Inhomogeneous high temperature melting and decoupling of charge density waves in spin-triplet superconductor UTe2

Charge, spin and Cooper-pair density waves have now been widely detected in exotic superconductors. Understanding how these density waves emerge - and become suppressed by external parameters - is a key research direction in condensed matter physics. Here we study the temperature and magnetic-field evolution of charge density waves in the rare spin-triplet superconductor candidate UTe2 using scanning tunneling microscopy/spectroscopy. We reveal that charge modulations composed of three different wave vectors gradually weaken in a spatially inhomogeneous manner, while persisting to surprisingly high temperatures of 10-12 K. We also reveal an unexpected decoupling of the three-component charge density wave state. Our observations match closely to the temperature scale potentially related to short-range magnetic correlations, providing a possible connection between density waves observed by surface probes and intrinsic bulk features. Importantly, charge density wave modulations become suppressed with magnetic field both below and above superconducting Tc in a comparable manner. Our work points towards an intimate connection between hidden magnetic correlations and the origin of the unusual charge density waves in UTe2.

Spin-polarized imaging of the antiferromagnetic structure and field-tunable bound states in kagome magnet FeSn

Kagome metals are an exciting playground for the explorations of novel phenomena at the intersection of topology, electron correlations and magnetism. The family of FeSn-based kagome magnets in particular attracted a lot of attention for simplicity of the layered crystal structure and tunable topological electronic band structure. Despite a significant progress in understanding their bulk properties, surface electronic and magnetic structures are yet to be fully explored in many of these systems. In this work, we focus on a prototypical kagome metal FeSn. Using a combination of spin-averaged and spin-polarized scanning tunneling microscopy, we provide the first atomic-scale visualization of the layered antiferromagnetic structure at the surface of FeSn. In contrast to the field-tunable electronic structure of cousin material Fe₃Sn₂ that is a ferromagnet, we find that electronic density-of-states of FeSn is robust to the application of external magnetic field. Interestingly, despite the field insensitive electronic band structure, FeSn exhibits bound states tied to specific impurities with large effective moments that strongly couple to the magnetic field. Our experiments provide microscopic insights necessary for theoretical modeling of FeSn and serve as a spring board for spin-polarized measurements of topological magnets in general.

Management of conduction disorders after transcatheter aortic valve implantation: results of an EHRA survey

Funding Acknowledgements

Type of funding sources: None.

Background

Left bundle branch block (LBBB) is common after transcatheter aortic valve implantation (TAVI) and is an indicator of subsequent high-grade atrioventricular block. Consensus regarding a reasonable strategy to manage cardiac conduction disturbances after TAVI has been elusive

Methods

The European Heart Rhythm Association (EHRA) conducted a survey to capture contemporary clinical practice for conduction disorders after TAVI. A 25-item online questionnaire was developed and distributed among the EHRA electrophysiology research network centres.

Results

Of 117 respondents, 44% were affiliated with university hospitals. This survey has revealed that a standardized management protocol for advanced conduction disorders such as LBBB or AVB after TAVR is available in 63% of participating centres. Telemetry was chosen by most participants as the most frequent management strategy for patients with new or preexisting LBBB after TAVI (79%, 70%, respectively, Figure 1). Duration of telemetry in patients with new LBBB varied: 18% chose 24 hours, 35% 48 hours, 27% 72 hours and 20% ≥ 72 hours. Similarly, in patients with new LBBB after TAVI undergoing EP study, the cut-off for a prolonged HV interval for PM implantation was heterogenous among European centers (7.4% ≥ 55ms and 44% ≥ 75ms). Conduction system pacing was chosen as preferred device therapy in patients with LBBB and normal LVEF in 3.7% and in patients with LBBB and reduced LVEF in 5.6%.

Conclusions

The management of conduction disorders after TAVI is very heterogeneous across European centres. Risk stratification strategies vary substantially. The role of conduction system pacing in patients with LBBB after TAVI needs to be defined. There is a considerable room for better uniformity in clinical practice.

Imaging antiferromagnetic domain fluctuations and the effect of atomic scale disorder in a doped spin-orbit Mott insulator

Correlated oxides can exhibit complex magnetic patterns. Understanding how magnetic domains form in the presence of disorder and their robustness to temperature variations has been of particular interest, but atomic scale insight has been limited. We use spin-polarized scanning tunneling microscopy to image the evolution of spin-resolved modulations originating from antiferromagnetic (AF) ordering in a spin-orbit Mott insulator perovskite iridate Sr₃Ir₂O₇ as a function of chemical composition and temperature. We find that replacing only several percent of lanthanum for strontium leaves behind nanometer-scale AF puddles clustering away from lanthanum substitutions preferentially located in the middle strontium oxide layer. Thermal erasure and reentry into the low-temperature ground state leads to a spatial reorganization of the AF puddles, which nevertheless maintain scale-invariant fractal geometry in each configuration. Our experiments reveal multiple stable AF configurations at low temperature and shed light onto spatial fluctuations of the AF order around atomic scale disorder in electron-doped Sr₃Ir₂O₇.

Nanoscale decoupling of electronic nematicity and structural anisotropy in FeSe thin films

In a material prone to a nematic instability, anisotropic strain in principle provides a preferred symmetry-breaking direction for the electronic nematic state to follow. This is consistent with experimental observations, where electronic nematicity and structural anisotropy typically appear hand-in-hand. In this work, we discover that electronic nematicity can be locally decoupled from the underlying structural anisotropy in strain-engineered iron-selenide (FeSe) thin films. We use heteroepitaxial molecular beam epitaxy to grow FeSe with a nanoscale network of modulations that give rise to spatially varying strain. We map local anisotropic strain by analyzing scanning tunneling microscopy topographs, and visualize electronic nematic domains from concomitant spectroscopic maps. While the domains form so that the energy of nemato-elastic coupling is minimized, we observe distinct regions where electronic nematic ordering fails to flip direction, even though the underlying structural anisotropy is locally reversed. The findings point towards a nanometer-scale stiffness of the nematic order parameter.

A cleanroom in a glovebox

The exploration of new materials, novel quantum phases, and devices requires ways to prepare cleaner samples with smaller feature sizes. Initially, this meant the use of a cleanroom that limits the amount and size of dust particles. However, many materials are highly sensitive to oxygen and water in the air. Furthermore, the ever-increasing demand for a quantum workforce, trained and able to use the equipment for creating and characterizing materials, calls for a dramatic reduction in the cost to create and operate such facilities. To this end, we present our cleanroom-in-a-glovebox, a system that allows for the fabrication and characterization of devices in an inert argon atmosphere. We demonstrate the ability to perform a wide range of characterization as well as fabrication steps, without the need for a dedicated room, all in an argon environment. Finally, we discuss the custom-built antechamber attached to the back of the glovebox. This antechamber allows the glovebox to interface with ultra-high vacuum equipment such as molecular-beam epitaxy and scanning tunneling microscopy.

P993Incidence of atrial fibrillation early after cavotricuspid isthmus ablation

Background

Atrial fibrillation (AF) is a common finding in patients undergoing cavotricuspid isthmus ablation for isthmus dependent right atrial flutter (RAF). Little is known about the time of its occurrence.

Purpose

We aimed to investigate the incidence of AF early after RAF ablation in a well-defined, prospective cohort.

Methods

A total of 255 participants with RAF ablation from 5 centers and at least one completed follow-up were included. Structured clinical follow-up was performed at 3, 6 and 12 months including a 24 hour Holter-ECG. The endpoint was incidence of AF detected clinically or by Holter-ECG. Risk factors associated with the occurrence of AF were assessed using separate, univariate Cox proportional-hazards models.

Results

Mean age was 67 years, 80% were male and previous episodes of AF were known in 40%. Over a mean follow-up of 7.4 (±4.4) months AF was detected in 35 (13.7%) participants after RAF ablation (Figure A). After 3, 6 and 12 months AF was detected in 18 (7.1%), 30 (11.7%) and 34 (13.3%) patients. No difference in the incidence of AF after RAF ablation was found comparing patients with and without a history of AF (log-rank p value = 0.44) (Figure B). Comparing patients with and without AF during follow-up, there was no difference in age (68 vs 66 years, p = 0.36), sex (69 vs 81% male, p = 0.08), prior heart failure (29 vs 19%, p = 0.20), hypertension (43 vs 38%, p = 0.56) or left atrial volume (46.6 vs 39.6 ml, p = 0.10), but patients with previous AF had a lower left ventricular ejection fraction (LVEF) (45.7 vs 52.3%, p = 0.02). In separate, univariate Cox proportional-hazards models only increasing LVEF (Hazard ratio 0.97, 95% confidence interval (0.95; 0.99, p = 0.02)) was associated with a lower risk of incident AF after RAF ablation, but no other risk factor.

Conclusions

AF occurred in 13.7% of patients early after cavotricuspid isthmus ablation for RAF. There was no difference in the occurrence of AF between patients with and without previously known episodes of AF. Only impaired LVEF was associated with AF occurrence.

Abstract Figure

P5691Independent assessment if an image-processing service for the treatment of patients with ventricular tachycardias

Background/Introduction

Substrate-based radiofrequency ablation (RFA) in combination with pre-procedural computed tomography (CT) or cardiac Magnetic Resonance Imaging (cMRI) emerged as a promising approach to treat ventricular tachycardias (VT). However, image-processing and 3D reconstruction of the relevant structures to embed them into a 3D electroanatomical mapping (EAM) system is time consuming and requires highly experienced personal and a dedicated software.

Purpose

The aim of the study was to present the first independent experience with a commercially available service of a internet platform in patients referred for RFA of VTs.

Methods

Seven consecutive patients (pts) with ischemic cardiomyopathy (ICM), non- ischemic cardiomyopathy (NICM) and dilated cardiomyopathy (DCM) referred for VT RFA underwent contrast-enhanced dual-energy CT. The anonymized DICOM dataset was uploaded to the internet platform. After processing by the specialists, the dataset was downloaded and exported in a format compatible with the 3D EAM System. The EAM was performed in sinus rhythm using a 3.5mm open-irrigated tip catheter or a magnetic remote 3.5mm open-irrigated tip catheter in combination with the remote magnetic navigation-system. A multipolar high-density mapping catheter was used in 6 pts. Scar was defined as bipolar voltage <0.5 mV, and scar border zone ≥0.5mV and <1.5 mV.

Results of the internet platform-derived wall thinning (WT), scars and the defined substrate based on 3d EAM voltage maps were transferred into a 17-segment model, and the filling of every single segment was rated as 0%, 25%, 50%, 75% and 100%. For analysis, agreement of the filling (percentage) of the individual segments was quantified.

Results

Mean age was 67±8 year, BMI was 28±5 kg/m2 and 86% were males. File transfers and image processing was feasible in all patients. Agreement between the defined substrate (<0,5mV) and WT of 4mm was very good (≥90%) in 3 pts, good (≥75% & <90%) in one patient, moderate (≥50% & <75%) in one patient and poor (<50%) in one patient.

Patient #1 #2 #3 #4 #5 #6 #7 Sex male male male female male male male Age 63y 56y 71y 65y 60y 69y 81y BMI 31kg/m2 32kg/m2 19kg/m2 25kg/m2 28kg/m2 34kg/m2 29kg/m2 LVEF 25% 60% 25% 25% 25% 31% 34% EDVI 123ml/m2 184ml/m2 69ml/m2 114ml/m2 142ml/m2 105ml/m2 75ml/m2 Catheter multipolar high-density + 3.5mm open-irrigated tip 3.5mm open-irrigated tip multipolar high-density + 3.5mm open-irrigated tip multipolar high-density + 3.5mm open-irrigated tip multipolar high-density + magnetic remote 3.5mm open-irrigated tip multipolar high-density + magnetic remote 3.5mm open-irrigated tip multipolar high-density + magnetic remote 3.5mm open-irrigated tip Quality 98% 96% 91% 66% 89% no match 53% Quality = Percentage match between defined substrate and WT.

Superimpose – wall thinning and FAM

Conclusion(s)

Integration of substrate-based segmentation using the service of the internet platform is feasible in daily practice. Agreement between voltage-map based substrate definition and internet platform-based WT was satisfactory in the majority of patients.

Charge-stripe crystal phase in an insulating cuprate

High-temperature (high-T_c) superconductivity in cuprates arises from carrier doping of an antiferromagnetic Mott insulator. This carrier doping leads to the formation of electronic liquid-crystal phases¹. The insulating charge-stripe crystal phase is predicted to form when a small density of holes is doped into the charge-transfer insulator state^1-3, but this phase is yet to be observed experimentally. Here, we use surface annealing to extend the accessible doping range in Bi-based cuprates and realize the lightly doped charge-transfer insulating state of the cuprate Bi₂Sr₂CaCu₂O_8+x. In this insulating state with a charge transfer gap on the order of ~1 eV, our spectroscopic imaging scanning tunnelling microscopy measurements provide strong evidence for a unidirectional charge-stripe order with a commensurate 4a₀ period along the Cu-O-Cu bond. Notably, this insulating charge-stripe crystal phase develops before the onset of the pseudogap and formation of the Fermi surface. Our work provides fresh insight into the microscopic origin of electronic inhomogeneity in high-T_c cuprates.

Interplay of orbital effects and nanoscale strain in topological crystalline insulators

Orbital degrees of freedom can have pronounced effects on the fundamental properties of electrons in solids. In addition to influencing bandwidths, gaps, correlation strength and dispersion, orbital effects have been implicated in generating novel electronic and structural phases. Here we show how the orbital nature of bands can result in non-trivial effects of strain on band structure. We use scanning–tunneling microscopy to study the effects of strain on the electronic structure of a heteroepitaxial thin film of a topological crystalline insulator, SnTe. By studying the effects of uniaxial strain on the band structure we find a surprising effect where strain applied in one direction has the most pronounced influence on the band structure along the perpendicular direction. Our theoretical calculations indicate that this effect arises from the orbital nature of the conduction and valence bands. Our results imply that a microscopic model capturing strain effects must include a consideration of the orbital nature of bands.

The role of orbital degrees of freedom in determining the electronic structure remains obscured. Here, Walkup et al. report strain-induced band structure changes in a topological crystalline insulator SnTe, whose surprising behavior reflects the  orbital nature of bands.

Etching of Cr tips for scanning tunneling microscopy of cleavable oxides

We report a detailed three-step roadmap for the fabrication and characterization of bulk Cr tips for spin-polarized scanning tunneling microscopy. Our strategy uniquely circumvents the need for ultra-high vacuum preparation of clean surfaces or films. First, we demonstrate the role of ex situ electrochemical etch parameters on Cr tip apex geometry, using scanning electron micrographs of over 70 etched tips. Second, we describe the suitability of the in situ cleaved surface of the layered antiferromagnet La_1.4Sr_1.6Mn₂O₇ to evaluate the spin characteristics of the Cr tip, replacing the ultra-high vacuum-prepared test samples that have been used in prior studies. Third, we outline a statistical algorithm that can effectively delineate closely spaced or irregular cleaved step edges, to maximize the accuracy of step height and spin-polarization measurements.

Effectiveness of cardiogoniometry compared with exercise-ECG test in diagnosing stable coronary artery disease in women

AIMS

To investigate the effectiveness of cardiogoniometry, a novel, non-invasive method, in diagnosing coronary artery disease (CAD) in women and compare it with exercise-ECG test, by using coronary angiography as a reference method.

METHODS

It was a single-centre, case-series study including consecutive female patients with stable angina pectoris (AP) undergoing coronary angiography. Exercise-ECG test, done according to the Bruce protocol, and cardiogoniometry were obtained prior to coronary angiography. Clinically significant CAD has been defined as one or more coronary lesions with >70% stenosis.

RESULTS

Study included 114 consecutive female patients with median age of 64.0 (58.0-71.0) years, out of which 32 (28.1%) had CAD. Cardiogoniometry yielded a total accuracy of 74.6% with a sensitivity of 75.0% (95% CI 56.6-88.5) and specificity of 74.4% (95% CI 63.6-83.4). Exercise-ECG test yielded a total accuracy of 45.1% with a sensitivity of 68.1% (95% CI 42.7-83.6) and specificity 36.6% (95% CI 25.2-50.3). Cardiogoniometry showed higher accuracy than exercise-ECG test ( P < 0.001). Pathological cardiogoniometry was associated with almost nine times higher risk for CAD (OR 8.7, 95%CI 3.4-22.3, P < 0.001), which remained significant after adjustment for age, and hypokinesia.

CONCLUSION

Cardiogoniometry is a non-invasive, easy-to-use and free-of-risk method which showed high effectiveness in diagnosing stable CAD in women and superior to exercise-ECG test. Cardiogoniometry could be introduced as a part of the diagnostic algorithm of screening women for stable CAD and is suitable for use in the primary setting, especially in women unable to undergo stress-testing.

Strain engineering Dirac surface states in heteroepitaxial topological crystalline insulator thin films

The unique crystalline protection of the surface states in topological crystalline insulators has led to a series of predictions of strain-generated phenomena, from the appearance of pseudo-magnetic fields and helical flat bands to the tunability of Dirac surface states by strain that may be used to construct 'straintronic' nanoswitches. However, the practical realization of this exotic phenomenology via strain engineering is experimentally challenging and is yet to be achieved. Here, we have designed an experiment to not only generate and measure strain locally, but also to directly measure the resulting effects on Dirac surface states. We grew heteroepitaxial thin films of topological crystalline insulator SnTe in situ and measured them using high-resolution scanning tunnelling microscopy to determine picoscale changes in the atomic positions, which reveal regions of both tensile and compressive strain. Simultaneous Fourier-transform scanning tunnelling spectroscopy was then used to determine the effects of strain on the Dirac electrons. We find that strain continuously tunes the momentum space position of the Dirac points, consistent with theoretical predictions. Our work demonstrates the fundamental mechanism necessary for using topological crystalline insulators in strain-based applications.

Dirac mass generation from crystal symmetry breaking on the surfaces of topological crystalline insulators

The tunability of topological surface states and controllable opening of the Dirac gap are of fundamental and practical interest in the field of topological materials. In the newly discovered topological crystalline insulators (TCIs), theory predicts that the Dirac node is protected by a crystalline symmetry and that the surface state electrons can acquire a mass if this symmetry is broken. Recent studies have detected signatures of a spontaneously generated Dirac gap in TCIs; however, the mechanism of mass formation remains elusive. In this work, we present scanning tunnelling microscopy (STM) measurements of the TCI Pb1-xSnxSe for a wide range of alloy compositions spanning the topological and non-topological regimes. The STM topographies reveal a symmetry-breaking distortion on the surface, which imparts mass to the otherwise massless Dirac electrons-a mechanism analogous to the long sought-after Higgs mechanism in particle physics. Interestingly, the measured Dirac gap decreases on approaching the trivial phase, whereas the magnitude of the distortion remains nearly constant. Our data and calculations reveal that the penetration depth of Dirac surface states controls the magnitude of the Dirac mass. At the limit of the critical composition, the penetration depth is predicted to go to infinity, resulting in zero mass, consistent with our measurements. Finally, we discover the existence of surface states in the non-topological regime, which have the characteristics of gapped, double-branched Dirac fermions and could be exploited in realizing superconductivity in these materials.

Nanoscale interplay of strain and doping in a high-temperature superconductor

The highest-temperature superconductors are electronically inhomogeneous at the nanoscale, suggesting the existence of a local variable that could be harnessed to enhance the superconducting pairing. Here we report the relationship between local doping and local strain in the cuprate superconductor Bi(2)Sr(2)CaCu(2)O(8+x). We use scanning tunneling microscopy to discover that the crucial oxygen dopants are periodically distributed in correlation with local strain. Our picoscale investigation of the intraunit-cell positions of all oxygen dopants provides essential structural input for a complete microscopic theory.

Scanning tunnelling microscopy imaging of symmetry-breaking structural distortion in the bismuth-based cuprate superconductors

A complicating factor in unravelling the theory of high-temperature (high-T(c)) superconductivity is the presence of a 'pseudogap' in the density of states, the origin of which has been debated since its discovery. Some believe the pseudogap is a broken symmetry state distinct from superconductivity, whereas others believe it arises from short-range correlations without symmetry breaking. A number of broken symmetries have been imaged and identified with the pseudogap state, but it remains crucial to disentangle any electronic symmetry breaking from the pre-existing structural symmetry of the crystal. We use scanning tunnelling microscopy to observe an orthorhombic structural distortion across the cuprate superconducting Bi(2)Sr(2)Ca(n-1)Cu(n)O(2n+4+x) (BSCCO) family tree, which breaks two-dimensional inversion symmetry in the surface BiO layer. Although this inversion-symmetry-breaking structure can impact electronic measurements, we show from its insensitivity to temperature, magnetic field and doping, that it cannot be the long-sought pseudogap state. To detect this picometre-scale variation in lattice structure, we have implemented a new algorithm that will serve as a powerful tool in the search for broken symmetry electronic states in cuprates, as well as in other materials.