Spontaneous gyrotropic electronic order in a transition-metal dichalcogenide.

Chirality is ubiquitous in nature, and populations of opposite chiralities are surprisingly asymmetric at fundamental levels1,2. Examples range from parity violation in the subatomic weak force to homochirality in biomolecules. The ability to achieve chirality-selective synthesis (chiral induction) is of great importance in stereochemistry, molecular biology and pharmacology2. In condensed matter physics, a crystalline electronic system is geometrically chiral when it lacks mirror planes, space-inversion centres or rotoinversion axes1. Typically, geometrical chirality is predefined by the chiral lattice structure of a material, which is fixed on formation of the crystal. By contrast, in materials with gyrotropic order3-6, electrons spontaneously organize themselves to exhibit macroscopic chirality in an originally achiral lattice. Although such order-which has been proposed as the quantum analogue of cholesteric liquid crystals-has attracted considerable interest3-15, no clear observation or manipulation of gyrotropic order has been achieved so far. Here we report the realization of optical chiral induction and the observation of a gyrotropically ordered phase in the transition-metal dichalcogenide semimetal 1T-TiSe2. We show that shining mid-infrared circularly polarized light on 1T-TiSe2 while cooling it below the critical temperature leads to the preferential formation of one chiral domain. The chirality of this state is confirmed by the measurement of an out-of-plane circular photogalvanic current, the direction of which depends on the optical induction. Although the role of domain walls requires further investigation with local probes, the methodology demonstrated here can be applied to realize and control chiral electronic phases in other quantum materials4,16.

Unconventional Hysteretic Transition in a Charge Density Wave.

Hysteresis underlies a large number of phase transitions in solids, giving rise to exotic metastable states that are otherwise inaccessible. Here, we report an unconventional hysteretic transition in a quasi-2D material, EuTe_{4}. By combining transport, photoemission, diffraction, and x-ray absorption measurements, we observe that the hysteresis loop has a temperature width of more than 400 K, setting a record among crystalline solids. The transition has an origin distinct from known mechanisms, lying entirely within the incommensurate charge density wave (CDW) phase of EuTe_{4} with no change in the CDW modulation periodicity. We interpret the hysteresis as an unusual switching of the relative CDW phases in different layers, a phenomenon unique to quasi-2D compounds that is not present in either purely 2D or strongly coupled 3D systems. Our findings challenge the established theories on metastable states in density wave systems, pushing the boundary of understanding hysteretic transitions in a broken-symmetry state.

Divergence of the quadrupole-strain susceptibility of the electronic nematic system YbRu2Ge2.

Ferroquadrupole order associated with local [Formula: see text] atomic orbitals of rare-earth ions is a realization of electronic nematic order. However, there are relatively few examples of intermetallic materials which exhibit continuous ferroquadrupole phase transitions, motivating the search for additional materials that fall into this category. Furthermore, it is not clear a priori whether experimental approaches based on transport measurements which have been successfully used to probe the nematic susceptibility in materials such as the Fe-based superconductors will be as effective in the case of [Formula: see text] intermetallic materials, for which the important electronic degrees of freedom are local rather than itinerant and are consequently less strongly coupled to the charge-carrying quasiparticles near the Fermi energy. In the present work, we demonstrate that the intermetallic compound [Formula: see text] exhibits a tetragonal-to-orthorhombic phase transition consistent with ferroquadrupole order of the Yb ions and go on to show that elastoresistivity measurements can indeed provide a clear window on the diverging nematic susceptibility in this system. This material provides an arena in which to study the causes and consequences of electronic nematicity.

Disorder raises the critical temperature of a cuprate superconductor.

With the discovery of charge-density waves (CDWs) in most members of the cuprate high-temperature superconductors, the interplay between superconductivity and CDWs has become a key point in the debate on the origin of high-temperature superconductivity. Some experiments in cuprates point toward a CDW state competing with superconductivity, but others raise the possibility of a CDW-superconductivity intertwined order or more elusive pair-density waves (PDWs). Here, we have used proton irradiation to induce disorder in crystals of [Formula: see text] and observed a striking 50% increase of [Formula: see text], accompanied by a suppression of the CDWs. This is in sharp contrast with the behavior expected of a d-wave superconductor, for which both magnetic and nonmagnetic defects should suppress [Formula: see text] Our results thus make an unambiguous case for the strong detrimental effect of the CDW on bulk superconductivity in [Formula: see text] Using tunnel diode oscillator (TDO) measurements, we find indications for potential dynamic layer decoupling in a PDW phase. Our results establish irradiation-induced disorder as a particularly relevant tuning parameter for the many families of superconductors with coexisting density waves, which we demonstrate on superconductors such as the dichalcogenides and [Formula: see text].

Reciprocal space imaging of ionic correlations in intercalation compounds.

The intercalation of alkali ions into layered materials has played an essential role in battery technology since the development of the first lithium-ion electrodes. Coulomb repulsion between the intercalants leads to ordering of the intercalant sublattice, which hinders ionic diffusion and impacts battery performance. While conventional diffraction can identify the long-range order that can occur at discrete intercalant concentrations during the charging cycle, it cannot determine short-range order at other concentrations that also disrupt ionic mobility. In this Article, we show that the use of real-space transforms of single-crystal diffuse scattering, measured with high-energy synchrotron X-rays, allows a model-independent measurement of the temperature dependence of the length scale of ionic correlations along each of the crystallographic axes in sodium-intercalated V2O5. The techniques described here provide a new way of probing the evolution of structural ordering in crystalline materials.

Author Correction: Reciprocal space imaging of ionic correlations in intercalation compounds.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Origin of long lifetime of band-edge charge carriers in organic-inorganic lead iodide perovskites.

Long carrier lifetime is what makes hybrid organic-inorganic perovskites high-performance photovoltaic materials. Several microscopic mechanisms behind the unusually long carrier lifetime have been proposed, such as formation of large polarons, Rashba effect, ferroelectric domains, and photon recycling. Here, we show that the screening of band-edge charge carriers by rotation of organic cation molecules can be a major contribution to the prolonged carrier lifetime. Our results reveal that the band-edge carrier lifetime increases when the system enters from a phase with lower rotational entropy to another phase with higher entropy. These results imply that the recombination of the photoexcited electrons and holes is suppressed by the screening, leading to the formation of polarons and thereby extending the lifetime. Thus, searching for organic-inorganic perovskites with high rotational entropy over a wide range of temperature may be a key to achieve superior solar cell performance.

Dual Nature of Magnetism in a Uranium Heavy-Fermion System.

The duality between the localized and itinerant nature of magnetism in 5f-electron systems has been a long-standing puzzle. Here, we report inelastic neutron scattering measurements, which reveal both local and itinerant aspects of magnetism in a single-crystalline system of UPt_{2}Si_{2}. In the antiferromagnetic state, we observe a broad continuum of diffuse magnetic scattering with a resonancelike gap of ≈7 meV and the surprising absence of coherent spin waves, suggestive of itinerant magnetism. While the gap closes above the Néel temperature, strong dynamic spin correlations persist to a high temperature. Nevertheless, the size and temperature dependence of the total magnetic spectral weight can be well described by a local moment with J=4. Furthermore, polarized neutron measurements reveal that the magnetic fluctuations are mostly transverse, with little or none of the longitudinal component expected for itinerant moments. These results suggest that a dual description of local and itinerant magnetism is required to understand UPt_{2}Si_{2} and, by extension, other 5f systems, in general.

Charge Density Wave in the New Polymorphs of RE2Ru3Ge5 (RE = Pr, Sm, Dy).

A new polymorph of the RE2Ru3Ge5 (RE = Pr, Sm, Dy) compounds has been grown as single crystals via an indium flux. These compounds crystallize in tetragonal space group P4/mnc with the Sc2Fe3Si5-type structure, having lattice parameters a = 11.020(2) Šand c = 5.853(1) Šfor RE = Pr, a = 10.982(2) Šand c = 5.777(1) Šfor RE = Sm, and a = 10.927(2) Šand c = 5.697(1) Šfor RE = Dy. These materials exhibit a structural transition at low temperature, which is attributed to an apparent charge density wave (CDW). Both the high-temperature average crystal structure and the low-temperature incommensurately modulated crystal structure (for Sm2Ru3Ge5 as a representative) have been solved. The charge density wave order is manifested by periodic distortions of the one-dimensional zigzag Ge chains. From X-ray diffraction, charge transport (electrical resistivity, Hall effect, magnetoresistance), magnetic measurements, and heat capacity, the ordering temperatures (TCDW) observed in the Pr and Sm analogues are ∼200 and ∼175 K, respectively. The charge transport measurement results indicate an electronic state transition happening simultaneously with the CDW transition. X-ray absorption near-edge spectroscopy (XANES) and electronic band structure results are also reported.

Magnitude and concurrence of anxiety and depression among attendees with multiple sclerosis at a tertiary care Hospital in Oman.

BACKGROUND: Anxiety, depression and functional impairments are commonly reported by persons with multiple sclerosis (PwMS) but no data, to our knowledge, has emerged from an Arab Islamic population. The study aims to investigate the prevalence of anxiety, depression and related disabilities among PwMS attending tertiary care in Sultan Qaboos University Hospital (SQUH), one of the urban hospitals in Oman. METHODS: Consecutive and consenting PwMS (n = 57) and healthy subjects (n = 53) completed the following measures: Hospital Anxiety and Depression Scale (HADS) which was used to measure anxiety (cut-point >7) and depression (>7); and Expanded Disability Status Scale (EDSS) to measure the level of disability (≥5). Characteristics such as socio-demographic and clinical variables were also explored. RESULTS: Fifty seven subjects with multiple sclerosis (MS) met the inclusion criteria. The majority of them were females who were 40 years old or younger and the majority were employed and unmarried. Approximately 86 % of the participants were using beta interferon, 96 % scored ≥5 in EDSS. MS of the Relapsing-Remitting type constituted the majority of the cohort (94 %). Approximately 35 % and 51 % endorsed symptoms of anxiety and depression respectively. The MS group scored significantly higher than controls on HADS measurements of depression and anxiety. CONCLUSION: Disability and symptoms of anxiety and depression are common among the PwMS attendees of tertiary care hospital in Oman. Such psychosocial variables have been largely unreported emerging from non-western populations. As these variables are strong indicators of the burden of MS, resolute effort is needed to address such psychosocial dysfunctions in the algorithms of care for PwMS in the Arab Islamic part of the world.

Rehabilitation of Reconstructed Maxilla Using Denture-Guided Epithelial Regeneration in DCIA Flap: 10-Year Follow-Up.

This 10-year follow-up report describes the interdisciplinary comprehensive management of a patient with aneurysmal bone cyst of the maxilla in a 24-year-old patient. The treatment included resection and primary reconstruction with vascularized deep circumflex iliac artery-based composite free flap, implant placement, and peri-implant soft tissue management using denture-guided epithelial regeneration with interim dentures. Definitive management was done using implant-supported cast partial dentures, and the patient followed up for 10 years.

Reversible non-volatile electronic switching in a near-room-temperature van der Waals ferromagnet.

Non-volatile phase-change memory devices utilize local heating to toggle between crystalline and amorphous states with distinct electrical properties. Expanding on this kind of switching to two topologically distinct phases requires controlled non-volatile switching between two crystalline phases with distinct symmetries. Here, we report the observation of reversible and non-volatile switching between two stable and closely related crystal structures, with remarkably distinct electronic structures, in the near-room-temperature van der Waals ferromagnet Fe5-δGeTe2. We show that the switching is enabled by the ordering and disordering of Fe site vacancies that results in distinct crystalline symmetries of the two phases, which can be controlled by a thermal annealing and quenching method. The two phases are distinguished by the presence of topological nodal lines due to the preserved global inversion symmetry in the site-disordered phase, flat bands resulting from quantum destructive interference on a bipartite lattice, and broken inversion symmetry in the site-ordered phase.

Reconstruction of the external ear using implant-supported alloplasts-Our experience.

Surgical reconstruction of the missing external ear is difficult, and the results are often far from satisfactory. An implant-retained auricular prosthesis is a suitable alternative. Microtia, malformation, deformity, and partial or complete loss of the external ear may be due to various congenital or acquired factors. A case series of three patients treated with implant-retained auricular prostheses is presented in this article. For each missing pinna, two titanium implants were placed in the temporal bone. After 6 months of osseointegration, the implants were loaded. All three cases were rehabilitated with a bar and clip retained prosthesis. There were two male and one female patient with an average age of 16.6 years. One patient had unilateral absence of external ear and two had bilateral absence. A total of 10 implants were placed, 4 on the right side and 6 on the left. The average post rehabilitation follow-up was 18 months. Peri-implant tissue reactions were observed at two sites. The implant-retained auricular prosthesis is an alternative treatment approach with good retention and patient satisfaction. Long-term follow-up is required to assess delayed sequelae.

Anomalous excitonic phase diagram in band-gap-tuned Ta2Ni(Se,S)5.

During a band-gap-tuned semimetal-to-semiconductor transition, Coulomb attraction between electrons and holes can cause spontaneously formed excitons near the zero-band-gap point, or the Lifshitz transition point. This has become an important route to realize bulk excitonic insulators - an insulating ground state distinct from single-particle band insulators. How this route manifests from weak to strong coupling is not clear. In this work, using angle-resolved photoemission spectroscopy (ARPES) and high-resolution synchrotron x-ray diffraction (XRD), we investigate the broken symmetry state across the semimetal-to-semiconductor transition in a leading bulk excitonic insulator candidate system Ta2Ni(Se,S)5. A broken symmetry phase is found to be continuously suppressed from the semimetal side to the semiconductor side, contradicting the anticipated maximal excitonic instability around the Lifshitz transition. Bolstered by first-principles and model calculations, we find strong interband electron-phonon coupling to play a crucial role in the enhanced symmetry breaking on the semimetal side of the phase diagram. Our results not only provide insight into the longstanding debate of the nature of intertwined orders in Ta2NiSe5, but also establish a basis for exploring band-gap-tuned structural and electronic instabilities in strongly coupled systems.

Order by quantum disorder in Er2Ti2O7.

Here we establish the systematic existence of a U(1) degeneracy of all symmetry-allowed Hamiltonians quadratic in the spins on the pyrochlore lattice, at the mean-field level. By extracting the Hamiltonian of Er(2)Ti(2)O(7) from inelastic neutron scattering measurements, we then show that the U(1)-degenerate states of Er(2)Ti(2)O(7) are its classical ground states, and unambiguously show that quantum fluctuations break the degeneracy in a way which is confirmed by experiment. The degree of symmetry protection of the classical U(1) degeneracy in Er(2)Ti(2)O(7) is unprecedented in other materials. As a consequence, our observation of order by disorder is unusually definitive. We provide further verifiable consequences of this phenomenon, and several additional comparisons between theory and experiment.

Silicone finger prosthesis. A clinical report.

The loss of all or part of a finger following traumatic amputation may have a negative impact on physical and psychological well being. An esthetic prosthesis can offer psychological, functional, and rehabilitative advantages. The success of a prosthetic restoration primarily depends on its retention. This clinical report describes an alternative method of retention by scoring the master cast of a partially amputated finger, thus enhancing the vacuum effect for the retention of the prosthesis. The methodology of treatment is also explained. Silicone material was used to provide function and esthetics.

Reversible MRI changes in prolonged status epilepticus: a case report.

MRI is an essential investigation in epilepsy and status epilepticus (SE) for determining the underlying cause. However, SE or prolonged seizures may themselves induce changes in the MRI resulting in difficulty in interpretation. This case report illustrates a patient who recovered completely from prolonged generalized idiopathic SE lasting more than 2 weeks and had transient bilateral external capsule, fronto-temporal, and insular cortical MRI changes. The mechanism of such MRI changes and their implications for survival even after prolonged SE are discussed.

Transcranial Doppler ultrasonography in acute ischemic stroke predicts stroke subtype and clinical outcome: a study in Omani population.

BACKGROUND: Transcranial Doppler ultrasonography (TCD) is being increasingly used for its ability to provide cerebral hemodynamic information in stroke. Few studies have explored its association with cerebral arteriographic changes and stroke subtype. This study explored the relation of TCD changes in acute stroke with stroke subtypes, MR cerebral arteriography and clinical outcome in Omani population. METHODS: Adult patients presenting with acute ischemic stroke within 4 days of stroke onset were subjected to TCD through the temporal and suboccipital windows using a 2 MHz probe; flow velocities, pulsatility and direction of flow were recorded from arteries at the skull base. MR arteriographic (MRA) changes on corresponding arteries were graded on a scale of 1-4. ANOVA, student's t test and ROC analysis were used to evaluate TCD in relation to stroke type, outcome and stenosis on MRA. RESULTS: Of 60 patients recruited, 52 (M:F::36:16; mean age: 60 + 13 years) had adequate bone window for TCD study. Large artery stroke occurred in 30 (58%) patients; lacunar stroke-11 (21%); cardioembolic and mixed groups 9 (17%), other specificed causes-2 (4%). 86.5% had evidence of intracranial disease. 10/52 patients (19%) died while 33 (63%) had good outcome (modified Rankin Score 0-3). Of the 186 arteries studied by the two methods, 52 had TCD evidence of stenosis while 42 were abnormal on MRA, giving a sensitivity of 60%, specificity: 81.25%; positive likelihood ratio: 3.18 and negative likelihood ratio: 0.5. 29/52 (56%) of patients had TCD changes in the arteries corresponding to stroke location. Abnormal TCD was associated with large artery strokes (p = 0.007), poor outcome (p = 0.038) and mortality (p = 0.01). CONCLUSION: This study of TCD in acute stroke in Omani population demonstrates a relatively higher burden of intracranial arterial disease. TCD changes are associated with type of stroke and outcome in this population. TCD is a simple and fairly useful method of evaluation in patients with acute stroke. Adopting TCD in evaluation of stroke patients may provide useful information regarding the pathophysiology which could enhance patient management.

Necrotizing vacuolar myopathy presenting with recurrent myoglobinuria.

Myoglobinuria occurs in a variety of systemic and neurological disorders and can pose diagnostic challenges. We report on a 23-year-old man in whom recurrent myoglobinuria was observed due to necrotizing vacuolar myopathy confirmed on muscle biopsy. Histopathologically the intramuscular vacuoles lacked the typical findings reported in vacuolar myopathy due to disorders of glycogen and lipid metabolism. We discuss the management approach to recurrent myoglobinuria. Recurrent myoglobinuria in the absence of toxin or drug exposure and seizure is more often due to primary muscle disease. Recognizing the presence of myoglobinuria and the proximate cause is essential in preventing the development of renal dysfunction and the future recurrence of symptoms.

Preferential quenching of 5d antiferromagnetic order in Sr3(Ir1-x Mn x )2O7.

The breakdown of [Formula: see text] antiferromagnetism in the limit of strong disorder is studied in Sr3(Ir1-x Mn x )2O7. Upon Mn-substitution, antiferromagnetic ordering of the Ir cations becomes increasingly two-dimensional, resulting in the complete suppression of long-range Ir magnetic order above [Formula: see text]. Long-range antiferromagnetism however persists on the Mn sites to higher Mn concentrations (x > 0.25) and is necessarily mediated via a random network of majority Ir sites. Our data suggest a shift in the Mn valence from Mn4+ to Mn3+ at intermediate doping levels, which in turn generates nonmagnetic Ir5+ sites and suppresses long-range order within the Ir network. The collapse of long-range [Formula: see text] antiferromagnetism and the survival of percolating antiferromagnetic order on Mn-sites demonstrates a complex 3d-5d exchange process that surprisingly enables minority Mn spins to order far below the conventional percolation threshold for a bilayer square lattice.