Sign reversal of the Josephson inductance magnetochiral anisotropy and 0-π-like transitions in supercurrent diodes

The recent discovery of the intrinsic supercurrent diode effect, and its prompt observation in a rich variety of systems, has shown that non-reciprocal supercurrents naturally emerge when both space-inversion and time-inversion symmetries are broken. In Josephson junctions, non-reciprocal supercurrent can be conveniently described in terms of spin-split Andreev states. Here we demonstrate a sign reversal of the Josephson inductance magnetochiral anisotropy, a manifestation of the supercurrent diode effect. The asymmetry of the Josephson inductance as a function of the supercurrent allows us to probe the current-phase relation near equilibrium, and to probe jumps in the junction ground state. Using a minimal theoretical model, we can then link the sign reversal of the inductance magnetochiral anisotropy to the so-called 0-π-like transition, a predicted but still elusive feature of multichannel junctions. Our results demonstrate the potential of inductance measurements as sensitive probes of the fundamental properties of unconventional Josephson junctions.

Half-Integer Conductance Plateau at the ν=2/3 Fractional Quantum Hall State in a Quantum Point Contact

The ν=2/3 fractional quantum Hall state is the hole-conjugate state to the primary Laughlin ν=1/3 state. We investigate transmission of edge states through quantum point contacts fabricated on a GaAs/AlGaAs heterostructure designed to have a sharp confining potential. When a small but finite bias is applied, we observe an intermediate conductance plateau with G=0.5(e^{2}/h). This plateau is observed in multiple QPCs, and persists over a significant range of magnetic field, gate voltage, and source-drain bias, making it a robust feature. Using a simple model that considers scattering and equilibration between counterflowing charged edge modes, we find this half-integer quantized plateau to be consistent with full reflection of an inner counterpropagating -1/3 edge mode while the outer integer mode is fully transmitted. In a QPC fabricated on a different heterostructure which has a softer confining potential, we instead observe an intermediate conductance plateau at G=(1/3)(e^{2}/h). These results provide support for a model at ν=2/3 in which the edge transitions from a structure having an inner upstream -1/3 charge mode and outer downstream integer mode to a structure with two downstream 1/3 charge modes when the confining potential is tuned from sharp to soft and disorder prevails.

Effect of Rashba and Dresselhaus spin-orbit coupling on supercurrent rectification and magnetochiral anisotropy of ballistic Josephson junctions

Simultaneous breaking of inversion- and time-reversal symmetry in Josephson junction (JJ) leads to a possible violation of theI(φ) = -I(-φ) equality for the current-phase relation. This is known as anomalous Josephson effect and it produces a phase shiftφ₀in sinusoidal current-phase relations. In ballistic JJs with non-sinusoidal current phase relation the observed phenomenology is much richer, including the supercurrent diode effect and the magnetochiral anisotropy (MCA) of Josephson inductance. In this work, we present measurements of both effects on arrays of JJs defined on epitaxial Al/InAs heterostructures. We show that the orientation of the current with respect to the lattice affects the MCA, possibly as the result of a finite Dresselhaus component. In addition, we show that the two-fold symmetry of the Josephson inductance reflects in the activation energy for phase slips.

Impact of bulk-edge coupling on observation of anyonic braiding statistics in quantum Hall interferometers

Quantum Hall interferometers have been used to probe fractional charge and statistics of quasiparticles. We present measurements of a small Fabry-Perot interferometer in which the electrostatic coupling constants which affect interferometer behavior can be determined experimentally. Near the center of the ν = 1/3 state this device exhibits Aharonov-Bohm interference interrupted by a few discrete phase jumps, and Φ0 oscillations at higher and lower magnetic fields, consistent with theoretical predictions for detection of anyonic statistics. We estimate the electrostatic parameters KI and KIL by two methods: using the ratio of oscillation periods in compressible versus incompressible regions, and from finite-bias conductance measurements. We find that the extracted KI and KIL can account for the deviation of the phase jumps from the theoretical anyonic phase θa = 2π/3. At integer states, we find that KI and KIL can account for the Aharonov-Bohm and Coulomb-dominated behavior of different edge states.

Hydrodynamic and Ballistic Transport over Large Length Scales in GaAs/AlGaAs

We study hydrodynamic and ballistic transport regimes through nonlocal resistance measurements and high-resolution kinetic simulations in a mesoscopic structure on a high-mobility two-dimensional electron system in a GaAs/AlGaAs heterostructure. We evince the existence of collective transport phenomena in both regimes and demonstrate that negative nonlocal resistances and current vortices are not exclusive to only the hydrodynamic regime. The combined experiments and simulations highlight the importance of device design, measurement schemes, and one-to-one modeling of experimental devices to demarcate various transport regimes.

Hidden Quantum Hall Stripes in Al_{x}Ga_{1-x}As/Al_{0.24}Ga_{0.76}As Quantum Wells

We report on transport signatures of hidden quantum Hall stripe (hQHS) phases in high (N>2) half-filled Landau levels of Al_{x}Ga_{1-x}As/Al_{0.24}Ga_{0.76}As quantum wells with varying Al mole fraction x<10^{-3}. Residing between the conventional stripe phases (lower N) and the isotropic liquid phases (higher N), where resistivity decreases as 1/N, these hQHS phases exhibit isotropic and N-independent resistivity. Using the experimental phase diagram, we establish that the stripe phases are more robust than theoretically predicted, calling for improved theoretical treatment. We also show that, unlike conventional stripe phases, the hQHS phases do not occur in ultrahigh mobility GaAs quantum wells but are likely to be found in other systems.

Coherent transport through a Majorana island in an Aharonov-Bohm interferometer

Majorana zero modes are leading candidates for topological quantum computation due to non-local qubit encoding and non-abelian exchange statistics. Spatially separated Majorana modes are expected to allow phase-coherent single-electron transport through a topological superconducting island via a mechanism referred to as teleportation. Here we experimentally investigate such a system by patterning an elongated epitaxial InAs-Al island embedded in an Aharonov-Bohm interferometer. With increasing parallel magnetic field, a discrete sub-gap state in the island is lowered to zero energy yielding persistent 1e-periodic Coulomb blockade conductance peaks (e is the elementary charge). In this condition, conductance through the interferometer is observed to oscillate in a perpendicular magnetic field with a flux period of h/e (h is Planck’s constant), indicating coherent transport of single electrons through the islands, a signature of electron teleportation via Majorana modes.

Theories predict teleportation of phase-coherent single electrons through a topological superconducting island. Here, the authors report persistent Coulomb blockade conductance peaks due to coherent transport of single electrons through patterned InAs-Al islands embedded in an Aharonov-Bohm interferometer.

Relating Andreev Bound States and Supercurrents in Hybrid Josephson Junctions

We demonstrate concomitant measurement of phase-dependent critical current and Andreev bound state spectrum in a highly transmissive InAs Josephson junction embedded in a dc superconducting quantum interference device (SQUID). Tunneling spectroscopy reveals Andreev bound states with near unity transmission probability. A nonsinusoidal current-phase relation is derived from the Andreev spectrum, showing excellent agreement with the one extracted from the SQUID critical current. Both measurements are reconciled within a short junction model where multiple Andreev bound states, with various transmission probabilities, contribute to the entire supercurrent flowing in the junction.

Anomalous Nematic States in High Half-Filled Landau Levels

It is well established that the ground states of a two-dimensional electron gas with half-filled high (N≥2) Landau levels are compressible charge-ordered states, known as quantum Hall stripe (QHS) phases. The generic features of QHSs are a maximum (minimum) in a longitudinal resistance R_{xx} (R_{yy}) and a nonquantized Hall resistance R_{H}. Here, we report on emergent minima (maxima) in R_{xx} (R_{yy}) and plateaulike features in R_{H} in half-filled N≥3 Landau levels. Remarkably, these unexpected features develop at temperatures considerably lower than the onset temperature of QHSs, suggestive of a new ground state.

Hybridization of Subgap States in One-Dimensional Superconductor-Semiconductor Coulomb Islands

We present measurements of one-dimensional superconductor-semiconductor Coulomb islands, fabricated by gate confinement of a two-dimensional InAs heterostructure with an epitaxial Al layer. When tuned via electrostatic side gates to regimes without subgap states, Coulomb blockade reveals Cooper-pair mediated transport. When subgap states are present, Coulomb peak positions and heights oscillate in a correlated way with magnetic field and gate voltage, as predicted theoretically, with (anti)crossings in (parallel) transverse magnetic field indicating Rashba-type spin-orbit coupling. Overall results are consistent with a picture of overlapping Majorana zero modes in finite wires.

Electron-electron interactions and the paired-to-nematic quantum phase transition in the second Landau level

In spite of its ubiquity in strongly correlated systems, the competition of paired and nematic ground states remains poorly understood. Recently such a competition was reported in the two-dimensional electron gas at filling factor ν = 5/2. At this filling factor a pressure-induced quantum phase transition was observed from the paired fractional quantum Hall state to the quantum Hall nematic. Here we show that the pressure-induced paired-to-nematic transition also develops at ν = 7/2, demonstrating therefore this transition in both spin branches of the second orbital Landau level. However, we find that pressure is not the only parameter controlling this transition. Indeed, ground states consistent with those observed under pressure also develop in a sample measured at ambient pressure, but in which the electron-electron interaction was tuned close to its value at the quantum critical point. Our experiments suggest that electron-electron interactions play a critical role in driving the paired-to-nematic transition.

Electron-Hole Asymmetric Chiral Breakdown of Reentrant Quantum Hall States

Reentrant integer quantum Hall (RIQH) states are believed to be correlated electron solid phases, although their microscopic description remains unclear. As bias current increases, longitudinal and Hall resistivities measured for these states exhibit multiple sharp breakdown transitions, a signature unique to RIQH states. A comparison of RIQH breakdown characteristics at multiple voltage probes indicates that these signatures can be ascribed to a phase boundary between broken-down and unbroken regions, spreading chirally from source and drain contacts as a function of bias current and passing voltage probes one by one. The chiral sense of the spreading is not set by the chirality of the edge state itself, instead depending on electron- or holelike character of the RIQH state.

Optical Emission Spectroscopy Study of Competing Phases of Electrons in the Second Landau Level

Quantum phases of electrons in the filling factor range 2≤ν≤3 are probed by the weak optical emission from the partially populated second Landau level and spin wave measurements. Observations of optical emission include a multiplet of sharp peaks that exhibit a strong filling factor dependence. Spin wave measurements by resonant inelastic light scattering probe breaking of spin rotational invariance and are used to link this optical emission with collective phases of electrons. A remarkably rapid interplay between emission peak intensities manifests phase competition in the second Landau level.

ν=5/2 fractional quantum Hall state in the presence of alloy disorder

We report quantitative measurements of the impact of alloy disorder on the ν = 5/2 fractional quantum Hall state. Alloy disorder is controlled by the aluminum content x in the Al(x)Ga(1-x)As channel of a quantum well. We find that the ν = 5/2 state is suppressed with alloy scattering. To our surprise, in samples with alloy disorder the ν = 5/2 state appears at significantly reduced mobilities when compared to samples in which alloy disorder is not the dominant scattering mechanism. Our results highlight the distinct roles of the different types of disorder present in these samples, such as the short-range alloy and the long-range Coulomb disorder.

Laparoscopic surgery and the common bile duct

Many biliary tract surgeons have now reached a level of sophistication with laparoscopic cholecystectomy that they are now able to deal with the common bile duct at the same time. Preoperative endoscopic cholangiography can be reserved for cases where choledocholithiasis has a high degree of probability. This has served to decrease the number of negative studies. The surgeon has five choices regarding stones confirmed by operative cholangiography during laparoscopic cholecystectomy: (1) do nothing, hoping the stones will pass spontaneously or that a postoperative sphincterotomy with stone extraction will be successful; (2) perform a transcystic laparoscopic common bile duct exploration (best for stones less than 1 cm and distal to the cystic duct); (3) perform a laparoscopic common bile duct exploration by choledochotomy (best for large stones in patients with common bile ducts greater than 1 cm. It is also the preferred approach with stones proximal to the insertion of the cystic duct.); (4) perform an intraoperative sphincterotomy with stone extraction, either retrograde or antegrade (this approach has some proponents but has not gained popularity among the majority of surgeons); and (5) place a double lumen catheter through the cystic duct with a proximal lumen in the common bile duct and the distal lumen in the duodenum. This can be used for serial postoperative cholangiography to confirm spontaneous stone passage or falsely positive operative cholangiograms. It is useful in situations when laparoscopic common bile duct exploration equipment or surgeon expertise is not available. If stones persist, a guidewire can be introduced through the distal lumen of the catheter for a guidewire-assisted sphincterotomy. Other CBD interventions that have been reported include laparoscopic biliary bypass and resection of choledochal cysts. Malignant lesions should not be approached by a laparoscopic method except in unusual circumstances.

An unusual case of gastric volvulus after laparoscopic paraesophageal hernia repair

Laparoscopic surgery for paraesophageal hernia is well accepted. However, the complications of this relatively new procedure have not been thoroughly investigated. Only four cases of recurrent volvulus after paraesophageal hernia repair have been reported. A 52-year-old man presented with a large right-side paraesophageal hernia. He experienced a retroperitoneal midgastric volvulus despite correct orientation of the stomach distally and proximally. We report an unusual complication that seems congenital in origin. Diagnostic and corrective measures are suggested.

Fibromyalgia following trauma: psychology or biology?

The concept that fibromyalgia may follow trauma is currently an area of intense debate within the medical field and is driven to a large extent by social and legal issues. This article questions whether the current literature supports the notion that trauma may cause fibromyalgia and explores the relative contribution of biology and psychology in the development of and sense of disability from fibromyalgia.

Laparoscopic repair of a Morgagni hernia

Morgagni hernias are unusual diaphragmatic hernias which usually present in adulthood. They have traditionally been repaired through transabdominal or transthoracic approaches. The authors present a case of a laparoscopic repair of a Morgagni hernia in a 52-year-old female. A tension free repair of the defect was accomplished utilizing Goretex (W.L. Gore & Associates, Inc., North Elkton, MD) mesh. The patient had an uneventful recovery and is asymptomatic at 6 months follow-up. The etiology, diagnosis and traditional surgical approaches to this problem are discussed. A technique for laparoscopic repair of a Morgagni hernia is described. The literature on the laparoscopic repair of a Morgagni hernia is reviewed and different operative techniques are discussed.

Endo-drgan surgery: a new approach to intragastric lesions

Gastric endo-organ surgery is a minimally invasive procedure combining the use of gastroesophageal endoscopy and laparoscopy to approach intragastric problems that require surgical intervention. The advantages include: less scarring; shorter hospital stays; and less postoperative discomfort than conventional laparotomy. The technique requires placement of two or three percutaneous endoscopic gastrostomies in various positions on the gastric wall. Filipi et al. developed a percutaneous endoscopic gastrostomy (PEG) that is large enough to allow the use of 5 and 10mm laparoscopic instruments for intragastric surgery. In this article we review the complications related to the introduction of this access port.

Quantitative magnetic resonance imaging predicts clinical outcome of core decompression for osteonecrosis of the femoral head

OBJECTIVE

To determine whether the course of femoral head osteonecrosis after core decompression can be predicted from the extent of necrotic bone in the preoperative magnetic resonance imaging (MRI).

METHODS

In 31 femoral head lesions (Ficat stage I or II), the percentage volume of necrotic bone was calculated by dividing the sum of the necrotic areas from all MRI slices by the sum of the femoral head areas. Osteonecrosis risk factors, pain scores, and the need for further surgery were assessed at a minimum of 12 mo post-core decompression. Clinical outcomes were considered good when post-core decompression pain scores improved and further surgery was not required.

RESULTS

Fourteen of the 15 hips with good outcomes after a mean followup of 32 mo had less than 21% femoral head involvement. All 16 hips with poor outcomes after a mean followup of 17 mo had more than 21% of the femoral head affected.

CONCLUSION

Quantitative MRI of femoral head necrosis was a useful predictor of clinical outcome following core decompression.

Pyarthrosis in patients with rheumatoid arthritis: a report of 13 cases and a review of the literature from the past 40 years

PURPOSE

The purpose of this study is to report 13 cases and review the literature for pyarthrosis occurring in the setting of rheumatoid arthritis (RA). Special emphasis is placed on evaluating both the changing, as well as the constant, features of this complication and on assessing diagnostic and therapeutic aspects that have a bearing upon outcome.

PATIENTS AND METHODS

A retrospective review of records from our institution revealed 13 cases of pyarthrosis in patients with RA over the past 14 years. Information obtained included patient demographics, RA history, concomitant illnesses and medications, length of symptoms prior to the diagnosis of pyarthrosis, peri-articular manifestations, probable source of infection, joint(s) involved, relevant laboratory data, and information on treatment and outcome based on initial surgical therapy versus closed needle drainage. In addition, 213 cases from 45 citations were reviewed for similar information.

RESULTS

Our series was notable for a high percentage of associated serious medical illnesses and peri-articular manifestations of the pyarthrosis (i.e., sinus tract formation, concomitant septic bursitis, or infected synovial cyst). The erythrocyte sedimentation rate was a useful monitor of adequate therapy and was often a signal of recurrent infection. In all patients, the skin was the major source of infection. The mortality from pyarthrosis has declined over the past 40 years but is still unacceptably high, especially in patients with polyarticular involvement. Preliminary observations suggest that an initial surgical approach to joint drainage may be preferable to closed needle drainage in order to improve joint outcome in patients with RA and pyarthrosis.

CONCLUSION

Pyarthrosis occurring in patients with RA continues to produce unacceptable morbidity and mortality despite 40 years' experience. Earlier recognition (which may include peri-articular features) and perhaps an aggressive surgical approach to drainage may improve the prognosis.