We present a theory for the lightly doped t-J model which is of possible relevance for the normal state of underdoped cuprates. Starting from an arbitrary dimer covering of the plane an exact representation of the t-J Hamiltonian in terms of bond bosons and fermions can be derived. Since all dimer coverings must give identical results for observable quantities we construct an approximate but translationally invariant Hamiltonian by averaging the bond particle Hamiltonian over all possible dimer coverings. Treating the resulting Hamiltonian in mean-field approximation we find fermi pockets centered near (pi/2,pi/2) with a total area of x/2 (with x the hole concentration) and a gapped spin-wave-like band of triplet excitations.
The question of whether the pseudogap in high $T_c$ cuprates is related to super conducting precursor effects or to the existence of extrinsic bosonic massive excitations is investigated on the basis of the Boson-Fermion model. The characteristic three peak structure of the electronic spectral function and the temperature dependent Fermi vector derived here are signatures for a two component scenario which can be tested by ARPES and BIS experiments.
The theoretical description of the anomalous properties of the pseudogap phase in the underdoped region of the cuprate phase diagram lags behind the progress in spectroscopic and other experiments. A phenomenological ansatz, based on analogies to the approach to Mott localization at weak coupling in lower dimensional systems, has been proposed by Yang, Rice and Zhang [Phys. Rev. B 73 (2006),174501]. This ansatz has had success in describing a range of experiments. The motivation underlying this ansatz is described and the comparisons to experiment are reviewed. Implications for a more microsco…
We consider thermal evolution of the spectral function A(Omega, T) in underdoped cuprates at T >Tc. We find that in the strong coupling limit, the fermionic Green's function near (0,π) behaves as G^{-1} (Omega) ~ \sqrt{Omega} in the whole frequency range relevant to photoemission experiments. The analysis of the pairing problem with this form of G yields a leading edge gap in A(Ω) and a broad maximum at larger frequencies. We find that classical fluctuations predominantly add a frequency independent term to G^{-1} (Omega). This term destroys the leading edge gap at T =T* (k)$which has a maximu…
A mean field SDW analysis of pseudogap in the underdoped cuprates is proposed on the basis of the $t-t^{\prime}-U$ Hubbard model. The prediction of our theory is consistent with the experiment quite well within the uncertainty of the present experimental measurement. Therefore we argue that the pseudogap phenomenon in the underdoped cuprates can be well explained within the mean field approximation.
We comment on transport experiments in underdoped LaSrCuO in the non-superconducting phase. The temperature dependence of the resistance strongly resembles what is expected from standard localization theory. However this theory fails, when comparing with experiments in more detail.
A microscopic basis is provided for the spin-fermion model used to describe the physics of the underdoped cuprates. In this way, a spin-fermion coupling is shown to take care of the local no double occupancy constraint, which is ignored in the weakly coupled regime. This ingredient is proved to be essential to capture the physics of strong correlations, however. We elaborate further on our recent proposal for the strong-coupling version of the spin-fermion model that may prove to be the correct starting point to deal with the strong correlation physics displayed by the underdoped cuprates.
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 an excellent probe 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.
The Mori's memory function approach to spin dynamics in doped antiferromagnetic insulator combined with the assumption of temperature independent static spin correlations and constant collective mode damping leads to w/T scaling in a broad range. The theory involving a nonuniversal scaling parameter is used to analyze recent inelastic neutron scattering results for underdoped cuprates. Adopting modified damping function also the emerging central peak in low-doped cuprates at low temperatures can be explained within the same framework.
I review some of the experimental evidence and theoretical arguments that suggest that pseudogap matter is a new form of matter that coexists with coherent electron matter in the normal state and with superconducting matter below the superconducting transition temperature. I describe work in progress on a phenomenological two-fluid description of the evolution of pseudogap behavior that offers an explanation for the unexpectedly simple scaling behavior for the uniform magnetic susceptibility found in the underdoped cuprates and use this to propose a physical picture of the underdoped cuprates …
A simple model is proposed as a possible explanation for the checkerboard pattern of modulations in the hole density observed in recent tunneling experiments on underdoped cuprates. Two assumptions are made; first, an enhanced hole density near the acceptor dopants and secondly short range correlations in the positions of these dopants caused by their electrostatic and anisotropic elastic interactions. Together these can lead to a structure factor in qualitative agreement with experiment.
We present the theory of the leading edge gap in the normal state of underdoped high-$T_c$ materials. The consideration is based on a magnetic scenario for cuprates. We show that as doping decreases, the increasing interaction with paramagnons gives rise to a near destruction of the Fermi liquid and this in turn yields precursors to $d-$wave pairing. We argue that the leading edge gap at $\sim 30 meV$ and a broad maximum in the spectral function at $\sim150 meV$ are byproducts of the same physical phenomenon.
The onset of the pseudogap in high-$T_c$ superconducting cuprates (HTSC) is marked by the $T^*$ line in the doping-temperature phase diagram, which ends at a point $p^*$ at zero temperature within the superconducting dome. Although various theoretical and experimental studies indicate a competition between the pseudogap and superconductivity, there is no general consensus on the effects of the pseudogap within the superconducting phase. We use cluster dynamical mean field theory on a three-band Hubbard model for the HTSC to study the superconducting phase at $T=0$, obtained when doping the cha…
We propose that an extension of the exciton concept to doped Mott insulators offers a fruitful insight into challenging issues of the copper oxide superconductors. In our extension, new fermionic excitations called cofermions emerge in conjunction to generalized excitons. The cofermions hybridize with conventional quasiparticles. Then a hybridization gap opens, and is identified as the pseudogap observed in the underdoped cuprates. The resultant Fermi-surface reconstruction naturally explains a number of unusual properties of the underdoped cuprates, such as the Fermi arc and/or pocket formati…
The conventional interpretation of the recent magneto-oscillation experiments in underdoped Cuprates, requires that there be a state of altered translational symmetry in the pseudogap state which is not supported by structural and Angle Resolved Photoemission Spectroscopy (ARPES) experiments. I show here that the observed oscillations may be reconciled with the conclusion arrived in ARPES experiments that the fermi-surface, suitably defined, has the shape of four arcs which shrink to four points as $T \to 0$. Experiments, including infrared absorption in a magnetic field, are suggested to dist…
We investigate the microscopic origin of the pseudogap in the weakly doped 2D Hubbard model using Quantum Monte Carlo within the dynamical cluster approximation. We compare our results with proposed scenarios for the pseudogap. All our numerical evidence is in favor of spin-charge separation as described in the resonating valence bond picture as the cause of the pseudogap behavior. Scenarios of "preformed pairs", the coupling of quasiparticles to antiferromagnetic spin-fluctuations and stripes are inconsistent with our results.
In this paper we show that local spin-singlet amplitude with d-wave symmetry can be induced by short-range spin correlations even in the absence of pairing interactions. In the present scenario for the pseudogap, the normal state pseudogap is caused by the induced local spin-singlet amplitude due to short-range spin correlations, which compete in the low energy sector with superconducting correlations to make $T_{c}$ go to zero near half-filling.
The single particle spectral function for the normal state of underdoped high $T_c$ cuprates is studied within the slave particle framework. We find that the presence of a massless dynamical gauge field - a direct consequence of the quantum order - explains the broad, but not totally incoherent, line-shapes observed in experiments. The issue of the negative anomalous dimension of a recently proposed gauge invariant single particle amplitude is also considered. We show how the anomalous behavior of the single particle amplitude can be incorporated within the slave particle approach and, thus re…
The origin of the Kerr rotation observed in the pseudogap phase of cuprates has been the subject of much speculation. Recently, it has been proposed that this rotation might be due to chiral charge order. Here, I investigate whether such order can be observed by x-ray natural circular dichroism (XNCD). Several types of charge order were considered, and they can give rise to an XNCD signal depending on the stacking of the order along the c-axis.
We show that the breakdown of time-reversal invariance, confirmed by the recent polar Kerr effect measurements in the cuprates, implies the existence of an anomalous Nernst effect in the pseudogap phase of underdoped cuprate superconductors. Modeling the time-reversal-breaking ordered state by the chiral d-density-wave state, we find that the magnitude of the Nernst effect can be sizable even at temperatures much higher than the superconducting transition temperature. These results imply that the experimentally found Nernst effect at the pseudogap temperatures may be due to the chiral d-densit…
High-temperature superconductivity in iron-arsenic materials (pnictides) near an antiferromagnetic phase raises the possibility of spin-fluctuation-mediated pairing. However, the interplay between antiferromagnetic fluctuations and superconductivity remains unclear in the underdoped regime, which is closer to the antiferromagnetic phase. Here we report that the superconducting gap of the underdoped pnictides scales linearly with the transition temperature, and that a distinct pseudogap coexisting with the SC gap develops on underdoping. This pseudogap occurs on Fermi surface sheets connected b…
While magnetic fields generally compete with superconductivity, a type II superconductor can persist to very high fields by confining the field in topological defects, namely vortices. We propose that a similar physics underlies the pseudogap phase in cuprates, where the relevant topological defects are the antiphase domain walls of an underlying antiferromagnetic (AFM) order. A key consequence of this scenario is that the termination of the pseudogap phase should be quantitatively described by the underlying AFM model. We demonstrate that this picture can explain a number of key experimentall…
Recent angle resolved photoemission \cite{yang-nature-08} and scanning tunneling microscopy \cite{kohsaka-nature-08} measurements on underdoped cuprates have yielded new spectroscopic information on quasiparticles in the pseudogap phase. New features of the normal state such as particle-hole asymmetry, maxima in the energy dispersion and accompanying drops in the spectral weight of quasiparticles agree with the ansatz of Yang \textit{et al.} for the single particle propagator in the pseudogap phase. The coherent quasiparticle dispersion and reduced asymmetry in the tunneling density of states …
Considering a possibility that the pseudogap state in the underdoped high-$T_{c}$ superconductors is not due to a superconducting correlation, we study the tunneling spectroscopy below $T_{c}$ based on the phenomenological models of the pseudogap state. Specifically we consider two cases: (1) the pseudogap is a simple suppression of the density of states with an unknown origin; (2) the pseudogap state is due to an antiferromagnetic correlation. For both cases we calculate $dI/dV$ using the BTK theory. The results are discussed in comparison with experiments.
Based on recently proposed U(1)xSU(2) Chern-Simons gauge field theory, an interpretation of the transport and magnetic relaxation properties of underdoped cuprates is proposed, taking into account the short range antiferromagnetic order. The interplay of the doping-dependent spin gap (explicitly derived by us) effect and dissipation due to gauge fluctuations gives rise to a crossover from metallic to insulating behavior of conductivity as temperature decreases, in semi-quantitative agreement with experimental data. For the same reason the magnetic relaxation rate shows a maximum nearby. Variou…
Motivated by recent quantum oscillation observations in the underdoped high-temperature superconductors, the effect of the short-range antiferromagnetic correlations on the electronic properties of the short-ranged d-density wave state is investigated. At intermediate d-density wave correlations, the cross section of the energy dispersion at the Fermi energy consists of hole pockets and an electron pocket. It is argued that the electron pocket feature is smeared out by the effect of the short-range antiferromagnetic correlation, which could be the reason why any electron pockets have never bee…
Spectral functions are evaluated numerically within the t-t'-J model as relevant for electron-doped cuprates. The Fermi surface develops from a pocket-like into a large one with doping. The corresponding pseudogap in the nodal direction is well resolved at low doping and vanishes at intermediate doping. Its presence is strongly temperature dependent and thus connected to longer-range antiferromagnetic correlations. Features including double effective band and optical conductivity are consistent with experiments on electron-doped cuprates without invoking the closing of the Mott-Hubbard gap.
The proposed loop-current order in cuprates cannot give the observed pseudogap and the Fermi-arcs because it preserves translation symmetry. A modification to a periodic arrangement of the four possible orientations of the order parameter with a large period of between about 12 to 30 lattice constants is proposed and shown in a simple and controlled calculation to give one-particle spectra with every feature as in the ARPES experiments. The results follow from (1) the currents at the boundaries of the periodic domains with similar topology as the Affleck-Marston flux phase, and (2) the mixing …
We reply to the criticism from the authors of arXiv:1502.02782 of the spin-fluctuation scenario for charge order in the cuprates. The authors of of arXiv:1502.02782 argued that spin-fluctuation exchange cannot give rise to charge order with observed momentum $(Q, 0)/(0, Q)$ due to the absence of nesting for a half of fermions involved. We explicitly show the instability towards charge order exists even in the "worst-case" scenario of anti-nesting for a half of fermions.
We present a theory of magnetic (Ni) and nonmagnetic (Zn) impurities substituted into planar Cu sites in the normal state of underdoped cuprates exhibiting a spin gap. Both types of impurities induce magnetic moments on neighboring Cu sites. In the case of Ni these moments partially screen the inherent impurity spin, resulting in an effective S=1/2 moment. The characteristic Kondo scale is found to have a power-law dependence on the coupling constant. We investigate the spatial shape of the impurity-induced spin density, taking into account the presence of short-ranged AF correlations, and cal…
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 consider the Nernst effect in the normal state of the underdoped cuprate superconductors, where recent quantum oscillation experiments have indicated the existence of Fermi surface pockets and quasiparticle ambipolarity in the excitation spectrum. Using an ambipolar d-density wave model for the pseudogap, we predict a peak in the Nernst coefficient with decreasing temperature below the pseudogap temperature. The existence of the peak and its sign, which we predict to be the same as that due to mobile vortices in a superconductor, result from the dominance of the electron pocket at low tempe…
It was proposed that the $id_{x^2-y^2}$ density-wave state (DDW) may be responsible for the pseudogap behavior in the underdoped cuprates. Here we show that the admixture of a small $d_{xy}$ component to the DDW state breaks the symmetry between the counter-propagating orbital currents of the DDW state and, thus, violates the macroscopic time-reversal symmetry. This symmetry breaking results in a non-zero polar Kerr effect, which has recently been observed in the pseudogap phase.
We show that the unusual observations of a pseudogap in the normal state of underdoped Bi_2Sr_2CaCu_2O_8+delta (BiSCO) using angle resolved photoemission spectroscopy (ARPES) is consistent with a new band structure for the cuprate superconductors in which the x2-y2 and z2 bands are seen to cross at the Fermi level. Limitations in the experimental method prevent the narrow 3D z2 band from being fully resolved, leading instead to a broad background with "stepfunction" character. As a consequence, the Fermi surface is mis-assigned and a pseudogap of approximately d-wave symmetry develops.
We study the doping evolution of the electronic structure in the pseudogap state of high-Tc cuprate superconductors, by means of a cluster extension of the dynamical mean-field theory applied to the two-dimensional Hubbard model. The calculated single-particle excitation spectra in the strongly underdoped regime show a marked electron-hole asymmetry and reveal a "s-wave" pseudogap, which display a finite amplitude in all the directions in the momentum space but not always at the Fermi level: The energy location of the gap strongly depends on momentum, and in particular in the nodal region, it …
The Josephson coupling between optimally cuprate superconductors separated by a spacer with a finite energy cooperon excitation which contributes to the Josephson coupling strength, is examined. For an underdoped cuprate barrier in its normal state, the YRZ model gives a good description of the temperature dependent enhanced Josephson coupling. A detailed examination of origin of the enhancement shows a significant contribution from the cooperon excitation which is comparable to that from nodal quasiparticles.
Conductivity due to superconducting fluctuations studied in optimally doped YBa2Cu3O7-d films displays a stronger decay law in temperature than explainable by theory. A formula is proposed, which fits the data very well with two superconductive parameters, Tc and the coherence length ksi_c0, and an energy scale Delta*. This is also valid in underdoped materials and enables to describe the conductivity up to 300 K with a single-particle excitations channel in parallel with a channel whose contribution is controlled by ksi_c0, Tc and Delta*. This allows to address the nature of the pseudogap in …
We consider a model of the pseudogap specifically designed to describe the underdoped cuprates and which exhibits particle-hole asymmetry. The presence of electron pockets, besides the usual hole pockets, leads to the appearance of new vectors beyond the usual so-called octet model in the joint density of states (JDOS), which underlies the analysis of Fourier-transform scanning tunneling spectroscopy (FT-STS) data. These new vectors are associated with distinct patterns of large amplitude in the JDOS and are expected to occur primarily at positive bias. Likewise a pseudogap Dirac point occurs …
Within the t-J model, the charge dynamics of copper oxide materials in the underdoped regime is studied based on the fermion-spin theory. It is shown that both in-plane charge dynamics and c-axis charge dynamics are mainly governed by the scattering from the in-plane fluctuation, which would be suppressed when the holon pseudogap opens at low temperatures, leading to the temperature linear to the nonlinear range in the in-plane resistivity and crossovers to the semiconducting-like range in the c-axis resistivity.
Information on the nature of the dominant inelastic processes operative in correlated metallic systems can be obtained from an analysis of their AC optical response. An electron-boson spectral density can usefully be extracted. This density is closely related to the optical scattering rate. However, in the underdoped region of the high Tc cuprate phase diagram a new energy scale (the pseudogap) emerges, which alters the optical scattering and needs to be taken into account in any fit to data. This can influence the shape and strength of the recovered boson spectral function. Including a pseudo…
We investigate the upper critical field in a stripe--phase and in the presence of a phenomenological pseudogap. Our results indicate that the formation of stripes affects the Landau orbits and results in an enhancement of $H_{c2}$. On the other hand, phenomenologically introduced pseudogap leads to a reduction of the upper critical field. This effect is of particular importance when the magnitude of the gap is of the order of the superconducting transition temperature. We have found that a suppression of the upper critical field takes place also for the gap that originates from the charge--den…
We show that the Néel transition and spin fluctuations near the Néel transition in planar cuprates can be described by an SU(2) invariant relativistic four-fermion model in 2+1 dimensions. Features of the pseudogap phenomenon are naturally described by the appearance of an anomalous dimension for the spinon propagator.
Semiconducting-like low-temperature in-plane resistivity indicates that there are no remnants of superconductivity above the resistive phase transition at T > Tc in underdoped cuprates. The model with the chemical potential pinned near the mobility edge inside the charge-transfer optical gap describes quantitatively the Nernst effect, thermopower, diamagnetism and the unusual low-temperature resistivity of underdoped cuprates as normal state phenomena above Tc.
The resonating valence bond spin liquid model for the underdoped cuprates has as an essential element, the emergence of a pseudogap. This new energy scale introduces asymmetry in the quasiparticle density of states because it is associated with the antiferromagnetic Brillouin zone. By contrast, superconductivity develops on the Fermi surface and this largely restores the particle-hole symmetry for energies below the superconducting energy gap scale. In the highly underdoped regime, these two scales can be separately identified in the density of states and also partial density of states for eac…
Recent experiments strongly suggest that a Fermi surface reconstruction and multiple Fermi pockets are important common features of the underdoped high-temperature cuprate superconductors. A related theoretical work [Phys. Rev. B 79, 134512 (2009)] has demonstrated that a number of hallmark phenomena observed in the underdoped cuprates appear naturally in the scenario of a paired electron pocket co-existing with unpaired hole pockets. We propose Gutzwiller-projected wave-functions to describe this two-fluid state as well as two competing states in its vicinity. It is argued that a pseudogap st…
The nodal $d_{x^2-y^2}$ superconducting gap is a hallmark of the cuprate high T$_c$ superconductors. Surprisingly recent angle-resolved photoemission spectroscopy of deeply underdoped cuprates revealed a nodeless energy gap which is adhered to the Fermi surface. Importantly this phenomenon is observed for compounds across several different cuprate families. In this letter we propose an exciting possibility, namely the fully gapped state is a topological superconductor.
Fluctuation effects in underdoped cuprates under high fields are examined by trying to fit theoretical results to resistivity and Nernst data in vortex states. The superconducting (SC) fluctuation in underdoped cuprates includes not only the ordinary thermal contribution but also a large amount of quantum dynamical contributions. Together with this, the presence of a SC pseudogap region T_0-T_{c0} increasing with underdoping is found to be the origin of the Nernst coefficient becoming anomalously smaller and the in-plane coherence length {\it apparently} increasing with underdoping.
The phenomenological Green's function developed in the works of Yang, Rice and Zhang has been very successful in understanding many of the anomalous superconducting properties of the deeply underdoped cuprates. It is based on considerations of the resonating valence bond spin liquid approximation and is designed to describe the underdoped regime of the cuprates. Here we emphasize the region of doping, $x$, just below the quantum critical point at which the pseudogap develops. In addition to Luttinger hole pockets centered around the nodal direction, there are electron pockets near the antinode…
Several models of the electronic spectrum in the pseudogap state of underdoped cuprates have been proposed to explain ARPES and STM measurements, which reveal only truncated Fermi pockets instead of a full metallic Fermi surface. We consider the transport properties expected of four physically distinct models, and calculate the thermal and electrical conductivity of the electronic quasiparticles. By proposing transport currents that reflect the close correspondence between quasiparticles on the Fermi pockets in the pseudogap and those near nodes in the superconducting state, we show that measu…
The Fermi surface in underdoped cuprates is reconstructed by the charge density wave (CDW) order in the pseudogap phase. Theoretical proposals can be divided into two classes: one assumes the underlying Fermi surface without CDW as a conventional large surface; the other assumes small hole-like Fermi pockets. In both scenarios, we theoretically study the quantum oscillation and find three evenly spaced peaks in the oscillation spectra. The central dominant peak is induced by the CDW order. Its effective mass is strongly enhanced as the CDW vanishes in agreement with experiments. But the two sc…
Central issues in the electronic structure of underdoped cuprate superconductors are to clarify the shape of the Fermi surfaces and the origin of the pseudogap. On the basis of the model proposed by Kamimura and Suwa, which bears important features originating from the interplay of Jahn-Teller physics and Mott physics, the feature of Fermi surfaces in underdoped cuprates is the presence of Fermi pockets constructed from doped holes under the coexistence of a metallic state and a local antiferromagnetic order. Below $T_{\rm c}$, the holes on Fermi pockets form Cooper pairs with d-wave symmetry …
By measuring the low temperature specific heat, the low energy quasi-particle excitation has been derived and analyzed in systematically doped La$_{2-x}$Sr$_{x}$CuO$_{4}$ single crystals. The Volovik's relation predicted for a d-wave superconductor has been well demonstrated in wide doping regime, showing a robust evidence for the d-wave pairing symmetry. Furthermore the nodal gap slope $v_Δ$ of the superconducting gap is derived and is found to follow the same doping dependence of the pseudogap obtained from ARPES and tunnelling measurement. This strongly suggests a close relationship between…
We studied interactions between the coherent excitations on disconnected arcs along a bare Fermi surface (the so-called Fermi arcs (FAs)) seen by angle-resolved photo emission spectroscopy (ARPES) in several underdoped (UD) cuprates and incommensurate charge density wave (IC CDW) ordering at lowering of the temperature.
Through the measurements of magnetic field dependence of specific heat in $La_{2-x}Sr_xCuO_4$ in zero temperature limit, we find that the nodal slope $v_Δ$ of the superconducting gap has a very similar doping dependence of the pseudogap temperature $T^*$ or value $Δ_p$. Meanwhile the maximum quasiparticle gap derived from $v_Δ$ is quite close to $T^*$. Both indicate a close relationship between the pseudogap and superconductivity. It is also found that $T_c \approx βv_Δγ_n(0)$, where $γ_n(0)$ is the extracted zero temperature value of the normal state specific heat coefficient which is proport…
Angle resolved photoemission data in the pseudogap phase of underdoped cuprates have revealed the presence of a truncated Fermi surface consisting of Fermi arcs. We compare a number of proposed models for the arcs, and find that the one that best models the data is a d-wave energy gap with a lifetime broadening whose temperature dependence is suggestive of fluctuating pairs.
It has become clear in the past several years that the cuprates show many unusual properties, both in the normal and superconducting states, especially in the underdoped region. In particular, gap-like behavior is observed in magnetic properties, c-axis conductivity and photoemission, whereas in-plane transport properties are only slightly affected by the pseudogap. I shall argue that these experimental evidences must be viewed in the context of the physics of a doped Mott insulator and that they support the notion of spin charge separation. I shall review recent theoretical developments, conc…
We examine the nature of the collective excitations in a strongly anisotropic system of bosons interacting via Coulomb interaction. Such a system has often been used in the past to model the effects of quantum and classical phase fluctuations on the superfluid density of underdoped cuprates. Depending on the anisotropy and the effective strength of the interaction we find four different regimes for the temperature dependence of the superfluid density. Coulomb interaction in underdoped cuprates is argued to be effectively short-ranged, and of order of unity in appropriately defined units.
Within the t-J model, we study the charge transport in underdoped bilayer cuprates by considering the bilayer interaction. Although the bilayer interaction leads to the band splitting in the electronic structure, the qualitative behavior of the charge transport is the same as in the case of single layer cuprates. The conductivity spectrum shows a low-energy peak and the unusual midinfrared band. This midinfrared band is suppressed severely with increasing temperatures, while the resistivity in the heavily underdoped regime is characterized by a crossover from the high temperature metallic-like…
For orthorhombic superconductors we define thermodynamic anisotropy $N \equiv d T_c/d ε_{22} - dT_c/d ε_{11}$ as the difference in how superconducting $T_c$ varies with strains $ε_{ii}$, $i=(1, 2)$, along the in-plane directions. We study the hole doping ($p$) dependence of $N$ on detwinned single crystals of underdoped YBa$_2$Cu$_3$O$_y$ (YBCO) using ultrasound technique. While the structural orthorhombicity of YBCO reduces monotonically with decreasing doping over $0.065 <p<0.16$, we find that the thermodynamic anisotropy shows an intriguing enhancement at intermediate doping level, which is…
A proposal to test the proposed time-reversal and inversion breaking phase in the Pseudogap region of the Cuprate compounds through the variation of Second-harmonic generation intensity with temperature and polarization and angle of incidence is presented.
We reconsider transport experiments in strongly anisotropic superconducting cuprates and we find that universal Aslamazov-Larkin (AL) paraconductivity in two dimensions is surprisingly robust even in the underdoped regime below the pseudogap crossover temperature T^*. We also establish that the underlying normal state resistivity in the pseudogap phase is (almost) linear in temperature, with all the deviations being quantitatively accounted by AL paraconductivity. The disappearence of paraconductivity is governed by the disappearence of gaussian pair fluctuations at an energy scale related to …
