Entropic Origin of Pseudogap Physics and a Mott-Slater Transition in Cuprates

We propose a new approach to understand the origin of the pseudogap in the cuprates, in terms of bosonic entropy. The near-simultaneous softening of a large number of different $q$-bosons yields an extended range of short-range order, wherein the growth of magnetic correlations with decreasing temperature $T$ is anomalously slow. These entropic effects cause the spectral weight associated with the Van Hove singularity (VHS) to shift rapidly and nearly linearly toward half filling at higher $T$, consistent with a picture of the VHS driving the pseudogap transition at a temperature $\sim T^*$. As a byproduct, we develop an order-parameter classification scheme that predicts supertransitions between families of order parameters. As one example, we find that by tuning the hopping parameters, it is possible to drive the cuprates across a {\it transition between Mott and Slater physics}, where a spin-frustrated state emerges at the crossover.Comment: 24 pgs, 15 figs + Supp. Material [6pgs, 3 figs]. Major revision of arXiv:1505.0477

Respective influence of in-plane and out-of-plane spin-transfer torques in magnetization switching of perpendicular magnetic tunnel junctions

The relative contributions of in-plane (damping-like) and out-of-plane (field-like) spin-transfer-torques in the magnetization switching of out-of-plane magnetized magnetic tunnel junctions (pMTJ) has been theoretically analyzed using the transformed Landau-Lifshitz (LL) equation with the STT terms. It is demonstrated that in a pMTJ structure obeying macrospin dynamics, the out-of-plane torque influences the precession frequency but it does not contribute significantly to the STT switching process (in particular to the switching time and switching current density), which is mostly determined by the in-plane STT contribution. This conclusion is confirmed by finite temperature and finite writing pulse macrospin simulations of the current-field switching diagrams. It contrasts with the case of STT-switching in in-plane magnetized MTJ in which the field-like term also influences the switching critical current. This theoretical analysis was successfully applied to the interpretation of voltage-field STT switching diagrams experimentally measured on perpendicular MTJ pillars 36 nm in diameter, which exhibit macrospin-like behavior. The physical nonequivalence of Landau and Gilbert dissipation terms in presence of STT-induced dynamics is also discussed

Design and synthesis of aromatic molecules for probing electric-fields at the nanoscale

We propose using halogenated organic dyes as nanoprobes for electric field and show their greatly enhanced Stark coefficients using density functional theory (DFT) calculations. We analyse halogenated variants of three molecules that have been of interest for cryogenic single molecule spectroscopy, perylene, terrylene, and dibenzoterrylene, with the zero-phonon optical transitions at blue, red, and near infrared. Out of all the combinations of halides and binding sites that are calculated, we have found that fluorination of the optimum binding site induces a dipole difference between ground and excited states larger than 0.5 D for all three molecules with the highest value of 0.69 D for fluoroperylene. We also report on synthesis of 3-fluoroterrylene and bulk spectroscopy of this compound in liquid and solid organic environments.Comment: Article presented in Faraday Discussions on September 201

Ab-initio Molecular Dynamics study of electronic and optical properties of silicon quantum wires: Orientational Effects

We analyze the influence of spatial orientation on the optical response of hydrogenated silicon quantum wires. The results are relevant for the interpretation of the optical properties of light emitting porous silicon. We study (111)-oriented wires and compare the present results with those previously obtained within the same theoretical framework for (001)-oriented wires [F. Buda {\it et al.}, {\it Phys. Rev. Lett.} {\bf 69}, 1272, (1992)]. In analogy with the (001)-oriented wires and at variance with crystalline bulk silicon, we find that the (111)-oriented wires exhibit a direct gap at ${\bf k}=0$ whose value is largely enhanced with respect to that found in bulk silicon because of quantum confinement effects. The imaginary part of the dielectric function, for the external field polarized in the direction of the axis of the wires, shows features that, while being qualitatively similar to those observed for the (001) wires, are not present in the bulk. The main conclusion which emerges from the present study is that, if wires a few nanometers large are present in the porous material, they are optically active independently of their specific orientation.Comment: 14 pages (plus 6 figures), Revte

Calculating energy derivatives for quantum chemistry on a quantum computer

Modeling chemical reactions and complicated molecular systems has been proposed as the `killer application' of a future quantum computer. Accurate calculations of derivatives of molecular eigenenergies are essential towards this end, allowing for geometry optimization, transition state searches, predictions of the response to an applied electric or magnetic field, and molecular dynamics simulations. In this work, we survey methods to calculate energy derivatives, and present two new methods: one based on quantum phase estimation, the other on a low-order response approximation. We calculate asymptotic error bounds and approximate computational scalings for the methods presented. Implementing these methods, we perform the world's first geometry optimization on an experimental quantum processor, estimating the equilibrium bond length of the dihydrogen molecule to within 0.014 Angstrom of the full configuration interaction value. Within the same experiment, we estimate the polarizability of the H2 molecule, finding agreement at the equilibrium bond length to within 0.06 a.u. (2% relative error).Comment: 19 pages, 1 page supplemental, 7 figures. v2 - tidied up and added example to appendice

Achievable rates for the Gaussian quantum channel

We study the properties of quantum stabilizer codes that embed a finite-dimensional protected code space in an infinite-dimensional Hilbert space. The stabilizer group of such a code is associated with a symplectically integral lattice in the phase space of 2N canonical variables. From the existence of symplectically integral lattices with suitable properties, we infer a lower bound on the quantum capacity of the Gaussian quantum channel that matches the one-shot coherent information optimized over Gaussian input states.Comment: 12 pages, 4 eps figures, REVTe

ACL ARTHROSCOPIC RECONSTRUCTION WITH DOUBLE-STRANDED HAMSTRING TENDONS

INTRODUCTION: In the past the ACL reconstruction was performed using patellar tendon. This technique involved several advantages like post operative good stability and easy tendon gathering. Nevertheless it causes some disadvantages like pain during the act of kneeling, longer period of rehabilitation because of the tendon stiffness and dysfunction of the patella movement that can provoke patellar-femoral osteoarthritis. This is the reason why a lot of authors tried to find out other techniques that could avoid these complications. We practised the ACL reconstruction using doubled semitendinosus and gracilis tendons because it is demonstrated that they have a biological structure and biomechanical behaviour more similar to normal ACL. In this sense the use of these tendons must include tensibility closer to normal ACL, larger surface of revascularization and low risk of joint stiffness after surgery. The purpose of the present study is to evaluate clinical results using this technique in patients involved both in not professional and professional sports