37 research outputs found
Quantized shift response in multi-gap topological phases
We show that certain 3D multi-gap topological insulators can host quantized
shift photoconductivities due to bulk invariants that are defined under reality
conditions imposed by additional symmetries. We recast the quantization in
terms of the integrated torsion tensor and the non-Abelian Berry connection
constituting Chern-Simons forms. Physically, we recognize that the topological
quantization emerges purely from virtual transitions contributing to the
optical response. Our findings provide another quantized electromagnetic DC
response due to the non-trivial band topology, beyond the quantum anomalous
Hall effect of Chern insulators and quantized circular photogalvanic effect
found in Weyl semimetals.Comment: 7+7 pages; 3+1 figure
Disorder-induced topological quantum phase transitions in Euler semimetals
We study the effect of disorder in systems having a non-trivial Euler class.
As these recently proposed multi-gap topological phases come about by braiding
non-Abelian charged band nodes residing between different bands to induce
stable pairs within isolated band subspaces, novel properties that include a
finite critical phase under the debraiding to a metal rather than a transition
point and a modified stability may be expected when the disorder preserves the
underlying or symmetry on average. Employing
elaborate numerical computations, we verify the robustness of associated
topology by evaluating the changes in the average densities of states and
conductivities for different types of disorders. Upon performing a scaling
analysis around the corresponding quantum critical points we retrieve a
universality for the localization length exponent of for
Euler-protected phases, relating to 2D percolation models. We generically find
that quenched disorder drives Euler semimetals into critical metallic phases.
Finally, we show that magnetic disorder can also induce topological transitions
to quantum anomalous Hall plaquettes with local Chern numbers determined by the
initial value of the Euler invariant.Comment: 6+7 pages, 4+6 figure
Optical manifestations of topological Euler class in electronic materials
We analyze quantum-geometric bounds on optical weights in topological phases
with pairs of bands hosting non-trivial Euler class, a multi-gap invariant
characterizing non-Abelian band topology. We show how the bounds constrain the
combined optical weights of the Euler bands at different dopings and further
restrict the size of the adjacent band gaps. In this process, we also consider
the associated interband contributions to DC conductivities in the flat-band
limit. We physically validate these results by recasting the bound in terms of
transition rates associated with the optical absorption of light, and
demonstrate how the Euler connections and curvatures can be determined through
the use of momentum and frequency-resolved optical measurements, allowing for a
direct measurement of this multi-band invariant. Additionally, we prove that
the bound holds beyond the degenerate limit of Euler bands, resulting in nodal
topology captured by the patch Euler class. In this context, we deduce optical
manifestations of Euler topology within models, which
include AC conductivity, and third-order jerk photoconductivities in doped
Euler semimetals. We showcase our findings with numerical validation in
lattice-regularized models that benchmark effective theories for real materials
and are themselves directly realizable in metamaterials and optical lattices.Comment: 8+9 pages, 3 figure
On the search for the right definition of heart failure with preserved ejection fraction
The definition of heart failure with preserved ejection fraction (HFpEF) has evolved from a clinically based “diagnosis of exclusion” to definitions focused on objective evidence of diastolic dysfunction and/or elevated left ventricular filling pressures. Despite advances in our understanding of HFpEF pathophysiology and the development of more sophisticated imaging modalities, the diagnosis of HFpEF remains challenging, especially in the chronic setting, given that symptoms are provoked by exertion and diagnostic evaluation is largely conducted at rest. Invasive hemodynamic study, and in particular — invasive exercise testing, is considered the reference method for HFpEF diagnosis. However, its use is limited as opposed to the high number of patients with suspected HFpEF. Thus, diagnostic criteria for HFpEF should be principally based on non-invasive measurements. As no single non-invasive variable can adequately corroborate or refute the diagnosis, different combinations of clinical, echocardiographic, and/or biochemical parameters have been introduced. Recent years have brought an abundance of HFpEF definitions. Here, we present and compare four of them: 1) the 2016 European Society of Cardiology criteria for HFpEF; 2) the 2016 echocardiographic algorithm for diagnosing diastolic dysfunction; 3) the 2018 evidence-based H2FPEF score; and 4) the most recent, 2019 Heart Failure Association HFA-PEFF algorithm. These definitions vary in their approach to diagnosis, as well as sensitivity and specificity. Further studies to validate and compare the diagnostic accuracy of HFpEF definitions are warranted. Nevertheless, it seems that the best HFpEF definition would originate from a randomized clinical trial showing a favorable effect of an intervention on prognosis in HFpEF
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Random Structure Searching with Orbital-Free Density Functional Theory.
The properties of a material depend on how its atoms are arranged, and predicting these arrangements from first principles is a longstanding challenge. Orbital-free density functional theory provides a quantum-mechanical model based solely on the electron density, not individual wave functions. The resulting speedups make it attractive for random structure searching, whereby random configurations of atoms are relaxed to local minima in the energy landscape. We use this strategy to map the low-energy crystal structures of Li, Na, Mg, and Al at zero pressure. For Li and Na, our searching finds numerous close-packed polytypes of almost-equal energy, consistent with previous efforts to understand their low-temperature forms. For Mg and Al, the searching identifies the expected ground state structures unambiguously, in addition to revealing other low-energy structures. This new role for orbital-free density functional theory-particularly as continued advances make it accurate for more of the periodic table-will expedite crystal structure prediction over wide ranges of compositions and pressures
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Efficiently Differentiating Agonists and Competitive Antagonists for Weak Allosteric Protein-Ligand Interactions with Linear Response Theory.
What makes an agonist and a competitive antagonist? In this work, we aim to answer this question by performing parallel tempering Monte Carlo simulations on the serotonin type 3A (5-HT3A) receptor. We use linear response theory to predict conformational changes in the 5-HT3A receptor active site after weak perturbations are applied to its allosteric binding sites. A covariance tensor is built from conformational sampling of its apo state, and a harmonic approximation allows us to substitute the calculation of ligand-induced forces with the binding site's displacement vector. Remarkably, our study demonstrates the feasibility of effectively discerning between agonists and competitive antagonists for multiple ligands, requiring computationally expensive calculations only once per protein