Spin noise spectroscopy in GaAs

We observe the noise spectrum of electron spins in bulk GaAs by Faraday rotation noise spectroscopy. The experimental technique enables the undisturbed measurement of the electron spin dynamics in semiconductors. We measure exemplarily the electron spin relaxation time and the electron Lande g-factor in n-doped GaAs at low temperatures and find good agreement of the measured noise spectrum with an unpretentious theory based on Poisson distribution probability.Comment: 4 pages, 4 figure

Anomalous Spin Dephasing in (110) GaAs Quantum Wells: Anisotropy and Intersubband Effects

A strong anisotropy of electron spin decoherence is observed in GaAs/(AlGa)As quantum wells grown on (110) oriented substrate. The spin lifetime of spins perpendicular to the growth direction is about one order of magnitude shorter compared to spins along (110). The spin lifetimes of both spin orientations decrease monotonically above a temperature of 80 and 120 K, respectively. The decrease is very surprising for spins along (110) direction and cannot be explained by the usual Dyakonov Perel dephasing mechanism. A novel spin dephasing mechanism is put forward that is based on scattering of electrons between different quantum well subbands.Comment: 4 pages, 3 postscript figures, corrected typo

Orbital Configurations and Magnetic Properties of Double-Layered Antiferromagnet Cs3_3Cu2_2Cl4_4Br3_3

We report the single-crystal X-ray analysis and magnetic properties of a new double-layered perovskite antiferromagnet, Cs$_3$Cu$_2$Cl$_4$Br$_3$. This structure is composed of Cu$_2$Cl$_4$Br$_3$ double layers with elongated CuCl$_4$Br$_2$ octahedra and is closely related to the Sr$_3$Ti$_2$O$_7$ structure. An as-grown crystal has a singlet ground state with a large excitation gap of $\Delta/k_{\rm B}\simeq 2000$ K, due to the strong antiferromagnetic interaction between the two layers. Cs$_3$Cu$_2$Cl$_4$Br$_3$ undergoes a structural phase transition at $T_{\rm s}\simeq330$ K accompanied by changes in the orbital configurations of Cu$^{2+}$ ions. Once a Cs$_3$Cu$_2$Cl$_4$Br$_3$ crystal is heated above $T_{\rm s}$, its magnetic susceptibility obeys the Curie-Weiss law with decreasing temperature even below $T_{\rm s}$ and does not exhibit anomalies at $T_{\rm s}$. This implies that in the heated crystal, the orbital state of the high-temperature phase remains unchanged below $T_{\rm s}$, and thus, this orbital state is the metastable state. The structural phase transition at $T_{\rm s}$ is characterized as an order-disorder transition of Cu$^{2+}$ orbitals.Comment: 6pages. 6figures, to appear in J. Phys. Soc. Jpn. Vol.76 No.

Gender and Misallocation in the Labor Market

Managers are important for firm productivity (Bloom and Van Reenen, 2007, Lazear, Shaw and Stanton, 2015). Consequently, firms must decide how to assign the right workers to higher-level jobs (Rosen, 1982, Holmstrom and Tirole, 1989). However, little is known about how firms’ organizational design affects different groups of workers and whether it can explain why women continue to be underrepresented in higher-level positions. In this dissertation, I collect a unique dataset in collaboration with a large multinational firm in order to provide new insights on the key impediments that women face in their career progression. In the first chapter, I focus on the role of managers for workers’ career progression, which is motivated by the fact that most organizations rely on managers to identify talented workers for promotions. However, managers who are evaluated on team performance have an incentive to hoard workers. I find that talent hoarding reduces workers’ applications for promotions by more than half, with particularly large effects on women. Marginal female applications who would have not applied under talent hoarding are twice as likely than their male counterparts to land a promotion and three times as likely to outperform their team at a higher level. Talent hoarding thus contributes to misallocation of talent and perpetuates gender inequality in representation and pay. The second chapter builds on these findings and attempts to identify when and why gender differences in representation first emerge in the leadership hierarchy. The rich personnel records allow me to construct a new and granular measure of job hierarchy that captures career progression throughout the job ladder. I find that the transition to first-level leadership positions represents a key bottleneck in women’s career progression. This early leadership gap is not fully explained by employee characteristics and is driven by internal promotions, not differential entry to or exit from the firm. Women who make it to the first-level leader- ship level are not less likely to get promoted than men, which contrasts the common notion of a glass ceiling. The third chapter demonstrates why women are less likely to advance to first-level leadership positions than men. Identifying the drivers of female underrepresentation is difficult, because the promotion gap can arise due to both labor supply and labor demand factors. By combining rich personnel records and the universe of application and hiring decisions at a large multinational firm, I am able to analyze employees’ labor supply decisions separately from the firm’s labor demand decisions. I find that women at lower hierarchy levels are less likely to apply for promotions to first-level leadership positions than observationally similar men, but do not experience lower hiring likelihoods than men. Using detailed information on every internal job opening in employees’ choice sets, I show that preferences for leading a team are a key determinant of the gender gap in applications for promotions. These gender differences in preferences for team leadership are not fully explained by other factors, including correlated job features such as flexibility and skill requirements or the gender composition of the coworkers associated with a job opening. Together, these findings imply that the organizational design within firms may have large impacts on gender differences in career progression, deterring high-quality women from climbing the job ladder and contributing to misallocation of talent. While all three chapters use the same setting and data, each chapter is intended to be a stand-alone set of research questions, so the respective description is included within each chapter

Unionville Serpentine Barrens: Analyzing the Relationship Between Soil Profiles and Forest Succession Rate

The Unionville Serpentine Barrens are a part of Natural Lands Trust’s ChesLen Preserve in Unionville, Chester County, Pennsylvania. This area of the Preserve is underlain with serpentine rock (serpentinite), known for its high magnesium and low calcium content, which inhibit growth in most plants. However, certain plants are tolerant of these conditions, and a very few have evolved a set of traits that confine them almost exclusively to this soil.1 The Unionville Barrens exist today in large part because of disturbances such as corundum mining, wildfires, and grazing that have prohibited plant succession from grassland to forest. The Unionville Barrens are home to at least 15 plant species that are categorized as endangered, threatened, or rare.2 The inspection of a series of aerial photographs taken from 1937 to 2002 clearly shows the decline in area of serpentine grassland from 58.1 acres in 1937 to just 8.9 acres in 2002. In order to sustain the rare plant communities, the grassland must be conserved and, where possible, forested areas converted back to grassland. In order to prioritize grassland restoration areas to make the most efficient use of limited land management resources, it is necessary first to understand if, and how, the rate of succession from grassland to forest is associated with soil conditions or other measurable features of the landscape. This research analyzes the status of current plant communities and their associated soil depths and other characteristics as they relate to the aerial photographs. A grid of 105 points placed 65 meters apart was overlain on top of the Unionville Barrens restoration study area. Soil horizon depth and color, soil depth to bedrock, and surrounding plant communities were recorded at each of these points. Statistical and spatial analyses of these results determined that certain variables best retrospectively “predicted” the likelihood of a quick succession from grassland to woods, when examining this data against a chronosequence of aerial photographs from 1937 to 2010. It was assumed that areas that underwent rapid succession from grassland to woods would require too costly a disturbance regime to sustain the grasslands long-term. Therefore, the restoration priority areas will be selected based on areas where succession must have occurred recently, or where measurements indicated a slow succession rate

Talent Hoarding in Organizations

Most organizations rely on managers to identify talented workers. However, managers who are evaluated on team performance have an incentive to hoard workers. This study provides the first empirical evidence of talent hoarding using personnel records and survey evidence from a large manufacturing firm. Talent hoarding is reported by three-fourths of managers, is detectable in managerial decisions, and occurs more frequently when hoarding incentives are stronger. Using quasi-random variation in exposure to talent hoarding, I demonstrate that hoarding deters workers from applying to new positions, inhibiting worker career progression and altering the allocation of talent in the firm

Because I Like It? No, They Made Me Do It!! Why Juveniles Engage In Sexting

Developments in technology have changed the way we do everything; advanced our research capabilities, enhanced our communication abilities and speeds, even the way people commit crimes. It provides perpetrators with a new way to commit traditional crimes as well as new forms of crime. One of the many opportunities involved with increased communication devices is known as sexting. Adolescent sexting has received national and local attention due to possible long-term implications such as registering as a sex offender and even suicide. Sexting, which is considered an antisocial behavior among adolescents, has progressively become implicated in peer pressure as well. Peer pressure causes individuals to commit cruel acts or crimes in which they normally would not do because they are forced, or feel obligated to do so, by their peers. Further study into peer pressure and sexting is needed to discover if peer pressure and opportunity are the reasons why adolescents engage in sexting. To discover this, I surveyed college undergraduate students to determine the causes behind their sexting habits in high school