Abstract: 2D materials, and in particular transition-metal dichalcogenides (TMDs) are elastic materials that can sustain high strain. The effects of uniform (uniaxial) strain and non-uniform strain have been investigated in the last decade. In this talk I will present recent studies done in our lab which reveal new phenomena that were not observed (or at least not understood) with different strain engineering methods. In the first part I will present new results of the photoluminescence from uniaxially strained TMDs where we observe fluctuating intensities as a function of strain for low strain magnitudes (<0.2%). By combining k-space imaging with the strain, we find that both the choice of substrate and the curvature define the intensity of the emission [1].

In the second part we will present recent results that resolve a long-standing debate between funneling of excitons under non-uniform strain and exciton-to-trion conversion due to limited funneling [2]. We show that by suspending monolayers on top of large holes, and by choosing the right configuration of substrate, funneling can be reached for micron-size regions while avoiding exciton-to-trion conversion that was observed in previous works [3].

[1] L. Grimberg, S. Kostyukovets, N. Basu, and M. G. Harats, Angular Emission Properties of Strained Transition-Metal Dichalcogenides in the Low Strain Regime, ACS Appl. Mater. Interfaces 18, 29337 (2026).
[2] M. G. Harats and K. I. Bolotin, Limits of funneling efficiency in non-uniformly strained 2D semiconductors, 2d Mater. 8, 015010 (2021).
[3] M. G. Harats, J. N. Kirchhof, M. Qiao, K. Greben, and K. I. Bolotin, Dynamics and efficient conversion of excitons to trions in non-uniformly strained monolayer WS2, Nature Photonics 14, 324 (2020).

Abstract: The dark photon is a well-motivated ultralight dark-matter candidate that may couple to the Standard Model through kinetic mixing. We search for dark-photon dark matter in the mass range 4 × 10⁻¹² – 2 × 10⁻⁹ eV (1-500kHz) using a three-axis magnetometer inside a large conductive shielded room. We set new laboratory limits on the kinetic-mixing parameter, improving upon previous laboratory bounds by up to two orders of magnitude. Our search exploits a geometry-defined null response along one axis as a noise reference to implement a subtraction procedure, lowering noise and enhancing sensitivity. These results establish the strongest laboratory constraints in this mass range and illustrate how null-axis magnetometry can broaden terrestrial searches for ultralight vector dark matter.

Abstract: We develop and apply quantum phase-space tomography as a general framework for analysis of emergent phenomena in small mesoscopic many-body systems. The focus is on Bose–Hubbard circuits, which provide experimentally relevant minimal models for thermalization, metastability, superfluidity and superconductivity. We highlight the implications of the underlying ``mixed" chaotic dynamics e.g. in the context  of  quantum irreversibility.

Abstract: Nonreciprocal interactions in which the influence of A on B differs from that of B on A are abundant in physical, chemical, biological, and ecological systems, and are known to give rise to oscillatory states. Yet, it remains unclear whether these states represent true phases of matter: Can they maintain long-range order in spatially extended, noisy environments in the thermodynamic limit? And what kinds of phase transitions do they exhibit? To address these questions, we introduce a minimal generalization of the Ising model with two species having opposing goals. We demonstrate that oscillatory phases are stable in three dimensions but not in two, and that nonreciprocity changes the critical exponents from those of the Ising model to those of the XY model. We further develop a Harris-like criterion that determines when nonreciprocity fundamentally alters universal behavior. Finally, we apply these insights to a recent model of biomolecular condensates, predicting exotic dynamical phases and suggesting experimental tests.

Abstract: The electronic wavefunction is at the heart of physical phenomena, defining the frontiers of quantum materials research. While the amplitude of the electron wavefunction in crystals can be measured with state-of-the-art probes in unprecedented resolution, its phase has remained largely inaccessible, obscuring rich electronic information. In this talk I will discuss our development of a quantum-path electron interferometer based on time- and angle-resolved photoemission spectroscopy (trARPES), enabling the reconstruction of the phase of electronic states in quantum materials – with energy and momentum resolution. We demonstrate the scheme by resolving the phase along the Dirac electronic band of a prototypical topological insulator and observe a resonance-associated phase jump as well as a momentum and phase synchronized inversion revealing the helicity of the Dirac cone. This photo-electron-interferometer scheme can be extended to a variety of materials, opening up the phase dimension in quantum materials research.

arXiv:2511.09560

Abstract: TBA