The physics of doped Mott insulators remains controversial after decades of active research, hindered by the interplay among competing orders and fluctuations. It is thus highly desired to distinguish the intrinsic characters of the Mott-metal crossover from those of other origins. Here we investigate the evolution of electronic structure and dynamics of the hole-doped pseudospin-1/2 Mott insulator Sr2IrO4. The effective hole doping is achieved by replacing Ir with Rh atoms, with the chemical potential immediately jumping to or near the top of the lower Hubbard band. The doped iridates exhibit multiple iconic low-energy features previously observed in doped cuprates—pseudogaps, Fermi arcs and marginal-Fermi-liquid-like electronic scattering rates. We suggest these signatures are most likely an integral part of the material's proximity to the Mott state, rather than from many of the most claimed mechanisms, including preformed electron pairing, quantum criticality or density-wave formation.

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Measuring how the magnetic correlations evolve in doped Mott insulators has greatly improved our understanding of the pseudogap, non-Fermi liquids and high-temperature superconductivity. Recently, photo-excitation has been used to induce similarly exotic states transiently. However, the lack of available probes of magnetic correlations in the time domain hinders our understanding of these photo-induced states and how they could be controlled. Here, we implement magnetic resonant inelastic X-ray scattering at a free-electron laser to directly determine the magnetic dynamics after photo-doping the Mott insulator Sr2IrO4. We find that the non-equilibrium state, 2 ps after the excitation, exhibits strongly suppressed long-range magnetic order, but hosts photo-carriers that induce strong, non-thermal magnetic correlations. These two-dimensional (2D) in-plane Néel correlations recover within a few picoseconds, whereas the three-dimensional (3D) long-range magnetic order restores on a fluence-dependent timescale of a few hundred picoseconds. The marked difference in these two timescales implies that the dimensionality of magnetic correlations is vital for our understanding of ultrafast magnetic dynamics.

A Fermi arc 1,2 is a disconnected segment of a Fermi surface observed in the pseudogap phase 3,4 of cuprate superconductors. This simple description belies the fundamental inconsistency in the physics of Fermi arcs, specifically that such segments violate the topological integrity of the band 5 . Efforts to resolve this contradiction of experiment and theory have focused on connecting the ends of the Fermi arc back on itself to form a pocket, with limited and controversial success 6-9 . Here we show the Fermi arc, although composed of real spectral weight, lacks the quasiparticles to be a true Fermi surface 5 . To reach this conclusion we developed a new photoemission-based technique that directly probes the interplay of pair-forming and pair-breaking processes with unprecedented precision. We find the spectral weight composing the Fermi arc is shifted from the gap edge to the Fermi energy by pair-breaking processes 10 . Although real, this weight does not form a true Fermi surface, because the quasiparticles, although significantly broadened, remain at the gap edge. This non-quasiparticle weight may account for much of the unexplained behaviour of the pseudogap phase of the cuprates.

We use the tomographic density of states (TDoS), which is a measure of the density of states for a single slice through the band structure of a solid, to study the temperature evolution of the superconducting gap in the cuprates. The TDoS provides unprecedented accuracy in determining both the superconducting pair-forming strength, ∆, and the pair-breaking rate, Γ. In both optimally-and under-doped Bi 2 Sr 2 CaCu 2 O 8+δ , we find the near-nodal ∆ smoothly evolves through the superconducting transition temperature -clear evidence for the existence of pre-formed pairs.Additionally, we find the long observed 'filling' of the superconducting gap in the cuprates is due to the strongly temperature dependent Γ.

In this letter we construct the Stückelberg holographic superconductor with Weyl corrections.Under such corrections, the Weyl coupling parameter γ plays an important role in the order of phase transitions and the critical exponents of second order phase transitions. So do the model parameters c α , α and c 4 . Moreover, we show that the Weyl coupling parameter γ and the model parameters c α , α, c 4 which together control the size and strength of the conductivity coherence peak and the ratio of gap frequency over critical temperature ω g /T

While condensed matter systems host both Fermionic and Bosonic quasi-particles, reliably predicting and empirically verifying topological states is only mature for Fermionic electronic structures, leaving topological Bosonic excitations sporadically explored. This is unfortunate, as Bosonic systems such a phonons offer the opportunity to assess spinless band structures where nodal lines can be realized without invoking special additional symetries to protect against spin-orbit coupling.Here we combine first-principles calculations and meV-resolution inelastic x-ray scattering to demonstrate the first realization of parity-time reversal (PT ) symmetry protected helical nodal lines in the phonon spectrum of MoB2. This structure is unique to phononic systems as the spin-orbit coupling present in electronic systems tends to lift the degeneracy away from high-symmetry locations. Our study establishes a protocol to accurately identify topological Bosonic excitations, opening a new route to explore exotic topological states in crystalline materials.

The magnetic excitations in electron doped (Sr1−xLax)2IrO4 with x = 0.03 were measured using resonant inelastic X-ray scattering at the Ir L3-edge. Although much broadened, well defined dispersive magnetic excitations were observed. Comparing with the magnetic dispersion from the undoped compound, the evolution of the magnetic excitations upon doping is highly anisotropic. Along the anti-nodal direction, the dispersion is almost intact. On the other hand, the magnetic excitations along the nodal direction show significant softening. These results establish the presence of strong magnetic correlations in electron doped (Sr1−xLax)2IrO4 with close analogies to the hole doped cuprates, further motivating the search for high temperature superconductivity in this system. PACS numbers: 71.27.+a, 74.25.Ha, 78.70.Dm Together with the tremendous research activity on the superconducting cuprates [1,2], efforts to compare the cuprates with other related systems have also been on-going for decades. Such comparison serves as a natural approach to clarify the roles of multiple emergent phenomena in the phase diagram of the cuprates, including magnetic fluctuations, superconductivity, pseudo gap and charge density waves etc. The 5d oxide Sr 2 IrO 4 is an excellent candidate for such study. This so called spin-orbit-coupling driven Mott insulator [3] is in close proximity to the single layered cuprate La 2 CuO 4 , both structure-wise [4] and electronically [5][6][7][8]. Sr 2 IrO 4 hosts a single hole in the t 2g manifold where a Mott gap is opened, assisted by strong spin-orbit coupling [3,9,10], and its magnetic excitation spectrum can be well described using a Heisenberg model of effective spin-1 2 moments on a square lattice [11,12]. With a minimum single band model, Sr 2 IrO 4 and La 2 CuO 4 are strikingly similar [13], leading to the proposal that this compound could also host unconventional high temperature superconductivity (HTS) upon doping [13,14]. Moreover, due to the opposite signs of the nextnearest-neighbor hopping integral in these two systems, theoretical work further suggests that the electron doped Sr 2 IrO 4 might be more closely analogous to those of hole (rather than electron) doped cuprates [13,14].Although the phase diagram of doped Sr 2 IrO 4 has not been fully explored, a large amount of experimental work supports the hypothesis that the Fermiology of the doped iridates is closely analogous to the cuprates. Upon doping with La up to 6%, Sr 2 IrO 4 evolves from an antiferromagnetically ordered insulator to a paramagnetic [15] or percolative [16] metal. A T-linear resistivity was observed with potassium substitution [15]. Further, angle-resolved photoemission spectroscopy (ARPES) data from several groups [5][6][7]17] has shown convincingly that doping indeed drives a similar low energy electron evolution as observed in the cuprates. An anisotropic pseudo gap opens on the Fermi surface, with the same symmetry as that of the cuprates. However, the related question of whether the magnetic correlations that ...