Publications

We investigate the effect of strain and film thickness on the orbital and magnetic properties of LaSrCrO

Topologically nontrivial two-dimensional materials hold great promise for next-generation optoelectronic applications. However, measuring the Hall or spin-Hall response is often a challenge and practically limited to the ground state. An experimental technique for tracing the topological character in a differential fashion would provide useful insights. In this work, we show that circular dichroism angle-resolved photoelectron spectroscopy (ARPES) provides a powerful tool which can resolve the topological and quantum-geometrical character in momentum space. In particular, we investigate how to map out the signatures of the local Berry curvature by exploiting its intimate connection to the orbital angular momentum. A spin-resolved detection of the photoelectrons allows to extend the approach to spin-Chern insulators. Our predictions are corroborated by state-of-the art

We introduce a simple determinant diagrammatic Monte Carlo algorithm to compute the ground-state properties of a particle interacting with a Fermi sea through a zero-range interaction. The fermionic sign does not cause any fundamental problem when going to high diagram orders, and we reach order N=30. The data reveal that the diagrammatic series diverges exponentially as (-1/R)

The Mott insulating phase of the parent compounds is frequently taken as starting point for the underdoped high-Tc cuprate superconductors. In particular, the pseudogap state is often considered as deriving from the Mott insulator. In this work, we systematically investigate different weakly-doped Mott insulators on the square and triangular lattice to clarify the relationship between the pseudogap and Mottness. We show that doping a two-dimensional Mott insulator does not necessarily lead to a pseudogap phase. Despite its inherent strong-coupling nature, we find that the existence or absence of a pseudogap depends sensitively on non-interacting band parameters and identify the crucial role played by the van Hove singularities of the system. Motivated by a SU(2) gauge theory for the pseudogap state, we propose and verify numerically a simple equation that governs the evolution of characteristic features in the electronic scattering rate.

Nonzero weak topological indices are thought to be a necessary condition to bind a single helical mode to lattice dislocations. In this work we show that higher-order topological insulators (HOTIs) can, in fact, host a single helical mode along screw or edge dislocations (including step edges) in the absence of weak topological indices. When this occurs, the helical mode is necessarily bound to a dislocation characterized by a fractional Burgers vector, macroscopically detected by the existence of a stacking fault. The robustness of a helical mode on a partial defect is demonstrated by an adiabatic transformation that restores translation symmetry in the stacking fault. We present two examples of HOTIs, one intrinsic and one extrinsic, that show helical modes at partial dislocations. Since partial defects and stacking faults are commonplace in bulk crystals, the existence of such helical modes can measurably affect the expected conductivity in these materials.

Detecting community-wide statistical relationships from targeted amplicon-based and metagenomic profiling of microbes in their natural environment is an important step toward understanding the organization and function of these communities. We present a robust and computationally tractable latent graphical model inference scheme that allows simultaneous identification of parsimonious statistical relationships among microbial species and unobserved factors that influence the prevalence and variability of the abundance measurements. Our method comes with theoretical performance guarantees and is available within the SParse InversE Covariance estimation for Ecological ASsociation Inference (SPIEC-EASI) framework (SpiecEasi R-package). Using simulations, as well as a comprehensive collection of amplicon-based gut microbiome datasets, we illustrate the methods ability to jointly identify compositional biases, latent factors that correlate with observed technical covariates, and robust statistical microbial associations that replicate across different gut microbial data sets.

Entropy is a fundamental thermodynamic quantity indicative of the accessible degrees of freedom in a system. While it has been suggested that the entropy of a mesoscopic system can yield nontrivial information on emergence of exotic states, its measurement in such small electron-number system is a daunting task. Here we propose a method to extract the entropy of a Coulomb-blockaded mesoscopic system from transport measurements. We prove analytically and demonstrate numerically the applicability of the method to such a mesoscopic system of arbitrary spectrum and degeneracies. We then apply our procedure to measurements of thermoelectric response of a single quantum dot, and demonstrate how it can be used to deduce the entropy change across Coulomb-blockade valleys, resolving, along the way, a long-standing puzzle of the experimentally observed finite thermoelectric response at the apparent particle-hole symmetric point.

We study the clustering properties of dark matter halos in real- and redshift-space in cosmologies with massless and massive neutrinos through a large set of state-of-the-art N-body simulations. We provide quick and easy-to-use prescriptions for the halo bias on linear and mildly non-linear scales, both in real and redshift space, which are valid also for massive neutrinos cosmologies. Finally we present a halo bias emulator,BE-HaPPY, calibrated on the N-body simulations, which is fast enough to be used in the standard Markov Chain Monte Carlo approach to cosmological inference. For a fiducial standard ΛCDM cosmology BE-HaPPY provides percent or sub-percent accuracy on the scales of interest (linear and well into the mildly non-linear regime), meeting therefore for the halo-bias the accuracy requirements for the analysis of next-generation large--scale structure surveys.

Inspired by the possibility that generative models based on quantum circuits can provide a useful inductive bias for sequence modeling tasks, we propose an efficient training algorithm for a subset of classically simulable quantum circuit models. The gradient-free algorithm, presented as a sequence of exactly solvable effective models, is a modification of the density matrix renormalization group procedure adapted for learning a probability distribution. The conclusion that circuit-based models offer a useful inductive bias for classical datasets is supported by experimental results on the parity learning problem.

The ground-state properties of correlated electron systems can be extraordinarily sensitive to external stimuli, offering abundant platforms for functional materials. Using the multi-messenger combination of atomic force microscopy, cryogenic scanning near-field optical microscopy, magnetic force microscopy and ultrafast laser excitation, we demonstrate both ‘writing’ and ‘erasing’ of a metastable ferromagnetic metal phase in strained films of La2/3Ca1/3MnO3 (LCMO) with nanometre-resolved finesse. By tracking both optical conductivity and magnetism at the nanoscale, we reveal how strain-coupling underlies the dynamic growth, spontaneous nanotexture and first-order melting transition of this hidden photoinduced metal. Our first-principles calculations reveal that epitaxially engineered Jahn–Teller distortion can stabilize nearly degenerate antiferromagnetic insulator and ferromagnetic metal phases. We propose a Ginzburg–Landau description to rationalize the co-active interplay of strain, lattice distortions and magnetism nano-resolved here in strained LCMO, thus guiding future functional engineering of epitaxial oxides into the regime of phase-programmable materials.