; the nematic tendency is weak in the electron-doped region. Nematicity consistent with the d-wave Pomeranchuk instability was reported for hole-doped cuprates in various experiments. Although the t-J and Hubbard models correctly predicted the proximity to the nematic instability in cuprates far before the experimental indications were obtained, full understanding of the charge ordering tendencies in hole-doped cuprates still requires further theoretical studies. In electron-doped cuprates, on the other hand, the d-wave bond-charge excitations around momentum q=(0.5pi,0) explain the resonant x-ray scattering data very well. Plasmon excitations are also present and the agreement between the large-N theory of the t-J model and resonant inelastic x-ray scattering measurements is nearly quantitative in both hole- and electron-doped cuprates. Theoretically the charge dynamics in cuprates is summarized as a dual structure in energy space: the low-energy region scaled by J, where the nematic and various bond-charge orders are relevant, and the high-energy region typically larger than J, where plasmons are predominant., 38 pages, 14 figures, concise review article

The presence of charge order in high-transition-temperature copper oxides (high-Tc cuprates) was identified a decade ago. Now it is a universally observed order like the antiferromagnetic and the superconducting orders of the cuprates. The charge order shows up in various forms depending on materials, and it overlaps other orders in the phase diagram. Because of this diversity and complexity it has been far from clear whether or not the charge order has a direct relevance to superconductivity and to the mysterious pseudogap phenomenon. However, the research development in the last few years has been successful in revealing universal aspects of the charge order and its fluctuations. It turns out that the charge order is compatible with superconductivity, and that its fluctuations have high onset temperature and high energy scale comparable to those of the pseudogap. The charge order correlations might be indispensable for creating the pseudogap and possibly generating high-Tc superconductivity by collaborating with spin and pairing correlations., Comment: 17 pages, 6 figures

We theoretically investigate the interlayer magnetoresistance in quasi-two-dimensional Dirac fermion systems, where the Fermi energy is at the Dirac point. If there is an intermediate insulating layer that has an overlap with the wave functions in the Dirac fermion layers, there appears a positive magnetoresistance regime due to the intervalley tunneling. We show that the interlayer magnetoresistance can be used to find whether Dirac fermions are massive or not from the minimum in the interlayer magnetoresistance. As a specific system, we consider \alphaI under high pressure. We also discuss that one has to be careful in analyzing the crossover temperature from the positive to negative magnetoresistance. A simple picture is applied to the crossover in the zero temperature limit but it does not apply to the data at finite temperatures. We show that the ratio of the Fermi velocity to the scattering rate is evaluated from the zero temperature limit of the crossover temperature., 8 pages, 7 figures

We discuss a close relationship between a quasiparticle on the Bogoliubov Fermi surface and an odd-frequency Cooper pair in a superconductor in which a Cooper pair consisting of two j=3/2 electrons forms the pseudospin-quintet even-parity pair potential with breaking time-reversal symmetry. It has been established in a single-band superconductor that a low-energy quasiparticle below the superconducting gap accompanies an odd-frequency Cooper pair. In this paper, we show that an odd-frequency pair characterized by chirality coexists with a quasiparticle on the Bogoliubov Fermi surface. The symmetry of odd-frequency Cooper pairs is analyzed in detail by taking realistic pair potentials into account in a cubic superconductor., 6 pages, 1 figure

We study the Anderson localization in nonlinear systems by taking a nonlinear transmission line realizing the Toda lattice. It is found that the randomness in inductance induces the Anderson localization in the voltage propagation. Furthermore, the nonlinearity enhances the Anderson localization. They are understood in terms of attractive interactions to form a soliton in a nonlinear system. Our results will be applicable in general to the Anderson localization in nonlinear systems that have solitons., 5 pages, 5 figures

Fe3−xMnxSi (x > 0.75) exhibits a ferromagnetic transition at TC and a transition to an antiferromagnetic phase with a ferromagnetic component at a temperature (TA) lower than TC, defined as the AF ...

The intertube conductance $G$ of the parallel side contacted armchair nanotubes is calculated by Landauer's formula as a function of the Fermi level $E$. When the intertube difference in the dope strength is large enough, a resonant peak dominant over the others appears in the $E$-$G$ curve. The overlap length and the interlayer configuration do not influence the resonant energy. The intervalley transmission at the resonant peak works as a reverser and a filter of the valley current., version 4. In part just above Table V in version 3, there is a typo, where $|q_{\rm r}|$ is replaced by $E'/E$ by mistake. (correct) The small nonzero $I_{-\sigma,\sigma}$ being inversely proportional to $\widetilde{E}^2$ originates from the slight difference of $|q_{\rm r}|$ from 1 as is explained by Appendix D

We discuss the Uranium 5f electron states in UPd3 and UAl3 on the basis of the theoretical calculation of the core level photoemission with the use of the impurity Anderson model. In order to suppr...

The spin-flop phase of a honeycomb antiferromagnet of Mn0.84Mg0.16TiO3 has been studied under magnetic field along normal direction to the honeycomb plane by neutron scattering. With increasing a m...

Spin waves and their quanta magnons are collective excitation of electron spins in magnetic materials which can serve as information carriers for future low-power-consumption computing systems. Fer...

In this review we introduce computer modelling and simulation techniques which are used for ferrimagnetic materials. We focus on models where thermal effects are accounted for, atomistic spin dynamics and finite temperature macrospin approaches. We survey the literature of two of the most commonly modelled ferrimagnets in the field of spintronics — the amorphous alloy GdFeCo and the magnetic insulator yttrium iron garnet. We look at how generic models and material specific models have been applied to predict and understand spintronic experiments, focusing on the fields of ultrafast magnetisation dynamics, spincaloritronics and magnetic textures dynamics and give an outlook for modelling in ferrimagnetic spintronics.

We theoretically study electrical responses of magnetization in Weyl semimetals. The Weyl semimetal is a new class of topological semimetals, possessing hedgehog type spin textures in momentum space. Because of this peculiar spin texture, an interplay of electron transport and spin dynamics might provide new method to electrical control of magnetization. In this paper, we consider the magnetically doped Weyl semimetals, and systematically study current- and charge-induced spin torque exerted on the local magnetization in three-dimensional Dirac-Weyl metals. We determine all current-induced spin torques including spin-orbit torque, spin-transfer torque, and the so-called $\beta$-term, up to first order with respect to spatial and temporal derivation and electrical currents. We find that spin-transfer torque and $\beta$-term are absent while spin-orbit torque is proportional to the axial current density. We also calculate the charge-induced spin torque microscopically. We find the charge-induced spin torque originates from the chiral anomaly due to the correspondence between spin operators and axial current operators in our model., Comment: 12 pages, 3 figures

We investigated Fe-substitution effects on ferromagnetic fluctuations in the superconducting overdoped and non-superconducting heavily overdoped regimes of the Bi-2201 cuprates by the magnetization and electrical-resistivity measurements. It was found that the spin-glass state was induced at low temperatures by the Fe substitution. The Curie constant and the effective Bohr magneton, estimated from the magnetic susceptibility, as well as the dimensionality of the ferromagnetic fluctuations from the resistivity, suggest the enhancement of the ferromagnetic fluctuations owing to the Fe substitution. A ferromagnetic spin-cluster model is proposed in the heavily overdoped regime of Bi-2201, while an antiferromagnetic spin-cluster model has been proposed in the overdoped regime of Bi-2201 [Hiraka et al., Phys. Rev. B 81, 144501 (2010)]., Comment: 5 pages, 4 figures

Magnetic skyrmions, which are topologically protected particle-like spin textures, exhibit Brownian motion at ambient temperatures in a ferromagnetic thin film. The potential applications of a skyr...

The 12%-S doped FeSe system has a high Tc of 30 K at a pressure of 3.0 GPa. We have successfully investigated its microscopic properties for the first time via 77Se-NMR measurements under pressure. The antiferromagnetic (AFM) fluctuations at the optimal pressure (∼3 GPa) exhibited unexpected suppression compared with the AFM fluctuations at ambient pressure, even though the optimal pressure is close to the phase boundary of the AFM phase induced at the high-pressure region. In addition, we revealed that the SC phase at an applied field of 6.02 T exhibited a remarkable double-dome structure in the pressure–temperature phase diagram, unlike the SC phase at zero field.

Magnetic pair distribution function (mPDF) of intermetallic antiferromagnet Mn3RhSi is estimated from the powder neutron diffraction data. The mPDF exhibits negative peak at about r = 2.7 A corresp...

We theoretically study the stability of magnetic skyrmion crystals (SkXs) in chiral cubic antiferromagnets with the EuPtSi hosting unconventional nanometric SkXs in mind. By performing numerical simulations for a minimal effective spin model with the long-range Dzyaloshinskii-Moriya interaction and the multiple-spin interaction arising from itinerant nature of electrons, we clarify two key ingredients for the emergence of the SkXs in EuPtSi: One is the low-symmetric ordering vectors that lead to the field-direction sensitive SkXs in an external magnetic field, while the other is the synergy between spin-charge and spin-orbit couplings in itinerant magnets that results in the nanometric SkXs. The present study will not only provide the microscopic mechanism of the SkXs in EuPtSi but also guide for a search of further materials hosting short-period SkXs., Comment: 5 pages, 5 figures

Magnetocaloric effect for a layered organic superconductor β′′-(BEDT-TTF)2SF5CH2CF2SO3 has been investigated. At low magnetic fields, a sinusoidal quantum oscillation, arising from a closed Fermi s...

The effect of the magnetic field in a two-orbital impurity Anderson model is studied by the numerical renormalization group method, focusing on the nature of a quantum phase transition and an assoc...

Using inelastic neutron scattering, we investigate the spin wave excitations on the antiferromagnetic MnTiO3 (TN = 65 K), which has the stacked honeycomb structure. At T = 2 K, the spin wave energy...

UTe$_2$ is a recently discovered promising candidate for a spin-triplet superconductor. In contrast to conventional spin-singlet superconductivity, spin-triplet superconductivity possesses spin and angular momentum degrees of freedom. To detect these degrees of freedom and obtain the solid evidence of spin-triplet superconductivity in UTe$_2$, we performed $^{125}$Te-NMR measurement. We previously reported that the shoulder signal appears in NMR spectra below the superconducting (SC) transition temperature $T_{\rm c}$ in $H \parallel b$, and that a slight decrease in the Knight shift along the $b$ and $c$ axes ($K_b$ and $K_c$, respectively) below $T_{\rm c}$ at a low magnetic field $H$. To clarify the origin of the shoulder signal and the trace of the decrease in $K_b$, we compared the $^{125}$Te-NMR spectra obtained when $H~\parallel~b$ and $H~\parallel~c$ and measured the $^{125}$Te-NMR spectra for $H~\parallel~b$ up to 14.5~T. The intensity of the shoulder signal observed for $H~\parallel~b$ has a maximum at $\sim 6$~T and vanishes above 10~T, although the superconductivity is confirmed by the $\chi_{\rm AC}$ measurements, which can survive up to 14.5~T (maximum $H$ in the present measurement). Moreover, the decrease in $K_b$ in the SC state starts to be small around 7~T and almost zero at 12.5~T. This indicates that the SC spin state gradually changes with the application of $H$. Meanwhile, in $H~\parallel~c$, unexpected broadening without the shoulder signals was observed below $T_{\rm c}$ at 1~T, and this broadening was quickly suppressed with increasing $H$. We construct the $H$--$T$ phase diagram for $H~\parallel~b$ and $H~\parallel~c$ based on the NMR measurements and discuss possible SC states with the theoretical consideration. We suggest that the inhomogeneous SC state characterized by the broadening of the NMR spectrum originates from the spin degrees of freedom., Comment: 8 pages, 7 figures

Complex oxides with $4d$ and $5d$ transition-metal ions recently emerged as a new paradigm in correlated electron physics, due to the interplay between spin-orbit coupling and electron interactions. For $4d$ and $5d$ ions, the spin-orbit coupling, $\zeta$, can be as large as 0.2-0.4 eV, which is comparable with and often exceeds other relevant parameters such as Hund's coupling $J_{\rm H}$, noncubic crystal field splitting $\Delta$, and the electron hopping amplitude $t$. This gives rise to a variety of spin-orbit-entangled degrees of freedom and, crucially, non-trivial interactions between them that depend on the $d$-electron configuration, the chemical bonding, and the lattice geometry. Exotic electronic phases often emerge, including spin-orbit assisted Mott insulators, quantum spin liquids, excitonic magnetism, multipolar orderings and correlated topological semimetals. This paper provides a selective overview of some of the most interesting spin-orbit-entangled phases that arise in $4d$ and $5d$ transition-metal compounds., Comment: 31 pages, 28 figures. Submitted to J. Phys. Soc. Jpn

We have measured and analyzed the in-plane thermal diffusivity of the Mott insulator Ca2RuO4 around room temperature under external currents with an infrared camera as a contactless thermometer. We...

We report IR and Raman spectra for a two-dimensional superconductor, β′′-(BEDT-TTF)4[Ga(C2O4)3(H3O)]C6H5NO2, below the superconducting transition temperature. The behavior of the lattice-sensitive ...

irac fermions display a singular response against magnetic and electric fields. A distinct manifestation is the large diamagnetism originating in the interband effect of Bloch bands, as observed in bismuth alloys. Through 209Bi NMR spectroscopy, we extract diamagnetic orbital susceptibility inherent to Dirac fermions in the semiconducting bismuth alloys Bi1−xSbx (x = 0.08–0.16). The 209Bi hyperfine coupling constant provides an estimate of the effective orbital radius. In addition to the interband diamagnetism, the NMR shift includes an anomalous temperature-independent term originating in the enhanced intraband diamagnetism under strong spin–orbit coupling. The nuclear spin–lattice relaxation rate 1/T1 is dominated by orbital excitation and follows cubic temperature dependence in an extensive temperature range. The result demonstrates the robust diamagnetism and low-lying orbital excitation against the small gap opening, whereas x-dependent spin excitation appears at low temperatures.

To analyze the many-body problem based on differential forms, we apply the Heisenberg equation of motion to the Hamiltonian including the many-body term, focusing on the simplest electron–phonon in...