Field theory for a fermionic ladder with generic intrachain interactions
Not Available
Tsvelik, A. M.↗
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J{sub 1}-J{sub 2} Heisenberg model at and close to its z=4 quantum critical point
We study the frustrated J{sub 1}-J{sub 2} Heisenberg model with ferromagnetic nearest-neighbor coupling J{sub 1}<0 and antiferromagnetic next-nearest-neighbor coupling J{sub 2}>0 at and close to the z=4 quantum critical point (QCP) at J{sub 1}/J{sub 2}=-4. The J{sub 1}-J{sub 2} model plays an important role for recently synthesized chain cuprates as well as in supersymmetric Yang-Mills theories. We study the thermodynamic properties using field theory, a modified spin-wave theory, as well as numerical density-matrix renormalization group calculations. Furthermore, we compare with results for the classical model obtained by analytical methods and Monte Carlo simulations. As one of our main results, we present numerical evidence that the susceptibility at the QCP seems to diverge with temperature T as {chi}{approx}T{sup -1.2} in the quantum case, in contrast to the classical model where {chi}{approx}T{sup -4/3}.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Quantum oscillations in a bilayer with broken mirror symmetry: A minimal model for YBa 2 Cu 3 O 6 + δ
Using an exact numerical solution and semiclassical analysis, we investigate quantum oscillations (QOs) in a model of a bilayer system with an anisotropic (elliptical) electron pocket in each plane. Key features of QO experiments in the high temperature superconducting cuprate YBCO can be reproduced by such a model, in particular the pattern of oscillation frequencies (which reflect “magnetic breakdown” between the two pockets) and the polar and azimuthal angular dependence of the oscillation amplitudes. However, the requisite magnetic breakdown is possible only under the assumption that the horizontal mirror plane symmetry is spontaneously broken and that the bilayer tunneling t ⊥ is substantially renormalized from its ‘bare’ value. Lastly, under the assumption that t ⊥ = $\sim\atop{Z}_t$ $(0)\atop{⊥}$, where $\sim\atop{Z}$ is a measure of the quasiparticle weight, this suggests that $\sim\atop{Z}$ ≲ 1/20. Detailed comparisons with new YBa 2 Cu 3 O 6.58 QO data, taken over a very broad range of magnetic field, confirm specific predictions made by the breakdown scenario.
36 MATERIALS SCIENCE↗
Reply to “Comment on ‘Magnetotransport signatures of a single nodal electron pocket constructed from Fermi arcs' ”
In this paper, we provide arguments relating to those recently made in a comment by Chakravarty and Wang, who question the validity of our proposed charge-density wave Fermi surface reconstruction model and its relation to sign changes in the Hall effect. First, we show that the form of rounding of the vertices (i.e. sharp corners) of the reconstructed electron pocket, as used in our model calculations of the Hall coefficient, is consistent with Bragg reflection from the periodic potential of a charge-density wave, rather than being arbitrarily chosen. Second, we provide further justifications for why an oscillatory transport scattering time provides a useful means for modeling Shubnikov–de Haas oscillations in the Hall effect, in the situation where a Fermi surface pocket departs from the ideal circular form. Third and finally, we discuss recent experimental evidence gathered from two different families of underdoped cuprates supporting the existence of a single electron pocket produced by biaxial charge-density wave order as a universal phenomena.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Coincident onset of charge-density-wave order at a quantum critical point in underdoped YBa 2 Cu 3 O x
The recently demonstrated x-ray scattering approach using a free electron laser with a high field pulsed magnet has opened new opportunities to explore the charge-density-wave (CDW) order in cuprate high temperature superconductors. Using this approach, in this paper we substantially degrade the superconductivity with magnetic fields up to 33 T to investigate the onset of CDW order in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{x}$ at low temperatures near a putative quantum critical point (QCP) at ${p}_{1}{\sim}0.08$ holes per Cu. We find no CDW can be detected in a sample with a doping concentration smaller than ${p}_{1}$. Finally, our results indicate that the onset of the CDW ground state lies inside the zero-field superconducting dome, and broken translational symmetry is associated with the putative QCP at ${p}_{1}$.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Antiferromagnetic ground state of La 2 CuO 4 : A parameter-free ab initio description
Here we show how an accurate first-principles treatment of the antiferromagnetic ground state of La 2 CuO 4 can be obtained without invoking any free parameters such as the Hubbard U. The magnitude and orientation of our theoretically predicted magnetic moment of 0.495μ B on Cu sites along the (100) direction are in excellent accord with experimental results. The computed values of the band gap (1.00 eV) and the exchange coupling (-138 meV) match the corresponding experimental values. We identify interesting band splittings below the Fermi energy, including an appreciable Hund's splitting of 1.25 eV. The magnetic form factor obtained from neutron scattering experiments is also well described by our calculations. Our study thus opens up a pathway for first-principles investigations of electronic and atomic structures and phase diagrams of cuprates and other complex materials.
36 MATERIALS SCIENCE↗
Emergent quantum criticality, Fermi surfaces, and AdS{sub 2}
Gravity solutions dual to d-dimensional field theories at finite charge density have a near-horizon region, which is AdS{sub 2}xR{sup d-1}. The scale invariance of the AdS{sub 2} region implies that at low energies the dual field theory exhibits emergent quantum critical behavior controlled by a (0+1)-dimensional conformal field theories (CFT). This interpretation sheds light on recently-discovered holographic descriptions of Fermi surfaces, allowing an analytic understanding of their low-energy excitations. For example, the scaling behavior near the Fermi surfaces is determined by conformal dimensions in the emergent IR CFT. In particular, when the operator is marginal in the IR CFT, the corresponding spectral function is precisely of the ''marginal Fermi liquid'' form, postulated to describe the optimally doped cuprates.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Direct Determination of the Electron-Phonon Coupling Matrix Element in a Correlated System
High-resolution electron energy loss spectroscopy measurements have been carried out on an optimally doped cuprate Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}. The momentum-dependent energy and linewidth of an A{sub 1} optical phonon were obtained. Based on these data as well as detailed knowledge of the electronic structure, we developed a scheme to determine the electron-phonon coupling (EPC) matrix element related to a specific phonon mode. Such an approach is general and applicable to elucidating the full structure of EPC in a system with anisotropic electronic structure.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Magneto-Optical Measurements of a Cascade of Transitions in Superconducting La 1.875 Ba 0.125 CuO 4 Single Crystals
Not Available
Karapetyan, Hovnatan↗
Fragility of Charge Order Near an Antiferromagnetic Quantum Critical Point
Here, we investigate the interplay between charge order and superconductivity near an antiferromagnetic quantum critical point using sign-problem-free Quantum Monte Carlo simulations. We establish that, when the electronic dispersion is particle-hole symmetric, the system has an emergent SU(2) symmetry that implies a degeneracy between d -wave superconductivity and charge order with d -wave form factor. Deviations from particle-hole symmetry, however, rapidly lift this degeneracy, despite the fact that the SU(2) symmetry is preserved at low energies. As a result, we find a strong suppression of charge order caused by the competing, leading superconducting instability. Across the antiferromagnetic phase transition, we also observe a shift in the charge order wave vector from diagonal to axial. We discuss the implications of our results to the universal phase diagram of antiferromagnetic quantum-critical metals and to the elucidation of the charge order experimentally observed in the cuprates.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Signatures of Enhanced Superconducting Phase Coherence in Optimally Doped Bi 2 Sr 2 Y 0.08 Ca 0.92 Cu 2 O 8+δ Driven by Midinfrared Pulse Excitations
Optimally doped cuprate are characterized by the presence of superconducting fluctuations in a relatively large temperature region above the critical transition temperature. We reveal here that the effect of thermal disorder, which decreases the condensate phase coherence at equilibrium, can be dynamically contrasted by photoexcitation with ultrashort midinfrared pulses. In particular, our findings reveal that light pulses with photon energy comparable to the amplitude of the superconducting gap and polarized in plane along the copper-copper direction can dynamically enhance the optical response associated with the onset of superconductivity. Furthermore, we propose that this effect can be rationalized by an effective d-wave BCS model, which reveals that midinfrared pulses result in a transient increase of the phase coherence.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Mode-Selective Coupling of Coherent Phonons to the Bi2212 Electronic Band Structure
Cuprate superconductors host a multitude of low-energy optical phonons. Using time- and angle-resolved photoemission spectroscopy, we study coherent phonons in Bi 2 Sr 2 Ca 0.92 Y 0.08 Cu 2 O 8+δ . Sub-meV modulations of the electronic band structure are observed at frequencies of 3.94 ± 0.01 and 5.59 ± 0.06 THz. For the dominant mode at 3.94 THz, the amplitude of the band energy oscillation weakly increases as a function of momentum away from the node. Theoretical calculations allow identifying the observed modes as CuO 2 -derived A 1 g phonons. The Bi- and Sr-derived A 1 g modes which dominate Raman spectra in the relevant frequency range are absent in our measurements. Furthermore, this highlights the mode selectivity for phonons coupled to the near-Fermi-level electrons, which originate from CuO 2 planes and dictate thermodynamic properties.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Evolution of the Magnetic Excitations in Electron-Doped La 2 - x Ce x CuO 4
Here we investigated the high energy spin excitations in electron-doped La 2-x Ce x CuO 4 , a cuprate superconductor, by resonant inelastic x-ray scattering (RIXS) measurements. Efforts were paid to disentangle the paramagnon signal from non-spin-flip spectral weight mixing in the RIXS spectrum at Q ∥ =(0.6π,0) and (0.9π,0) along the (1 0) direction. Our results show that, for doping level x from 0.07 to 0.185, the variation of the paramagnon excitation energy is marginal. We discuss the implication of our results in connection with the evolution of the electron correlation strength in this system.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Electron Glass Phase with Resilient Zhang-Rice Singlets in LiCu 3 O 3
LiCu 3 O 3 is an antiferromagnetic mixed valence cuprate where trilayers of edge-sharing Cu(II)O (3d 9 ) are sandwiched in between planes of Cu(I) (3d 10 ) ions, with Li stochastically substituting Cu(II). Angle-resolved photoemission spectroscopy (ARPES) and density functional theory reveal two insulating electronic subsystems that are segregated in spite of sharing common oxygen atoms: a Cu d z 2 /O p z derived valence band (VB) dispersing on the Cu(I) plane, and a Cu 3d x 2 -y 2 /O 2p x,y derived Zhang-Rice singlet (ZRS) band dispersing on the Cu(II)O planes. First-principle analysis shows the Li substitution to stabilize the insulating ground state, but only if antiferromagnetic correlations are present. Li further induces substitutional disorder and a 2D electron glass behavior in charge transport, reflected in a large 530 meV Coulomb gap and a linear suppression of VB spectral weight at E F that is observed by ARPES. Surprisingly, the disorder leaves the Cu(II)-derived ZRS largely unaffected. Finally, this indicates a local segregation of Li and Cu atoms onto the two separate corner-sharing Cu(II)O 2 sub-lattices of the edge-sharing Cu(II)O planes, and highlights the ubiquitous resilience of the entangled two hole ZRS entity against impurity scattering.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
From a Single-Band Metal to a High-Temperature Superconductor via Two Thermal Phase Transitions
The nature of the pseudogap phase of cuprate high-temperature superconductors is one of the most important unsolved problems in condensed matter physics. We studied the commencement of the pseudogap state at temperature T* using three different techniques (angle-resolved photoemission spectroscopy, polar Kerr effect, and time-resolved reflectivity) on the same optimally-doped Bi2201 crystals. We observe the coincident onset at T* of a particle-hole asymmetric antinodal gap, a non-zero Kerr rotation, and a change in the relaxational dynamics, consistent with a phase transition. Upon further cooling, spectroscopic signatures of superconductivity begin to grow close to the superconducting transition temperature (T{sub c}), entangled in an energy-momentum dependent fashion with the pre-existing pseudogap features.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Structure of complexes of nitrilo tris methylene phosphonic acid with copper, [CuN(CH{sub 2}PO{sub 3}){sub 3}(H{sub 2}O){sub 3}] and Na{sub 4}[CuN(CH{sub 2}PO{sub 3}){sub 3}]{sub 2} · 19H{sub 2}O, as bactericides and inhibitors of scaling and corrosion
Nitrilotris methylene phosphonate triaqua copper and octasodium bis(nitrilotris methylene phosphonate cuprate(II)) nonadecahydrate have been synthesized and investigated. [CuN(CH{sub 2}PO{sub 3}){sub 3}(H{sub 2}O){sub 3}] is crystallized in the sp. gr. P2{sub 1}/c, Z = 4, a = 9.2506(2) Å, b = 15.9815(2) Å, c = 9.5474(2) Å, β = 113.697(2)°. The copper atom is coordinated by oxygen atoms in the configuration of elongated octahedron; the ligand (of bridge type) links neighboring copper atoms. Na{sub 8}[CuN(CH{sub 2}PO{sub 3}){sub 3}]{sub 2} · 19H{sub 2}O is crystallized in the sp. gr. P2{sub 1}/c, Z = 2, a = 11.24550(10) Å, b = 17.38980(10) Å, c = 13.5852(2) Å, β = 127.8120(10)°. This complex is chelating; the copper atom closes three five-membered N-C-P-O-Cu cycles with a shared Cu-N bond. Copper is coordinated in a distorted trigonal-bipyramidal configuration.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗