Quantum ballistic transport in in-plane-gate transistors showing onset of a novel ferromagnetic phase transition

We study one-dimensional transport in focused-ion-beam written in-plane-gate transistors on III-V heterostructures at moderately low temperatures at zero bias without any external magnetic field applied. In accordance with a recent proposal of A. Gold and L. Calmels, Valley- and spin-occupancy instability in the quasi-one-dimensional electron gas, Phil. Mag. Lett. 74, 33-42 (1996) and earlier experimental data, we observe plateaux in the source-drain conductivity considered as a function of the gate voltage, not only at multliples of 2e^2/h but also clearly at e^2/h, just before the channel closes to zero conductivity. This may be interpreted as a many electron effect, namely as a novel ballistic ferromagnetic ground state evading standard descriptions and theorems.Comment: 19 pages, 9 figures, 22 reference

Spin & Statistics in Nonrelativistic Quantum Mechanics, I

A necessary and sufficient condition for Pauli's spin-statistics relation is given for nonrelativistic anyons, bosons, and fermions in two and three spatial dimensions. For any point particle species in two spatial dimensions, denote by J the total (i.e., spin plus orbital) angular momentum of a single particle, and denote by j the total angular momentum of the corresponding two-particle system with respect to its center of mass. In three spatial dimensions, write J_z and j_z for the z-components of these vector operators. In two spatial dimensions, the spin statistics connection holds if and only if there exists a unitary operator U such that j=2UJU^*. In three dimensions, the analogous relation cannot hold as it stands, but restricting it to an appropriately chosen subspace of the state space yields a sufficient and necessary condition for the spin-statistics connection.Comment: 15 pages, revised and polished versio

Endogenous life expectancy and R&D-based economic growth

We propose an overlapping generations framework in which life expectancyis determined endogenously by governmental health investments. As a nov-elty, we are able to examine the feedback effects between life expectancy andR&D-driven economic growth for the transitional dynamics. We find that i)higher survival induces economic growth through higher savings and higherlabor force participation; ii) longevity-induced reductions in fertility hampereconomic development; iii) the positive life expectancy effects of larger savingsand higher labor force participation outweigh the negative effect of a reductionin fertility, and iv) there exists a growth-maximizing size of the health caresector that might lie beyond what is observed in most countries. Altogether,the results support a rather optimistic view on the relationship between lifeexpectancy and economic growth and contribute to the debate surroundingrising health shares and economic development

Essays on demographic change and R&D-based economic growth

This dissertation analyzes the economic growth effects of demographic change embedded in a framework of endogenous R&D. Substantial changes in fertility and longevity are the two main demographic features that all industrialized countries have experienced during the twentieth century and are still experiencing until today. Although the individual gains of higher life expectancy and better education, initiated by a quantity-quality tradeoff, are huge, there exist concerns about the macroeconomic effects. To improve the understanding about the aforementioned relationships, this work extends the existing literature on the growth effects of population aging by 1) introducing exogenous longevity into a growth framework with vertical innovations; 2) by endogenizing life expectancy in a growth framework with horizontal innovations; and 3) by examining the growth effects of basic scientific knowledge over the very long run. Chapter two contains the first paper titled Longevity-induced Vertical Innovation and the Tradeoff Between Life and Growth, which is joint work with Annarita Baldanzi and Klaus Prettner. In this paper, the positive effect of a longer retirement period on individual savings is utilized. A higher exogenous probability to survive to old age raises savings, placing a downward pressure on the market interest rate. On the production side, a lower interest rate increases the present value of holding a patent, which, in turn, makes R&D more profitable. As a result, R&D employment increases, leading to a higher frequency of quality improving ideas and, with it, faster economic growth. It is shown that the relationship between life expectancy and economic growth is strictly positive. In a welfare analysis, the utility gains of living longer are disentangled from the longevity-induced utility gains of higher consumption. The analysis concludes that the direct welfare gains of higher life expectancy, usually, outweigh the indirect welfare gains of faster economic growth. Chapter three contains a single-authored paper and is titled Endogenous Life Expectancy and R&D-based Economic Growth. As the title suggests, life expectancy is endogenized and increases in the public resources devoted toward health. Again, the longevity-saving-channel is present. Additionally, a quantity-quality tradeoff is introduced, such that parents have to decide on the number of children to have and on the childrens level of education. Besides the positive saving effect, life expectancy impacts positively on the labor force participation rate and negatively on the fertility rate. The reason is that adults need to work more (at the expense of having fewer children), to compensate for a prolonged retirement period. The feedback effects with production, characterized by horizontal innovation, are then analyzed in a calibrated version of the model. Using U.S. data, the model suggests that the overall effect of life expectancy on economic growth is positive and amounts to 11.9 % of the increases in the real GDP p.c. over the period 1960-2017. From a welfare perspective, the results indicate that the growth-maximizing size of the health care sector might lie beyond what is observed in most industrialized countries, nowadays. The finding that the size of the health care sector that maximizes life expectancy is substantially larger than the growth-maximizing size supports the view to not only consider the growth effects of health care. Chapter four contains the third paper which is co-authored with Klaus Prettner and is titled The Scientific Revolution and Its Role in the Transition to Sustained Economic Growth. Basic scientific knowledge is introduced as a necessary input in applied R&D and increases in the number of tinkerers in the economy and in their education. For low levels of development, fertility is high and educational investments are zero. Once income surpasses a certain threshold, education turns positive. Together with the consequent fertility transition, this marks the takeoff to sustained economic growth. It is shown that the growth rate of as well as the access to basic scientific knowledge is crucial in determining the timing and the magnitude of the takeoff. For low growth rates and low access, the takeoff is delayed by up to one generation because applied R&D takes longer to become profitable. In the extreme case of zero basic scientific knowledge, no takeoff might occur at all. The results improve the understanding of economic growth processes over the very long run and provide one possible explanation why some regions experienced the takeoff to sustained economic growth earlier than others.Diese Dissertation analysiert die ökonomischen Wachstumseffekte des demographischen Wandels im Rahmen endogener Wachstumsmodelle. Substantielle Veränderungen der Fertilität und der Lebenserwartung sind die beiden demographischen Hauptmerkmale, welche alle Industrieländer charakterisieren. Obwohl die individuellen Gewinne aufgrund gestiegener Lebenserwartung und besserer Bildung substantiell sind, bestehen Bedenken hinsichtlich der makroökonomischen Auswirkungen. Um das Verständnis hierüber zu verbessern, erweitert diese Dissertation die bestehende Literatur, indem sie 1) eine exogene Überlebenswahrscheinlichkeit in ein Wachstumsmodell mit vertikalen Innovationen integriert; 2) die Lebenserwartung in einem Wachstumsmodell mit horizontalen Innovationen endogenisiert; und 3) die Wachstumseffekte von Grundlagenforschung innerhalb eines Unified Growth Modells untersucht. Kapitel zwei enthält das erste Papier mit dem Titel "Longevity-induced Vertical Innovation and the Tradeoff between Life and Growth", welches gemeinsam mit Annarita Baldanzi und Klaus Prettner verfasst wurde. In diesem Papier wird der positive Effekt einer steigenden Lebenserwartung auf die individuelle Ersparnisbildung verwendet. Eine höhere exogene Wahrscheinlichkeit, bis ins Rentenalter zu überleben, erhöht die Ersparnisbildung und senkt somit den Marktzins. Auf Produktionsseite erhöht ein niedrigerer Zinssatz den Gegenwartswert eines Patents, was wiederum Forschung profitabler macht. Infolgedessen steigt die Anzahl an Wissenschaftlern, was zu einer höheren Frequenz von qualitätsverbessernden Patenten und somit zu höherem Wirtschaftswachstum führt. Es wird analytisch gezeigt, dass die Beziehung zwischen Lebenserwartung und Wirtschaftswachstum strikt positiv ist. In einer Wohlfahrtsanalyse wird zudem zwischen dem Nutzengewinn eines längeren Lebens und dem Nutzengewinn durch höheren Konsum differenziert. Die Analyse zeigt, dass die direkten Wohlfahrtsgewinne einer höheren Lebenserwartung in der Regel die indirekten Wohlfahrtsgewinne schnelleren Wirtschaftswachstums übersteigen. Kapitel drei enthält das zweite Papier mit dem Titel "Endogenous Life-Expectancy and R&D-based Economic Growth". Die Lebenserwartung wird endogenisiert, indem staatliche Gesundheitsinvestitionen die Überlebenswahrscheinlichkeit erhöhen. Zusätzlich zur individuellen Ersparnisbildung entscheiden Eltern über die Anzahl der Kinder und deren Bildungsgrad. Neben dem Spareffekt wirkt sich die Lebenserwartung positiv auf die Erwerbsquote und negativ auf die Fertilitätsrate aus. Der Grund hierfür ist, dass Arbeitnehmer mehr arbeiten müssen (auf Kosten von weniger Kindern), um eine längere Rentenzeit zu finanzieren. Die Rückkopplungseffekte mit der Produktionsseite werden in einer kalibrierten Version des Modells analysiert. Unter Verwendung von U.S.-Daten legen die Ergebnisse nahe, dass der Gesamteffekt der Lebenserwartung für das Wirtschaftswachstum positiv ist und 11,9 % der Steigerungen des realen BIP p.c. im Zeitraum 1960-2017 ausgemacht hat. Aus Wohlfahrtsperspektive deuten die Ergebnisse darauf hin, dass die Größe des Gesundheitssektors in den meisten Industrieländern unter der wachstumsmaximierenden Größe liegt. Die Feststellung, dass die Größe des Gesundheitssektors, der die Lebenserwartung maximiert, wesentlich größer ist als die wachstumsmaximierende Größe, unterstützt die Ansicht, nicht nur die Wachstumseffekte von Gesundheit zu berücksichtigen. Kapitel vier enthält das dritte Papier, welches gemeinsam mit Klaus Prettner verfasst wurde und den Titel The Scientific Revolution and Its Role in the Transition to Sustained Economic Growth trägt. Wissenschaftliches Grundlagenwissen wird als notwendiger Input für angewandte Forschung integriert und wächst in Abhängigkeit von der Bevölkerungsgröße und den Bildungsinvestitionen. Für einen niedrigen ökonomischen Entwicklungsgrad ist die Fertilität hoch und es gibt keine Bildungsinvestitionen. Sobald das Einkommen einen bestimmten Schwellenwert überschreitet, werden Bildungsinvestitionen positiv. Zusammen mit dem dadurch initiierten Fertilitätsübergang markiert dies den Beginn der Phase anhaltenden Wirtschaftswachstums. Es wird gezeigt, dass die Wachstumsrate von sowie der Zugang zu grundlegenden wissenschaftlichen Kenntnissen entscheidend für den Zeitpunkt und das Ausmaß des ökonomischen Takeoffs sind. Für niedrige Wachstumsraten und einen reduzierten Zugang zu Grundlagenforschung verzögert sich der Takeoff um eine Generation, da angewandte Forschung erst später profitabel wird. Für den Fall, dass gar keine Grundlagenforschung verfügbar ist, stagniert die Ökonomie für immer. Diese Ergebnisse verbessern das Verständnis über langfristige ökonomische Wachstumsprozesse und liefern eine mögliche Erklärung, weshalb einige Regionen den Takeoff zu anhaltendem Wirtschaftswachstum früher als andere erlebt haben

Endogenous life expectancy and R&D-based economic growth

We propose an overlapping generations framework in which life expectancyis determined endogenously by governmental health investments. As a nov-elty, we are able to examine the feedback effects between life expectancy andR&D-driven economic growth for the transitional dynamics. We find that i)higher survival induces economic growth through higher savings and higherlabor force participation; ii) longevity-induced reductions in fertility hampereconomic development; iii) the positive life expectancy effects of larger savingsand higher labor force participation outweigh the negative effect of a reductionin fertility, and iv) there exists a growth-maximizing size of the health caresector that might lie beyond what is observed in most countries. Altogether,the results support a rather optimistic view on the relationship between lifeexpectancy and economic growth and contribute to the debate surroundingrising health shares and economic development

The scientific revolution and its role in the transition to sustained economic growth

We propose a Unified Growth model that analyzes the role of the Scientific Revolution in the takeoff to sustained modern economic growth. Basic scientific knowledge is a necessary input in the production of applied knowledge, which, in turn, fuels productivity growth and leads to rising incomes. Eventually, rising incomes instigate a fertility transition and a takeoff of educational investments and human capital accumulation. In regions where scientific inquiry is severely constrained (for religious reasons or because of oppressive rulers), the takeoff to modern growth is delayed or might not occur at all. The novel mechanism that we propose for the latent transition towards the takeoff could contribute to our understanding of why sustained growth emerged first in Europe

Efficient Charge Separation of Cold Charge-Transfer States in Organic Solar Cells Through Incoherent Hopping

We demonstrate that efficient and nearly field-independent charge separation of electron hole pairs in organic planar heterojunction solar cells can be described by an incoherent hopping mechanism. Using kinetic Monte Carlo simulations that include the effect of on-chain delocalization as well as entropic contributions, we simulate the dissociation of the charge-transfer state in polymer fullerene bilayer solar cells. The model further explains experimental results of almost field independent charge separation in bilayers of molecular systems with fullerenes and provides important guidelines at the molecular level for maximizing the efficiencies of organic solar cells. Thus, utilizing coherent phenomena is not necessarily required for highly efficient charge separation in organic solar cells.This project has received funding from the Universidad Carlos III de Madrid, the European Union’s Seventh Framework Programme for research, technological development, and demonstration under Grant Agreement No. 600371, el Ministerio de Economı́a, Industria y Competitividad (COFUND2014-51509), el Ministerio de Educación, cultura y Deporte (CEI-15-17), and Banco Santander. We also acknowledge additional funding from the German Research Foundation DFG (GRK1640) and the Bavarian University Centre for Latin America (BAYLAT)