Vortex creep at very low temperatures in single crystals of the extreme type-II superconductor Rh9In4 S4

We image vortex creep at very low temperatures using scanning tunneling microscopy in the superconductor Rh9In4S4 (Tc=2.25K). We measure the superconducting gap of Rh9In4S4, finding Δ≈0.33meV, and image a hexagonal vortex lattice up to close to Hc2, observing slow vortex creep at temperatures as low as 150 mK. We estimate thermal and quantum barriers for vortex motion and show that thermal fluctuations likely cause vortex creep, in spite of being at temperatures T/Tc<0.1. We study creeping vortex lattices by making images during long times and show that the vortex lattice remains hexagonal during creep with vortices moving along one of the high-symmetry axes of the vortex lattice. Furthermore, the creep velocity changes with the scanning window suggesting that creep depends on the local arrangements of pinning centers. Vortices fluctuate on small-scale erratic paths, indicating that the vortex lattice makes jumps trying different arrangements during its travel along the main direction for creep. The images provide a visual account of how vortex lattice motion maintains hexagonal order, while showing dynamic properties characteristic of a glassWe acknowledge R. Willa and V. G. Kogan for helpful and critical comments and discussions with S. Vieira. We wish to acknowledge the support of the Departamento Administrativo de Ciencia, Tecnología e Innovación, COLCIENCIAS (Colombia) Programa Doctorados en el Exterior Convocatoria 568-2012. We further acknowledge support by the Spanish Ministry of Economy and Competitiveness (Grants No. FIS2014-54498-R and No. MDM-2014-0377), the Comunidad de Madrid through program Nanofrontmag-CM (Grant No. S2013/MIT-2850), the EU (IG, European Research Council PNICTEYES Grant Agreements No. 679080, No. FP7-PEOPLE-2013-CIG 618321, and No. Cost MP-1201), and by Axa Research Fund. SEGAINVEX-UAM and Banco Santander are also acknowledged. Work done at the Ames Laboratory was supported by the U.S. Department of Energy, Office of Basic Energy Science, Division of Materials Sciences and Engineering. Ames Laboratory is operated for the U.S. Department of Energy by Iowa State University under Contract No. DE-AC02-07CH1135

Influence of multiband sign-changing superconductivity on vortex cores and vortex pinning in stoichiometric high-Tc CaKFe4 As4

We use a scanning tunneling microscope to study the superconducting density of states and vortex lattice of single crystals of CaKFe 4 As 4 . This material has a critical temperature of T c = 35 K, one of the highest among stoichiometric iron based superconductors (FeBSCs), and is comparable to T c found near optimal doping in other FeBSCs. We observe quasiparticle scattering from defects with a pattern related to interband scattering between zone centered hole sheets. We measure the tunneling conductance in vortex cores and find a peak due to Caroli–de Gennes–Matricon bound states. The peak is located above the Fermi level, showing that CaKFe 4 As 4 is a clean superconductor with vortex core bound states close to the so-called extreme quantum limit. We identify locations where the superconducting order parameter is strongly suppressed due to pair breaking. Vortices are pinned at these locations, and the length scale of the suppression of the order parameter is of order of the vortex core size. As a consequence, the vortex lattice is disordered up to 8 T

Direct visualization of phase separation between superconducting and nematic domains in Co-doped CaFe2As2 close to a first-order phase transition

We show that biaxial strain induces alternating tetragonal superconducting and orthorhombic nematic domains in Co-substituted CaFe2As2. We use atomic force, magnetic force, and scanning tunneling microscopy to identify the domains and characterize their properties, finding in particular that tetragonal superconducting domains are very elongated, more than several tens of micrometers long and about 30 nm wide; have the same Tc as unstrained samples; and hold vortices in a magnetic field. Thus, biaxial strain produces a phase-separated state, where each phase is equivalent to what is found on either side of the first-order phase transition between antiferromagnetic orthorhombic and superconducting tetragonal phases found in unstrained samples when changing Co concentration. Having such alternating superconducting domains separated by normal conducting domains with sizes of the order of the coherence length opens opportunities to build Josephson junction networks or vortex pinning arrays and suggests that first-order quantum phase transitions lead to nanometric-size phase separation under the influence of strainWork done in Madrid was supported by the Spanish Ministry of Economy and Competitiveness (Grants No. FIS2014-54498-R, No. MDM-2014-0377, No. MAT2014-52405-C2-2-R, No. RYC-2014-16626, and No. RYC-2014-15093), by the Comunidad de Madrid through program Nanofrontmag-CM (S2013/MIT-2850), by European Research Council PNICTEYES Grant Agreement No. 679080, by FP7-PEOPLE-2013-CIG 618321, by the EU Flagship Graphene Core1 under Grant Agreement No. 696656, by COST-EU, Grant No. CA16218 and by Axa Research Fund. SEGAINVEX-UAM is also acknowledged. Work done in Ames Lab was supported by the U.S. Department of Energy, Office of Basic Energy Science, Division of Materials Sciences and Engineering. Ames Laboratory is operated for the U.S. Department of Energy by Iowa State University under Contract No. DE-AC02-07CH1135

Anisotropic superconductivity in the spin-vortex antiferromagnetic superconductor CaK(Fe0.95Ni0.05)(4)As-4

High critical temperature superconductivity often occurs in systems where an antiferromagnetic order is brought near T=0 K by slightly modifying pressure or doping. CaKFe4As4 is a superconducting, stoichiometric iron-pnictide compound showing optimal superconducting critical temperature with Tc as large as 35 K. Doping with Ni induces a decrease in Tc and the onset of spin-vortex crystal (SVC) antiferromagnetic order, which consists of spins pointing inwards to or outwards from alternating As sites on the diagonals of the in-plane square Fe lattice. Here we study the band structure of CaK(Fe0.95Ni0.05)4As4 (Tc=10 K, TSVC=50 K) using quasiparticle interference with a scanning tunneling microscope and show how the SVC modifies the band structure and induces a fourfold superconducting gap anisotropy

Psychological Distress Among the U.S. General Population During the COVID-19 Pandemic

The COVID-19 pandemic is taking a significant global toll on emotional well-being, but evidence of mental health impacts in the United States remains limited. In April 2020, we conducted an exploratory survey of U.S. residents to understand prevalence of and factors associated with psychological distress during the pandemic. Data collection was conducted using Qualtrics, an online survey platform, and U.S. adult respondents were recruited via Amazon's Mechanical Turk platform. Among 1,366 respondents, 42% (n = 571) reported clinically significant anxiety and 38% (n = 519) reported clinically significant depression. Factors associated with anxiety and depressive symptoms included Hispanic/Latino ethnicity; younger age; lower income; employment as or living with a health care worker-first responder; caregiver status; SARS-CoV-2 infection status; decreased frequency of engagement in healthy behaviors; and changed frequency of engagement in unhealthy behaviors. That some of these factors are associated with elevated distress during the pandemic is not yet widely appreciated and might be useful in informing management of mental health care resources

Superconducting density of states and band structure at the surface of the candidate topological superconductor Au2 Pb

The electronic band structure of Au2Pb has a Dirac cone which gaps when undergoing a structural transition into a low temperature superconducting phase. This suggests that the superconducting phase (Tc = 1.1 K) might hold topological properties at the surface. Here we make Scanning Tunneling Microscopy experiments on the surface of superconducting Au2Pb. We measure the superconducting gap and find a sizable superconducting density of states at the Fermi level. We discuss possible origins for this finding in terms of superconductivity induced into surface state

Band structure, superconductivity and polytypism in AuSn4_4

The orthorhombic compound AuSn4 is compositionally similar to the Dirac node arc semimetal PtSn$_4$. AuSn$_4$ is, contrary to PtSn$_4$, superconducting with a critical temperature of T$_c$ = 2.35 K. Recent measurements present indications for quasi two-dimensional superconducting behavior in AuSn$_4$. Here we present measurements of the superconducting density of states and the band structure of AuSn$_4$ through Scanning Tunneling Microscopy (STM) and Angular Resolved Photoemission Spectroscopy (ARPES). The superconducting gap values in different portions of the Fermi surface are spread around {\Delta}0 = 0.4 meV, which is close to but somewhat larger than $\Delta =$ 1.76kBT$_c$ expected from BCS theory. We observe superconducting features in the tunneling conductance at the surface up to temperatures about 20% larger than bulk Tc. The band structure calculated with Density Functional Theory (DFT) follows well the results of ARPES. The crystal structure presents two possible stackings of Sn layers, giving two nearly degenerate polytypes. This makes AuSn$_4$ a rather unique case with a three dimensional electronic band structure but properties ressembling those of low dimensional layered compounds

Diplopia Is Frequent and Associated with Motor and Non-Motor Severity in Parkinson’s Disease: Results from the COPPADIS Cohort at 2-Year Follow-Up

[Background and objective] Diplopia is relatively common in Parkinson’s disease (PD) but is still understudied. Our aim was to analyze the frequency of diplopia in PD patients from a multicenter Spanish cohort, to compare the frequency with a control group, and to identify factors associated with it.[Patients and Methods] PD patients who were recruited from January 2016 to November 2017 (baseline visit; V0) and evaluated again at a 2-year ± 30 days follow-up (V2) from 35 centers of Spain from the COPPADIS cohort were included in this longitudinal prospective study. The patients and controls were classified as “with diplopia” or “without diplopia” according to item 15 of the Non-Motor Symptoms Scale (NMSS) at V0, V1 (1-year ± 15 days), and V2 for the patients and at V0 and V2 for the controls.[Results] The frequency of diplopia in the PD patients was 13.6% (94/691) at V0 (1.9% in controls [4/206]; p < 0.0001), 14.2% (86/604) at V1, and 17.1% (86/502) at V2 (0.8% in controls [1/124]; p < 0.0001), with a period prevalence of 24.9% (120/481). Visual hallucinations at any visit from V0 to V2 (OR = 2.264; 95%CI, 1.269–4.039; p = 0.006), a higher score on the NMSS at V0 (OR = 1.009; 95%CI, 1.012–1.024; p = 0.015), and a greater increase from V0 to V2 on the Unified Parkinson’s Disease Rating Scale–III (OR = 1.039; 95%CI, 1.023–1.083; p < 0.0001) and Neuropsychiatric Inventory (OR = 1.028; 95%CI, 1.001–1.057; p = 0.049) scores were independent factors associated with diplopia (R2 = 0.25; Hosmer and Lemeshow test, p = 0.716).[Conclusions] Diplopia represents a frequent symptom in PD patients and is associated with motor and non-motor severity.Martínez-Martin P. has received honoraria from National School of Public Health (ISCIII), Editori-al Viguera and Takeda Pharmaceuticals for lecturing in courses, and from the International Parkinson and Movement Disorder Society (MDS) for management of the Program on Rating Scales. Mir P. has received honoraria from AbbVie, Abbott, Allergan, Bial, Merz, UCB, and Zambon and have received grants from the Spanish Ministry of Economy and Competitiveness [PI16/01575], co-founded by ISCIII (Subdirección General de Evaluación y Fomento de la Investigación) and by Fondo Europeo de Desarrollo Regional (FEDER), the Consejería de Economía, Innovación, Ciencia y Empleo de la Junta de Andalucía [CVI-02526, CTS-7685], the Consejería de Salud y Bienestar Social de la Junta de Andalucía [ PI-0437-2012, PI-0471-2013], the Sociedad Andaluza de Neurología, the Jacques and Gloria Gossweiler Foundation, the Fundación Alicia Koplowitz, the Fundación Mutua Madrileña.Peer reviewe

Superconducting density of states and band structure at the surface of the candidate topological superconductor Au2Pb

[EN] The electronic band structure of Au2Pb has a Dirac cone which gaps when undergoing a structural transition into a low temperature superconducting phase. This suggests that the superconducting phase (Tc = 1.1 K) might hold topological properties at the surface. Here we make Scanning Tunneling Microscopy experiments on the surface of superconducting Au2Pb. We measure the superconducting gap and find a sizable superconducting density of states at the Fermi level. We discuss possible origins for this finding in terms of superconductivity induced into surface states.This work was supported by the Spanish Research State Agency (Grants No. PID2020-114071RB-I00, No. FIS2017-84330-R, No. CEX2018-000805-M, No. RYC-2014-15093, and No. MAT2017-87134-C2-2-R), by the Comunidad de Madrid through program NANOFRONTMAG-CM (Grant No. S2013/MIT-2850), by the European Research Council PNICTEYES Grant Agreement No. 679080 and by the Swedish Research Council (Vetenskapsrådet Grant No. 2018-03488). F.M. and M.G.H. acknowledge European Union’s Horizon 2020 research and innovation program Grant Agreement No. 881603 Graphene Core3-Graphene-based disruptive technologies, EU FLAG-ERA through the project To2Dox, JTC-2019-009 and the Comunidad de Madrid through the project CAIRO-CM project, Y2020/NMT-6661.We acknowledge collaborations through EU program Cost CA16218 (Nanocohybri). J.J.B. acknowledges the Marie Curie Fellowship program (H2020 MSCA-IF2016-751047) and the Generalitat Valenciana (CDEIGENT/2019/022). Ames Laboratory is operated for the U.S. Department of Energy by Iowa State University under Contract No. DE-AC02-07CH11358. We acknowledge SEGAINVEX at UAM for design and construction of cryogenic equipment.Peer reviewe