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We analyze the interplay between charge-density-wave (CDW) orders with axial momenta (Q,0) and (0,Q) (Δx and Δy, respectively), detected in the underdoped cuprates. The CDW order in real space can be unidirectional (either Δx or Δy is nonzero) or bidirectional (both Δx and Δy are nonzero). To understand which of the two orders develop, we adopt the magnetic scenario, in which the CDW order appears due to spin-fluctuation exchange, and derive the Ginzburg-Landau action to the sixth order in Δx and Δy. We argue that at the mean-field level, the CDW order is bidirectional at the onset, with equal amplitudes of Δx and Δy, but changes to unidirectional inside the CDW phase. This implies that at a given temperature, CDW order is unidirectional at smaller dopings but becomes bidirectional at larger dopings. This is consistent with recent x-ray data on YBa2Cu3Oy, which detected tendency towards bidirectional order at larger dopings. We discuss the role of discrete symmetry breaking at a higher temperature for the interplay between bidirectional and unidirectional CDW orders and also discuss the role of pair-density-wave (PDW) order, which may appear along with CDW. We argue that PDW with the same momentum as CDW changes the structure of the bidirectional charge order by completely replacing either Δx or Δy CDW components by PDW. However, if a so-called Amperean PDW order, which pairs fermions with approximately the same momenta, is also present, both Δx and Δy remain nonzero in the bidirectional phase, albeit with nonequal amplitudes. This is again consistent with x-ray experiments, which at larger doping found nonequal Δx and Δy in every domain. [ABSTRACT FROM AUTHOR]

We analyze the magnetic form factor of Cu2+ in low-dimensional quantum magnets by taking the metal-ligand hybridization into account explicitly. In this analysis, we use the form of magnetic Wannier orbitals, derived from first-principles calculations, and identify contributions of different atomic sites. We demonstrate that covalency of metal-ligand interactions has a strong effect on the magnetic form factor and must be taken into account in the evaluation of magnetic neutron scattering. The use of covalent form factors facilitates quantitative description of inelastic neutron-scattering data for BaCuSi2O6 that would not be possible when ionic form factors are used. We also propose easy-to-use approximations of the partial orbital contributions to the magnetic form factor in order to give microscopic explanation for the results obtained in previous first-principles studies. [ABSTRACT FROM AUTHOR]

Using the Ong construction for a two-dimensional metal, we show that the sign change in the Hall coefficient Rh ot underdoped hole-doped cuprates at low temperature is consistent with the emergence of biaxial charge order recently proposed to explain the observation of low-frequency quantum oscillations. The sharp evolution of RH with temperature, however, can only be reconciled by incorporating a highly anisotropic quasiparticle scattering rate. The magnitude and form of the scattering rate extracted from the fitting imply that those quasiparticles at the vertices of the reconstructed pocket(s) approach the boundary of incoherence at the onset of charge order. [ABSTRACT FROM AUTHOR]

While both the hole and electron doped cuprates can exhibit dx2-y2-wave superconductivity, the local distribution of the doped carriers is known to be significantly different with the doped holes going primarily on the O sites while the doped electrons go on the Cu sites. Here we report the results of density matrix renormalization calculations for a three-orbital model of a CuO2 lattice. In addition to the asymmetric dependence of the intra-unit-cell occupation of the Cu and O for hole and electron doping, we find important differences in the longer range spin and charge correlations. As expected, the pair-field response has a dx2-y2-like structure for both the hole and electron doped systems. [ABSTRACT FROM AUTHOR]

We have performed an angle-resolved photoemission study of the nodal quasiparticle spectra of the high-Tc cuprate trilayer Bi2Sr2Ca2Cu3O10+δ (Tc ~ 110 K). The spectral weight Z of the nodal quasiparticle increases with decreasing temperature across Tc. Such a temperature dependence is qualitatively similar to that of the coherence peak intensity in the antinodal region of various high-Tc cuprates, although the nodal spectral weight remains finite and large above Tc. We attribute this observation to the reduction of electron correlation strength in going from the normal metallic state to the superconducting state, a characteristic behavior of a superconductor with strong electron correlation. [ABSTRACT FROM AUTHOR]

Recently, several groups have reported observations of collective modes of the charge order present in underdoped cuprates. Motivated by these experiments, we study theoretically the oscillations of the order parameters, both in the case of pure charge order and for charge order coexisting with superconductivity. Using a hot-spot approximation we find in the coexistence regime two Higgs modes arising from hybridization of the amplitude oscillations of the different order parameters. One of them has a minimum frequency that is within the single-particle energy gap and which is a nonmonotonic function of temperature. The other--high-frequency--mode is smoothly connected to the Higgs mode in the single-order-parameter region, but quickly becomes overdamped in the case of coexistence. We explore an unusual low-energy damping channel for the collective modes, which relies on the band reconstruction caused by the coexistence of the two orders. For completeness, we also consider the damping of the collective modes originating from the nodal quasiparticles. At the end we discuss some experimental consequences of our results. [ABSTRACT FROM AUTHOR]

We demonstrate that the zero-temperature superconducting phase diagram of underdoped cuprates can be quantitatively understood in the strong binding limit, using only the experimental spectral function of the "normal" pseudogap phase without any free parameter. In the prototypical (La1-xSrx)2CuO4, a kinetics-driven d-wave superconductivity is obtained above the critical doping δc ~ 5.2%, below which complete loss of superfluidity results from local quantum fluctuation involving local p-wave pairs. Near the critical doping, an enormous mass enhancement of the local pairs is found responsible for the observed rapid decrease of phase stiffness. Finally, a striking mass divergence is predicted at δc that dictates the occurrence of the observed quantum critical point and the abrupt suppression of the Nemst effects in the nearby region. [ABSTRACT FROM AUTHOR]

We study the Josephson effect of d-wave superconductor (DS)/ferromagnet insulator (FI)/DS junctions on a surface of topological insulator (TI), We calculate Josephson current I (φ) for various orientations of the junctions where φ is the macroscopic phase difference between two DSs. In certain configurations, we find anomalous current-phase relation I(φ) = - I (-φ + π) with 2π periodicity. In the case where the first-order Josephson coupling is absent without magnetization in FI, I(φ) can be proportional to cosφ. In symmetric junctions, the magnitude of the obtained Josephson current is enhanced due to the zero-energy states on the edge of DS on TI. Even if we introduce an s-wave component of pair potential in DS, we can still expect the anomalous current-phase relation in asymmetric DS junctions with I(φ = 0) ≠ 0. This can be used to probe the induced d-wave component of pair potential on a TI surface in high-Tc cuprate/TI hybrid structures. [ABSTRACT FROM AUTHOR]

Quasiparticle tunnel current either between identical d-wave superconductors partially gapped by charge density waves (SCDWs) or between an SCDW and a normal metal was calculated. The cases of unidirectional and checkerboard CDWs were considered. The tunnel conductance was found in both cases to possess a number of peculiarities, which cannot be described by introducing a single combined gap. The results are in qualitative agreement with experimental data obtained for a number of cuprates by the scanning tunnel spectroscopy, intrinsic-tunneling, and break-junction measurements. The difference between the experiment and the theory seems to stem from the spread of gap values occurring due to the intrinsic spatial inhomogeneity of nonstoichiometric oxides and reflected in the cuprate tunnel spectra. [ABSTRACT FROM AUTHOR]

How does Fermi surface develop upon doping of cuprates, does it consist of large barrels or small pockets, which of them is responsible for superconductivity, and what is a role of the pseudogap? Those are actively debated questions, important for understanding of high temperature superconductivity. We study doping dependence of intrinsic tunneling in Bi2Sr2Ca1-xYxCu208+δ cuprates, which allows independent analysis of Cooper pair and quasiparticle transport. We observe that with decreasing doping the supercurrent is rapidly decreasing at a rate much faster than the doping level, but the quasiparticle resistance at a sufficiently high bias remains almost doping independent. This remarkable discrepancy indicates that Cooper pairs and quasiparticles are originating from different parts of the Brillouin zone: Cooper pairs are residing on small pockets, which are progressively shrinking with decreasing doping, but the majority of the quasiparticle current is integrated over large barrels, which are only weakly doping dependent. The expanding pseudogap areas along the barrels do not contribute to pair current. This provides direct evidence for nonsuperconducting origin of the pseudogap. We present numerical calculations, taking into account Fermi surface topology, that support our conclusions. [ABSTRACT FROM AUTHOR]

We report Raman scattering measurements on Bi2Sr2CaCu2O8+δ single crystals with a different degree of out-of-plane disorder to examine the effect of Tc change on the the electronic Raman response at the optimal doping level. The Blg peak energies for lower Tc disordered samples are essentially independent of Tc. However, a further increase of Tc by minimizing the degree of out-of-plane disorder leads to a high-energy shift of the B1g peak. Interestingly, abrupt change of the B1g peak energy occurs when the the superconducting gap energy exceeds the pseudogap energy, which results in the recovery of superconductivity-dominated Raman response in B1g symmetry. It suggests that these anomalous properties of the antinodal electrons are a consequence of the unconventional superconducting state of the cuprates where superconductivity coexists with the pseudogap in the ground state. [ABSTRACT FROM AUTHOR]

Recent experiments in the cuprates have seen evidence of a transient superconducting state upon optical excitation polarized along thee axis [R. Mankowsky et al., Nature (London) 516, 71 (2014)]. Motivated by these experiments, we propose an extension of the single-layer t - J - V model of cuprates to three dimensions in order to study the effects of interplane tunneling on the competition between superconductivity and bond density wave order. We find that an optical pump can suppress the charge order and simultaneously enhance superconductivity, due to the inherent competition between the two. We also provide an intuitive picture of the physical mechanism underlying this effect. Furthermore, based on a simple Floquet theory, we estimate the magnitude of the enhancement. [ABSTRACT FROM AUTHOR]

Motivated by the earlier experimental results and ab initio studies on the electronic structure of layered ruthenates (Sr2RuO4 and Ca2RuO4) we introduce and investigate the multiband d-p charge transfer model describing a single RuO4 layer, similar to the charge transfer model for a single CuO2 plane including apical oxygen orbitals in high Tc cuprates. The present model takes into account nearest-neighbor anisotropic ruthenium-oxygen d-p and oxygen-oxygen p-p hopping elements, crystal-field splittings, and spin-orbit coupling. The intraorbital Coulomb repulsion and Hund's exchange are defined not only at ruthenium but also at oxygen ions. Our results demonstrate that the RuO4 layer cannot be regarded to be a pure ruthenium t2g system. We examine a different scenario in which ruthenium eg orbitals are partly occupied and highlight the significance of oxygen orbitals. We point out that the predictions of an idealized model based on ionic configuration (with n0=4+4×6=28 electrons per RuO4 unit) do not agree with the experimental facts for Sr2RuO4 which support our finding that the electron number in the d-p states is significantly smaller. In fact, we find the electron occupation of d and p orbitals for a single RuO4 unit n=28-x, being smaller by at least 1-1.5 electrons from that in the ionic model and corresponding to self-doping with x≃1.5. [ABSTRACT FROM AUTHOR]

We show that the anomalous temperature scaling of five distinct transport quantities in the strange metal regime of the cuprate superconductors can be reproduced with only two nontrivial critical exponents. The quantities are (i) the electrical resistivity, (ii) the Hall angle, (iii) the Hall-Lorenz ratio, (iv) the magnetoresistance, and (v) the thermopower. The exponents are the dynamical critical exponent z = 4/3 and an anomalous scaling dimension Φ = -2/3 for the charge density operator. [ABSTRACT FROM AUTHOR]

Recent experiments have addressed the nature of the charge order seen in underdoped cuprates. Here I show that x-ray absorption and linear dichroism are excellent probes of such order. Ab initio calculations reveal that a d-wave charge density wave order involving the oxygen ions is a much better description of the data than alternate models. [ABSTRACT FROM AUTHOR]

We revisit the problem of electrons on a square lattice below half-filling close to an Ising-nematic quantum critical point. For Fermi surfaces with sufficiently strong antinodal nesting, the static nematic susceptibility is maximal at the antinodal nesting wave vector within a simple random phase approximation calculation. We present a detailed analysis of the nematic susceptibility within Eliashberg theory and show that the strong interaction between fermions in the antinodal regions shifts the maximum of the nematic susceptibility to slightly larger wave vectors. The corresponding order is akin to the incommensurate charge-density wave with d-wave form factor found recently in some underdoped cuprate materials. At sufficiently high temperatures around T/t ~ 0.1, nematic fluctuations are strongest at zero wave vector. [ABSTRACT FROM AUTHOR]

We examine trends in the wave vectors and form factors of charge density wave instabilities of three-band models of the underdoped cuprates. For instabilities from a high-temperature state with a large Fermi surface, we extend a study by Bulut et al. [Phys. Rev. B 88, 155132 (2013)] to include a direct antiferromagnetic exchange coupling between the Cu sites. As in previous work, we invariably find that the primary instability has a diagonal wave vector (±Q0, ±Q0) and a d-form factor. The experimentally observed wave vectors along the principal axes (±g0,0), (0, ±Q0) have higher energy, but they also have a predominantly d-form factor. Next, we gap out the Fermi surface in the antinodal regions of the Brillouin zone by including static, long-range antiferromagnetic order at the wave vector (π,π): this is a simple model of the pseudogap in which we assume the antiferromagnetic order averages to zero by "renormalized classical" thermal fluctuations in its orientation, valid when the antiferromagnetic correlation length is large. The charge density wave instabilities of this pseudogap state are found to have the optimal wave vector (±Q0,0), (0, ±Q0), with the magnitude of the d-form factor decreasing with increasing magnetic order. [ABSTRACT FROM AUTHOR]

We analyze a candidate theory for the strange metal near optimal hole doping in the cuprate superconductors. The theory contains a quantum phase transition between metals with large and small Fermi surfaces of spinless fermions carrying the electromagnetic charge of the electron, but the transition does not directly involve any broken global symmetries. The two metals have emergent SU(2) and U(1) gauge fields respectively, and the transition is driven by the condensation of a real Higgs field, carrying a finite lattice momentum and an adjoint SU(2) gauge charge. This Higgs field measures the local antiferromagnetic correlations in a "rotating reference frame." We propose a global phase diagram around this Higgs transition, and describe its relationship to a variety of recent experiments on the cuprate superconductors. [ABSTRACT FROM AUTHOR]

We analyze the interplay between charge-density-wave (CDW) and pair-density-wave (PDW) orders within the spin-fermion model for the cuprates. We specifically consider CDW order with transferred momenta (±Q,0)/(0,±Q), as seen in experiments on the cuprates, and PDW order with total momenta (0,±Q)/(±Q,0). Both orders have been proposed to explain the pseudogap phase in the cuprates. We show that both emerge in the spin-fermion model near the onset of antiferromagnetism. Each order parameter is constructed out of pairs of fermions in "hot" regions on the Fermi surface, breaks U(1) translational symmetry, and changes sign when the momenta of the fermions change by (π,π). We further show that the two orders are nearly degenerate due to an approximate SU(2) particle-hole symmetry of the model. This near degeneracy is similar in origin to that relating conventional d -wave superconducting order and bond charge order with momentum (Q,±Q). The SU(2) symmetry becomes exact if one neglects the curvature of the Fermi surface in hot regions, in which case U(1), CDW, and PDW order parameters become components of an SO (4) -symmetric PDW/CDW "supervector." We develop a Ginzburg-Landau theory for four PDW/CDW order parameters and find two possible ground states: a "stripe" state in which both CDW and PDW orders develop with either (±Q,0) or (0,±Q), and a "checkerboard" state, where each order can develop with (±Q,0) and (0,±Q). We show that the SO (4) symmetry between CDW and PDW can be broken by two separate effects. One is the inclusion of Fermi surface curvature, which selects a PDW order immediately below the instability temperature. Another is the overlap between different hot regions, which favors CDW order at low temperatures. For the stripe state, we show that the competition between the two effects gives rise to a first-order transition from PDW to CDW inside the ordered state. We also argue that beyond mean-field theory, the onset temperature for CDW order is additionally enhanced due to feedback from a preemptive breaking of Z2 time-reversal symmetry. We discuss the ground-state properties of a pure PDW state and a pure CDW state, and show in particular that the PDW checkerboard state yields a vortex-antivortex lattice. For the checkerboard state, we considered a situation when both CDW and PDW orders are present at low T and show that at small but finite Fermi surface curvature the presence of both condensates induces a long sought chiral s + idxy superconductivity. [ABSTRACT FROM AUTHOR]

We analyze the Hall conductivity σxy(ω) of a charge ordered state with momentum Q = (0,2 Q) and calculate the intrinsic contribution to the Ken' angle ΘK using the fully reconstructed tight-binding band structure for layered cuprates beyond the low energy hot spot model and particle-hole symmetry. We show that such a unidirectional charge density wave (CDW), which breaks time-reversal symmetry, as recently put forward by Wang and Chubukov [Phys. Rev, B 90, 035149 (2014)], leads to a nonzero polar Kerr effect, as observed experimentally. In addition, we model a fluctuating CDW via a large quasiparticle damping of the order of the CDW gap and discuss possible implications for the pseudogap phase. We can qualitatively reproduce previous measurements of underdoped cuprates, but making quantitative connections to experiments is hampered by the sensitivity of the polar Kerr effect with respect to the complex refractive index n(ω). [ABSTRACT FROM AUTHOR]

We study bond order parameters for generalized t-J models on a square lattice. Using the plane-wave limit the considered order parameters form basis functions for irreducible representations of the symmetry transformations of the point group and of time reversal. We show that, for instability wave vectors along the diagonals, all possible basis functions either are fine tuned (i.e., obey restrictions beyond the requirements of symmetry) or break time-reversal symmetry and thus describe flux states. For instability wave vectors along the crystalline axes, corresponding to the observed case in underdoped cuprates, there are only three representations with At, Bi, and E symmetry which do not break time-reversal symmetry in the general case. We suggest that one of them has recently been observed in resonant elastic x-ray scattering. [ABSTRACT FROM AUTHOR]

We investigate the ground-state wave function of a prototypical strongly correlated system, a three-band (p-d) Hubbard model of cuprates, using full configuration interaction quantum Monte Carlo. We show that the configuration interaction description of the exact ground state wave function is profoundly affected by the choice of single-particle representation, in a counterintuitive manner. Thus a broken-symmetry unrestricted Hartree-Fock basis, which at a single configuration level produces a qualitatively correct description of the antiferromagnet, results in a highly entangled exact solution consisting of high particle-hole excitations of the reference. This wave function is found to be very difficult to approximate using subspace diagonalizations. Conversely, a restricted Hartree-Fock basis, which yields at a single configuration level a qualitatively incorrect paramagnetic metal, results in a relatively rapidly converging configuration interaction expansion. Convergence can be further accelerated by adopting a natural orbital representation. Our results suggest that with the correct single-particle basis, such strongly correlated systems may be described by relatively compact wave functions. [ABSTRACT FROM AUTHOR]

Kinetic properties of a two-dimensional model of fermions interacting with antiferromagnetic spin excitations near the quantum critical point are considered. The temperature or doping are assumed to be sufficiently high, such that the pseudogap does not appear. In contrast to standard spin-fermion models, it is assumed that there are intrinsic inhomogeneities in the system suppressing space correlations of the antiferromagnetic excitations. It is argued that the inhomogeneities in the spin excitations in the "strange metal" phase can be a consequence of the existence of "π -shifted" domain walls in the doped antiferromagnetic phase. Averaging over the inhomogeneities and calculating physical quantities such as resistivity and some others one can explain unusual properties of cuprates unified under the name "marginal Fermi liquid." The dependence of the slope of the linear temperature dependence of the resistivity on doping is compared with experimental data. [ABSTRACT FROM AUTHOR]

We theoretically analyse the process of charge recombination in the planar Mott-Hubbard insulators with the aim to explain short picosecond-range lifetime of photoexcited carriers, experimentally studied via pump-probe experiments on the undoped cuprates. The recombination mechanism consists of two essential ingredients: the formation of a metastable s-type bound holon-doublon pair, i.e. the Mott exciton, and the decay of such an excitonic state via the multimagnon emission. In spite of the large gap that requires many bosons to be emitted, latter process is fast due to large exchange scale and strong charge-spin coupling in planar systems. As the starting microscopic model we consider the single-band Hubbard model, and then more realistic three-band model for cuprates, both leading to the same minimal one. The decay rate of the exciton is evaluated numerically via the Fermi golden rule, having consistency also with the direct time-evolution calculation. The decay rate reveals exponential dependence on the ratio of the Mott-Hubbard gap and the exchange coupling - the result qualitatively reproduced also within a toy exciton-boson model. [ABSTRACT FROM AUTHOR]

There is a multiplicity of charge-ordered, pairing-based, or pair density wave theories of the cuprate pseudogap, albeit arising from different microscopic mechanisms. For mean-field schemes (of which there are many) we demonstrate here that they have precise implications for two-body physics in the same way that they are able to address the one-body physics of photoemission spectroscopy. This follows because the full vertex can be obtained exactly from the Ward-Takahashi identity. As an illustration, we present the spin response functions, finding that a recently proposed pair density wave (Amperean pairing) scheme is readily distinguishable from other related scenarios. [ABSTRACT FROM AUTHOR]

The emergence of carrier pairing from the electronically inhomogeneous phase of lightly hole-doped copper oxides has been investigated through magnetoresistance measurements on 1222-type ruthenocuprates RuSr2(R,Ce)2Cu2O10-δ, principally with R = Gd, Sm, Nd. A well-defined transition at which superconducting fluctuations emerge is discovered at a remarkably low critical doping, pc = 0.0084, deep within the antiferromagnetic phase. Systematic variations of the low-temperature fluctuation density with doping and cell volume demonstrate the intrinsic nature of the electronic inhomogeneity and provide new support for bosonic models of the superconducting mechanism. [ABSTRACT FROM AUTHOR]

The cuprate high temperature superconductors exhibit a pronounced trend in which the superconducting transition temperature Tc increases with the number of CuC2planes n in the crystal structure. We compare the magnetic excitation spectrum of Bi2+xSr2-xCuO6+δ (Bi-2201) and Bi2Sr2Ca2CuO10+δ (Bi-2223), with n = 1 and 3, respectively, using Cu L3-edge resonant inelastic x-ray scattering. Near the antinodal zone boundary we find the paramagnon energy in Bi-2223 is substantially higher than that in Bi-2201, indicating that multilayer cuprates host stronger effective magnetic exchange interactions, providing a possible explanation for the Tc vs n scaling. In contrast, the nodal direction exhibits very strongly damped, almost nondispersive excitations. We argue that this implies that the magnetism in the doped cuprates is partially itinerant in nature. [ABSTRACT FROM AUTHOR]

Where the doped holes reside in cuprate superconductors has crucial implications for the understanding of the mechanism responsible for their high-temperature superconductivity. It has been generally assumed that doped holes reside in hybridized Cu dx2- y2 -O pσ orbitals in the CuO2 planes, based on results of density functional band-structure calculations. Instead, we propose that doped holes in the cuprates reside in O pπ orbitals in the plane, perpendicular to the Cu-O bond, that are raised to the Fermi energy through local orbital relaxation, that is not taken into account in band-structure calculations that place the bands associated with these orbitals well below the Fermi energy. We use a dynamic Hubbard model to incorporate the orbital relaxation degree of freedom and find in exact diagonalization of a small Cu4O4 cluster that holes will go to the O pπ orbitals for relaxation energies comparable to what is expected from atomic properties of oxygen anions. The bandwidth of this band becomes significantly smaller than predicted by band-structure calculations due to the orbital relaxation effect. Within the theory of hole superconductivity the heavy hole carriers in this almost full band will pair and drive the system superconducting through lowering of their [ABSTRACT FROM AUTHOR]

Motivated by recent experimental evidence of charge order in the pseudogap phase of cuprates, we perform a variational analysis of spin-singlet density wave ordering in metals with antiferromagnetic interactions on the square lattice, using a wave function with double occupancy projected out. We examine ordering with and without time-reversal symmetry, with an arbitrary wave vector and a tunable form factor. Depending on parameters, we find d-form factor density wave ordering, with a wave vector either parallel to the lattice generators or diagonally oriented, or a ground state which carries a time-reversal breaking pattern of spontaneous currents. [ABSTRACT FROM AUTHOR]

We investigate the pressure and temperature dependence of the lattice dynamics of the underdoped, stoichiometric, high-temperature superconductor YBa2Cu4O8 by means of Raman spectroscopy and ab initio calculations. This system undergoes a reversible pressure-induced structural phase transition around 10 GPa to a collapsed orthorhombic structure that is well reproduced by the calculation. The coupling of the B1g-like buckling phonon mode to the electronic continuum is used to probe superconductivity. In the low pressure phase, self-energy effects through the superconducting transition renormalize this phonon, and the amplitude of this renormalization strongly increases with pressure. Whereas our calculation indicates that this mode's coupling to the electronic system is only marginally affected by the structural phase transition, the aforementioned renormalization is completely suppressed in the high pressure phase, demonstrating that under hydrostatic pressures higher than 10 GPa, superconductivity in YBa2Cu4O8 is greatly weakened or obliterated. [ABSTRACT FROM AUTHOR]

The strongly correlated cuprate Cu2OSeO3 has been recently identified as the first insulating system exhibiting a skyrmion lattice phase. Using a microscopic multiboson theory for its magnetic ground state and excitations, we establish the presence of two distinct types of modes: a low-energy manifold that includes a gapless Goldstone mode and a set of weakly dispersive high-energy magnons. These spectral features are the most direct signatures of the fact that the essential magnetic building blocks of Cu2OSeO3 are not individual Cu spins, but rather weakly coupled Cu4 tetrahedra. Several of the calculated excitation energies are in excellent agreement with terahertz electron spin resonance, Raman, and far-infrared experiments, while the magnetoelectric effect determined within the present quantum-mechanical framework is alsofully consistent with experiments, giving strong evidence in the entangled Cu4 tetrahedra picture of Cu2OSeO3. The predicted energy and momentum dependence of the dipole and quadrupole spin structure factors call for further experimental tests of this picture. [ABSTRACT FROM AUTHOR]

Metals interacting via short-range antiferromagnetic fluctuations are unstable to sign-changing superconductivity at low temperatures. For the cuprates, this leading instability leads to the well-known d-wave superconducting state. However, there is also a secondary instability to an incommensurate charge-density wave, with a predominantly d-wave form factor, arising from the same antiferromagnetic fluctuations. Recent experiments in the pseudogap regime of the hole-doped cuprates have found strong evidence for such a charge-density wave order and, in particular, the predicted d-wave form factor. However, the observed wave vector of the charge order differs from the leading instability in Hartree-Fock theory, and is that of a subleading instability. In this paper, we examine the feedback of superconducting fluctuations on these different charge-density wave states, and find that over at least a small temperature window, they prefer the experimentally observed wave vector. [ABSTRACT FROM AUTHOR]

Motivated by recent observations of charge order in the pseudogap regime of hole-doped cuprates, we show that crisscrossed stripe order can be stabilized by coherent, momentum-dependent interlayer tunneling, which is known to be present in several cuprate materials. We further describe how subtle variations in the couplings between layers can lead to a variety of stripe ordering arrangements, and discuss the implications of our results for recent experiments in underdoped cuprates. [ABSTRACT FROM AUTHOR]

We report the observation of a bulk charge modulation in La1.88Sr0.12CuO4 (LSCO) with a characteristic in-plane wave vector of (0.236, ±δ), with δ = 0.011 r.l.u. The transverse shift of the ordering wave vector indicates the presence of rotated charge-stripe ordering, demonstrating that the charge ordering is not pinned to the Cu-O bond direction. On cooling through the superconducting transition, we find an abrupt change in the growth of the charge correlations and a suppression of the charge order parameter indicating competition between the two orderings. Orthorhombic LSCO thus helps bridge the apparent disparities between the behavior previously observed in the tetragonal "214" cuprates and the orthorhombic yttrium and bismuth-based cuprates and thus lends strong support to the idea that there is a common motif to charge order in all cuprate families. [ABSTRACT FROM AUTHOR]

Essential to understanding the cuprate pseudogap phase is a study of the charge (and spin) response functions, which we address here via a consistent approach to the Fermi arcs and the Fermi pockets scenario of Yang, Rice, and Zhang (YRZ). The two schemes are demonstrated to be formally similar, and to share a common physics platform; we use this consolidation to address the inclusion of vertex corrections which have been omitted in YRZ applications. We show vertex corrections can be easily implemented in a fashion analytically consistent with sum rules and that they yield important contributions to most observables. A study of the charge ordering susceptibility of the YRZ scenario makes their simple physics evident: They represent the inclusion of charged bosonic, spin singlet degrees of freedom, and are found to lead to a double peak structure. [ABSTRACT FROM AUTHOR]

We report systematic 17O-NMR measurements on the high-7) cuprate (CaxLa1-x)(Ba1.75La0.25+x)Cu3Oy, for four different families (different x). Using Knight shift data, we show that the pseudogap opening temperature T* is much higher than Tc near optimal doping, unlike structurally similar YBCO. In addition, at constant doping the pseudogap temperature does not vary with x, in contrast to Tc. This puts constraints on the nature of the pseudogap and position of the quantum critical point inside the superconducting dome. [ABSTRACT FROM AUTHOR]

We study the Ginzburg-Landau free energy functional for two coupled U(1) charge order parameters describing two nonequivalent charge orders with wave vector Q detected in x-ray and STM measurements of underdoped cuprates. We do not rely on a mean-field analysis, but rather utilize a field-theoretical technique suitable to study the interplay between vortex physics and discrete symmetry breaking in two-dimensional systems with U(1) symmetry. Our calculations support the idea that in the clean systems there are two transitions: from a high-temperature disordered state into a state with a composite charge order which breaks time-reversal symmetry, but leaves U( 1) fields disordered, and then into a state with quasi-long-range order in the U( 1) fields. [ABSTRACT FROM AUTHOR]

We report 63Cu nuclear magnetic resonance and muon spin rotation measurements on the S = 1 / 2 antiferromagnetic Heisenberg spin chain compound Sr1.9Ca0.1CuO3. An exponentially decreasing spin-lattice relaxation rate T 1-1 indicates the opening of a spin gap. This behavior is very similar to what has been observed for the cognate zigzag spin chain compound Sr0.9Ca0.1CuO2, and it confirms that the occurrence of a spin gap upon Ca doping is independent of the interchain exchange coupling J'. Our results therefore suggest that the appearance of a spin gap in an antiferromagnetic Heisenberg spin chain is induced by a local bond disorder of the intrachain exchange coupling J . A low-temperature upturn of T 1-1 evidences growing magnetic correlations. However, zero-field muon spin rotation measurements down to 1.5 K confirm the absence of magnetic order in this compound, which is most likely suppressed by the opening of the spin gap. [ABSTRACT FROM AUTHOR]

The Meissner effect has been directly demonstrated by depth-resolved muon spin rotation measurements in high-quality thin films of the T'-structured cuprate, T'-La1.9Y0.1CuO4, to confirm bulk superconductivity (Tc ≃ 21 K) in its undoped state. The gradual expelling of an external magnetic field is observed over a depth range of ∼ 100 nm in films with a thickness of 275(15) nm, from which the penetration depth is deduced to be 466(22) nm. Based on this result, we argue that the true ground state of the "parent" compound of the n-type cuprates is not a Mott insulator but a strongly correlated metal with colossal sensitivity to apical oxygen impurities. [ABSTRACT FROM AUTHOR]

The dressing of quasiparticles in solids is investigated by changes in the electronic structure E(k) driven by femtosecond laser pulses. Employing time- and angle-resolved photoemission on an optimally doped cuprate above Tc, we observe two effects with different characteristic temporal evolutions and, therefore, different microscopic origins. First, a marked change in the effective mass due to the 70-meV kink in E(k) is found to occur during the experiment's 100-fs temporal resolution and is assigned to laser-driven perturbation of an electronic interaction dressing the bare band. Second, a change in kF is explained by effective photodoping due to particle-hole asymmetry and offers opportunities for ultrafast optoelectronic switches based on an optically driven insulator-superconductor transition. [ABSTRACT FROM AUTHOR]

Chemical substitution, combined with strain, allows the charge-transfer energy in hole-doped cuprates to be broadly tuned. We theoretically characterize the structural and electronic properties of the family of compounds R2CuO2S2, constructed by sulfur replacement of the apical oxygens and rare-earth substitutions in the parent cuprate La2CuO4. Additionally, the enthalpies of formation for possible synthesis pathways are determined. [ABSTRACT FROM AUTHOR]

A computation of the cuprate phase diagram is presented. Adiabatic deformability back to the density function band structure plus symmetry constraints lead to a Fermi liquid theory with five interaction parameters. Two of these are forced to zero by experiment. The remaining three are fit to the moment of the antiferromagnetic state at half-filling, the superconducting gap at optimal doping, and the maximum pseudogap. The latter is identified as orbital antiferromagnetism. Solution of the Hartree-Fock equations gives, in quantitative agreement with experiment, (1) quantum phase transitions at 5% and 16% p-type doping, (2) insulation below 5%, (3) a rf-wave pseudogap quasiparticle spectrum, (4) pseudogap and superconducting gap values as a function of doping, (5) superconducting Tc versus doping, (6) London penetration depth versus doping, and (7) spin wave velocity. The fit points to superexchange mediated by the bonding O atom in the Cu-O plane as the causative agent of all three ordering phenomena. [ABSTRACT FROM AUTHOR]

We use time- and angle-resolved photoemission to measure the nodal nonequilibrium electronic states in various dopings of Bi2Sr2CaCu2O8+8. We find that the initial pump-induced transient signal of these ungapped states is strongly affected by the onset of the superconducting gap at Tc, superconducting pairing fluctuations at Tp, and the pseudogap at T". Moreover, Tp marks a suggestive threshold in the fluence-dependent transient signal, with the appearance of a critical fluence below Tp that corresponds to the energy required to break apart all Cooper pairs. These results challenge the notion of a nodal-antinodal dichotomy in cuprate superconductors by establishing a link between nodal quasiparticles and the cuprate phase diagram. [ABSTRACT FROM AUTHOR]

We propose that the nonequilibrium current measured in the a-b plane of an underdoped cuprate (in either the strange metal or pseudogap regime) in contact with either an overdoped cuprate or a standard Fermi liquid can be used to diagnose how different the pseudogap and strange metals are from a Fermi liquid. Naively, one expects the strange metal to be more different from a Fermi liquid than the pseudogap is. We compute the expected nonequilibrium transport signal with the three Green's functions that are available in the literature: (1) marginal Fermi-liquid theory, (2) the phenomenological ansatz for the pseudogap regime, and (3) the Wilsonian reduction of the Hubbard model which contains both the strange metal and pseudogap. All three give linear 7-V curves at low bias voltages. Significant deviations from linearity at higher voltages obtain only in the marginal Fermi-liquid approach. The key finding, however, is that I-V curves for the strange metal/Fermi-liquid contact exceed that of the pseudogap/Fermi-l iquid system. If this is borne out experimentally, this implies that the strange metal is less orthogonal to a Fermi liquid than the pseudogap is. Within the Wilsonian reduction of the Hubbard model, this result is explained in terms of a composite-particle picture. Namely, the pseudogap corresponds to a confinement transition of the charge degrees of freedom present in the strange metal. In the strange metal the composite excitations break up and electron quasiparticles scatter off bosons. The bosons here, however, do not arise from phonons but from the charge degrees of freedom responsible for dynamical spectral weight transfer. [ABSTRACT FROM AUTHOR]

We present measurements of the microwave surface impedance of the single-layer cuprate TI2Ba2CuO6+δ, deep in the overdoped regime, with Tc ≈25 K. Measurements have been made using cavity perturbation of a dielectric resonator at 17 discrete frequencies ranging from 2.50 to 19.16 GHz, and at temperatures from 0.12 to 27.5 K. From the surface impedance we obtain the microwave conductivity, penetration depth, and superfluid density. The superfluid density displays a strong linear temperature dependence from 2 to 14 K, indicative of line nodes in the energy gap. The microwave data are compared with theoretical predictions for a d-wave superconductor with pointlike impurities, with the conclusion that disorder in TI2Ba2CuO6+δ acts predominantly in the weak-to-intermediate-strength scattering regime, and that small-angle scattering is important. [ABSTRACT FROM AUTHOR]

We present in-plane infrared reflectance measurement on two superconducting cuprates with relatively low Tc: nearly optimally doped Bi2Sr1.6La0.4CuO6+δ with Tc = 33 K and underdoped La1.89Sr0.11CuO4 with Tc = 30 K. The measurement clearly reveals that the superconducting energy gap is distinct from the pseudogap. They have different energy scales and appear at different temperatures. The results suggest that the pseudogap is not a precursor to the superconducting state. The data also challenge the longstanding and predominant viewpoint that the superconductivity within the ab plane is in the clean limit and the superconducting pairing energy gap could not be detected by in-plane infrared spectroscopy. [ABSTRACT FROM AUTHOR]

We report the results of a muon spin rotation (μSR) study of the bulk of Bi2+xSr2-xCaCu2O8+δ, as well as pure and Ca-doped YBa2Cu3Oy, which together with prior measurements reveal a universal inhomogeneous magnetic-field response of hole-doped cuprates extending to temperatures far above the critical temperature Tc. The primary features of our data are incompatible with the spatially inhomogeneous response being dominated by known charge-density-wave and spin-density-wave orders. Instead, the normal-state inhomogeneous line broadening is found to scale with the maximum value Tcmax for each cuprate family, indicating it is controlled by the same energy scale as Tc. Since the degree of chemical disorder varies widely among the cuprates we have measured, the observed scaling constitutes evidence for an intrinsic electronic tendency toward inhomogeneity above Tc. [ABSTRACT FROM AUTHOR]

The Fermi-liquid-like (FL) resistivity recently observed in clean Hg1201 below the pseudogap temperature was related to carriers at the nodal points on the Fermi surface (FS) (N. Barišić et al., arXiv: 1207.1504, doi: 10.1073/pnas. 13019891109). We show that this has important implications for the electronic spectrum of underdoped (UD) cuprates as a whole. Photoemission experiments (angle-resolved photoemission spectroscopy) in other cuprates picture the spectrum as "metallic arcs" separated from each other by regions with large energy gaps. We rigorously solve the kinetic equation in such a model. The Fermi arcs' carriers contribute to the FL resistivity, if scattering between the opposite nodal points admits the umldapp processes. The Hall coefficient defines the effective number of carriers on the arcs and at weak magnetic fields it has a positive sign. All parameters that determine the arcs' widths are measurable experimentally. We conclude that the T² resistivity gives support to the Fermi arcs' concept and argue that the idea of a reconstructed FS in UD cuprates is not consistent with the latter. [ABSTRACT FROM AUTHOR]

We revisit the problem of spin-mediated superconducting pairing at the antiferromagnetic quantum-critical point with the ordering momentum (π,π) = 2kF. The problem has been previously considered by one of the authors [P. Krotkov and A. V. Chubukov, Phys. Rev. Lett. 96, 107002 (2006); Phys. Rev. B 74, 014509 (2006)]. However, it was later pointed out [D. Bergeron et al., Phys. Rev. B 86, 155123 (2012)] that the analysis neglected umklapp processes for the spin polarization operator. We incorporate umklapp terms and reevaluate the normal state self-energy and the critical temperature of the pairing instability. We show that the self-energy has a Fermi-liquid form and obtain the renormalization of the quasiparticle residue Z, the Fermi velocity, and the curvature of the Fermi surface. We argue that the pairing is a BCS-type problem, but go one step beyond the BCS theory and calculate the critical temperature Tc with the prefactor. We apply the results to electron-doped cuprates near optimal doping and obtain Tc ⩾ 10 K, which matches the experimental results quite well. [ABSTRACT FROM AUTHOR]

We report the discovery of superconductivity in Nb3PdxSe7 with an x-dependent superconducting transition temperature as high as Tc ≃2.1 K for x ≃ 0.7 (middle point of the resistive transition). Needlelike single crystals display anisotropic upper-critical fields with an anisotropy y = Hc2b/c2a as large as 6 between fields applied along their needle axis (or b axis) or along the a axis. As for the Fe based superconductors γ is temperature-dependent, suggesting that Nb3Pd0.7Se7 is a multiband superconductor. This is supported by band structure calculations which reveal a Fermi surface composed of quasi-one-dimensional and quasi-two-dimensional sheets of hole character, as well as three-dimensional sheets of both hole and electron character. Remarkably, Hc2b is observed to saturate at Hc2b(T → 0 K) ≃ 14.1 T which is 4.26 × Hp where Hp is the Pauli-limiting field in the weak-coupling regime. The synthesis procedure yields additional crystals belonging to the Nb2PdxSe5 phase which also becomes superconducting when the fraction of Pd is varied. For both phases we find that superconductivity condenses out of an anomalous metallic state, i.e., displaying ∂ρ/∂T < 0 above Tc similarly to what is observed in the pseudogap phase of the underdoped cuprates. An anomalous metallic state, low-dimensionality, multiband character, extremely high and anisotropic Hc2's are all ingredients for unconventional superconductivity. [ABSTRACT FROM AUTHOR]