2022 New's Items

Nonlocal Screening Dictates the Radiative Lifetimes of Excitations in Lead Halide Perovskites

Park Y
Obliger A
Limmer DT
2022

We use path integral molecular dynamics simulations and theory to elucidate the interactions between charge carriers, as mediated by a lead halide perovskite lattice. We find that the charge–lattice coupling of MAPbI3 results in a repulsive interaction between electrons and holes at intermediate distances. The effective interaction is understood using a Gaussian field theory, whereby the underlying soft, polar lattice contributes a nonlocal screening between quasiparticles. Path integral calculations of this nonlocal screening model are used to rationalize...

Scale-dependent tipping points of bacterial colonization resistance

Karita Y
Limmer DT
Hallatschek O
2022

Bacteria are efficient colonizers of a wide range of secluded microhabitats, such as soil pores, skin follicles, or intestinal crypts. How the structural diversity of these habitats modulates microbial self-organization remains poorly understood, in part because of the difficulty to precisely manipulate the physical structure of microbial environments. Using a microfluidic device to grow bacteria in crypt-like incubation chambers of systematically varied lengths, we show that small variations in the physical structure of the microhabitat can drastically alter bacterial colonization...

Direct Evaluation of Rare Events in Active Matter From Variational Path Sampling

Das A
Kuznets-Speck B
Limmer DT
2022

Active matter represents a broad class of systems that evolve far from equilibrium due to the local injection of energy. Like their passive analogs, transformations between distinct metastable states in active matter proceed through rare fluctuations; however, their detailed balance violating dynamics renders these events difficult to study. Here, we present a simulation method for evaluating the rate and mechanism of rare events in generic nonequilibrium systems and apply it to study the conformational changes of a passive solute in an active fluid. The method employs a variational...

Peptide Isomerization is Suppressed at the Air–Water Interface

Singh AN
Limmer DT
2022

We use molecular dynamics simulations to study the thermodynamics and kinetics of alanine dipeptide isomerization at the air–water interface. Thermodynamically, we find an affinity of the dipeptide to the interface. This affinity arises from stabilizing intramolecular interactions that become unshielded as the dipeptide is desolvated. Kinetically, we consider the rate of transitions between the αL and β conformations of alanine dipeptide and evaluate it as a continuous function of the distance from the interface using a recent extension of transition path...

Polarization dependent photoemission as a probe of the magnetic ground state in the van der Waals ferromagnet VI3

Bergner, D
Kong, T
Ai, P
Cava, RJ
Lanzara, A
Ojeda-Aristizabal, C
2022

Van der Waals ferromagnets are thrilling materials from both a fundamental and technological point of view. VI3 is an interesting example, with a complex magnetism that differentiates it from the first reported Cr based layered ferromagnets. Here, we show in an indirect way through angle resolved photoemission spectroscopy experiments, the importance of spin-orbit coupling setting the electronic properties of this material. Our light polarized photoemission measurements point to a ground state with a half-filled doublet, where a gap opening is triggered by spin-orbit coupling...

Exciton-driven renormalization of quasiparticle band structure in monolayer MoS 2

Lin, Y
Chan, YN
Lee, W
Lu, LS
Chang, WH
Kaindl, RA
Louie, SG
Lanzara, A
2022

Optical excitation serves as a powerful approach to control the electronic structure of layered van der Waals materials via many-body screening effects, induced by photoexcited free carriers, or via light-driven coherence, such as optical Stark and Bloch-Siegert effects. Although theoretical work has also pointed to an exotic mechanism of renormalizing band structure via excitonic correlations in bound electron-hole pairs (excitons), experimental observation of such exciton-driven band renormalization and the full extent of their implications is still lacking, largely due to the...

Driving ultrafast spin and energy modulation in quantum well states via photo-induced electric fields

Ciocys, ST
Maksimovic, N
Analytis, J
Lanzara, A
2022

The future of modern optoelectronics and spintronic devices relies on our ability to control the spin and charge degrees of freedom at ultrafast timescales. Rashba spin-split quantum well states, 2D states that develop at the surface of strong spin-orbit coupling materials, are ideal given the tunability of their energy and spin states. So far, however, most studies have only demonstrated such control in a static way. In this study, we demonstrate control of the spin and energy degrees of freedom of surface quantum well states on Bi2Se3...

Mapping the dispersion of the occupied and unoccupied band structure in photoexcited 1T-TiSe2

Huber, M
Lin, Y
Dale, N
Kaindl, RA
Lanzara, A
2022

Charge density waves (CDW) are states of broken symmetry with a periodic modulation of charge and lattice typically leading to the opening of a gap in the band structure. In the model CDW system 1T-TiSe2 such a gap opens up between its Se4p valence and Ti3d...

Evidence of nested quasi-one-dimensional Fermi surface and decoupled charge-lattice orders in layered TaTe 2

Lin, Y
Huber, M
Rajpurohit, S
Zhu, Y
Tan, LZ
Lanzara, A
2022

The formations of charge and lattice orders are generally coupled in charge density wave (CDW) materials and share identical order wave vectors. Although this situation is usually satisfied in a large class of two-dimensional materials, it falls short in describing the so-called CDW-like phase transition in layered tantalum ditelluride (TaTe2), accompanied by anomalous low temperature...

Observation of a Flat and Extended Surface State in a Topological Semimetal

Mori, R
Wang, K
Morimoto, T
Paglione, J
Lanzara, A
2022
A flat band structure in momentum space is considered key for the realization of novel phenomena. A topological flat band, also known as a drumhead state, is an ideal platform to drive new exotic topological quantum phases. Using angle-resolved photoemission spectroscopy experiments, we reveal the emergence of a highly localized surface state in a topological semimetal BaAl4 and provide its full energy and momentum space topology. We find that the observed surface...