Using strain to uncover the interplay between two- and three-dimensional charge density waves in high-temperature superconducting YBa2Cu3Oy.

Uniaxial pressure provides an efficient approach to control charge density waves in YBa2Cu3Oy. It can enhance the correlation volume of ubiquitous short-range two-dimensional charge-density-wave correlations, and induces a long-range three-dimensional charge density wave, otherwise only accessible at large magnetic fields. Here, we use x-ray diffraction to study the strain dependence of these charge density waves and uncover direct evidence for a form of competition between them. We show that this interplay is qualitatively described by including strain effects in a nonlinear sigma model of competing superconducting and charge-density-wave orders. Our analysis suggests that strain stabilizes the 3D charge density wave in the regions between disorder-pinned domains of 2D charge density waves, and that the two orders compete at the boundaries of these domains. No signatures of discommensurations nor of pair density waves are observed. From a broader perspective, our results underscore the potential of strain tuning as a powerful tool for probing competing orders in quantum materials.

Designing the stripe-ordered cuprate phase diagram through uniaxial-stress.

The ability to efficiently control charge and spin in the cuprate high-temperature superconductors is crucial for fundamental research and underpins technological development. Here, we explore the tunability of magnetism, superconductivity, and crystal structure in the stripe phase of the cuprate La[Formula: see text]Ba[Formula: see text]CuO[Formula: see text], with [Formula: see text] = 0.115 and 0.135, by employing temperature-dependent (down to 400 mK) muon-spin rotation and AC susceptibility, as well as X-ray scattering experiments under compressive uniaxial stress in the CuO[Formula: see text] plane. A sixfold increase of the three-dimensional (3D) superconducting critical temperature [Formula: see text] and a full recovery of the 3D phase coherence is observed in both samples with the application of extremely low uniaxial stress of [Formula: see text]0.1 GPa. This finding demonstrates the removal of the well-known 1/8-anomaly of cuprates by uniaxial stress. On the other hand, the spin-stripe order temperature as well as the magnetic fraction at 400 mK show only a modest decrease under stress. Moreover, the onset temperatures of 3D superconductivity and spin-stripe order are very similar in the large stress regime. However, strain produces an inhomogeneous suppression of the spin-stripe order at elevated temperatures. Namely, a substantial decrease of the magnetic volume fraction and a full suppression of the low-temperature tetragonal structure is found under stress, which is a necessary condition for the development of the 3D superconducting phase with optimal [Formula: see text]. Our results evidence a remarkable cooperation between the long-range static spin-stripe order and the underlying crystalline order with the three-dimensional fully coherent superconductivity. Overall, these results suggest that the stripe- and the SC order may have a common physical mechanism.

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.

Charge Density Waves in YBa_{2}Cu_{3}O_{6.67} Probed by Resonant X-Ray Scattering under Uniaxial Compression.

We report a comprehensive Cu L_{3}-edge resonant x-ray scattering (RXS) study of two- and three-dimensional (2D and 3D) incommensurate charge correlations in single crystals of the underdoped high-temperature superconductor YBa_{2}Cu_{3}O_{6.67} under uniaxial compression up to 1% along the two inequivalent Cu─O─Cu bond directions (a and b) in the CuO_{2} planes. We confirm the strong in-plane anisotropy of the 2D charge correlations and observe their symmetric response to pressure: pressure along a enhances correlations along b, and vice versa. Our results imply that the underlying order parameter is uniaxial. In contrast, 3D long-range charge order is only observed along b in response to compression along a. Spectroscopic RXS measurements show that the 3D charge order resides exclusively in the CuO_{2} planes and may thus be generic to the cuprates. We discuss implications of these results for models of electronic nematicity and for the interplay between charge order and superconductivity.

Heat-capacity measurements under uniaxial pressure using a piezo-driven device.

We report the development of a technique to measure heat capacity at large uniaxial pressure using a piezoelectric-driven device generating compressive and tensile strain in the sample. Our setup is optimized for temperatures ranging from 8 K down to millikelvin. Using an AC heat-capacity technique, we are able to achieve an extremely high resolution and to probe a homogeneously strained part of the sample. We demonstrate the capabilities of our setup on the unconventional superconductor Sr2RuO4. By replacing thermometer and adjusting the remaining setup accordingly, the temperature regime of the experiment can be adapted to other temperature ranges of interest.

Using Uniaxial Stress to Probe the Relationship between Competing Superconducting States in a Cuprate with Spin-stripe Order.

We report muon spin rotation and magnetic susceptibility experiments on in-plane stress effects on the static spin-stripe order and superconductivity in the cuprate system La_{2-x}Ba_{x}CuO_{4} with x=0.115. An extremely low uniaxial stress of ∼0.1 GPa induces a substantial decrease in the magnetic volume fraction and a dramatic rise in the onset of 3D superconductivity, from ∼10 to 32 K; however, the onset of at-least-2D superconductivity is much less sensitive to stress. These results show not only that large-volume-fraction spin-stripe order is anticorrelated with 3D superconducting coherence but also that these states are energetically very finely balanced. Moreover, the onset temperatures of 3D superconductivity and spin-stripe order are very similar in the large stress regime. These results strongly suggest a similar pairing mechanism for spin-stripe order and the spatially modulated 2D and uniform 3D superconducting orders, imposing an important constraint on theoretical models.

Constraints on the superconducting order parameter in Sr2RuO4 from oxygen-17 nuclear magnetic resonance.

Phases of matter are usually identified through spontaneous symmetry breaking, especially regarding unconventional superconductivity and the interactions from which it originates. In that context, the superconducting state of the quasi-two-dimensional and strongly correlated perovskite Sr2RuO4 is considered to be the only solid-state analogue to the superfluid 3He-A phase1,2, with an odd-parity order parameter that is unidirectional in spin space for all electron momenta and breaks time-reversal symmetry. This characterization was recently called into question by a search for an expected 'split' transition in a Sr2RuO4 crystal under in-plane uniaxial pressure, which failed to find any such evidence; instead, a dramatic rise and a peak in a single-transition temperature were observed3,4. Here we use nuclear magnetic resonance (NMR) spectroscopy of oxygen-17, which is directly sensitive to the order parameter via hyperfine coupling to the electronic spin degrees of freedom, to probe the nature of superconductivity in Sr2RuO4 and its evolution under strain. A reduction of the Knight shift is observed for all strain values and at temperatures below the critical temperature, consistent with a drop in spin polarization in the superconducting state. In unstrained samples, our results contradict a body of previous NMR work reporting no change in the Knight shift5 and the most prevalent theoretical interpretation of the order parameter as a chiral p-wave state. Sr2RuO4 is an extremely clean layered perovskite and its superconductivity emerges from a strongly correlated Fermi liquid, and our work imposes tight constraints on the order parameter symmetry of this archetypal system.

Uniaxial pressure control of competing orders in a high-temperature superconductor.

Cuprates exhibit antiferromagnetic, charge density wave (CDW), and high-temperature superconducting ground states that can be tuned by means of doping and external magnetic fields. However, disorder generated by these tuning methods complicates the interpretation of such experiments. Here, we report a high-resolution inelastic x-ray scattering study of the high-temperature superconductor YBa2Cu3O6.67 under uniaxial stress, and we show that a three-dimensional long-range-ordered CDW state can be induced through pressure along the a axis, in the absence of magnetic fields. A pronounced softening of an optical phonon mode is associated with the CDW transition. The amplitude of the CDW is suppressed below the superconducting transition temperature, indicating competition with superconductivity. The results provide insights into the normal-state properties of cuprates and illustrate the potential of uniaxial-pressure control of competing orders in quantum materials.

Resistivity in the Vicinity of a van Hove Singularity: Sr_{2}RuO_{4} under Uniaxial Pressure.

We report the results of a combined study of the normal-state resistivity and superconducting transition temperature T_{c} of the unconventional superconductor Sr_{2}RuO_{4} under uniaxial pressure. There is strong evidence that, as well as driving T_{c} through a maximum at ∼3.5 K, compressive strains ϵ of nearly 1% along the crystallographic [100] axis drive the γ Fermi surface sheet through a van Hove singularity, changing the temperature dependence of the resistivity from T^{2} above, and below the transition region to T^{1.5} within it. This occurs in extremely pure single-crystals in which the impurity contribution to the resistivity is <100 nΩ cm, so our study also highlights the potential of uniaxial pressure as a more general probe of this class of physics in clean systems.

Creation of a novel risk score for surgical site infection and occurrence after ventral hernia repair.

BACKGROUND: Complex ventral hernia repair (VHR) is a common surgical operation but carries a risk of complications from surgical site infections (SSI) and occurrences (SSO). We aimed to create a predictive risk score to identify patients at increased risk for SSO or SSI within 30 days of surgery. METHODS: Data were prospectively collected on all patients undergoing VHR between January 2008 and February 2015 by a single surgeon. Multivariable logistic regression was used to identify independent factors predictive of SSO and SSI. Significant predictors of SSO and SSI were assigned point values based on their odds ratios to create a novel risk score, the Hopkins ventral hernia repair SSO/SSI risk score; predicted and actual rates of outcomes were then compared using weighted regression. RESULTS: During the study period, 362 patients underwent open VHR. Thirty-day SSO and SSI occurred in 18.5 and 10% of patients, respectively. After risk adjustment, ASA class ≥3 (1 point), operative time ≥4 h (2 points), and the absence of a postoperative wound vacuum dressing (1 point) were predictive of 30-day SSO. Predicted risk of SSO utilizing this scoring system was 9.7, 19.4, 29.1, and 38.8% for 1, 2, 3, and 4 points (AUC = 0.73). For SSI, operative time ≥4 h (1 point) and the lack of a wound vacuum dressing (1 point) were predictive. Predicted risk of SSI based on this scoring system was 12.5% for 1 point and 25% for 2 points (AUC = 0.71). Actual vs. predicted rates of SSO and SSI correlated strongly for risk model with a coefficient of determination (R 2) of 0.92 and 0.91, respectively. CONCLUSION: The novel Hopkins ventral hernia repair risk score accurately predicts risk of SSO and SSI after complex VHR. Further studies using a prospective randomized controlled trial will be needed to further validate our findings.

Effect of hernia size on operative repair and post-operative outcomes after open ventral hernia repair.

BACKGROUND: Ventral hernia repair (VHR) is a commonly performed operation, but analysis of patient outcomes based upon hernia size is lacking. We sought to identify differences in operative repair and post-operative morbidity and mortality after open VHR based on hernia defect size. METHODS: Patient and operative data were retrospectively reviewed on all patients undergoing open incisional VHR between January 2008 and February 2015 by a single surgeon at the Johns Hopkins Hospital. Patient variables were described by means for continuous variables and percentages for discrete variables, with differences between groups calculated by Chi-squared analysis. RESULTS: During the study period, 228 patients underwent open VHR during which intraoperative defect size was measured. Patients were split into four groups based upon defect size: less than 200 cm2, 200-300 cm2, 301-400 cm2, and over 400 cm2. Patients with large defects were more likely to present with a recurrent hernia (P = 0.007) and trended towards a history of wound infections (P = 0.07). Operative time was significantly longer as defect size increased (P < 0.001). Component separation was most frequently used in patients with defects 200-300 cm2 in size (P = 0.001), in whom primary closure was most likely to occur. While mesh was used in almost all patients, the specific location (overlay only, underlay only, or overlay with underlay) depended on hernia size (P < 0.001). Mean length of stay increased with defect size (P < 0.001). Larger defect size was associated with increased 30-day morbidity (P = 0.03) but not readmission (P = 0.53), recurrence (P = 0.99), or mortality (P = 0.99). CONCLUSION: Hernia defect size affects operative time and surgical technique for repair of a ventral hernia. Larger defect size is associated with increased post-operative morbidity and length of stay but not readmission, recurrence, or mortality. Hernia size greater than 400 cm2 should not be a limitation to operative repair.

Outcomes of Endovascular Aortic Aneurysm Repair in Kidney Transplant Recipients: Results From a National Quality Initiative.

Contrast-induced nephropathy after endovascular aortic aneurysm repair (EVAR) in kidney transplant recipients (KTRs) can have devastating consequences. The Vascular Quality Initiative (VQI) database was queried to select all KTRs who underwent EVAR between January 2003 and December 2014. Our primary outcome was renal dysfunction, defined as acute kidney injury (AKI; elevation of serum creatinine >0.5 mg/dL from baseline) or new postoperative hemodialysis requirement. Within the EVAR VQI dataset, 40 patients were KTRs (40 of 17 213, or 0.2%). Renal dysfunction occurred in five of 40 patients in the KTR group in comparison to 779 of 17 173 patients in the nontransplanted group (12.5% versus 4.5%, p < 0.01). Emergent EVAR was required in 2 (5%) patients, one of whom required dialysis after surgery and subsequently died. One-year survival after EVAR was similar in the two groups (92.9% versus 93.1%, p = 0.73). KTRs who developed renal dysfunction had significantly lower preoperative estimated glomerular filtration rates (eGFRs) (29.5 versus 54.7, p = 0.007) and a significantly higher iodine:eGFR ratio (0.78 versus 0.39, p = 0.02) despite receiving a similar volume of contrast (70.0 versus 68.8, p = 0.97). Renal dysfunction is 3 times more frequent in KTRs treated with EVAR, though overall survival did not differ between the groups. Decreased preoperative eGFR and a higher iodine:eGFR ratio are associated with postoperative renal dysfunction.

A validated, risk assessment tool for predicting readmission after open ventral hernia repair.

BACKGROUND/PURPOSE: To present a validated model that reliably predicts unplanned readmission after open ventral hernia repair (open-VHR). STUDY DESIGN: A total of 17,789 open-VHR patients were identified using the 2011-2012 ACS-NSQIP databases. This cohort was subdivided into 70 and 30% random testing and validation samples, respectively. Thirty-day unplanned readmission was defined as unexpected readmission for a postoperative occurrence related to the open-VHR procedure. Independent predictors of 30-day unplanned readmission were identified using multivariable logistic regression on the testing sample (n = 12,452 patients). Subsequently, the predictors were weighted according to ß-coefficients to generate an integer-based Clinical Risk Score (CRS) predictive of readmission, which was validated using receiver operating characteristics (ROC) analysis of the validation sample (n = 5337 patients). RESULTS: The rate of 30-day unplanned readmission was 4.7%. Independent risk factors included inpatient status at time of open-VHR, operation time, enterolysis, underweight, diabetes, preoperative anemia, length of stay, chronic obstructive pulmonary disease, history of bleeding disorders, hernia with gangrene, and panniculectomy (all P < 0.05). ROC analysis of the validation cohort rendered an area under the curve of 0.71, which demonstrates the accuracy of this prediction model. Predicted incidence within each 5 risk strata was statistically similar to the observed incidence in the validation sample (P = 0.18), further highlighting the accuracy of this model. CONCLUSION: We present a validated risk stratification tool for unplanned readmissions following open-VHR. Future studies should determine if implementation of our CRS optimizes safety and reduces readmission rates in open-VHR patients.

The effect of TISSEEL fibrin sealant on seroma formation following complex abdominal wall hernia repair: a single institutional review and derived cost analysis.

PURPOSE: The authors evaluated the ability of a fibrin sealant (TISSEEL™: Baxter Healthcare Corp, Deerfield, IL, USA) to reduce the incidence of post-operative seroma following abdominal wall hernia repair. METHODS: We performed a 4-year retrospective review of patients undergoing abdominal wall hernia repair, with and without TISSEEL, by a single surgeon (FEE) at The Johns Hopkins Hospital. Demographics, surgical risk factors, operative data and 30-day outcomes, including wound complications and related interventions, were compared. The quantity and cost of Tisseel per case was reviewed. RESULTS: A total of 250 patients were evaluated: 127 in the TISSEEL group and 123 in the non-TISSEEL control group. The average age for both groups was 56.6 years (P = 0.97). The majority of patients were female (TISSEEL 52.8%, non-TISSEEL 56.1%, P = 0.59) and ASA Class III (TISSEEL 56.7%, non-TISSEEL 58.5%, P = 0.40). There was no difference in the average defect size for both groups (TISSEEL 217 ± 187.6 cm(2), non-TISSEEL 161.3 ± 141.5 cm(2), P = 0.36). Surgical site occurrences occurred in 18.1% of the TISSEEL and 13% of the non-TISSEEL group (P = 0.27). There was a trend towards an increased incidence of seroma in the TISSEEL group (TISSEEL 11%, non-TISSEEL 4.9%, P = 0.07). A total of $124,472.50 was spent on TISSEEL, at an average cost of $995.78 per case. CONCLUSIONS: In the largest study to date, TISSEEL™ application offered no advantage for the reduction of post-operative seroma formation following complex abdominal hernia repair. Moreover, the use of this sealant was associated with significant costs.

History of methicillin-resistant Staphylococcus aureus (MRSA) surgical site infection may not be a contraindication to ventral hernia repair with synthetic mesh: a preliminary report.

PURPOSE: A history of methicillin-resistant Staphylococcus aureus (MRSA) surgical site infection presents a significant surgical dilemma as to the risk of subsequent mesh infection, even if no active infection is present. We investigated the outcomes of ventral hernia repair with synthetic mesh in patients with prior MRSA surgical site infections (SSIs). METHODS: All patients with a clean wound but prior MRSA SSI undergoing open ventral hernia repair with mesh by a single surgeon over a 3-year period were reviewed for the development of any major (need for readmission, operative debridement, or mesh removal) or minor SSI. All patients received peri-operative intravenous vancomycin and prolonged suppressive oral trimethoprim/sulfamethoxazole or doxycycline. RESULTS: Ten patients (male = 7, female = 3) with clean wounds and a history of MRSA SSI underwent open ventral hernia repair with retrorectus synthetic mesh placement. Mean follow-up was 13.5 ± 3.3 months. Overall, two patients (20 %) developed SSIs (minor = 2, major = 0). Both SSIs were successfully managed with therapeutic oral antibiotics and local wound care without need for surgical debridement or mesh removal. There have been no hernia recurrences in any of the patients. CONCLUSIONS: Preliminary results suggest that history of MRSA infection may not be a contraindication to the use of synthetic mesh for ventral hernia repair. Macroporous lightweight meshes, combined with use of prolonged suppressive antibiotics and sublay retromuscular mesh placement that provides complete tissue coverage, should be further investigated as an acceptable prosthetic choice when planning a complex ventral hernia repair in the setting of prior MRSA SSI.

Are rectoceles the cause or the result of obstructed defaecation syndrome? A prospective anorectal physiology study.

AIM: To determine the relationship between obstructed defaecation syndrome (ODS) and rectoceles. METHOD: From December 2007 to November 2011, all female patients with ODS were prospectively evaluated with full interview, clinical examination and anorectal physiology testing. The characteristics of patients with and without rectoceles were compared, and logistic regression was utilized to identify factors predictive of patients having a rectocele beyond the introitus. RESULTS: Of 239 patients with ODS, 90 (mean age: 52.3 ± 1.7 years) had a rectocele. Patients with rectoceles (R+) had a similar prevalence of incomplete emptying compared with patients with no rectocele (R-) (P ≥ 0.21), but only R+ patients reported splinting with defaecation (36.7% vs 0%; P < 0.0001). Anorectal manometry measurements, including mean resting pressure, maximum resting pressure and maximum squeeze pressure, were similar between groups (P ≥ 0.12). There were also no significant differences in rectal compliance (maximum tolerated volume) or rectal sensitivity (volume of first sensation) (P ≥ 0.65). R+ patients had greater difficulty expelling a 60 cm(3) balloon (70.1% R+ patients vs 57.5% R- patients; P = 0.05), but the prevalence of pelvic floor dyssynergia, as quantified by nonrelaxation on electromyography (EMG) testing, was similar to that of R- patients (P = 0.49). Logistic regression suggested that only difficulty with balloon expulsion was associated with higher odds of having a rectocele (OR = 3.00; P = 0.002), whereas mean resting pressure, EMG nonrelaxation and symptoms of incomplete emptying were not (P ≥ 0.12). CONCLUSION: Rectoceles are not associated with an increased severity of ODS-type symptoms, anorectal abnormalities or pelvic floor dyssynergia in patients with ODS. This suggests that rectoceles may be the result, rather than the cause, of ODS.

Valproate for the treatment of medication-induced impulse-control disorders in three patients with Parkinson's disease.

Impulse-control disorders (ICDs) are becoming more commonly recognized in the Parkinson disease (PD) population. To date, there are no definitive methods of treating dopamine dysregulation syndromes in PD patients. We sought to uncover an effective treatment option for future study. We report a series of 3 PD patients with ICDs who were effectively treated with valproate. Based on these encouraging preliminary observations, future controlled clinical trials investigating the efficacy of valproate for ICDs in PD are recommended.