Theory of optical spectral weights in Mott insulators with orbital degrees of freedom

Introducing partial sum rules for the optical multiplet transitions, we outline a unified approach to magnetic and optical properties of strongly correlated transition metal oxides. On the example of LaVO$_3$ we demonstrate how the temperature and polarization dependences of different components of the optical multiplet are determined by the underlying spin and orbital correlations dictated by the low-energy superexchange Hamiltonian. Thereby the optical data provides deep insight into the complex spin-orbital physics and the role played by orbital fluctuations.Comment: 6 pages, 3 figures, expanded versio

Oxygen phonon branches in overdoped La1.7_{1.7}Sr0.3_{0.3}CuO4_4

The dispersion of the Cu-O bond-stretching vibrations in overdoped La$_{1.7}$Sr$_{0.3}$CuO$_4$ (not superconducting) has been studied by high resolution inelastic neutron scattering. It was found that the doping-induced renormalization of the so-called breathing and the half-breathing modes is larger than in optimally doped La$_{1.85}$Sr$_{0.15}$CuO$_4$. On the other hand, the phonon linewidths are generally smaller in the overdoped sample. Features observed in optimally doped La$_{1.85}$Sr$_{0.15}$CuO$_4$ which suggest a tendency towards charge stripe formation are absent in overdoped La$_{1.7}$Sr$_{0.3}$CuO$_4$.Comment: 6 pages, 8 figure

Spectral properties of orbital polarons in Mott insulators

We address the spectral properties of Mott insulators with orbital degrees of freedom, and investigate cases where the orbital symmetry leads to Ising-like superexchange in the orbital sector. The paradigm of a hole propagating by its coupling to quantum fluctuations, known from the spin t-J model, then no longer applies. We find instead that when one of the two orbital flavors is immobile, as in the Falicov-Kimball model, trapped orbital polarons coexist with free hole propagation emerging from the effective three-site hopping in the regime of large on-site Coulomb interaction U. The spectral functions are found analytically in this case within the retraceable path approximation in one and two dimensions. On the contrary, when both of the orbitals are active, as in the model for $t_{2g}$ electrons in two dimensions, we find propagating polarons with incoherent scattering dressing the moving hole and renormalizing the quasiparticle dispersion. Here, the spectral functions, calculated using the self-consistent Born approximation, are anisotropic and depend on the orbital flavor. Unbiased conclusions concerning the spectral properties are established by comparing the above results for the orbital t-J models with those obtained using the variational cluster approximation or exact diagonalization for the corresponding Hubbard models. The present work makes predictions concerning the essential features of photoemission spectra of certain fluorides and vanadates.Comment: 26 pages, 16 figures; to appear in Physical Review

Wigner crystallization in Na(3)Cu(2)O(4) and Na(8)Cu(5)O(10) chain compounds

We report the synthesis of novel edge-sharing chain systems Na(3)Cu(2)O(4) and Na(8)Cu(5)O(10), which form insulating states with commensurate charge order. We identify these systems as one-dimensional Wigner lattices, where the charge order is determined by long-range Coulomb interaction and the number of holes in the d-shell of Cu. Our interpretation is supported by X-ray structure data as well as by an analysis of magnetic susceptibility and specific heat data. Remarkably, due to large second neighbor Cu-Cu hopping, these systems allow for a distinction between the (classical) Wigner lattice and the 4k_F charge-density wave of quantum mechanical origin.Comment: 4 pages, 4 figure

Signatures of a staggered-flux phase in the t-J model with two holes on a 32-site lattice

We study the relevance of the staggered-flux phase in the t-J model using a system with two holes on a 32-site lattice with periodic boundary conditions. We find a staggered-flux pattern in the current-current correlation in the lowest energy d-wave state where there is mutual attraction between the holes. This staggered correlation decays faster with distance when the hole binding becomes stronger. This is in complete agreement with a recent study by Ivanov, Lee and Wen (Phys. Rev. Lett. 84, 3958, (2000)) based on the SU(2) theory, and strongly suggests that the staggered-flux phase is a key ingredient in the t-J model. We further show that this staggered-flux pattern does not exist in a state where the holes repel each other. Correlations of the chirality operator S_1.(S_2xS_3) show that the staggered pattern of the chirality is closely tied to the holes.Comment: To appear in Phys. Rev. B (Rapid Communications

Reducing childbirth-related intrusive memories and PTSD symptoms via a single-session behavioural intervention including a visuospatial task: A proof-of-principle study.

Intrusive memories (IMs) of traumatic events are a key symptom of posttraumatic stress disorder (PTSD), and contribute to its maintenance. This translational proof-of-principle study tested whether a single-session behavioural intervention reduced the number of childbirth-related IMs (CB-IMs) and childbirth-related PTSD (CB-PTSD) symptoms, in women traumatised by childbirth. The intervention was assumed to disrupt trauma memory reconsolidation. In this pre-post study, 18 participants, whose traumatic childbirth had occurred between seven months and 6.9 years before, received an intervention combining childbirth-related reminder cues (including the return to maternity unit) with a visuospatial task. They recorded their daily CB-IMs in the two weeks pre-intervention (diary 1), the two weeks post-intervention (diary 2; primary outcome), and in week 5 and 6 post-intervention (diary 3). CB-PTSD symptom severity was assessed five days pre-intervention and one month post-intervention. Compared to diary 1, 15/18 participants had ≥ 50% fewer CB-IMs in diary 2. The median (IQR) reduction of the number of CB-IMs was 81.89% (39.58%) in diary 2, and persisted in diary 3 (n = 17). At one month post-intervention, CB-PTSD symptom severity was reduced by ≥ 50% in 10/18 participants. Of the 8 participants with a CB-PTSD diagnosis pre-intervention, none met diagnostic criteria post-intervention. The intervention was rated as highly acceptable. The design limits the causal interpretation of observed improvements. This is the first time such a single-session behavioural intervention was tested for old and real-life single-event trauma. The promising results justify a randomized controlled trial, and may be a first step toward an innovative CB-PTSD treatment

Cu KK-edge Resonant Inelastic X-Ray Scattering in Edge-Sharing Cuprates

We present calculations for resonant inelastic x-ray scattering (RIXS) in edge-shared copper oxide systems, such as CuGeO$_{3}$ and Li$_{2}$CuO$_{2}$, appropriate for hard x-ray scattering where the photoexcited electron lies above oxygen 2p and copper 3d orbital energies. We perform exact diagonalizations of the multi-band Hubbard and determine the energies, orbital character and resonance profiles of excitations which can be probed via RIXS. We find excellent agreement with recent results on Li$_{2}$CuO$_{2}$ and CuGeO$_{3}$ in the 2-7 eV photon energy loss range.Comment: Updated with new data, expanded 9 pages, 9 figure

Informing about childbirth without increasing anxiety: a qualitative study of first-time pregnant women and partners' perceptions and needs.

Complications requiring medical interventions during childbirth are far from rare, even after uncomplicated pregnancies. It is often a challenge for maternity healthcare professionals to know how to prepare future parents for these eventualities without causing unnecessary anxiety. Studies on traumatic birth experiences have shown that feelings of loss of control, insufficient information, and lack of participation in medical decisions during childbirth are factors of difficult experiences. However, little is known about the information and communication needs of expectant parents about childbirth during the prenatal period. To gain a deeper understanding of the information and communication needs of first-time pregnant women and partners, we explored their perceptions and expectations for their upcoming childbirth, and the actions they initiated to prepare for it. Semi-structured interviews were conducted individually with first-time pregnant women and partners of pregnant women aged 18 years or older, with an uncomplicated pregnancy. Thematic analysis was used to identify themes and sub-themes. Twenty expectant parents (15 pregnant women and five partners of pregnant women) were interviewed. Six themes were identified: Childbirth event; Childbirth experience; Childbirth environment; Organisation of care; Participation in decision making; Roles within the couple and transition to parenthood. This study contributes to a better understanding of the information needs of future parents expecting their first child. Results highlighted that the notion of "childbirth risks" went beyond the prospect of complications during birth, but also encompassed concerns related to a feeling of loss of control over the event. Expectant parents showed an ambivalent attitude towards consulting risk information, believing it important to prepare for the unpredictability of childbirth, while avoiding information they considered too worrying. They expressed a desire to receive concrete, practical information, and needed to familiarise themselves in advance with the birth environment. Establishing a respectful relationship with the healthcare teams was also considered important. The findings suggest that information on childbirth should not be limited to the transmission of knowledge, but should primarily be based on the establishment of a relationship of trust with healthcare professionals, taking into account each person's individual values and expectations