Soft superconducting gap in semiconductor-based Majorana nanowires

We develop a theory for the proximity effect in superconductor-semiconductor-normal metal tunneling structures, which have recently been extensively studied experimentally, leading to the observation of transport signatures consistent with the predicted zero-energy Majorana bound states. We show that our model for the semiconductor nanowire having multiple occupied subbands with different transmission probabilities through the barrier reproduces the observed "soft-gap" behavior associated with substantial subgap tunneling conductance. We study the manifestations of the soft gap phenomenon both in the tunneling conductance and in local density of states measurements and discuss the correlations between these two quantities. We emphasize that the proximity effect associated with the hybridization between low-lying states in the multiband semiconductor and the normal metal states in the lead is an intrinsic effect leading to the soft gap problem. In addition to the intrinsic contribution, there may be extrinsic effects, such as, for example, interface disorder, exacerbating the soft gap problem. Our work establishes the generic possibility of an ubiquitous presence of an intrinsic soft gap in the superconductor-semiconductor-normal metal tunneling transport conductance induced by the inverse proximity effect of the normal metal.Comment: published version, 11+ pages, 8 figure

Dimensional crossover in spin-orbit-coupled semiconductor nanowires with induced superconducting pairing

We show that the topological Majorana modes in nanowires much longer than the superconducting coherence length are adiabatically connected with discrete zero-energy states generically occurring in short nanowires. We demonstrate that these zero-energy crossings can be tuned by an external magnetic field and are protected by the particle-hole symmetry. We study the evolution of the low-energy spectrum and the splitting oscillations as a function of magnetic field, wire length, and chemical potential, manifestly establishing that the low-energy physics of short wires is related to that occurring in long wires. This physics, which represents a hallmark of spinless p-wave superconductivity, can be observed in tunneling conductance measurements.Comment: published version, 7 pages, 7 color figure

Proximity effect at the superconductor - topological insulator interface

We study the excitation spectrum of a topological insulator in contact with an s-wave superconductor, starting from a microscopic model, and develop an effective low-energy model for the proximity effect. In the vicinity of the Dirac cone vertex, the effective model describing the states localized at the interface is well approximated by a model of Dirac electrons experiencing superconducting s-wave pairing. Away from the cone vertex, the induced pairing potential develops a p-wave component with a magnitude sensitive to the structure of the interface. Observing the induced s-wave superconductivity may require tuning the chemical potential close to the Dirac point. Furthermore, we find that the proximity of the superconductor leads to a significant renormalization of the original parameters of the effective model describing the surface states of a topological insulator.Comment: 4+ pages, 3 figures (published version

Non-equilibrium spin dynamics in a trapped Fermi gas with effective spin-orbit interaction

We consider a trapped atomic system in the presence of spatially varying laser fields. The laser-atom interaction generates a pseudospin degree of freedom (referred to simply as spin) and leads to an effective spin-orbit coupling for the fermions in the trap. Reflections of the fermions from the trap boundaries provide a physical mechanism for effective momentum relaxation and non-trivial spin dynamics due to the emergent spin-orbit coupling. We explicitly consider evolution of an initially spin-polarized Fermi gas in a two-dimensional harmonic trap and derive non-equilibrium behavior of the spin polarization. It shows periodic echoes with a frequency equal to the harmonic trapping frequency. Perturbations, such as an asymmetry of the trap, lead to the suppression of the spin echo amplitudes. We discuss a possible experimental setup to observe spin dynamics and provide numerical estimates of relevant parameters.Comment: 5 pages, 4 figures; published versio

Nodal/Antinodal Dichotomy and the Two Gaps of a Superconducting Doped Mott Insulator

We study the superconducting state of the hole-doped two-dimensional Hubbard model using Cellular Dynamical Mean Field Theory, with the Lanczos method as impurity solver. In the under-doped regime, we find a natural decomposition of the one-particle (photoemission) energy-gap into two components. The gap in the nodal regions, stemming from the anomalous self-energy, decreases with decreasing doping. The antinodal gap has an additional contribution from the normal component of the self-energy, inherited from the normal-state pseudogap, and it increases as the Mott insulating phase is approached.Comment: Corrected typos, 4.5 pages, 4 figure

High-grade cervical dysplasia in pregnancy – psychological and medical challenges

Despite being rare, the incidence of pregnancy-related cancer is expected to rise as women continue to delay childbearing and give birth later in their reproductive years. In this broad category, tumors like breast cancer, dermatological neoplasia and cervical cancer are most common and tend to arise in women of childbearing age. All pregnant women with clinical and cytologic suspicion of cervical cancer, except for squamous atypia or low-grade squamous intraepithelial lesions, should undergo colposcopy, with or without biopsy, the latter being avoided if possible due to possible complications which, although rare, may involve preterm labor initiation. Some studies have attempted to assimilate comparable results of USG with MRI during the gestational period by determining the sensitivity, specificity, and accuracy of trans-rectal ultrasound (TRUS) in comparison to magnetic resonance imaging (MRI). In order to identify the proper way to diagnose and treat the disease, because of the complexity due to pregnancy, a multidisciplinary team consisting of a gynecologist, medical and surgical oncologist, and radiologist should be assembled. Both maternal and fetal wellbeing should be taken into consideration when the medical team must choose among termination of pregnancy, delay of maternal treatment, and iatrogenic preterm delivery. Psychological counseling also plays an important role and due to the sensitivity of the issue, should continue through gestation and the postpartum. In order to develop optimal guidelines for diagnosis, treatment, and outcome issues, large scale prospective studies are needed, but feasibility may be limited due to the scarcity of cervical cancer cases associated with pregnancy

The psychosocial impact of vaginal delivery and cesarean section in primiparous women

The aim of this study was to identify how the method of delivery and birth experience interfere with maternal psychological status early after puerperium. We conducted a prospective study on 148 women after puerperium from November 2017 to January 2018 in Bucur Maternity Hospital. Women that delivered vaginally mobilized in the first 6 hours in 73.7% of the cases, but for cesarean section after 12- 24 hours in 43.6% of the cases. Women described good support from the obstetrician in 58.1% of the cases. 90.5% of the women reported that the method of delivery did not have an impact on infant care and 73% had no lactation problems. The majority described little trauma, in 32.4% of the cases. 70.3% of the patients reported that they wanted to have more children and 59.5% of them desired the same method of delivery. Negative feelings, lactation, and taking care of the baby were not influenced in this study by the method of delivery, but by prematurity of birth and the complications that women experienced at birth

Electronic and magnetic properties of metallic phases under coexisting short-range interaction and diagonal disorder

We study a three-dimensional Anderson-Hubbard model under the coexistence of short-range interaction and diagonal disorder within the Hartree-Fock approximation. We show that the density of states at the Fermi energy is suppressed in the metallic phases near the metal-insulator transition as a proximity effect of the soft Hubbard gap in the insulating phases. The transition to the insulator is characterized by a vanishing DOS in contrast to formation of a quasiparticle peak at the Fermi energy obtained by the dynamical mean field theory in pure systems. Furthermore, we show that there exist frozen spin moments in the paramagnetic metal.Comment: 4 pages, 2 figures, published versio