IIn the pseudogap regime of the cuprates, charge order breaks a $\mathbb{Z}_{2}$ symmetry. Therefore, the interaction of charge order and quenched disorder due to potential scattering, can, in principle, be treated as a random field Ising model. A numerical analysis of the ground state of such a random field Ising model reveals local, glassy dynamics in both $2D$ and $3D$. The glassy dynamics are treated as a heat bath which couple to the itinerant electrons, leading to an unusual electronic non-Fermi liquid. If the dynamics are strong enough, the electron spectral function has no quasiparticle peak and the effective mass diverges at the Fermi surface, precluding quantum oscillations. In contrast to charge density, $d$-density wave order (reflecting staggered circulating currents) does not directly couple to potential disorder, allowing it to support quantum oscillations. At fourth order in Landau theory, there is a term consisting of the square of the $d$-density wave order parameter, and the square of the charge order. This coupling could induce parasitic charge order, which may be weak enough for the Fermi liquid behavior to remain uncorrupted. Here, we argue that this distinction must be made clear, as one interprets quantum oscillations in cuprates.
We study the dynamical spin susceptibility of a correlated d-wave superconductor (dSC) in the presence of disorder, using an unrestricted Hartree-Fock approach. This model provides a concrete realization of the notion that disorder slows down spin fluctuations, which eventually "freeze out". The evolution of disorder-induced spectral weight transfer agrees qualitatively with experimental observations on underdoped cuprate superconductors. For sufficiently large disorder concentrations, static spin density wave (SDW) order is created when droplets of magnetism nucleated by impurities overlap. W…
A fundamental connection between superconductivity and quantum spin fluctuations in underdoped cuprates, is revealed. A variational calculation shows that {\em Cooper pair hopping} strongly reduces the local magnetization $m_0$. This effect pertains to recent neutron scattering and muon spin rotation measurements in which $m_0$ varies weakly with hole doping in the poorly conducting regime, but drops precipitously above the onset of superconductivity.
Present-day angle-resolved photoemission spectroscopy (ARPES) has offered a tremendous advance in the understanding of electron energy spectra in cuprate superconductors and some related compounds. However, in high magnetic field, magnetic quantum oscillations at low temperatures indicate the existence of small electron (hole) Fermi pockets seemingly missing in ARPES of hole (electron) doped cuprates. Here ARPES and quantum oscillations are reconciled in the framework of an impurity band in the charge-transfer Mott-Hubbard insulator.
This paper comments on the recently reported quantum oscillations in underdoped YBCO crystals. The implications to other experiments and some hurdles to validating the proposed interpretation are discussed.
The coexistence state of antiferromagnetism (AF) and superconductivity (SC) has been observed in five-layered cuprates. However, this coexistence state disappears, and the AF phase and SC phase lose contact in the doping phase diagram toward double- and single-layered cuprates. We investigate the mechanism of the disappearance of the coexistence of AF and SC in disordered cuprate superconductors in order to understand these doping phase diagrams. In single- and double-layered cuprates, electrons on the CuO$_2$ plane experience the disorder effect through inhomogeneity in the charge reservoir l…
We have studied the influence of disorder induced by electron irradiation on the normal state resistivities $ρ(T)$ of optimally and underdoped YBa2CuOx single crystals, using pulsed magnetic fields up to 60T to completely restore the normal state. We evidence that point defect disorder induces low T upturns of rho(T) which saturate in some cases at low T in large applied fields as would be expected for a Kondo-like magnetic response. Moreover the magnitude of the upturns is related to the residual resistivity, that is to the concentration of defects and/or their nanoscale morphology. These upt…
We have studied the influence of disorder induced by electron irradiation on the Nernst effect in optimally and underdoped YBa2Cu3O(7-d) single crystals. The fluctuation regime above T_{c} expands significantly with disorder, indicating that the T_{c} decrease is partly due to the induced loss of phase coherence. In pure crystals the temperature extension of the Nernst signal is found to be narrow whatever the hole doping, contrary to data reported in the low-T_{c} cuprates families. Our results show that the presence of "intrinsic" disorder can explain the enhanced range of Nernst signal foun…
On the basis of the Hubbard model, we extend the fluctuation-exchange (FLEX) approach to investigating the properties of antiferromagnetic (AF) phase in electron-doped cuprate superconductors. Furthermore, by incorporating the effect of scatterings due to the disordered dopant-atoms into the FLEX formalism, our numerical results show that the antiferromagnetic transition temperature, the onset temperature of pseudogap due to spin fluctuations, the spectral density of the single particle near the Fermi surface, and the staggered magnetization in the AF phase as a function of electron doping can…
We report extensive muon spin rotation measurements on the lightly doped Y1-xCaxBa2Cu3O6+y compound, which allows us to disentangle the effect of disorder, controlled by random Ca2+ substitution, from that of mere doping. A 3D phase diagram of lightly doped cuprates is accurately drawn, showing that a thermally activated antiferromagnetic phase competes with superconductivity around a quantum critical point, hidden underneath a frozen insulating magnetic state. Disorder suppresses both competing order parameters and unveils the underlying frozen state. Doping and disorder destroy the activated…
Using a dynamical cluster quantum Monte Carlo approximation, we investigate the effect of local disorder on the stability of d-wave superconductivity including the effect of electronic correlations in both particle-particle and particle-hole channels. With increasing impurity potential, we find an initial rise of the critical temperature due to an enhancement of anti-ferromagnetic spin correlations, followed by a decrease of Tc due to scattering from impurity-induced moments and ordinary pairbreaking. We discuss the weak initial dependence of Tc on impurity concentration found in comparison to…
Using model calculations of a disordered d-wave superconductor with on-site Hubbard repulsion, we show how dopant disorder can stabilize novel states with antiferromagnetic order. We find that the critical strength of correlations or impurity potential necessary to create an ordered magnetic state in the presence of finite disorder is reduced compared to that required to create a single isolated magnetic droplet. This may explain why in cuprates like LSCO low-energy probes have identified a static magnetic component which persists well into the superconducting state, whereas in cleaner systems…
We calculate the de Haas-van Alphen (dHvA) effect waveform using the canonical ensemble for different Fermi surface scenarios applicable to the underdoped cuprate superconductor YBa2Cu3O6.5, in which quantum oscillations have recently been observed. The harmonic content of the dHvA waveform of the principal F ~ 500 T frequency is consistent with the existence of a second thermodynamically dominant section of Fermi surface that acts primarily as a charge reservoir. Oscillations in the charge density to and from this reservoir are shown to potentially contribute to the observed large quantum osc…
We study disorder-induced magnetism within the Gutzwiller approximation applied to the t-J model relevant for cuprate superconductors. In particular, we show how disorder generates magnetic phases by inducing local droplets of antiferromagnetic order which eventually merge, and form a quasi-long range ordered state in the underdoped regime. We identify two distinct disorder-induced magnetic phases of this type depending on the strength of the scatterers. For weak potential scatterers used to model dopant disorder, charge reorganization may push local regions in-between the impurities across th…
A theory of Kondo lattices is applied to the crossover between local-moment magnetism and itinerant-electron magnetism in the t-J model on a quasi-two dimensional lattice. The Kondo temperature T_K is defined as a characteristic temperature or energy scale of local quantum spin fluctuations. Magnetism with T_N >> T_K, where T_N is the N\eel temperature, is characterized as local-moment one, while magnetism with T_N << T_K is characterized as itinerant-electron one. The Kondo temperature, which also gives a measure of the strength of the quenching of magnetic moments, is renormalized by the Foc…
We study the stability of the spin gap phase in the U(1) slave-boson theory of the t-J model in connection to the underdoped cuprates. We approach the spin gap phase from the superconducting state and consider the quantum phase transition of the slave-bosons at zero temperature by introducing vortices in the boson superfluid. At finite temperatures, the properties of the bosons are different from those of the strange metal phase and lead to modified gauge field fluctuations. As a result, the spin gap phase can be stabilized in the quantum critical and quantum disordered regime of the boson sys…
A d-wave high temperature cuprate superconductor exhibits a nematic ordering transition at zero temperature. Near the quantum critical point, the coupling between gapless nodal quasiparticles and nematic order parameter fluctuation can result in unusual behaviors, such as extreme anisotropy of fermion velocities. We study the disorder effect on the nematic quantum critical behavior and especially on the flow of fermion velocities. The disorders that couple to nodal quasiparticles are divided into three types: random mass, random gauge field, and random chemical potential. A renormalization gro…
We calculate superfluid density for a dirty d-wave superconductor. The effects of impurity scattering are treated within the self-consistent t-matrix approximation, in weak-coupling BCS theory. Working from a realistic tight-binding parameterization of the Fermi surface, we find a superfluid density that is both correlated with T_c and linear in temperature, in good correspondence with recent experiments on overdoped La2-xSrxCuO4.
The de Haas-van Alphen effect was observed in the underdoped cuprate YBa$_2$Cu$_3$O$_{6.5}$ via a torque technique in pulsed magnetic fields up to 59 T. Above an irreversibility field of $\sim$30 T, the magnetization exhibits clear quantum oscillations with a single frequency of 540 T and a cyclotron mass of 1.76 times the free electron mass, in excellent agreement with previously observed Shubnikov-de Haas oscillations. The oscillations obey the standard Lifshitz-Kosevich formula of Fermi-liquid theory. This thermodynamic observation of quantum oscillations confirms the existence of a well-de…
Kinematic constraint arising in the case of superconducting pairing with large momentum results in a cutoff of the screened Coulomb potential excluding large momentum transfers. This leads to a pairing potential oscillating in the real space that ensures a rise of bound singlet pairs. In multilayer cuprates, there is strong Coulomb interaction between particles composing the pair not only in the same cuprate layer but in the neighboring layers as well. In the framework of such a scenario, we explain a universal dependence of the superconducting transition temperature on the number of layers in…
Contrary to a widely accepted view the phase diagrams of La$_{2-x}$Sr$_x$CuO$_4$ and YBa$_2$Cu$_3$O$\rm_{6+y}$, in spite of similarities are remarkably different. Both the electric conduction properties and the commensurate/incommensurate spin ordering properties differ dramatically. It is argued that the role of disorder in YBCO is insignificant while the bilayer structure is crucial. On the other hand in LSCO the intrinsic disorder to a large extent drives the properties of the system. The developed approach explains the low-temperature magnetic properties of the systems. The most important …
According to the celebrated Onsagar-Lifshitz paradigm, the observation of Shubnikov de-Haas and de-Haas van Alphen (SdHvA) oscillations is an indication of the presence of `closed' orbit Fermi surface in the bulk. We present a real-space based calculation of SdHvA oscillations in generalized quasi-one-dimensional lattices by relaxing the quasi-classical approximations embedded in this decades old Onsagar-Lifshitz paradigm. We find that sizable quantum oscillation can arise from `open' Fermi surfaces as long as cyclotron orbits can form in real-space with finite, but not necessarily equal, elec…
We follow the line of reasoning that hidden broken symmetries are the root of quantum oscillations observed in underdoped superconductors and examine the role of bilayer splitting and incommensuration. This is a view that eschews the notion of a featureless Mott liquid as the source of complexity. Instead, our view is grounded in a conventional Fermi surface and quasiparticles. We show that bilayer splitting and/or incommensurate $d$-density wave order can lead to many interesting results, in particular a splitting of the main frequency of the quantum oscillations.
We study the effect of disorder induced by doping on the transition temperature in high $T_c$ cuprates. Since the impurity lies between the CuO$_2$ planes, the momentum transfer is restricted by small angle with a range of order of $1/(d k_F)$, where $k_F$ is the Fermi momentum and $d$ is the distance between the plane and the impurity. We find that the leading correction on the transition temperature in this case is in cubic order of $1/(d k_F)$, while the single particle scattering rate is linearly proportional to $1/(d k_F)$. Therefore, we conclude that the disorder induced by doping has ra…
We report the observation of quantum oscillations in the underdoped cuprate superconductor YBa2Cu4O8 using a tunnel-diode oscillator technique in pulsed magnetic fields up to 85T. There is a clear signal, periodic in inverse field, with frequency 660+/-15T and possible evidence for the presence of two components of slightly different frequency. The quasiparticle mass is m*=3.0+/-0.3m_e. In conjunction with the results of Doiron-Leyraud et al. for YBa2Cu3O6.5, the present measurements suggest that Fermi surface pockets are a general feature of underdoped copper oxide planes and provide informat…
Magneto-oscillations in kinetic and magnetic response functions of a few underdoped cuprates are perhaps one of the most striking observations since many probes of underdoped cuprates clearly point to a non Fermi-liquid normal state. Their observation in the vortex state well below the upper critical field raises a doubt concerning their normal state origin. Here I propose an explanation of the magneto-oscillations as emerging from the quantum interference of the vortex lattice and checkerboard modulations of the electron density of states revealed by STM with atomic resolution in some cuprate…
We report an angular quantum oscillation study of Tl_2Ba_2CuO_{6+delta} for two different doping levels (Tc = 10K and 26 K) and determine the Fermi surface size and topology in considerable detail. Our results show that Fermi liquid behavior is not confined to the edge of the superconducting dome and is robust up to at least T_c^{max}/3.5. Superconductivity is found to survive up to a larger doping p_c = 0.31 than in La_{2-x}Sr_xCuO_4. Our data imply that electronic inhomogeneity does not play a significant role in the loss of superconductivity and superfluid density in overdoped cuprates, and…
By solving the Bogoliubov-de Gennes equations for a $d$-wave superconductor, we explore how the interplay between disorder and the orbital depairing of an external magnetic field influences the superconductor-metal transition of the hole-overdoped cuprates. For highly disordered systems, we find granular Cooper paring to persist above the critical field where the superfluid stiffness goes to zero. We also show that because the vortices are attracted to regions where the superconducting pairing is already weak, the Caroli-de Gennes-Matricon zero-bias peak in the local density of states at the v…
The central puzzle of the cuprate superconductors at low hole density is the nature of the pseudogap regime. It has a number of seemingly distinct experimental signatures: a suppression of the paramagnetic spin susceptibility at high temperatures, low energy electronic excitations that extend over arcs in the Brillouin zone, X-ray detection of charge density wave order at intermediate temperatures, and quantum oscillations at high magnetic fields and low temperatures. We show that a model of competing charge density wave and superconducting orders provides a unified description of the intermed…
When combining the BCS expression of Tc with a shear modulus constant model, we can demonstrate that Tc oscillates depending on the number of the cuprate planes and that it reaches its first maximum for three planes. This is in good agreement with experimental data and suggests that the electron- phonon coupling is essential to the superconductivity of the cuprates.
We present a theoretical framework for understanding the behavior of the normal and superconducting states of overdoped cuprate high temperature superconductors in the vicinity of the doping-tuned quantum superconductor-to-metal transition. The key ingredients on which we focus are d-wave pairing, a flat antinodal dispersion, and disorder. Even for homogeneous disorder, these lead to effectively granular superconducting correlations and a superconducting transition temperature determined in large part by the superfluid stiffness rather than the pairing scale.
Since the early days of the discovery of hole doped high-Tc cuprates, the variation of the oxygen isotope exponent (IE) with the number of doped holes, p, in the CuO2 planes has been a source of considerable debate. There is a growing acceptance in the high-Tc community that the mediating bosons leading to Cooper pairing have largely electronic character. At the same time there is an increasing acknowledgement that at some level the lattice-charge interactions might be important in cuprates. The experimentally observed substantially large IE over certain doping range always casts a shadow over…
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…
Understanding the rich and competing electronic orders in cuprate superconductors may provide important insight into the mechanism of high-temperature superconductivity. Here, by measuring Bi2Sr2CaCu2O8+x in the extremely underdoped regime, we obtain evidence for a distinct type of ordering, which manifests itself as resistance oscillations at low magnetic fields (<10 T) and at temperatures around the superconducting transition. By tuning the doping level p continuously, we reveal that these low-field oscillations occur only when p<0.1. The oscillation amplitude increases with decreasing p but…
We present a way to quantum-disorder a pair density wave, and propose it to be a candidate of the effective low-energy description of the pseudogap metal which may reveal itself in a sufficiently high magnetic field that suppresses the d-wave pairing. The ground state we construct is a small-pocket Fermi liquid with a bosonic Mott insulator in the density-wave-enlarged unit cell. At low energy, the charge density is mainly carried by charge 2e bosons, which develop a small insulating gap. As an intermediate step, we discuss the quantum disordering of a fully gapped superconductor and its excit…
Yamaji effect and quantum oscillation in Yang-Rice-Zhang model of underdoped cuprates
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）；Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences（中国科学院大学理论科学研究所）
At the nematic quantum critical point that exists in the $d_{x^2-y^2}$-wave superconducting dome of cuprates, the massless nodal fermions interact strongly with the quantum critical fluctuation of nematic order. We study this problem by means of renormalization group approach and show that, the fermion damping rate $\left|\mathrm{Im}Σ^R(ω)\right|$ vanishes more rapidly than the energy $ω$ and the quasiparticle residue $Z_f\rightarrow 0$ in the limit $ω\rightarrow 0$. The nodal fermions thus constitute an unconventional non-Fermi liquid that represents an even weaker violation of Fermi liquid t…
Impurity doping like Zn atoms in cuprates were systematically studied to provide important information on the pseudogap phase because this process substantially reduces $T_c$ without effect $T^*$. Despite many important results and advances, the normal phase of these superconductors is still subject of a great debate. We show that the observed Zn-doped data can be reproduced by constructing a nanoscale granular superconductor whose resistivity transition is achieved by Josephson coupling, what provides also a simple interpretation to the pseudogap phase.
We solve the problem of $N$ non magnetic impurities in the staggered flux phase of the Heisenberg model which we assume to be a good mean-field approximation for the spin-gap phase of the cuprates. The density of states is evaluated exactly in the unitary limit and is porportional to $1/\left (ω\ln^2(|ω|/D))$, in analogy with the 1D case of doped spin-Peierls and two-leg ladders compounds. We argue that the system exhibits a quasi long-range order at T=0 with instantaneous spin-spin correlations decreasing as $n_i/ \ln^2\left (n_i R_{ij})$ for large distances $R_{ij}$ and we predict enhanced l…
A series of recent experiments on the Nernst effect, upper critical field $H_{c2}$ and enhanced diamagnetic magnetization $M$ by Wang et al (PRB 73, 024510), were interpreted as to provide evidence for the pseudogap scenario which long-range phase coherence is destroyed by thermally-created vortices. We present here calculations in good agreement with these measurements but based on the local formation of conventional Bogoliubov-deGennes (BdG) superconducting regions in doped disordered cuprate superconductors. Our results imply in an alternate scenario which the disorder plays a fundamental r…
Magnetic field induced antiferromagnetic phase of the underdoped cuprates is studied within the t-t'-J model. A magnetic field suppresses the pairing amplitude, which in turn may induce antiferromagnetism. We apply our theory to interpret the recently reported quantum oscillations in high magnetic field in ortho-II YBa2Cu3O6.5 and propose that the total hole density abstracted from the oscillation period is reduced by 50% due to the antiferromagnetism.
We have studied the electronic structure of electron-doped cuprate superconductors via measurements of high-field Shubnikov-de Haas oscillations in thin films. In optimally doped Pr$_{2-x}$Ce$_{x}$CuO$_{4\pmδ}$ and La$_{2-x}$Ce$_{x}$CuO$_{4\pmδ}$, quantum oscillations indicate the presence of a small Fermi surface, demonstrating that electronic reconstruction is a general feature of the electron-doped cuprates, despite the location of the superconducting dome at very different doping levels. Negative high-field magnetoresistance is correlated with an anomalous low-temperature change in scatter…
We study the influence of disorder and lattice effects on the striped phase and the incommensurate spin fluctuations of the cuprates and nickelates. Starting from a phenomenological model of a discrete quantum string on a lattice with disorder, we derive the renormalisation group equations in leading order in the lattice and disorder strength. Three regimes are identified, the quantum membrane phase, the flat phase pinned by the lattice and the disorder pinned phase. We compare our results with measurements on nickelates and cuprates and find good agreement.
Implications of the small Fermi surface are discussed. We demonstrate that superconductivity in this system can be described in terms of two coupled condensates. The two condensates result in a collective excitation corresponding to the relative phase oscillation - a phason. We discuss the possibility of searching for this collective excitation in the dynamic resistance of the SQUID.
We calculate angle-dependent magnetoresistance oscillations (AMRO) for interlayer transport of cuprate superconductors in the presence of ($π,π$) order. The order reconstructs the Fermi surface, creating magnetic breakdown junctions; we show how such magnetic breakdown effects can be incorporated into calculations of interlayer conductivity for this system. We successfully fit experimental data with our model, and these fits suggest a connection between ($π,π$) order and the anisotropic scattering observed in overdoped cuprates. This work paves the way for the use of AMRO as a tool to distingu…
Recent experiments have revealed incommensurate charge density wave (CDW) in the pseudogap regime in underdoped cuprates, e.g. YBa$_2$Cu$_3$O$_{6+δ}$ and HgBa$_2$CuO$_{4+δ}$. However, its relationship with the pseudogap is still controversial. In this work, we take a phenomenological synthesis of the doped resonating valence bond (RVB) state and the CDW order. Starting from the Yang-Rice-Zhang Green's function ansatz for the doped RVB state [Phys. Rev. B {\bf 73}, 174501 (2006)], in which the Fermi surface is partially truncated into four nodal hole-like Fermi pockets by the antinodal RVB gap,…
Compelling efforts to improve the critical temperature ($T_{c}$) of superconductors have been made through high-pressure application. Understanding the underlying mechanism behind such improvements is critically important, however, much remains unclear. Here we studied ortho-III YBa$_{2}$Cu$_{3}$O$_{6.73}$ (YBCO) using x-ray scattering under hydrostatic-pressure (HP) up to ~6.0 GPa. We found the reinforced oxygen order (OO) of YBCO under HP, revealing an oxygen rearrangement in the Cu-O layer, which evidently shows the charge transfer phenomenon between the CuO$_{2}$ plane and Cu-O layer. Conc…
Vertically Correlated Disorder and Structured Interlayer Tunneling in Cuprates
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine（乌克兰国家科学院 B.维尔金低温物理与工程学院研究所）；Smart Materials Group, Mads Clausen Institute, University of Southern Denmark, Sønderborg（南丹麦大学马兹·克拉斯恩学院智能材料研究组）
Using the Tc formula given by BCS, together with a shear modulus varying with the numbering of planes, we can demonstrate that Tc oscillates depending on the number of the cuprate planes. The maximum of Tc in these oscillations appears for three planes irrespective of the cuprate family. Comparison with experimental data shows good agreement and suggests that the electron-phonon coupling predominate in the superconductivity of these materials. This model predicts that such oscillations can also occur in many others physical quantities that depend on Tc. The new Tc formula shows interesting pro…
We argue that the standard Abrikosov-Gorkov (AG) type theory of $T_c$ in disordered $d$-wave superconductors breaks down in short coherence length high-$T_c$ cuprates. Numerical calculations within the Bogoliubov-de Gennes formalism demonstrate that the correct description of such systems must allow for the spatial variation of the order parameter, which is strongly suppressed in the vicinity of impurities but mostly unaffected elsewhere. Suppression of $T_c$ as measured with respect to the attendant decrease in the superfluid density is found to be significantly weaker than that predicted by …
We study a model of the quantum critical point of cuprates associated with the "circulating current" order parameter proposed by Varma. An effective action of the order parameter in the quantum disordered phase is derived using functional integral method, and the physical properties of the normal state are studied based on the action. The results derived within the ladder approximation indicate that the system is like Fermi liquid near the quantum critical point and in disordered regime up to minor corrections. This implies that the suggested marginal Fermi liquid behavior induced by the circu…
We report on superconducting(SC) characteristics for oxygen-reduced Cu-based five-layered high-temperature superconductor (Cu,C)Ba2Ca4Cu5Oy(Cu-1245(OPT)), which includes five-fold outer planes (OP) and four-fold inner planes (IP).As a result of the reduction of the carrier density, the bulk SC for Cu-1245 (OPT) takes place at the nearly optimally-doped OP with Tc= 98 K that is different from previously-reported Cu-1245(OVD) where IP plays a primary role for the onset of SC. It gives an evidence that the carrier density of the optimally-doped layer determines its bulk Tc.Static antiferromagneti…
The electron-phonon and spin-phonon coupling in typical high-T_C cuprates, like LSCO and HBCO are peaked for just a few q-vectors because of the 2-dimensional Fermi surface shape. The activation of few spin-phonon modes compensates for the low electronic density-of-states, and the superconducting T_C can be high. Thermal disorder of the lattice perturbs the strongly coupled modes already at moderately high temperature. This happens because of incoherent potential fluctuations of the Madelung term and reduced spin-phonon coupling. This effect puts a limit on long-range superconductivity, while …
The magnetic oscillations in YBCO high-temperature superconductors have been widely studied over the last decade and consist of three equidistant low frequencies with a central frequency several times more intense than its two shoulders. This remains a puzzle in spite of numerous attempts to explain the corresponding small Fermi-surface pockets. Furthermore the ARPES data indicate only four Fermi-arcs with bilayer splitting, and show no sign of such small areas in the Fermi surface. Here we argue that the magnetic oscillations measured in under-doped bilayer high temperature superconductors, i…
The recent confirmation of closed Fermi surface in the high temperature cuprates via de Haas-van Alphen and Shubnikov-de haas oscillations calls for a theoretical investigation of the origin of such oscillations. We study de Haas-van Alphen oscillations and magnetic breakdown in the context of ortho-II high temperature cuprates to understand the origin of the multiple frequencies. We find that the magnetic breakdown is highly sensitive not only to the ortho-II potential, but also to the Fermi surface topology, and is thus useful to distinguish between various theoretical proposals related to q…
In a recent manuscript Phys. Rev. Lett. 127, 197001 (2021) Puviani et al. claim that the Higgs mode gives an enhancement of the Raman response in the symmetric $A_{1g}$ Raman channel of cuprates. Here we report a series of technical mistakes in their derivation that completely invalidate this conclusion. In particular, the Raman response function contains two renormalized vertices, with a clearly overcounting of diagrams and uncontrolled results for the Higgs-mode contribution.
