Eigenstate–Specific Temperatures in Two–Level Paramagnetic Spin Lattices

Increasing interest in the thermodynamics of small and/or isolated systems, in combination with recent observations of negative temperatures of atoms in ultracold optical lattices, has stimulated the need for estimating the conventional, canonical temperature Tconvc of systems in equilibrium with heat baths using eigenstate-specific temperatures (ESTs). Four distinct ESTs—continuous canonical, discrete canonical, continuous microcanonical, and discrete microcanonical—are accordingly derived for two-level paramagnetic spin lattices (PSLs) in external magnetic fields. At large N, the four ESTs are intensive, equal to Tconvc, and obey all four laws of thermodynamics. In contrast, for N \u3c 1000, the ESTs of most PSL eigenstates are non-intensive, differ from Tconvc, and violate each of the thermodynamic laws. Hence, in spite of their similarities to Tconvc at large N, the ESTs are not true thermodynamic temperatures. Even so, each of the ESTs manifests a unique functional dependence on energy which clearly specifies the magnitude and direction of their deviation from Tconvc; the ESTs are thus good temperature estimators for small PSLs. The thermodynamic uncertainty relation is obeyed only by the ESTs of small canonical PSLs; it is violated by large canonical PSLs and by microcanonical PSLs of any size. The ESTs of population-inverted eigenstates are negative (positive) when calculated using Boltzmann (Gibbs) entropies; the thermodynamic implications of these entropically induced differences in sign are discussed in light of adiabatic invariance of the entropies. Potential applications of the four ESTs to nanothermometers and to systems with long-range interactions are discussed

Dynamics and Energetics of Layered Materials and their Interfaces

Atomic and organic semiconductors interfaces with inorganic semiconductors are promising materials for use in next-generation electronic and optoelectronic devices. A predictive-level understanding of the interfaces is lacking which hinders rational design of such devices. This is attributed to the key processes, e.g. charge generation, separation, delocalization and extraction, which are heavily interfacial in nature and difficult to simulate. Thus, it is imperative to understand the fundamental processes at individual interfaces to enable design and optimization of next-generation technologies. This work aims to understand these interfaces by studying the interfacial processes using optical photoemission spectroscopy techniques. In this dissertation, I focus on alkali metal and molecular interfaces with layered materials to understand and control the dynamics and electronic and optical properties of the interface. Initially, I aim to characterize the nature of layered materials (SnS2 and MoS2) that exhibit unusual thickness-dependent properties, which already affords tunable materials properties. I demonstrate the anisotropy of the many-layered crystal at ultrafast timescales not yet realized. Pairing the layered material with thin films (K, CuPc and PTCDA) demonstrates layer decoupling and quantum confinement effects that show an enhancement of carrier delocalization at the interface. Furthermore, studies show a systematic tuning of the dielectric environment of the layered material dependent upon adsorbate thin film thickness. Overall, this work elucidates key interfacial interactions of select atoms and molecules on layered materials that can be used to understand this class of materials and their implementation in nanodevices

Anisotropic attosecond charge carrier dynamics and layer decoupling in quasi-2D layered SnS2

Strong quantum confinement effects lead to striking new physics in two-dimensional materials such as graphene or transition metal dichalcogenides. While spectroscopic fingerprints of such quantum confinement have been demonstrated widely, the consequences for carrier dynamics are at present less clear, particularly on ultrafast timescales. This is important for tailoring, probing, and understanding spin and electron dynamics in layered and two-dimensional materials even in cases where the desired bandgap engineering has been achieved. Here we show by means of core-hole clock spectroscopy that SnS2 exhibits spin-dependent attosecond charge delocalization times (tau(deloc)) for carriers confined within a layer, tau(deloc) 2.7 fs. These layer decoupling dynamics are a direct consequence of strongly anisotropic screening established within attoseconds, and demonstrate that important two-dimensional characteristics are also present in bulk crystals of van der Waals-layered materials, at least on ultrafast timescales.National Science Foundation [CHE 1213243, CHE 1565497]; U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-76SF00515]UA Open Access Publishing Fund.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Eigenstate-specific temperatures in two-level paramagnetic spin lattices

Increasing interest in the thermodynamics of small and/or isolated systems, in combination with recent observations of negative temperatures of atoms in ultracold optical lattices, has stimulated the need for estimating the conventional, canonical temperature T-c(conv) of systems in equilibrium with heat baths using eigenstate-specific temperatures (ESTs). Four distinct ESTs-continuous canonical, discrete canonical, continuous microcanonical, and discrete microcanonical-are accordingly derived for two-level paramagnetic spin lattices (PSLs) in external magnetic fields. At large N, the four ESTs are intensive, equal to T-c(conv), and obey all four laws of thermodynamics. In contrast, for N < 1000, the ESTs of most PSL eigenstates are non-intensive, differ from T-c(conv), and violate each of the thermodynamic laws. Hence, in spite of their similarities to T-c(conv) at large N, the ESTs are not true thermodynamic temperatures. Even so, each of the ESTs manifests a unique functional dependence on energy which clearly specifies the magnitude and direction of their deviation from T-c(conv); the ESTs are thus good temperature estimators for small PSLs. The thermodynamic uncertainty relation is obeyed only by the ESTs of small canonical PSLs; it is violated by large canonical PSLs and by microcanonical PSLs of any size. The ESTs of population-inverted eigenstates are negative (positive) when calculated using Boltzmann (Gibbs) entropies; the thermodynamic implications of these entropically induced differences in sign are discussed in light of adiabatic invariance of the entropies. Potential applications of the four ESTs to nanothermometers and to systems with long-range interactions are discussed. Published by AIP Publishing.National Science Foundation [NSF-EPS-0132295]; Howard Hughes Medical Institute12 month embargo; published online: 5 December 2017This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Photocatalytic setup for in situ and operando ambient-pressure X-ray photoelectron spectroscopy at MAX IV Laboratory

Abstract The Ambient-Pressure X-ray Photoelectron Spectroscopy (APXPS) endstation at the SPECIES beamline at MAX IV Laboratory has been improved. The latest upgrades help in performing photo-assisted experiments under operando conditions in the mbar pressure range using gas and vapour mixtures whilst also reducing beam damage to the sample caused by X-ray irradiation. This article reports on endstation upgrades for APXPS and examples of scientific cases of in situ photocatalysis, photoreduction and photo-assisted atomic layer deposition (photo-ALD)