We report a persistent low-energy phonon broadening around $q_{B} \sim 0.28$ r.l.u. along the Cu-O bond direction in the high-$T_c$ cuprate Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (Bi-2212). We show that such broadening exists both inside and outside the conventional charge density wave (CDW) phase, via temperature dependent measurements in both underdoped and heavily overdoped samples. Combining inelastic hard x-ray scattering, diffuse scattering, angle-resolved photoemission spectroscopy, and resonant soft x-ray scattering at the Cu $L_3$-edge, we exclude the presence of a CDW in the heavily overdoped Bi-2212 similar to that observed in the underdoped systems. Finally, we discuss the origin of such anisotropic low-energy phonon broadening, and its potential precursory role to the CDW phase in the underdoped region.
Establishing the presence and the nature of a quantum critical point in their phase diagram is a central enigma of the high-temperature superconducting cuprates. It could explain their pseudogap and strange metal phases, and ultimately their high superconducting temperatures. Yet, while solid evidences exist in several unconventional superconductors of ubiquitous critical fluctuations associated to a quantum critical point, in the cuprates they remain undetected until now. Here using symmetry-resolved electronic Raman scattering in the cuprate Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$, we report the obser…
The Fermi surface (FS) of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (Bi2212) predicted by band theory displays Bi-related pockets around the $(π,0)$ point, which have never been observed experimentally. We show that when the effects of hole doping either by substituting Pb for Bi or by adding excess O in Bi2212 are included, the Bi-O bands are lifted above the Fermi energy ($E_F$) and the resulting first-principles FS is in remarkable accord with measurements. With decreasing hole-doping the Bi-O bands drop below $E_F$ and the system self-dopes below a critical hole concentration. Computations on other Bi…
We investigate the high-energy magnetic excitation spectrum of the high-$T_c$ cuprate superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (Bi-2212) using Cu $L_3$ edge resonant inelastic x-ray scattering (RIXS). Broad, dispersive magnetic excitations are observed, with a zone boundary energy of $\sim$300 meV and a weak dependence on doping. These excitations are strikingly similar to the bosons proposed to explain the high-energy `kink' observed in photoemission. A calculation of the spin-response based on the ARPES-derived electronic structure and YRZ-quasi-particles reproduces the key features of t…
A major remaining challenge in the superconducting cuprates is the unambiguous differentiation of the composition and electronic structure of the CuO$_2$ layers and those of the intermediate layers. The large c axis for these materials permits employing soft x-ray (930.3 eV) standing wave (SW) excitation in photoemission that yields atomic layer-by-atomic layer depth resolution of these properties. Applying SW photoemission to Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ yields the depth distribution of atomic composition and the layer-resolved densities of states. We detect significant Ca presence in the Sr…
Using high energy resolution angle resolved photoemission spectroscopy, we have resolved the bilayer splitting effect in a wide range of dopings of the bilayer cuprate $Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}$. This bilayer splitting is due to a nonvanishing intracell coupling $t_{\perp}$, and contrary to expectations, it is not reduced in the underdoped materials. This has implications for understanding the increased c-axis confinement in underdoped materials.
Using resonant X-ray diffraction and Raman spectroscopy, we study charge correlations and lattice dynamics in two model cuprates, HgBa$_{2}$CuO$_{4+δ}$ and HgBa$_{2}$CaCu$_{2}$O$_{6+δ}$. We observe a maximum of the characteristic charge order temperature around the same hole concentration ($p \approx 0.09$) in both compounds, and concomitant pronounced anomalies in the lattice dynamics that involve the motion of atoms in and/or adjacent to the CuO$_2$ layers. These anomalies are already present at room temperature, and therefore precede the formation of the static charge correlations, and we a…
We perform a comparative $2 \times 2$ real space cluster DMFT study on minimal models for NdNiO$_2$ and CaCuO$_2$ obtained from downfolding DFT states, using a Nambu formalism that allows for both superconducting and antiferromagnetic order. We produce a phase diagram in temperature and doping. We find that for the nickelate, like the cuprate, the stoichiometric compound is antiferromagnetic. We find superconductivity in a doping range bounded, with a small coexistence region, by the onset of antiferromagnetism at low doping and with transition temperature becoming immeasurably small at high d…
The real part of the optical in-plane conductivity of p-- and n--type cuprates thin films at various doping levels was deduced from highly accurate reflectivity measurements. We present here a comprehensive set of optical spectral weight data as a function of the temperature $T (> T_c$), for underdoped and overdoped samples. The temperature dependence of the spectral weight is not universal. Using various cut-off frequencies for the spectral weight, we show that n--type Pr$_{2-x}$Ce$_x$CuO$_4$ and p--type Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ exhibit both similarities and striking differences. The Fer…
We report systematic, high-precision measurements of the low-T (down to 70 mK) thermal conductivity κof YBa_{2}Cu_{3}O_{y}, La_{2-x}Sr_{x}CuO_{4} and Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}. Careful examinations of the Zn- and hole-doping dependences of the residual thermal conductivity κ_{0}/T, as well as the in-plane anisotropy of κ_{0}/T in Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}, indicate a breakdown of the universal thermal conductivity, a notable theoretical prediction for d-wave superconductors. Our results point to an important role of electronic inhomogeneities, that are not considered in the standard pertur…
We report the transverse relaxation rates 1/$T_2$'s of the $^{63}$Cu nuclear spin-echo envelope for double-layer high-$T_c$ cuprate superconductors HgBa$_{2}$CaCu$_{2}$O$_{6+d}$ from underdoped to overdoped. The relaxation rate 1/$T_{2L}$ of the exponential function (Lorentzian component) shows a peak at 220$-$240 K in the underdoped ($T_c$ = 103 K) and the optimally doped ($T_c$ = 127 K) samples but no peak in the overdoped ($T_c$ = 93 K) sample. The enhancement in 1/$T_{2L}$ suggests development of the zero frequency components of local field fluctuations. Ultraslow fluctuations are hidden i…
The in-plane optical properties of two crystals of the bilayer cuprate \LSxCCO, one with excess Ca and $x=0.10$ and the other with Sr and $x=0.15$, were investigated over the frequency range of 45--25000 cm$^{-1}$. The optical conductivity has been derived from Kramers-Kronig transformation. Each crystal exhibits a peak at around 15000 cm$^{-1}$ which corresponds to the charge-transfer gap of the parent insulator. With increasing carrier density, spectral weight shifts from the CT excitation to the low-$ω$ region. For the superconducting sample ($x=0.15$), the optical conductivity displays a p…
Fluctuating superconductivity - vestigial Cooper pairing in the resistive state of a material - is usually associated with low dimensionality, strong disorder or low carrier density. Here, we report single particle spectroscopic, thermodynamic and magnetic evidence for persistent superconducting fluctuations in heavily hole-doped cuprate superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ ($T_c$ = 66~K) despite the high carrier density. With a sign-problem free quantum Monte Carlo calculation, we show how a partially flat band at ($π$,0) can help enhance superconducting phase fluctuations. Finally, w…
Bulk charge density modulations, recently observed in high critical-temperature ($T_\mathrm{c}$) cuprate superconductors, coexist with the so-called pseudogap and compete with superconductivity. However, its direct observation has been limited to a narrow doping region in the underdoped regime. Using energy-resolved resonant x-ray scattering we have found evidence for such bulk charge modulations, or soft collective charge modes (soft CCMs), in optimally doped Bi$_{1.5}$Pb$_{0.6}$Sr$_{1.54}$CaCu$_{2}$O$_{8+δ}$ (Pb-Bi2212) around the summit of the superconducting dome with momentum transfer $q_…
In the high-temperature ($T_{c}$) cuprate superconductors, increasing evidence suggests that the pseudogap, existing below the pseudogap temperature $T$*, has a distinct broken electronic symmetry from that of superconductivity. Particularly, recent scattering experiments on the underdoped cuprates have suggested that a charge ordering competes with superconductivity. However, no direct link of this physics and the important low-energy excitations has been identified. Here we report an antagonistic singularity at $T_{c}$ in the spectral weight of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ as a compel…
We report measurements of the phase of the conductivity, $ϕ_σ\equiv arg(σ)$, in the normal state of a $Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}$ (BSCCO) thin film from 0.2-1.0 THz. From $ϕ_σ$ we obtain the time delay of the current response, $τ_σ\equivϕ_σ/ω$. After discovering a systematic error in the data analysis, the extracted $τ_σ$ has changed from that reported earlier. The revised data is shown in the sole figure below. Analysis and discussion of these data will follow.
A magnetic field applied to type-II superconductors introduces quantized vortices that locally quench superconductivity, providing a unique opportunity to investigate electronic orders that may compete with superconductivity. This is especially true in cuprate superconductors in which mutual relationships among superconductivity, pseudogap, and broken-spatial-symmetry states have attracted much attention. Here we observe energy and momentum dependent bipartite electronic superstructures in the vortex core of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ using spectroscopic-imaging scanning tunneling microscop…
When Cooper pairs are formed with finite center-of-mass momentum, the defining characteristic is a spatially modulating superconducting energy gap $Δ(r)$. Recently, this concept has been generalized to the pair density wave (PDW) state predicted to exist in a variety of strongly correlated electronic materials such as the cuprates. Although the signature of a cuprate PDW has been detected in Cooper-pair tunnelling, the distinctive signature in single-electron tunneling of a periodic $Δ(r)$ modulation has never been observed. Here, using a new approach, we discover strong $Δ(r)$ modulations in …
Recent in-plane thermal (Nernst) and interlayer (tunnelling) transport experiments in Bi$_2$Sr$_2$CaCu$_2$O$_{8+y}$ high temperature superconductors report hugely different limiting magnetic fields. Based on pairing (and the uncertainty principle) combined with the definitions of the Zeeman energy and the magnetic length, we show that in the underdoped regime both fields convert to the same (normal state) pseudogap energy scale $T^*$ upon transformation as orbital and spin (Zeeman) critical fields, respectively. We reconcile these seemingly disparate findings invoking separated spin and charge…
We study a model of a d-wave superconductor with strong potential scatterers in the presence of antiferromagnetic correlations and apply it to experimental nuclear magnetic resonance (NMR) results on Zn impurities in the superconducting state of YBCO. We then focus on the contribution of impurity-induced paramagnetic moments, with Hubbard correlations in the host system accounted for in Hartree approximation. We show that local magnetism around individual impurities broadens the line, but quasiparticle interference between impurity states plays an important role in smearing out impurity satell…
We present a theory of magnetic (S=1) Ni and nonmagnetic Zn impurities in underdoped cuprates. Both types of impurities are shown to induce S=1/2 moments on Cu sites in the proximity of the impurity, a process which is intimately related to the spin gap phenomenon in cuprates. Below a characteristic Kondo temperature, the Ni spin is partially screened by the Cu moments, resulting in an effective impurity spin S=1/2. We further analyze the Ruderman-Kittel-Kasiya-Yosida-type response of planar Cu spins to a polarization of the effective impurity moments and derive expressions for the correspondi…
Recent observations of broken symmetries have partly demystified the pseudogap phase. Here we review evidence for long-range intra-unit-cell(IUC) nematic order and its unexpectedly strong coupling to the phase of the fluctuating stripes in the pseudogap states of underdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$. In particular, we focus on the analysis techniques that reveal this evidence in scanning tunneling spectroscopy data, the definition of the extracted IUC nematic order parameter, and a phenomenological theory of the coupling between the IUC nematic order and the previously reported coexisting …
Superconductivity studied by solving ab initio low-energy effective Hamiltonians for carrier doped CaCuO$_2$, Bi$_2$Sr$_2$CuO$_6$, Bi$_2$Sr$_2$CaCu$_2$O$_8$, and HgBa$_2$CuO$_4$
Both electronic Raman scattering (ERS) and angle-resolved photoemission spectra (ARPES) revealed two energy scales for the gap in different momentum spaces in the cuprates. However, the interpretations were different, and the gap values were also different in two experiments. In order to clarify the origin of these discrepancies, we directly compared ERS and ARPES by calculating ERS from the experimental data of ARPES through the Kubo formula. The calculated ERS spectra were in good agreement with the experimental results except for the B$_{1g}$ peak energies. The doping-dependent B$_{2g}$ pea…
Angle-resolved photoemission spectroscopy (ARPES) presents significant simplications in analyzing strictly two-dimensional (2D) materials, but even the most anisotropic physical systems display some residual three-dimensionality. Here we demonstrate how this third dimension manifests itself in ARPES spectra of quasi-2D materials by considering the example of the cuprate Bi$_2$Sr$_2$CaCu$_2$O$_{8}$ (Bi2212). The intercell, interlayer hopping, which is responsible for $k_z$-dispersion of the bands, is found to induce an irreducible broadening to the ARPES lineshapes with a characteristic depende…
The nature of the spin excitations in superconducting cuprates is a key question toward a unified understanding of the cuprate physics from long-range antiferromagnetism to superconductivity. The intense spin excitations up to the over-doped regime revealed by resonant inelastic X-ray scattering bring new insights as well as questions like how to understand their persistence or their relation to the collective excitations in ordered magnets (magnons). Here, we study the evolution of the spin excitations upon hole-doping the superconducting cuprate Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ by disentangling…
We show that the spectral lineshape of superconducting La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) and Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (Bi2212) can be well described by the coupling of the charge carriers to collective incommensurate charge-density wave (CDW) excitations. Our results imply that besides antiferromagnetic (AF) fluctuations also low-energy CDW modes can contribute to the observed dip-hump structure in the Bi2212 photoemission spectra. In case of underdoped LSCO we propose a possible interpretation of ARPES data in terms of a grid pattern of fluctuating stripes where the charge and spin scatteri…
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.
Toward the detection of spin-vortex-induced loop currents in a single bilayer Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ thin film and their possible use as qubits: Model calculations for three nano-island architecture
The possibility of driving phase transitions in low-density condensates through the loss of phase coherence alone has far-reaching implications for the study of quantum phases of matter. This has inspired the development of tools to control and explore the collective properties of condensate phases via phase fluctuations. Electrically-gated oxide interfaces, ultracold Fermi atoms, and cuprate superconductors, which are characterized by an intrinsically small phase-stiffness, are paradigmatic examples where these tools are having a dramatic impact. Here we use light pulses shorter than the inte…
We study the $τ_1$-impurity induced $\mathbf{q}$-space pattern of the energy derivative local density of states (LDOS) in a d-wave superconductor. We are motivated in part by the recent scanning tunneling microscopy (STM) observation of strong gap inhomogeneity with weak charge density variation in Bi$_{2}$Sr$_2$CaCu$_2$O$_{8+δ}$ (BSCCO). The hypothesis is that the gap inhomogeneity might be triggered by the disorder in pair potential. We focus on the effects of electron coupling to various bosonic modes, at the mode energy shifted by the d-wave superconducting gap. The pattern due to a highly…
Extended Drude model formalism has been successfully utilized for analyzing optical spectra of strongly correlated electron systems including heavy-fermion systems and high-$T_c$ superconducting iron pnictides and cuprates. Furthermore, generalized Allen's formulas has been developed and applied to extract the electron-boson spectral density function from measured optical data of high temperature superconductors including cuprates in various material phases. Here we used a reverse process to obtain various optical quantities starting from two typical electron-boson spectral density model funct…
Remote magnon sensing detects the universal phase stiffness jump in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$
University of Washington（华盛顿大学）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；University of Chemistry and Technology Prague（布拉格化学与技术大学）；Columbia University（哥伦比亚大学）；National Institute for Materials Science（物质材料研究机构）；National Institute of Advanced Industrial Science and Technology（产业技术综合研究所）
Explaining the mechanism of superconductivity in the high-$T_c$ cuprates requires an understanding of what causes electrons to form Cooper pairs. Pairing can be mediated by phonons, the screened Coulomb force, spin or charge fluctuations, excitons, or by a combination of these. An excitonic pairing mechanism has been postulated, but experimental evidence for coupling between conduction electrons and excitons in the cuprates is sporadic. Here we use resonant inelastic x-ray scattering (RIXS) to monitor the temperature dependence of the $\underline{d}d$ exciton spectrum of Bi$_2$Sr$_2$CaCu$_2$O$…
Eliashberg theory generalized for the account of the electron-hole nonequivalence and electron correlations in the vertex function is used. The phonon contribution to the nodal electron Green function in cuprates is viewed. At non- zero temperatures the singularities (kinks) in the frequency behavior of a real and imaginary part of an electron nodal Green function, and also in the nodal part of the density of the electron states modified by an electron-phonon interaction are studied. It is shown that near the optimal doping both the low-energy and high-energy nodal Green function kinks and als…
Recent transport experiments in the original cuprate high temperature superconductor, {La$_{2-x}$Ba$_x$CuO$_4$}, have revealed a remarkable sequence of transitions and crossovers which give rise to a form of dynamical dimensional reduction, in which a bulk crystal becomes essentially superconducting in two directions while it remains poorly metallic in the third. We identify these phenomena as arising from a distinct new superconducting state, the "striped superconductor," in which the superconducting order is spatially modulated, so that its volume average value is zero. Here, in addition to …
We consider the effect of a short antiferromagnetic correlation length $ξ$ on the electronic bandstructure of the underdoped cuprates. Starting with a Fermi-surface topology similar to that detected in magnetic quantum-oscillation experiments, we show that a reduced $ξ$ gives an assymmetric broadening of the quasiparticle dispersion, resulting in simulated ARPES data very similar to those observed in experiment. Predicted features include the presence of `Fermi arcs' close to $a{\bf k}=(π/2,π/2)$, without the need to invoke a d-wave pseudogap order parameter. The statistical variation in the $…
Recent experiments indicate that the tendency toward the formation of unidirectional charge density waves ("stripes") is common to various underdoped cuprates. We discuss momentum-resolved spectral properties of valence-bond stripes, comparing the situations of ideal and short-range stripe order, the latter being relevant for weak and/or disorder-pinned stripes. We find clear signatures of ordered stripes, although matrix element effects suppress most shadow band features. With decreasing stripe correlation length, stripe signatures are quickly washed out, the only remaining effect being a bro…
It is shown that a quasi two dimensional (layered) Heisenberg antiferromagnet with fully frustrated interplane couplings ({\it e.g.} on a body-centered tetragonal lattice) generically exhibits two thermal phase transitions with lowering temperature -- an upper transition at $T_{TO}$ (``order from disorder without order'') in which the lattice point-group symmetry is spontaneously broken, and a lower Néel transition at $T_{N}$ at which spin-rotation symmetry is broken. Although this is the same sequence of transitions observed in La$_2$CuO$_4$, in the Heisenberg model (without additional lattic…
We have performed a detailed study of Cu $2p$ core-level spectra in single layer La$_{2-x}$Sr$_{x}$CuO$_{4}$, La doped Bi$_2$Sr$_{1.6}$La$_{0.4}$CuO$_{6+δ}$ (Bi2201) and bilayer Bi$_2$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ (Bi2212) high-temperature superconductors by using hard x-ray photoemission (HX-PES). We identify the Cu$^{2+}$ derived (i) the Zhang-Rice singlet (ZRS) feature, (ii) the $d^{n+1}\underline{L}$ (ligand screened) feature, (iii) the $d^{n}$ satellite feature, as well as the hole-doping derived high binding energy feature in the main peak. In Bi-based cuprates, intensities of the $d^{n}$ …
We report nuclear quadrupole resonance (NQR) studies on the chain Cu sites of PrBa$_{2}$Cu$_{4}$O$_{8}$, a quasi-one-dimensional conductor with a nearly quarter-filled band. The nuclear spin-lattice relaxation rate $1/T_{1}$ shows a pronounced peak near 100 K caused by fluctuations of electric field gradient (EFG). Similar peak was observed for the spin-echo decay rate $1/T_{2}$, however, at a different temperature near 50 K. These results and broadening of the NQR spectrum at low temperatures indicate that slow charge fluctuations of either electronic or ionic origin freeze gradually at low t…
We theoretically analyze the intensity of the resonant inelastic X-ray scattering (RIXS) based on Ansatz that the electron is fractionalized into two components. By fitting the angle resolved photoemission spectroscopy (ARPES) data of a cuprate high-$T_{\rm c}$ superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ and the accompanied machine learning results obtained before by Yamaji {\it et al.} (arXiv:1903.08060), we determine the paprameters of the two-component fermion model which describes the electron fractionalization. The RIXS spectra are predicted by using this description. We find that the in…
In the material SmLa$_{1-x}$Sr$_x$CuO$_{4-δ}$ with alternating intrinsic Josephson junctions we explain theoretically the relative amplitude of the two plasma peaks in transmission by taking into account the spatial dispersion of the Josephson Plasma Resonance in $c$ direction due to charge coupling. From this and the magnetic field dependence of the plasma peaks in the vortex solid and liquid states it is shown that the electronic compressibility of the CuO$_2$ layers is consistent with a free electron value. Also the London penetration depth $λ_{ab} \approx 1100 {\rm Å}$ near $T_c$ can be de…
While electron-phonon coupling (EPC) is crucial for Cooper pairing in conventional superconductors, its role in high-$T_c$ superconducting cuprates is debated. Using resonant inelastic x-ray scattering at the oxygen $K$-edge, we studied the EPC in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (Bi2212) and Nd$_{1+x}$Ba$_{2-x}$Cu$_3$O$_{7-δ}$ (NBCO) at different doping levels ranging from heavily underdoped ($p =0.07$) to overdoped ($p=0.21$). We analyze the data with a localized Lang-Firsov model that allows for the coherent excitations of two phonon modes. While electronic band dispersion effects are non-negl…
Electron quasiparticles play a crucial role in simplifying the description of many-body physics in solids with surprising success. Conventional Landau's Fermi-liquid and quasiparticle theories for high-temperature superconducting cuprates have, however, received skepticism from various angles. A path-breaking framework of electron fractionalization has been established to replace the Fermi-liquid theory for systems that show the fractional quantum Hall effect and the Mott insulating phenomena; whether it captures the essential physics of the pseudogap and superconducting phases of cuprates is …
The linear-in-temperature resistivity is one of the important mysteries in the strange metal state of high-temperature cuprate superconductors. To uncover this anomalous property, the energy-momentum-dependent imaginary part of the self-energy Im ${\rm Σ}(k, ω)$ holds the key information. Here we perform systematic doping, momentum, and temperature-dependent angle-resolved photoemission spectroscopy measurements of electron-doped cuprate ${\rm La}_{2-x}{\rm Ce}_x{\rm CuO}_4$ and extract the evolution of the strange metal scattering in momentum space. At low doping levels and low temperatures, …
Twisted bilayers of high-$T_c$ cuprate superconductors have been argued to form topological phases with spontaneously broken time reversal symmetry ${\cal T}$ for certain twist angles. With the goal of helping to identify unambiguous signatures of these topological phases in transport experiments, we theoretically investigate a suite of Josephson phenomena between twisted layers. We find an unusual non-monotonic temperature dependence of the critical current at intermediate twist angles which we attribute to the unconventional sign structure of the $d$-wave order parameter. The onset of the ${…
Rotational Phonons Drive Low-Energy Kinks in Cuprate Superconductors
Department of Physics and Engineering Physics, Tulane University（杜兰大学物理与工程物理系）；VASP Software GmbH（VASP软件有限公司）；Theoretical Division, Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室理论部）；Department of Physics, School of Engineering Science, LUT University（拉彭兰塔理工大学工程科学学院物理系）；Department of Physics, Northeastern University（东北大学物理系）；Quantum Materials and Sensing Institute, Northeastern University（东北大学量子材料与传感研究所）
Identifying what broken symmetries are present in the cuprates has become a major area of research. Many authors have reported evidence for so-called "$Q \sim 0$" order that involves broken inversion, mirror, chiral, or time-reversal symmetry that is uniform in space. Not all these observations are well understood and new experimental probes are needed. Here we use resonant soft x-ray scattering (RSXS) to search for $Q \sim 0$ order in Bi$_{2.1}$Sr$_{1.9}$CaCu$_2$O$_{8+x}$ (Bi-2212) by measuring the region of a forbidden Bragg peak, $(0,0,3)$, which is normally extinguished by symmetry but may…
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…
The role of Coulomb disorder, either of extrinsic origin or introduced by dopant ions in undoped and lightly-doped cuprates, is studied. We demonstrate that charged surface defects in an insulator lead to a Gaussian broadening of the Angle-Resolved Photoemisson Spectroscopy (ARPES) lines. The effect is due to the long-range nature of the Coulomb interaction. A tiny surface concentration of defects about a fraction of one per cent is sufficient to explain the line broadening observed in Sr$_2$CuO$_2$Cl$_2$, La$_2$CuO$_{4}$, and Ca$_{2}$CuO$_{2}$Cl$_{2}$. Due to the Coulomb screening, the ARPES …
The strange-metal phase of the cuprate high temperature superconductors, above where the superconductivity sets in as a function of temperature, is widely considered more exotic and mysterious than the superconductivity itself. Here, based upon detailed angle resolved photoemission spectroscopy measurements of Bi$_2$Sr$_2$CaCu$_2$O$_8$$_+$$_δ$ over a wide range of doping levels, we present a new unifying phenomenology for the non-Fermi liquid normal-state interactions (scattering rates) in the nodal direction. This new phenomenology has a continuously varying power law exponent (hence named a …
