9 research outputs found
Paramagnon dispersion and damping in doped NaCaCuOCl
Using Resonant Inelastic X-ray Scattering, we measure the paramagnon
dispersion and damping of undoped, antiferromagnetic CaCuOCl as
well as doped, superconducting NaCaCuOCl. Our estimation
of the spin-exchange parameter and width of the paramagnon peak at the zone
boundary confirms that no simple relation can be drawn between
these parameters and the critical temperature . Consistently with
other cuprate compounds, we show that upon doping there is a slight softening
at , but not at the zone boundary . In combination with these
measurements we perform calculations of the dynamical spin structure factor of
the one-band Hubbard model using cluster dynamical mean-field theory. The
calculations are in excellent agreement with the experiment in the undoped
case, both in terms of energy position and width. While the increase in width
is also captured upon doping, the dynamical spin structure factor shows a
sizable softening at , which provides insightful information on the
length-scale of the spin fluctuations in doped cuprates.Comment: 11 pages, 5 figures, 2 tables, V2 typo corrected in title and
reference
Bulk charge density wave and electron-phonon coupling in superconducting copper oxychlorides
Bulk charge density waves (CDWs) are now reported in nearly all
high-temperature superconducting (HTS) cuprates, with the noticeable exception
of one particular family: the copper oxychlorides. Here, we used resonant
inelastic X-ray scattering (RIXS) to reveal a bulk CDW in these materials.
Combining RIXS with non-resonant IXS, we investigate the interplay between the
lattice excitations and the CDW, and evidence bond-stretching (BS) phonon
anomalies at the CDW wave-vector. We propose that such electron-phonon
anomalies occur in the presence of dispersive charge excitations emanating from
the CDW and interacting with the BS phonon. Our observations in a structurally
simple cuprate promises to better connect bulk and surface properties and
bridge the gap between theory and experiment
Acoustic phonon dispersion of α−RuCl3
Acoustic phonons have recently been posited as playing an integral role in
explaining the half-quantized thermal Hall effect in -RuCl.
Therefore, we present much needed inelastic x-ray scattering measurements of
its acoustic phonon dispersion, along with calculations using the frozen-phonon
method. We also discuss a temperature study which conclusively shows a
first-order structural transition to a non- space group at low
temperature. Together these results are an important backbone for future
theoretical and experimental studies of -RuCl
Nonlocal features of the spin-orbit exciton in Kitaev materials
A comparative resonant inelastic x-ray scattering (RIXS) study of three well-known Kitaev materials is presented: alpha-Li2IrO3, Na2IrO3, and alpha-RuCl3. Despite similar low-energy physics, these materials show distinct electronic properties, such as the large difference in the size of the charge gap. The RIXS spectra of the spin-orbit exciton for these materials show remarkably similar three-peak features, including sharp low energy peak (peak A) as well as transitions between jeff = 1/2 and jeff = 3/2 states. Comparison of experimental spectra with cluster calculations reveals that the observed three-peak structure reflects the significant role that nonlocal physics plays in the electronic structure of these materials. In particular, the low-energy peak A arises from a holon-doublon pair rather than a conventional particle-hole exciton as proposed earlier. Our study suggests that while spin-orbit assisted Mott insulator is still the best description for these materials, electron itinerancy cannot be ignored when formulating low-energy Hamiltonian of these materials.11Nsciescopu
Superconductivity, pseudo-gap, and stripe correlations in high-T c cuprates
International audienceUnder-doped La-214 cuprates show a charge-and spin-modulation known as " stripes " [1]. These stripe modulations are (quasi)-static close to 1/8 hole doping where superconductivity is suppressed. The pseudo-gap phase of other cuprate compounds recently also revealed charge modulation, but interpreted rather as a charge density wave (CDW) [2, 3, 4], that possibly competes with superconductivity. In this context, to better understand the interplay between the stripe phase and the superconductivity, we use angle-resolved photoemission spectroscopy to study the electronic band structure and gap in La-214 cuprates near 1/8 doping (La 2−x−y Nd y Sr x CuO 4 (x = 0.12; y = 0.0 & 0.4)) and compare with the previous results in the same system [5] and La 1.86 Ba 0.14 CuO 4 [6]. Our data shows a loss of spectral intensity towards the end of the Fermi arcs, that is possibly due to a strong renormalisation, as already pointed out elsewhere * [email protected] Néel CNRS-25, av des Martyrs-38042 Grenoble cedex 9; tel: (+33)(0)4 76 88 12 84 [5], with a noisy but still measurable gap. On the nodal direction no gap is observed within our statistics, but a sizeable decrease in intensity with temperature. Moreover, we do not see any shadow band, but our Fermi surface can be well modelled with a single electron band calculation in the tight binding approximation, even very close to the 1/8 doping La 2−x−y Nd y Sr x CuO 4 with and without Nd substitution
Sensitivity of revised diagnostic criteria for the behavioural variant of frontotemporal dementia
Based on the recent literature and collective experience, an international consortium developed revised guidelines for the diagnosis of behavioural variant frontotemporal dementia. The validation process retrospectively reviewed clinical records and compared the sensitivity of proposed and earlier criteria in a multi-site sample of patients with pathologically verified frontotemporal lobar degeneration. According to the revised criteria, 'possible' behavioural variant frontotemporal dementia requires three of six clinically discriminating features (disinhibition, apathy/inertia, loss of sympathy/empathy, perseverative/compulsive behaviours, hyperorality and dysexecutive neuropsychological profile). 'Probable' behavioural variant frontotemporal dementia adds functional disability and characteristic neuroimaging, while behavioural variant frontotemporal dementia 'with definite frontotemporal lobar degeneration' requires histopathological confirmation or a pathogenic mutation. Sixteen brain banks contributed cases meeting histopathological criteria for frontotemporal lobar degeneration and a clinical diagnosis of behavioural variant frontotemporal dementia, Alzheimer's disease, dementia with Lewy bodies or vascular dementia at presentation. Cases with predominant primary progressive aphasia or extra-pyramidal syndromes were excluded. In these autopsy-confirmed cases, an experienced neurologist or psychiatrist ascertained clinical features necessary for making a diagnosis according to previous and proposed criteria at presentation. Of 137 cases where features were available for both proposed and previously established criteria, 118 (86%) met 'possible' criteria, and 104 (76%) met criteria for 'probable' behavioural variant frontotemporal dementia. In contrast, 72 cases (53%) met previously established criteria for the syndrome (P < 0.001 for comparison with 'possible' and 'probable' criteria). Patients who failed to meet revised criteria were significantly older and most had atypical presentations with marked memory impairment. In conclusion, the revised criteria for behavioural variant frontotemporal dementia improve diagnostic accuracy compared with previously established criteria in a sample with known frontotemporal lobar degeneration. Greater sensitivity of the proposed criteria may reflect the optimized diagnostic features, less restrictive exclusion features and a flexible structure that accommodates different initial clinical presentations. Future studies will be needed to establish the reliability and specificity of these revised diagnostic guidelines