We present inelastic neutron scattering experiments on a single-domain crystal of lightly-doped La1.96Sr0.04CuO4. We find that the magnetic excitation spectrum in this insulating phase with a diagonal incommensurate spin modulation is remarkably similar to that in the superconducting regime, where the spin modulation is bond parallel. In particular, we find that the dispersion slope at low energy is essentially independent of doping and temperature over a significant range. The energy at which the excitations cross the commensurate antiferromagnetic wave vector increases roughly linearly with doping through the underdoped regime.
The effects of the application of a magnetic field on the diagonal stripe spin-glass phase is studied in lightly doped La_{2-x}Sr_xCuO_4 (x=0.014 and 0.024). With increasing magnetic field, the magnetic elastic intensity at the diagonal incommensurate (DIC) positions (1,\pmε,0) decreases as opposed to the increase seen in superconducting samples. This diminution in intensity with increasing magnetic field originates from a spin reorientation transition, which is driven by the antisymmetric exchange term in the spin Hamiltonian. On the other hand, the transition temperature, the incommensurabil…
Inelastic neutron scattering experiments have been performed on lightly-doped La$_{1.96}$Sr$_{0.04}$CuO$_{4}$, which shows diagonal incommensurate spin correlations at low temperatures. We previously reported that this crystal, with a single orthorhombic domain, exhibits the "hourglass" dispersion at low energies [Phys. Rev. Lett. 101, 197001 (2008)]. In this paper, we investigate in detail the energy evolution of the magnetic excitations up to 65 meV. It is found that the anisotropic excitations at low energies, dispersing only along the spin modulation direction, crossover to an isotropic, c…
We study the static magnetic correlations in lightly doped La(2-x)Sr(x)CuO(4) within the framework of a dipolar frustration model for a canted antiferromagnet. We show that the stability of the canted Neel state for x<2% is due to the Dzyaloshinskii-Moriya and XY anisotropies. For higher doping the ground state is unstable towards a helicoidal magnetic phase where the transverse components of the staggered magnetization rotate in a plane perpendicular to the orthorhombic b-axis. Our theory reconciles, for the first time, the incommensurate peaks observed in elastic neutron scattering with Rama…
Hole induced changes in the antiferromagnetic structure of a lightly Ca doped Gd:Y_{1-x}Ca_xBa_2Cu_3O_6 copper oxide single crystal with x~0.008 is investigated by Gd3+ electron spin resonance. Holes do not localize to Ca2+ ions above 2.5 K since the charge distribution and spin susceptibility next to the Ca2+ are independent of temperature. Both hole doped and pristine crystals are magnetically twinned with an external magnetic field dependent antiferromagnetic domain structure. Unlike the undoped crystal, where the easy magnetic axis is along [100] at all temperatures, the easy direction in …
Numerical studies of the two-dimensional d-p model using the Gutzwiller ansatz have exhibited the incommensurate antiferromagnetic state coexisting with superconductivity in the under- and lightly doped regions. Our results are based on the variational Monte Carlo method for the three-band Hubbard model with d and p orbitals. We obtained the finite superconducting condensation energy for the coexistent sate at the doping rate $x=1/8$, 1/12, and 1/16, up to the systems of 256 unit cells with 768 atoms (oxygen and copper atoms). The phase diagram for the hole-doped case is consistent with recent…
Lightly-doped La$_{2-x}$Sr$_x$CuO$_4$ in the so-called "insulating" spin-glass/diagonal-stripe phase has been studied by angle-resolved photoemission spectroscopy. A quasi-particle (QP) peak crossing the Fermi level has been observed in the node direction of the d-wave superconducting gap, forming an "arc" of Fermi surface consistent with the recently observed metallic transport behavior at high temperatures of lightly-doped materials. The spectral weight of the nodal QP smoothly increases with hole doping, corresponding to the $n \sim x$ behavior of the carrier number in the underdoped and li…
The hole concentration dependence of the magnetic correlations is studied in very lightly-doped La$_{2-x}$Sr$_x$CuO$_4$ ($x<$0.02), which shows coexistence of a three-dimensional antiferromagnetic (AF) long-range ordered phase and a spin-glass phase at low temperatures. It is found that the spin-glass phase in the coexistence region also shows a diagonal spin modulation as in the pure spin-glass phase in La$_{2-x}$Sr$_x$CuO$_4$ (0.02$\le x\le$0.055). Below $x\sim$0.02 the diagonal stripe structure is the same as that in $x\sim$0.02 with a volume fraction almost proportional to hole concentrati…
We device and investigate numerically a minimal yet detailed spin polaron model that describes lightly doped CuO$_2$ layers. The low-energy physics of a hole is studied by total-spin-resolved exact diagonalization on clusters of up to 32 CuO$_2$ unit cells, revealing features missed by previous studies. In particular, spin-polaron states with total spin 3/2 are the lowest eigenstates in several regions of the Brillouin zone. In these regions, and also at other points the quasiparticle weight is identically zero, indicating orthogonal states to those represented in the one electron Green's func…
We have studied incommensurate spin ordering in single crystal underdoped La_{2-x}Ba_{x}CuO_{4} with x~0.08, 0.05 and 0.025 using neutron scattering techniques. Static incommensurate magnetic order is observed in the La_{2-x}Ba_{x}CuO_{4} (x=0.05 and 0.025) compounds with ordering wavevectors which are rotated by 45 degree about the commensurate (0.5,0.5,0) position, with respect to that in the superconducting x=0.08 material. These spin modulations are one dimensional in the x=0.05 and 0.025 samples, with ordering wavevectors lying along the orthorhombic b* direction. Such a rotation in the o…
Experimental observations of lightly doped La_{2-x}Sr_xCuO_4, x < 0.02, revealed remarkable magnetic properties such as the incommensurate noncollinear ordering (additional to the Neel ordering) and a tremendous doping dependence of the uniform longitudinal susceptibility. We show that the spiral solution of the t-t'-t''-J model obtained by taking into account the Coulomb trapping of holes by Sr ions describes these puzzling data perfectly well. Our solution firstly explains why the incommensurate structure is directed along the orthorhombic b-axis, and secondly allows a numerical calculation …
Neutron scattering experiments have been carried out to explore Ni-impurity effects on static spin correlations in La2-xSrxCuO4 (LSCO) in the vicinity of the superconductor-insulator boundary where both parallel and diagonal spin-density modulations (SDM) coexist at low temperature. Upon dilute Ni substitution the incommensurability decreases for both types of SDM, while the volume fraction of the diagonal (parallel) SDM increases (decreases). Subsequent Ni doping induces a bulk three-dimensional antiferromagnetic (AF) order when x ~ Ni concentration. TN of such the AF order depends on x and s…
Using a spin-rotation invariant version of the slave-boson approach we investigate the relative stability and band structure of various incommensurate phases in the cuprates. Our findings obtained in the Hubbard model with next-nearest neighbor hopping $-t'/t\simeq 0.15$, as appropriate for the La$_{2-x}$Sr$_x$CuO$_4$ family, support the formation of diagonal (vertical) stripe phases in the doping regime $x=1/16$ ($x=1/8$), respectively. In contrast, based on the fact that a larger value $-t'/t=0.3$ expected for YBa$_2$Cu$_3$O$_{6+δ}$ triggers a crossover to the diagonal (1,1) spiral phase at …
In a recent Letter (Phys. Rev. Lett. 106, 036401 (2011)), Lau, et al. investigated the single hole problem in an effective model containing Cu $d$ and O $2p$ orbitals by exact diagonalization on clusters composed of 32 CuO$_2$ unit cells. With full quantum fluctuations due to the antiferromagnetic (AFM) backgroud, they found that spin-polaron solutions with spin 3/2 become lowest energy solutions in certain region of Brillouin zone (BZ), which they claimed no similiar solutions were obtained in other models or approximations before. In this Comment, we would like to point out that such high-sp…
The anisotropic triangular model, which is believed to describe the materials Cs$_2$CuCl$_4$ and Cs$_2$CuBr$_4$, among others, is dominated by incommensurate spiral physics and is thus extremely resistant to numerical analysis on small system sizes. In this paper we use twisted boundary conditions and exact diagonalization techniques to study the phase diagram of this model. With these boundary conditions we are able to extract the inter- and intrachain ordering $q$-vectors for the $\frac{J'}{J} < 1$ region finding very close agreement with recent DMRG results on much larger systems. Our resul…
FeGe_2, and lightly doped compounds based on it, have a Fermi surface driven instability which drive them into an incommensurate spin density wave state. Studies of the temperature and magnetic field dependence of the resistivity have been used to determine the magnetic phase diagram of the pure material which displays an incommensurate phase at high temperatures and a commensurate structure below 263 K in zero field. Application of a magnetic field in the tetragonal basal plane decreases the range of temperatures over which the incommensurate phase is stable. We have used inelastic neutron sc…
We propose a new form of inhomogeneous phases consisting of out-of-phase staggered flux domains separated by diagonal charged domain walls centered on bonds or on sites. Remarkably, such domain flux phases are spin-rotationally symmetric and exhibit cone-like quasiparticle dispersion as well as incommensurate order of orbital currents. Such features are consistent with the pseudogap behavior and the diagonal stripes observed experimentally in lightly doped cuprates. A renormalized mean field theory shows that such solutions are competitive candidates within the $t$--$J$ model.
We establish the qualitative behavior of the incommensurability $ε$, optimal domain wall filling $ν$ and chemical potential $μ$ for increasing doping by a systematic slave-boson study of an array of vertical stripes separated by up to $d=11$ lattice constants. Our findings obtained in the Hubbard model with the next-nearest neighbor hopping $t'=-0.15t$ agree qualitatively with the experimental data for the cuprates in the doping regime $x\lesssim 1/8$. It is found that $t'$ modifies the optimal filling $ν$ and triggers the crossover to the diagonal (1,1) spiral phase at increasing doping, stab…
The relaxation function theory of doped two-dimensional $S=1/2$ Heisenberg antiferromagnetic (AF) system in the paramagnetic state is presented taking into account the hole subsystem as well as both the electron and AF correlations. The expression for fourth frequency moment of relaxation shape function is derived within the $t-J$ model. The presentation obeys rotational symmetry of the spin correlation functions and is valid for all wave vectors through the Brillouin zone. The spin diffusion contribution to relaxation rates is evaluated and is shown to play a significant role in carrier free …
Close to half filling and in the limit of strong interactions the Hubbard model leads a spin Hamiltonian. In its original isotropic form this is the Heisenberg model with antiferromagnetic coupling $J$. On a square lattice there is no frustration and the ground state is a classical antiferromagnet denoted by the commensurate order vector ${\bf Q}=(π,π)$. In this work we show that the inclusion of spin orbit coupling (SOC) in the fermionic Hubbard model on a square lattice leads to an incommensurate spin density wave (ISDW) in the strong interactions limit at half filling. In this limit the Hub…
Recent scattering experiments in the 3D Kitaev magnet $β$-Li$_2$IrO$_3$ have shown that a relatively weak magnetic field along the crystallographic ${\bf b}$-axis drives the system from its incommensurate counter-rotating order to a correlated paramagnet, with a significant uniform `zigzag' component superimposing the magnetization along the field. Here it is shown that the zigzag order is not emerging from its linear coupling to the field (via a staggered, off-diagonal element of the ${\bf g}$-tensor), but from its intertwining with the incommensurate order and the longitudinal magnetization.…
Mechanism of Incommensurate Magnetic Order in $\mathrm{BaCo_2(AsO_4)_2}$: Interplay of Frustrated Further-Neighbor Exchanges and Bond-Directional Anisotropy
Qom University of Technology（库姆理工大学）；University of Toronto（多伦多大学）；Shahrekord University（沙赫里克尔德大学）
The bulk properties and impurity effect in the one-dimensional S=1/2 Heisenberg model with dimerization and next-nearest-neighbor exchange are studied by the density matrix renormalization group (DMRG) and exact diagonalization methods. This model widely covers the S=1 Heisenberg model, two-leg ladders, bond-alternating chains and the S=1/2 Heisenberg model. Almost the whole parameter space belongs to the Haldane phase. In the non-dimerizing limit a transition to a kind of spin liquid takes place, characterized by the delocalized spin polarization. This transition causes the distinct impurity …
Motivated by a recent neutron scattering experiment on detwinned YBa$_2$Cu$_3$O$_{6+δ}$ superconductor, we examine the frequency and doping dependence of the anisotropy in the spin and charge fluctuation arising from the coupling between the plane and the chain. Starting from the two-dimensional $t$-$t^{'}$-$J$ model and using the random-phase approximation (RPA), we find a pronounced anisotropy of the incommensurate (IC) peaks in the spin channel, namely the peak intensity at the $(π\pmδ,π)$ direction is stronger than that at the $(π,π\pmδ)$ direction in a wide frequency range from $ω=0.2J$ t…
The theoretical inception of the Kitaev honeycomb model has had defining influence on the experimental hunt for quantum spin liquids, bringing unprecedented focus onto the synthesis of materials with bond-directional interactions. Numerous Kitaev materials, which are believed to harbor ground states parametrically close to the Kitaev spin liquid, have been investigated since. Yet, in these materials the Kitaev interaction often comes hand in hand with off-diagonal $Γ$ interactions -- with the competition of the two potentially giving rise to a magnetically ordered ground state. In an attempt t…
We study the interplay between strong correlations and incommensurability on fermions using mean field as well as exact many-body Lanczos diagonalization techniques. In a two-dimensional parameter space, mean field phase diagram of infinite system shows a critical phase with multifractal characteristics sandwiched between a Bloch-type extended and a localized phase. Exact numerical computation on finite size systems of the Kohn charge stiffness Dc, characterizing transport properties, and the charge exponent Krho, characterizing the superconducting pairing fluctuations, shows the existence of …
Based on the unrestricted Gutzwiller approximation we study the possibility that the diagonal incommensurate spin scattering in the spin glass phase of lanthanum cuprates originates from stripe formation. Similar to the metallic phase two types of diagonal stripe structures appear to be stable: (a) site-centered textures which have one hole per site along the stripe and (b) ferromagnetic stair-case structures which are the diagonal equivalent to bond-centered stripes in the metallic phase and which on average have a filling of 3/4 holes per stripe site. We give a detailed analysis of the stabi…
Although La(2)Cu(1-x)Li(x)O(4) [Li-LCO] differs from La(2-x)Sr(x)CuO(4) [Sr-LCO] in many ways (e.g., the absence of metallic transport, high-Tc superconductivity, and incommensurate antiferromagnetic correlations), it has been known that certain magnetic properties are remarkably similar. The present work establishes the detailed bulk magnetic phase diagram of Li-LCO (0 <= x <= 0.07), which is found to be nearly identical to that of lightly-doped Sr-LCO, and therefore extends the universality of the phase diagram to hole-doped but nonsuperconducting cuprates.
We present neutron scattering measurements on single crystals of lightly doped $La_{2-x}Ba_{x}CuO_{4}$, with $0 \leq x \leq? 0.035$. These reveal the evolution of the magnetism in this prototypical doped Mott insulator from a three dimensional (3D) commensurate (C) antiferromagnetic ground state, which orders at a relatively high TN, to a two dimensional (2D) incommensurate (IC) ground state with finite ranged static correlations, which appear below a relatively low effective TN. At low temperatures, the 2D IC magnetism co-exists with the 3D C magnetism for doping concentrations as low as ? 0.…
We present a Quantum Monte Carlo study of the Ising model in a transverse field on a square lattice with nearest-neighbor antiferromagnetic exchange interaction J and one diagonal second-neighbor interaction $J'$, interpolating between square-lattice ($J'=0$) and triangular-lattice ($J'=J$) limits. At a transverse-field of $B_x=J$, the disorder-line first introduced by Stephenson, where the correlations go from Neel to incommensurate, meets the zero temperature axis at $J'\approx 0.7 J$. Strong evidence is provided that the incommensurate phase at larger $J'$, at finite temperatures, is a floa…
Using a fermiology approach to the computation of the magnetic susceptibility measured by neutron scattering in hole-doped high-Tc superconductors, we estimate the effects on the incommensurate peaks caused by higher d-wave harmonics of the superconducting order parameter induced by underdoping. The input parameters for the Fermi surface and d-wave gap are taken directly from angle resolved photoemission (ARPES) experiments on Bi{2}Sr{2}CaCu{2}O{8+x} (Bi2212). We find that higher d-wave harmonics lower the momentum dependent spin gap at the incommensurate peaks as measured by the lowest spectr…
In a strongly frustrated square-lattice antiferromagnet with diagonal coupling J', for J/(2J') < 1, an incommensurate spiral state with propagation vector Q = (π+/- δ, π+/- δ) near (π,π) competes closely with the Neel collinear antiferromagnetic ground state. For classical Heisenberg spins the energy of the spiral state can be lowered as it adapts to the distortion of the crystal lattice. As a result, a weak superstructural modulation such as exist in doped cuprates might stabilize an incommensurate spiral phase for some range of the parameter J/(2J') close to 1.
We present spectral and optical properties of the Hubbard model on a two-dimensional square lattice using a generalization of dynamical mean-field theory to magnetic states in finite dimension. The self-energy includes the effect of spin fluctuations and screening of the Coulomb interaction due to particle-particle scattering. At half-filling the quasiparticles reduce the width of the Mott-Hubbard `gap' and have dispersions and spectral weights that agree remarkably well with quantum Monte Carlo and exact diagonalization calculations. Away from half-filling we consider incommensurate magnetic …
Based on the time-dependent Gutzwiller approximation we study the possibility that the diagonal incommensurate spin scattering in strongly underdoped lanthanum cuprates originates from antiferromagnetic domain walls (stripes). Calculation of the dynamic spin response for stripes in the diagonal phase yields the characteristic hour glass dispersion with the crossing of low energy Goldstone and high-energy branches at a characteristic energy Ecross at the antiferromagnetic wave-vector Q_{AF}. The high energy part is close to the parent antiferromagnet. Our results suggest that inelastic neutron …
We study the ground-state properties of weakly frustrated Heisenberg ferrimagnetic chains with nearest and next-nearest neighbor antiferromagnetic exchange interactions and two types of alternating sublattice spins S_1 > S_2, using 1/S spin-wave expansions, density-matrix renormalization group, and exact- diagonalization techniques. It is argued that the zero-point spin fluctuations completely destroy the classical commensurate- incommensurate continuous transition. Instead, the long-range ferrimagnetic state disappears through a discontinuous transition to a singlet state at a larger value of…
Recent experiments on the Co-based $d^7$ honeycomb materials BaCo$_2$(AsO$_4$)$_2$ and BaCo$_2$(PO$_4$)$_2$ have drawn renewed interest to XXZ models with competing interactions beyond the nearest neighbor exchange. While the case of dominant antiferromagnetic exchange has been extensively studied, the actual materials exhibit a ferromagnetic nearest neighbor exchange. Here we show that such a sign change of the dominant nearest neighbor coupling has substantial consequences on the phase diagram. In particular, the nature of the quantum disordered phase of interest changes from a plaquette val…
The bond-dependent Kitaev model on the honeycomb lattice with anyonic excitations has recently attracted considerable attention. However, in solid state materials other spin interactions are present, and among such additional interactions, the off-diagonal symmetric Gamma interaction, another type of bond-dependent term, has been particularly challenging to fully understand. A minimal Kitaev-Gamma (KG) model has been investigated by various numerical techniques under a magnetic field, but definite conclusions about field-induced spin liquids remain elusive and one reason may lie in the limited…
We use the t-J model and Mori projection operator formalism for calculating the magnetic susceptibility of p-type cuprates in the superconducting and pseudogap phases. The lack of extended tails in the peaks of the hole spectral function was shown to provide an incommensurate low-frequency response with hole dispersions derived from photoemission. The theory reproduces the hourglass dispersion of the susceptibility maxima with the upper branch reflecting the dispersion of localized spin excitations and the lower branch being due to incommensurate maxima of their damping. The intensive resonanc…
The dynamical spin structure factor and the Raman response are calculated for structurally dimerized and spin-Peierls chains in a magnetic field, using exact diagonalization techniques. In both cases there is a spin liquid phase composed of interacting singlet dimers at small fields h < h_c1, an incommensurate regime (h_c1 < h < h_c2) in which the modulation of the triplet excitation spectra adapts to the applied field, and a fully spin polarized phase above an upper critical field h_c2. For structurally dimerized chains, the spin gap closes in the incommensurate phase, whereas spin-Peierls ch…
We argue that several empirical constraints strongly restrict parameters of the effective microscopic spin model describing $α$-RuCl$_3$. In particular, such constraints dictate a substantial \emph{positive} off-diagonal anisotropic coupling, $Γ^\prime\!>\!0$, not anticipated previously. The renormalization by quantum fluctuations allows to reconcile larger values of the advocated bare parameters with their earlier assessments and provides a consistent description of the field evolution of spin excitations in the paramagnetic phase. We assert that large anisotropic terms inevitably result in s…
We discuss the rich phase diagram of doped AB2 $t-J$ chains by using data from density matrix renormalization group and exact diagonalization techniques. The $J$ vs $δ$ (hole doping) phase diagram exhibits regions of itinerant ferrimagnetism, incommensurate, resonating valence bond and Nagaoka states, phase separation, and Luttinger liquid (LL) physics. Several features are highlighted, such as the modulated ferrimagnetic structure, the occurrence of Nagaoka spin polarons in the underdoped regime and small values of $J=4t^2/U$, where $t$ is the first-neighbor hopping amplitude and $U$ is the o…
The spin-1/2 chain with isotropic exchange J1, J2 > 0 between first and second neighbors is frustrated for either sign of J1 and has a singlet ground state (GS) for J1/J2 $\ge - 4$. Its rich quantum phase diagram supports gapless, gapped, commensurate (C), incommensurate (IC) and other phases. Critical points J1/J2 are evaluated using exact diagonalization (ED) and density matrix renormalization group (DMRG) calculations. The wave vector $q_G$ of spin correlations is related to GS degeneracy and obtained as the peak of the spin structure factor $S(q)$. Variable $q_G$ indicates IC phases in two…
We study the distribution of electronic spectral weight in a doped antiferromagnet with various types of charge order and compare to angle resolved photoemission experiments on lightly doped La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) and electron doped Nd$_{2-x}$Ce$_x$CuO$_{4\pmδ}$. Calculations on in-phase stripe and bubble phases for the electron doped system are both in good agreement with experiment including in particular the existence of in-gap spectral weight. In addition we find that for in-phase stripes, in contrast to anti-phase stripes, the chemical potential is likely to move with doping. For …
We present macroscopic and neutron diffraction data on multiferroic lightly Co-doped Ni$_3$V$_2$O$_8$. Doping Co into the parent compound suppresses the sequence of four magnetic phase transitions and only two magnetically ordered phases, the paraelectric high temperature incommensurate (HTI) and ferroelectric low temperature incommensurate (LTI), can be observed. Interestingly, the LTI multiferroic phase with a spiral (cycloidal) magnetic structure is stabilized down to at least 1.8 K, which could be revealed by measurements of the electric polarization and confirmed by neutron diffraction on…
The diffusion of vortices down a thermal gradient produces a Josephson signal which is detected as the vortex Nernst effect. In a recent report, Xu et al., Nature 406, 486 (2000), an enhanced Nernst signal identified with vortex-like excitations was observed in a series of La_{2-x}Sr_xCuO_4 (LSCO) crystals at temperatures 50-100 K above T_c. To pin down the onset temperature T_ν of the vortex-like signal in the lightly doped regime (0.03 < x < 0.07), we have re-analyzed in detail the carrier contribution to the Nernst signal. By supplementing new Nernst measurements with thermopower and Hall-a…
We show that the lightly doped La_{2-x}Sr_{x}CuO_{4} can be described in terms of a stripe magnetic structure or soliton picture. The internal relationship between the recent neutron observation of the diagonal (x=0.05) to vertical (x >= 0.06) stripe transition, which was predicted, and the concomitant metal-insulator transition is clarified by this solitonic physics. The phase diagram with the unidentified transition lines between antiferromagnetic to stripe phases, the doping dependence of the modulation period, the origin of the mid-infrared optical absorption are investigated comparatively…
We have generalized the dynamical mean-field theory to study the doping dependence of the crossover from antiferromagnetic to short-range order modelled by an incommensurate spin density wave in the Hubbard model. The local selfenergy which includes spin fluctuations gives quasiparticle weights and spectral properties in good agreement with quantum Monte Carlo and exact diagonalization data in two dimensions. The spectra at finite doping are characterized by a Mott-Hubbard `gap' accompanied by a pseudogap induced by the local spin order.
Charge current static and dynamical correlations are computed by exact diagonalisation methods on a 2-leg t-t'-J ladder which exhibits a sharp transition between a Luther-Emery (LE) phase of hole pairs and a phase with deconfined holes. In the LE phase, we find short-range low-energy incommensurate current fluctuations which are intrinsically connected to the internal charge dynamics within one hole pair. On the contrary, when holes unbind, the maximum of the current susceptibility moves abruptly to the commensurate wavevector $π$ and strongly increases for decreasing doping suggesting an inst…
The magnetic properties of the cobaltite {\BCAO}, a good realization of the quasi two-dimensional frustrated honeycomb-lattice system with strong planar anisotropy, have been reinvestigated by means of spherical neutron polarimetry with CRYOPAD. From accurate measurements of polarization matrices both on elastic and inelastic contributions as a function of the scattering vector {\bf{Q}}, we have been able to determine the low-temperature magnetic structure of {\BCAO} and reveal its puzzling in-plane spin dynamics. Surprisingly, the ground-state structure (described by an incommensurate propaga…
Eclipsing Kitaev: off-diagonal exchange governs the correlated high-field phases of $β$-Li$_2$IrO$_3$
Institute of Science and Technology Austria（奥地利科学技术研究院）；Loughborough University（拉夫堡大学）；University of California, Berkeley（加州大学伯克利分校）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）
We investigate a model of hard-core bosons with infinitely repulsive nearest- and next-nearest-neighbor interactions in one dimension, introduced by Fendley, Sengupta and Sachdev in Phys. Rev. B 69, 075106 (2004). Using a combination of exact diagonalization, tensor network, and quantum Monte Carlo simulations, we show how an intermediate incommensurate phase separates a crystalline and a disordered phase. We base our analysis on a variety of diagnostics, including entanglement measures, fidelity susceptibility, correlation functions, and spectral properties. According to theoretical expectati…
Results for a doped 3-leg t-J ladder obtained using the density matrix renormalization group are reported. At low hole doping, the holes form a dilute gas with a uniform density. The momentum occupation of the odd band shows a sharp decrease at a large value of k_F similar to the behavior of a lightly doped t-J chain, while the even modes appear gapped. The spin-spin correlations decay as a power law consistent with the absence of a spin gap, but the pair field correlations are negligible. At larger doping we find evidence for a spin gap and as x increases further we find 3-hole diagonal domai…
Neutron scattering experiments reveal that a diagonal spin modulation, which is a one-dimensional modulation rotated away by 45$^\circ$ from that in the superconducting phase, occurs universally across the insulating spin-glass phase in La$_{2-x}$Sr$_x$CuO$_4$ (0.02$\le x\le$0.055). This establishes an intimate relation between the magnetism and the transport properties in the high-temperature copper oxide superconductors. Furthermore, it is found that the charge density per unit length estimated using a charge stripe model is almost constant throughout the phase diagram, even when the modulat…
We study the t-t'-t''-J model with parameters chosen to model an electron-doped high temperature superconductor. The model with one, two and four charge carriers is solved on a 32-site lattice using exact diagonalization. Our results demonstrate that at doping levels up to x=0.125 the model possesses robust antiferromagnetic correlation. When doped with one charge carrier, the ground state has momenta (\pmπ,0) and (0,\pmπ). On further doping, charge carriers are unbound and the momentum distribution function can be constructed from that of the single-carrier ground state. The Fermi surface res…
Materials that exhibit both strong spin orbit coupling and electron correlation effects are predicted to host numerous new electronic states. One prominent example is the Jeff =1/2 Mott state in Sr2IrO4, where introducing carriers is predicted to manifest high temperature superconductivity analogous to the S=1/2 Mott state of La2CuO4. While bulk superconductivity currently remains elusive, anomalous quasi-particle behaviors paralleling those in the cuprates such as pseudogap formation and the formation of a d-wave gap are observed upon electron-doping Sr2IrO4. Here we establish a magnetic para…
