Verwey transition as evolution from electronic nematicity to trimerons via electron-phonon coupling

Understanding the driving mechanisms behind metal-insulator transitions (MITs) is a critical step toward controlling material's properties. Since the proposal of charge order-induced MIT in magnetite Fe3O4 in 1939 by Verwey, the nature of the charge order and its role in the transition have remained elusive. Recently, a trimeron order was found in the low-temperature structure of Fe3O4; however, the expected transition entropy change in forming trimeron is greater than the observed value, which arises a reexamination of the ground state in the high-temperature phase. Here, we use electron diffraction to unveil that a nematic charge order on particular Fe sites emerges in the high-temperature structure of bulk Fe3O4 and that, upon cooling, a competitive intertwining of charge and lattice orders arouses the Verwey transition. Our findings discover an unconventional type of electronic nematicity in correlated materials and offer innovative insights into the transition mechanism in Fe3O4 via the electron-phonon coupling.

Origin of the quasi-quantized Hall effect in ZrTe5

The quantum Hall effect (QHE) is traditionally considered to be a purely two-dimensional (2D) phenomenon. Recently, however, a three-dimensional (3D) version of the QHE was reported in the Dirac semimetal ZrTe5. It was proposed to arise from a magnetic-field-driven Fermi surface instability, transforming the original 3D electron system into a stack of 2D sheets. Here, we report thermodynamic, spectroscopic, thermoelectric and charge transport measurements on such ZrTe5 samples. The measured properties: magnetization, ultrasound propagation, scanning tunneling spectroscopy, and Raman spectroscopy, show no signatures of a Fermi surface instability, consistent with in-field single crystal X-ray diffraction. Instead, a direct comparison of the experimental data with linear response calculations based on an effective 3D Dirac Hamiltonian suggests that the quasi-quantization of the observed Hall response emerges from the interplay of the intrinsic properties of the ZrTe5 electronic structure and its Dirac-type semi-metallic character.

A light-induced phononic symmetry switch and giant dissipationless topological photocurrent in ZrTe5

Dissipationless currents from topologically protected states are promising for disorder-tolerant electronics and quantum computation. Here, we photogenerate giant anisotropic terahertz nonlinear currents with vanishing scattering, driven by laser-induced coherent phonons of broken inversion symmetry in a centrosymmetric Dirac material ZrTe₅. Our work suggests that this phononic terahertz symmetry switching leads to formation of Weyl points, whose chirality manifests in a transverse, helicity-dependent current, orthogonal to the dynamical inversion symmetry breaking axis, via circular photogalvanic effect. The temperature-dependent topological photocurrent exhibits several distinct features: Berry curvature dominance, particle-hole reversal near conical points and chirality protection that is responsible for an exceptional ballistic transport length of ~10 μm. These results, together with first-principles modelling, indicate two pairs of Weyl points dynamically created by B_1u phonons of broken inversion symmetry. Such phononic terahertz control breaks ground for coherent manipulation of Weyl nodes and robust quantum transport without application of static electric or magnetic fields.

Unconventional Hall response in the quantum limit of HfTe5

Interacting electrons confined to their lowest Landau level in a high magnetic field can form a variety of correlated states, some of which manifest themselves in a Hall effect. Although such states have been predicted to occur in three-dimensional semimetals, a corresponding Hall response has not yet been experimentally observed. Here, we report the observation of an unconventional Hall response in the quantum limit of the bulk semimetal HfTe5, adjacent to the three-dimensional quantum Hall effect of a single electron band at low magnetic fields. The additional plateau-like feature in the Hall conductivity of the lowest Landau level is accompanied by a Shubnikov-de Haas minimum in the longitudinal electrical resistivity and its magnitude relates as 3/5 to the height of the last plateau of the three-dimensional quantum Hall effect. Our findings are consistent with strong electron-electron interactions, stabilizing an unconventional variant of the Hall effect in a three-dimensional material in the quantum limit.

Utilization of guideline-directed medical therapy in patients with de novo heart failure with reduced ejection fraction: A Veterans Affairs study

BACKGROUND

The utilization of guideline-directed medical therapy (GDMT) significantly reduces morbidity and mortality in patients with heart failure with reduced ejection fraction (HFrEF). Previous studies have documented the underutilization of GDMT in HFrEF. The present study aimed to determine reasons for underutilization and achievement of target doses of GDMT in patients with de novo diagnosis of HFrEF.

METHODS

Patients presenting with de novo HFrEF at the Veterans Affairs Medical Center were included. Baseline demographic, clinical, and echocardiographic data were collected. The utilization of target doses of GDMT was assessed at the time of discharge and 1-, 3-, 6-, and 12-month follow-up.

RESULTS

Of the 95 patients who met the criteria for de novo HFrEF, 48 were included in the final analysis. Dose titration of either beta-blocker or angiotensin converting enzyme inhibitors/angiotensin receptor blockers (ACEi/ARB) was attempted in 20 patients (42%) at 1 month, 21 patients (44%) at 3 months, 13 patients (27%) at 6 months, and 14 patients (29%) at 12 months. Nine (19%) patients were on a target dose of beta-blockers and three (6%) patients were on a target dose of an ACEi/ARB at 12 months. The most common reasons for underutilization were patient-level factors, such as hypotension, acute kidney injury/hyperkalemia, and patient noncompliance.

CONCLUSIONS

Utilization and achievement of target doses of GDMT were suboptimal among patients discharged with de novo HFrEF during a 1-year follow-up. Although patient factors may limit the up-titration of therapies, concerted efforts are needed to support primary care physicians in improving adherence to target doses of GDMT in patients with HFrEF.

Atrial myxoma and bone changes: a paraneoplastic syndrome?

Atrial myxomas are the most common benign tumors of the heart and are difficult to diagnose due to a wide variety of presenting symptoms. We present a patient with a five-year history of visual loss, vertigo, ataxia, tinnitus, and bone lesions that resolved after diagnosis and resection of an atrial myxoma. This case not only highlights an unusual presentation of atrial myxomas but also raises the question of whether atrial myxomas can produce paraneoplastic syndromes, including bone abnormalities. 

A case of critical aortic stenosis masquerading as acute coronary syndrome

Serum cardiac troponins I and T are reliable and highly specific markers of myocardial injury. Studies have shown that at least 20% of patients with severe aortic stenosis have detectable serum troponins. This case report describes a patient who presented as suspected acute coronary syndrome with markedly elevated troponin levels, who was later found to have normal coronaries and critical aortic stenosis. This case highlights the need for comprehensive and accurate physical examination in patients who present with angina. Critical aortic stenosis may cause such severe subendocardial ischemia as to cause marked elevation in cardiac markers and mimic an acute coronary syndrome. Careful physical examination will lead to an earlier use of non invasive techniques, such as echocardiography to confirm the correct diagnosis and the avoidance of inappropriate treatments such as intravenous nitroglycerin and glycoprotein IIb/IIIa inhibitors.