2024 New's Items

Unraveling the mechanisms of triplet state formation in a heavy-atom free photosensitizer

Fay, T. P.
Limmer, D. T.
2024

Triplet excited state generation plays a pivotal role in photosensitizers, however the reliance on transition metals and heavy atoms can limit the utility of these systems. In this study, we demonstrate that an interplay of competing quantum effects controls the high triplet quantum yield in a prototypical boron dipyrromethene-anthracene (BD-An) donor–acceptor dyad photosensitizer, which is only captured by an accurate treatment of both inner and outer sphere reorganization energies. Our ab initio-derived model provides excellent agreement with experimentally measured spectra,...

Splitting probabilities as optimal controllers of rare reactive events

Singh, A. N.
Limmer, D. T
2024

The committor constitutes the primary quantity of interest within chemical kinetics as it is understood to encode the ideal reaction coordinate for a rare reactive event. We show the generative utility of the committor in that it can be used explicitly to produce a reactive trajectory ensemble that exhibits numerically exact statistics as that of the original transition path ensemble. This is done by relating a time-dependent analog of the committor that solves a generalized bridge problem to the splitting probability that solves a boundary value problem under a bistable assumption. By...

Design principles for energy transfer in the photosystem II supercomplex from kinetic transition networks

Yang, S. J.
Wales, D. J.
Woods, E. J.
Fleming, G. R.
2024

Photosystem II (PSII) has the unique ability to perform water-splitting. With light-harvesting complexes, it forms the PSII supercomplex (PSII-SC) which is a functional unit that can perform efficient energy conversion, as well as photoprotection, allowing photosynthetic organisms to adapt to the naturally fluctuating sunlight intensity. Achieving these functions requires a collaborative energy transfer network between all subunits of the PSII-SC. In this work, we perform kinetic analyses and characterise the energy landscape of the PSII-SC with a structure-based energy transfer model....

SiGe/Si heterojunction drain transistor for faster 3D NAND flash memory erase

Dasom Lee
Tsu-Jae King Liu
2024
Some 3D NAND flash memory technologies utilize the phenomenon of Gate Induced Drain Leakage (GIDL) for erase operation. As the number of memory cells stacked in a 3D NAND string increases, larger GIDL current is needed to maintain the same erase speed. In this work, the use of silicon-germanium (SiGe), which has a smaller band-gap energy compared to silicon (Si), is proposed to augment GIDL current through enhanced band-to-band tunneling. TCAD simulation confirms that, when the heavily doped drain and a portion of the undoped channel region of the drain transistor comprise SiGe, both GIDL...

MOSFET Probabilistic-Bit Behavior

Tatum LP
Kong X
Stojanovic V
Liu TJK
2024
Probabilistic computing is a physics-based beyond-von-Neumann framework proposed to meet the high energy-efficiency and performance demands of modern AI and combinatorial optimization problems [1] . A probabilistic computing platform is a control loop made up of probabilistic-bits (p-bits), which are essentially tunable random-number-generators (RNGs) [2] , and classical circuitry that updates the p-bit inputs ( Fig. 1a ). When a p-bit’s input is high, it is usually “1”, and when a p-bit’s input is low, it is usually “0” ( Fig. 1b ); in-between is a stochastic region wherein the probability...

Advanced Ferroelectric Modeling for BEOL Negative Capacitance Nanoelectromechanical Switches

Collin Finnan
Lars Tatum
Tsu-Jae King Liu
2024
Negative capacitance (NC) - achieved by adding a ferroelectric layer in series with the dielectric layer (air gap) of an electrostatic actuator - has been proposed as a means of reducing the pull-in voltage of a nano-electro-mechanical (NEM) switch without physically scaling down the gap size. This paper introduces a two-dimensional device simulation framework for NC NEM switches using the ferroelectric material hafnium zirconium oxide. The ferroelectric layer is simulated using both a simplified single polarization domain model and two different multi-domain models. While a dramatic...

Ultrafast optical control of charge orders in kagome metals

Yu-Ping Lin
Vidya Madhavan
Joel E Moore
2024

We show that ultrafast optical pump pulses provide effective control over charge orders in the kagome metals AV3Sb5 with A = K, Rb, and Cs. Starting from the real charge density waves (rCDWs) at the p-type Van Hove singularity, we conduct a thorough analysis of the post-pump dynamics by time-dependent Hartree-Fock theory. Our analysis uncovers distinct dynamical phenomena under linearly and circularly polarized pumps. Linearly polarized pumps induce directional preferences in the rCDWs, accompanied by an enhancement in the flat band. Unexpectedly, charge nematicity also emerges and...

Coherent Magneto-Conductance Oscillations in Amorphous Topological Insulator Nanowires

Siddhant Mal
Elizabeth J Dresselhaus
Joel E Moore
2024
Recent experiments on amorphous materials have established the existence of surface states similar to those of crystalline three-dimensional topological insulators (TIs). Amorphous topological insulators are also independently of interest for thermo-electric and other properties. To develop an understanding of transport in these systems, we carry out quantum transport calculations for a tight-binding model of an amorphous nano-wire pierced by an axial magnetic flux, then compare the results to known features in the case of crystalline models with disorder. Our calculations complement previous...

Crystallography, Group Cohomology, and Lieb-Schultz-Mattis Constraints

Chunxiao Liu
Weicheng Ye
2024
We compute the mod-2 cohomology ring for three-dimensional (3D) space groups and establish a connection between them and the lattice structure of crystals with space group symmetry. This connection allows us to obtain a complete set of Lieb-Schultz-Mattis constraints, specifying the conditions under which a unique, symmetric, gapped ground state cannot exist in 3D lattice magnets. We associate each of these constraints with an element in the third mod-2 cohomology of the space group, when the internal symmetry acts on-site and its projective representations are classified by powers of . We...

Spin-liquid-based topological qubits

Klocke, K.
Liu, Y.
Halász, G. B.
Alicea, J.
2024
Topological quantum computation relies on control of non-Abelian anyons for inherently fault-tolerant storage and processing of quantum information. By now, blueprints for topological qubits are well developed for electrically active topological superconductor and fractional quantum Hall platforms. We leverage recent insights into the creation and detection of non-Abelian anyons in electrically insulating spin systems to propose topological qubit architectures based on quantum spin liquids. We present two types of prototype designs that enable the requisite control in a potentially scalable...