Suppressed Fluctuations as the Origin of the Static Magnetic Order in Strained Sr_{2}RuO_{4}.

Combining first-principles density-functional calculations and Moriya's self-consistent renormalization theory, we explain the recently reported counterintuitive appearance of an ordered magnetic state in uniaxially strained Sr_{2}RuO_{4} beyond the Lifshitz transition. We show that strain weakens the quantum spin fluctuations, which destroy the static order, more strongly than the tendency to magnetism. A different rate of decrease of the spin fluctuations vs magnetic stabilization energy promotes the onset of a static magnetic order beyond a critical strain.

One-year outcomes after transcarotid artery revascularization (TCAR) in the ROADSTER 2 trial.

OBJECTIVES: Transcarotid artery revascularization (TCAR) is a carotid stenting technique that utilizes reversal of cerebral arterial flow to confer cerebral protection. Although carotid endarterectomy (CEA) remains the standard for treatment of symptomatic and asymptomatic carotid stenosis, the search for the optimal minimally invasive option for the high-risk surgical patient continues. The goal of the current study is to evaluate the 1-year safety and efficacy of TCAR in a prospective clinical trial. METHODS: ROADSTER 2 is a prospective, open-label, single-arm, multicenter, post-approval registry for patients undergoing TCAR. All patients were considered high risk for CEA and underwent independent neurological assessments preoperatively, postoperatively, and had long-term clinical follow-up. The primary end point was incidence of ipsilateral stroke after treatment with the ENROUTE Transcarotid Stent System. Secondary end points included individual/composite rates of stroke, death, and perioperative myocardial infarction. RESULTS: Between June 2016 and November 2018, 155 patients at 21 centers in the United States and one in the European Union were enrolled and represented a subset of the overall trial. Asymptomatic (n = 119; 77%) and symptomatic patients (n = 36; 23%) with high-risk anatomic (ie, high lesion, restenosis, radiation injury; 43%), physiologic (32%), or combined factors (25%) were enrolled. No patient suffered a perioperative myocardial infarction or stroke. Over the year, no patient had an ipsilateral stroke, but four patients died (2.6%), all from non-neurological causes. Additionally, a technical success rate of 98.7% with a low cranial nerve deficit rate of 1.3% was achieved. CONCLUSIONS: In patients with high risk factors, TCAR yields high technical success with a low stroke and death rate at 1 year. Further comparative studies with CEA are warranted.

Magnetization Process of Atacamite: A Case of Weakly Coupled S=1/2 Sawtooth Chains.

We present a combined experimental and theoretical study of the mineral atacamite Cu_{2}Cl(OH)_{3}. Density-functional theory yields a Hamiltonian describing anisotropic sawtooth chains with weak 3D connections. Experimentally, we fully characterize the antiferromagnetically ordered state. Magnetic order shows a complex evolution with the magnetic field, while, starting at 31.5 T, we observe a plateaulike magnetization at about M_{sat}/2. Based on complementary theoretical approaches, we show that the latter is unrelated to the known magnetization plateau of a sawtooth chain. Instead, we provide evidence that the magnetization process in atacamite is a field-driven canting of a 3D network of weakly coupled sawtooth chains that form giant moments.

Intravascular Lithotripsy for Treatment of Calcified Lesions During Carotid Artery Stenting.

PURPOSE: To report the use of intravascular lithotripsy (IVL) in the treatment of calcified carotid artery lesions. MATERIALS AND METHODS: The records of 21 high-surgical-risk patients (mean age 75.1±8.1 years; 17 men) who were treated at 8 centers for carotid artery stenosis ≥70% were retrospectively reviewed. Twelve patients had a history of cerebrovascular disease. All patients had heavily calcified carotid artery lesions: 19 de novo and 2 in-stent restenoses (ISR). The mean baseline stenosis was 82.3%±9.7%. IVL was utilized at the discretion of the operator, followed by balloon angioplasty. Embolic protection devices were used in all cases. RESULTS: In 19 patients, IVL was followed by stent implantation; the 2 ISR lesions were dilated only. The mean IVL balloon diameter was 4.64±1.13 mm, and the mean number of IVL pulses applied was 67.2±61.4 (range 10-180). All procedures were technically successful (<30% residual stenosis). No patients developed symptomatic bradycardia or hypotension due to IVL, and there were no adverse events associated with IVL delivery. All patients were discharged on dual antiplatelet therapy. Seventeen days after the procedure, 1 patient experienced an ischemic stroke that was deemed due to aortic arch manipulation during transfemoral access. Carotid duplex ultrasound examination identified significant restenosis (>70%) in 1 asymptomatic patient at 12 months after the index procedure. No patients required reintervention during a median follow-up of 6 months (range 1-12). CONCLUSION: This preliminary experience demonstrates that IVL can be a safe and effective approach for the management of severely calcified carotid lesions. Further research is warranted to determine the longer-term safety and efficacy of IVL for dilation of calcified carotid artery lesions as an adjunct to carotid artery stenting.

Duration of blood flow reversal during transcarotid artery revascularization does not affect outcome.

OBJECTIVE: Transcarotid artery revascularization (TCAR) has become an increasingly popular alternative for the treatment of carotid bifurcation stenosis. TCAR employs carotid blood flow reversal through an ex vivo common carotid artery to femoral vein shunt for neuroprotection during the placement and angioplasty of the carotid artery stent. There is a lack of data regarding an association between the duration of flow reversal and neurologic complications or other adverse events. We analyzed TCAR flow reversal time in relation to major adverse events. METHODS: There were 307 patients who underwent TCAR at four high-volume academic institutions. Patients were separated on the basis of the duration of carotid flow reversal as follows: group I, ≤8 minutes (n = 138); group II, 9-13 minutes (n = 105); group III, 14-20 minutes (n = 42); and group IV, >20 minutes (n = 22). Adverse events including stroke (assessed by a National Institute of Health Stroke Scale-certified examiner), myocardial infarction (MI), and death at discharge and 30 days were collected in all patients and were compared between groups using one-way analysis of variance and χ2 analysis. RESULTS: There were four strokes in the total cohort, yielding an overall stroke rate of 1.3%. All strokes were minor in nature; two were ipsilateral and two were contralateral. All patients demonstrated full recovery at 30 days. We found no significant difference in the stroke rate between any of the groups: I, 1.5% (2/138); II, 1.9% (2/105); III, 0% (0/42); and IV, 0% (0/22; P = .76). The four strokes occurred in patients with flow reversal time of 6, 7, 11, and 12 minutes. There was also no difference in the 30-day composite stroke/death or stroke/death/MI rates among the groups. CONCLUSIONS: The length of flow reversal during TCAR does not affect rates of stroke, MI, or death. These data suggest that operators should focus on the technical aspects of the procedure during flow reversal rather than on its duration.

Reduction of the Spin Susceptibility in the Superconducting State of Sr_{2}RuO_{4} Observed by Polarized Neutron Scattering.

Recent observations [A. Pustogow et al., Nature (London) 574, 72 (2019).NATUAS0028-083610.1038/s41586-019-1596-2] of a drop of the ^{17}O nuclear magnetic resonance (NMR) Knight shift in the superconducting state of Sr_{2}RuO_{4} challenged the popular picture of a chiral odd-parity paired state in this compound. Here we use polarized neutron scattering (PNS) to show that there is a 34±6% drop in the magnetic susceptibility at the Ru site below the superconducting transition temperature. We measure at lower fields H∼1/3H_{c2} than a previous PNS study allowing the suppression to be observed. The PNS measurements show a smaller susceptibility suppression than NMR measurements performed at similar field and temperature. Our results rule out the chiral odd-parity d=z[over ^](k_{x}±ik_{y}) state and are consistent with several recent proposals for the order parameter including even-parity B_{1g} and odd-parity helical states.

The learning curve of transcarotid artery revascularization.

BACKGROUND: In the pivotal U.S. Food and Drug Administration approval trial, ROADSTER, transcarotid artery revascularization (TCAR) using the ENROUTE Transcarotid Neuroprotection System (Silk Road Medical Inc, Sunnyvale, Calif) was shown to have one of the lowest reported complication rates, not only for carotid artery stent placement, but also for any carotid intervention, including endarterectomy. The number of cases required for a surgeon to gain the proficiency to realize these outcomes has not been studied. Our objective was to determine the learning curve for vascular surgeons performing the TCAR procedure. We examined the effect of surgeon procedural experience on intraoperative data and postoperative outcome. METHODS: This retrospective review analyzed data from a prospectively maintained database of 188 consecutive patients from three large academic centers who underwent TCAR. Procedures were ordered chronologically for each surgeon and grouped into bins of five. Operative times and flow reversal times were analyzed by analysis of variance. Results led to comparison of surgeons' early experience (cases 1-15) with their later experience (cases 16-50). The primary outcome was postoperative stroke and death. RESULTS: The mean procedural time for all cases was 75.0 ± 23.8 minutes. When the procedural time of cases 1 through 15 (mean, 79.0 ± 28.3 minutes) were compared with cases 16 through 50 (mean, 71.8 ± 19.0 minutes), a significant difference was noted (P = .02). The mean flow reversal time was 10.6 ± 6.8 minutes. When flow reversal times were compared using analysis of variance testing, cases 1 through 15 were statistically similar and cases 11 through 50 were also similar, but the two groups differed from each other (P < .001). For flow reversal, cases 1 through 15 had mean reversal times of 13.3 ± 8.8 minutes compared with 8.5 ± 3.5 minutes for cases 16 through 50 (P < .001). Postoperative stroke rates were similar in the 1 through 15 and 16 through 50 case groups (2.4% vs 1.0%; P = .59), as were death rates (0.0% vs 1.0%; P > .99). The combined stroke/death rates were also comparable at 2.4% in the early cohort vs 1.9% in the late cohort (P > .99). CONCLUSIONS: There seems to be a relatively short learning curve for the TCAR procedure. After 15 cases, surgeons are able to reduce procedural decrease by 10% (from 79.0 to 71.8 minutes), and flow reversal times by an average of 40% (from 13.3 to 8.5 minutes). More important, the rates of stroke and death do not differ between early and late experience with TCAR. The TCAR procedure may be quickly and safely adopted by vascular surgeons for carotid intervention.

A multi-institutional analysis of transcarotid artery revascularization compared to carotid endarterectomy.

OBJECTIVE: Transcarotid artery revascularization (TCAR) is a novel approach to carotid intervention that uses a direct carotid cut-down approach coupled with cerebral blood flow reversal to minimize embolic potential. The initial positive data with TCAR indicates that it may be an attractive alternative to trans-femoral carotid artery stenting and possibly carotid endarterectomy (CEA) for high-risk patients. The purpose of this study was to present 30-day and 1-year outcomes after treatment by TCAR and to compare these outcomes against a matched control group undergoing CEA at the same institutions. METHODS: A retrospective review of all patients who underwent TCAR at four institutions between 2013 and 2017 was performed to evaluate the use of the ENROUTE Transcarotid Neuroprotection System (Silk Road Medical, Inc, Sunnyvale, Calif). TCAR patients had high-risk factors and were either enrolled in prospective trials or treated with a commercially available TCAR device after US Food and Drug Administration approval. Contemporaneous patients undergoing CEA at each institution were also reviewed. Patients were propensity matched in a 1:1 (CEA:TCAR) fashion with respect to preoperative comorbidities. Data were analyzed using statistical models with a P value of less than .05 considered significant. Individual and composite stroke, myocardial infarction, and death at 30 days and 1 year postoperatively were assessed. RESULTS: Consecutive patients undergoing TCAR or CEA were identified (n = 663) and compared. Patients undergoing the TCAR procedure (n = 292) had higher rates of diabetes (P = .01), hyperlipidemia (P = .02), coronary artery disease (P < .01), and renal insufficiency (P < .01) compared with unmatched CEA patients (n = 371). Stroke rates were similar at 30 days (1.0% TCAR vs 1.1% CEA) and 1 year (2.8% TCAR vs 3.0% CEA) in the unmatched groups. After propensity matching by baseline characteristics including gender, age, symptom status (36.3%, 35.3%) and diabetes, 292 TCAR patients were compared with 292 CEA patients. TCAR patients were more likely to be treated preoperative and postoperatively with clopidogrel (preoperatively, 82.2% vs 39.4% [P < .01]; postoperatively, 98.3% vs 36.0% [P < .01]) and statins (preoperatively, 88.0% vs 75.0% [P < .01]; postoperatively, 97.8% vs 78.8% [P < .01]). Stroke (1.0% TCAR vs 0.3% CEA; P = .62) and death (0.3% TCAR vs 0.7% CEA; P = NS) rates were similar at 30 days and comparable at 1 year (stroke, 2.8% vs 2.2% [P = .79]; death 1.8% vs 4.5% [P = .09]). The composite end point of stroke/death/myocardial infarction at 1 month postoperatively was 2.1% vs 1.7% (P = NS). TCAR was associated with a decreased rate of cranial nerve injury (0.3% vs 3.8%; P = .01). CONCLUSIONS: These early data suggest that patients undergoing TCAR, even those with high-risk comorbidities, achieve broadly similar outcomes compared with patients undergoing CEA while mitigating cranial nerve injury. Further comparative studies are warranted.

Novel Fe-Based Superconductor LaFe_{2}As_{2} in Comparison with Traditional Pnictides.

The recently discovered Fe-based superconductor (FeBS) LaFe_{2}As_{2} seems to break away from an established pattern that doping an FeBS beyond 0.2e/Fe destroys superconductivity. LaFe_{2}As_{2} has an apparent doping of 0.5e, yet superconducts at 12.1 K. Its Fermi surface bears no visual resemblance with the canonical FeBS fermiology. It also exhibits two phases, none magnetic and only one superconducting. We show that the difference between them nonetheless has a magnetic origin, the one featuring disordered moments, and the other locally nonmagnetic. We find that La there assumes an unusual valence of +2.6 to +2.7, so that the effective doping is reduced to 0.30-0.35e. A closer look reveals the same key elements: hole Fermi surfaces near Γ-Z and electron ones near the X-P lines, with the corresponding peak in susceptibility, and a strong tendency to stripe magnetism. The physics of LaFe_{2}As_{2} is thus more similar to the FeBS paradigm than hitherto appreciated.

Spin Fluctuations in Sr_{2}RuO_{4} from Polarized Neutron Scattering: Implications for Superconductivity.

Triplet pairing in Sr_{2}RuO_{4} was initially suggested based on the hypothesis of strong ferromagnetic spin fluctuations. Using polarized inelastic neutron scattering, we accurately determine the full spectrum of spin fluctuations in Sr_{2}RuO_{4}. Besides the well-studied incommensurate magnetic fluctuations, we do find a sizable quasiferromagnetic signal, quantitatively consistent with all macroscopic and microscopic probes. We use this result to address the possibility of magnetically driven triplet superconductivity in Sr_{2}RuO_{4}. We conclude that, even though the quasiferromagnetic signal is stronger and sharper than previously anticipated, spin fluctuations alone are not enough to generate a triplet state strengthening the need for additional interactions or an alternative pairing scenario.

Uncovering the Mechanism of the Impurity-Selective Mott Transition in Paramagnetic V_{2}O_{3}.

While the phase diagrams of the one- and multiorbital Hubbard model have been well studied, the physics of real Mott insulators is often much richer, material dependent, and poorly understood. In the prototype Mott insulator V_{2}O_{3}, chemical pressure was initially believed to explain why the paramagnetic-metal to antiferromagnetic-insulator transition temperature is lowered by Ti doping while Cr doping strengthens correlations, eventually rendering the high-temperature phase paramagnetic insulating. However, this scenario has been recently shown both experimentally and theoretically to be untenable. Based on full structural optimization, we demonstrate via the charge self-consistent combination of density functional theory and dynamical mean-field theory that changes in the V_{2}O_{3} phase diagram are driven by defect-induced local symmetry breakings resulting from dramatically different couplings of Cr and Ti dopants to the host system. This finding emphasizes the high sensitivity of the Mott metal-insulator transition to the local environment and the importance of accurately accounting for the one-electron Hamiltonian, since correlations crucially respond to it.

Nontrivial Role of Interlayer Cation States in Iron-Based Superconductors.

Unconventional superconductivity in iron pnictides and chalcogenides has been suggested to be controlled by the interplay of low-energy antiferromagnetic spin fluctuations and the particular topology of the Fermi surface in these materials. Based on this premise, one would also expect the large class of isostructural and isoelectronic iron germanide compounds to be good superconductors. As a matter of fact, they, however, superconduct at very low temperatures or not at all. In this work we establish that superconductivity in iron germanides is suppressed by strong ferromagnetic tendencies, which surprisingly do not originate from changes in bond angles or bond distances with respect to iron pnictides and chalcogenides, but are due to changes in the electronic structure in a wide range of energies happening upon substitution of atom species (As by Ge and the corresponding spacer cations). Our results indicate that superconductivity in iron-based materials may not always be fully understood based on d or d-p model Hamiltonians only.

Structural origin of the anomalous temperature dependence of the local magnetic moments in the CaFe2As2 family of materials.

We report a combination of Fe Kß x-ray emission spectroscopy and density functional reduced Stoner theory calculations to investigate the correlation between structural and magnetic degrees of freedom in CaFe2(As1-xPx)2. The puzzling temperature behavior of the local moment found in rare earth-doped CaFe2As2 [H. Gretarsson et al., Phys. Rev. Lett. 110, 047003 (2013)] is also observed in CaFe2(As1-xPx)2. We explain this phenomenon based on first-principles calculations with scaled magnetic interaction. One scaling parameter is sufficient to describe quantitatively the magnetic moments in both CaFe2(As1-xPx)2 (x=0.055) and Ca0.78La0.22Fe2As2 at all temperatures. The anomalous growth of the local moments with increasing temperature can be understood from the observed large thermal expansion of the c-axis lattice parameter combined with strong magnetoelastic coupling. These effects originate from the strong tendency to form As-As dimers across the Ca layer in the CaFe2As2 family of materials. Our results emphasize the dual local-itinerant character of magnetism in Fe pnictides.

Successful open repair of syphilitic thoracoabdominal aneurysm.

Most syphilitic aneurysms involve the ascending aorta. Those involving the descending aorta are less common, and those involving the abdominal aorta are unusual. Rarer yet, we present the case of a 40-year-old man with HIV and a history of syphilis with a thoracoabdominal aneurysm. The patient underwent antiretroviral therapy before elective open repair. His postoperative course was uneventful, and he was discharged home. Pathology demonstrated medial necrosis. Postoperatively, he was seen well in our multidisciplinary aorta center clinic. Today's vascular surgeons should be cognizant of cardiovascular syphilis. Successful care requires awareness of atypical presentations in addition to multispecialty care.

The Current State of Physician-Modified Endovascular Grafts in Complex Abdominal Aortic Aneurysms.

Physician modified endografts (PMEGs) for the treatment of complex abdominal aortic aneurysms and thoracoabdominal aortic aneurysms are a viable option. Other endovascular options include custom and off-the-shelf devices for fenestrated and branched endovascular aortic repair, parallel grafts, and in-situ laser fenestration. Limitations of these devices include time to development, strict anatomic criteria, and durability with regards to parallel grafts. PMEGs fill this void with perioperative and long-term outcomes similar to custom made devices. Post dissection aneurysms also present a unique role for PMEGs given the added complexity with fixing these aneurysms and have been reported with good outcomes. Lastly, we discuss the approach to preoperative planning and the operative component of PMEGs in this brief review.

Giant lattice softening at a Lifshitz transition in Sr2RuO4.

The interplay of electronic and structural degrees of freedom in solids is a topic of intense research. More than 60 years ago, Lifshitz discussed a counterintuitive possibility: lattice softening driven by conduction electrons at topological Fermi surface transitions. The effect that he predicted, however, was small and has not been convincingly observed. Using a piezo-based uniaxial pressure cell to tune the ultraclean metal strontium ruthenate while measuring the stress-strain relationship, we reveal a huge softening of the Young's modulus at a Lifshitz transition of a two-dimensional Fermi surface and show that it is indeed driven entirely by the conduction electrons of the relevant energy band.

Giant staghorn stone causing inferior vena cava compression: a novel case report.

Staghorn calculi (SC) are defined as large kidney stones that fill the renal pelvis and at least one renal calyx. They represent 10-20% of all renal stones in developing countries and require prompt diagnosis and management. Massive SC (over 5 cm) are treated exclusively via open surgery, despite percutaneous nephrolithotomy (PCNL) being the gold standard treatment for large stones. Descriptions of PCNL for massive SC are very limited in the literature. Case Presentation: We report a case of a 63-year-old male who presented with chronic abdominal pain, hepatosplenomegaly, and normal renal function. He was later diagnosed with polycythemia vera. Computed tomography of the abdomen revealed massive, bilateral staghorn stones measuring 7.3×5.5 cm and 1.8×4.5 cm on the right and left, respectively. Additionally, the right stone was found to be compressing the inferior vena cava (IVC). The patient was promptly scheduled for right-sided PCNL and the target of 80% stone fragmentation was successfully attained. Discussion: We present the first case of a stone of such size in the Middle East, as well as the first known case of a renal stone compressing the IVC. Unlike previous reports, the stone was successfully fragmented via PCNL - a procedure that has not been described for stones of such size. Conclusion: This report highlights that ultrasound-guided PNCL without any other intervention is sufficient for the successful treatment of giant SC. Greater research is needed on the potential utility of using ultrasound-guided PCNL for the fragmentation of stones sized over 5 cm.

Na2IrO3 as a molecular orbital crystal.

Contrary to previous studies that classify Na(2)IrO(3) as a realization of the Heisenberg-Kitaev model with a dominant spin-orbit coupling, we show that this system represents a highly unusual case in which the electronic structure is dominated by the formation of quasimolecular orbitals (QMOs), with substantial quenching of the orbital moments. The QMOs consist of six atomic orbitals on an Ir hexagon, but each Ir atom belongs to three different QMOs. The concept of such QMOs in solids invokes very different physics compared to the models considered previously. Employing density functional theory calculations and model considerations we find that both the insulating behavior and the experimentally observed zigzag antiferromagnetism in Na(2)IrO(3) naturally follow from the QMO model.

de Haas-van Alphen study of the Fermi surfaces of superconducting LiFeP and LiFeAs.

We report a de Haas-van Alphen oscillation study of the 111 iron pnictide superconductors LiFeAs with T(c) ≈ 18 K and LiFeP with T(c) ≈ 5 K. We find that for both compounds the Fermi surface topology is in good agreement with density functional band-structure calculations and has almost nested electron and hole bands. The effective masses generally show significant enhancement, up to ~3 for LiFeP and ~5 for LiFeAs. However, one hole Fermi surface in LiFeP shows a very small enhancement, as compared with its other sheets. This difference probably results from k-dependent coupling to spin fluctuations and may be the origin of the different nodal and nodeless superconducting gap structures in LiFeP and LiFeAs, respectively.

Spin waves and revised crystal structure of honeycomb iridate Na2IrO3.

We report inelastic neutron scattering measurements on Na2IrO3, a candidate for the Kitaev spin model on the honeycomb lattice. We observe spin-wave excitations below 5 meV with a dispersion that can be accounted for by including substantial further-neighbor exchanges that stabilize zigzag magnetic order. The onset of long-range magnetic order below T(N)=15.3 K is confirmed via the observation of oscillations in zero-field muon-spin rotation experiments. Combining single-crystal diffraction and density functional calculations we propose a revised crystal structure model with significant departures from the ideal 90° Ir-O-Ir bonds required for dominant Kitaev exchange.