Job Market Signalling and Screening: An Experimental Comparison

We analyze the Spence education game in experimental markets.We compare a signaling and a screening variant, and we analyze the e®ect of increasing the number of employers from two to three.In all treatments, there is a strong tendency to separate.More efficient workers invest more often and employers bid higher for workers who have invested.More efficient workers also earn higher wages.Employers' pro¯ts are usually not different from zero.Increased competition leads to higher wages only in the signaling sessions.We ¯nd that workers in the screening sessions invest more often and earn higher wages when there are two employers.labour market;games

Electrical read out for coherent phenomena involving Rydberg atoms in thermal vapor cells

We present a very sensitive and scalable method to measure the population of highly excited Rydberg states in a thermal vapor cell of rubidium atoms. We detect the Rydberg ionization current in a 5 mm electrically contacted cell. The measured current is found to be in excellent agreement with a theory for the Rydberg population based on a master equation for the three level problem including an ionization channel and the full Doppler distributions at the corresponding temperatures. The signal-to-noise ratio of the current detection is substantially better than purely optical techniques.Comment: 4 pages, 4 figure

Job Market Signalling and Screening:An Experimental Comparison

We analyze the Spence education game in experimental markets.We compare a signaling and a screening variant, and we analyze the e®ect of increasing the number of employers from two to three.In all treatments, there is a strong tendency to separate.More efficient workers invest more often and employers bid higher for workers who have invested.More efficient workers also earn higher wages.Employers' pro¯ts are usually not different from zero.Increased competition leads to higher wages only in the signaling sessions.We ¯nd that workers in the screening sessions invest more often and earn higher wages when there are two employers.

Wannier-function approach to spin excitations in solids

We present a computational scheme to study spin excitations in magnetic materials from first principles. The central quantity is the transverse spin susceptibility, from which the complete excitation spectrum, including single-particle spin-flip Stoner excitations and collective spin-wave modes, can be obtained. The susceptibility is derived from many-body perturbation theory and includes dynamic correlation through a summation over ladder diagrams that describe the coupling of electrons and holes with opposite spins. In contrast to earlier studies, we do not use a model potential with adjustable parameters for the electron-hole interaction but employ the random-phase approximation. To reduce the numerical cost for the calculation of the four-point scattering matrix we perform a projection onto maximally localized Wannier functions, which allows us to truncate the matrix efficiently by exploiting the short spatial range of electronic correlation in the partially filled d or f orbitals. Our implementation is based on the FLAPW method. Starting from a ground-state calculation within the LSDA, we first analyze the matrix elements of the screened Coulomb potential in the Wannier basis for the 3d transition-metal series. In particular, we discuss the differences between a constrained nonmagnetic and a proper spin-polarized treatment for the ferromagnets Fe, Co, and Ni. The spectrum of single-particle and collective spin excitations in fcc Ni is then studied in detail. The calculated spin-wave dispersion is in good overall agreement with experimental data and contains both an acoustic and an optical branch for intermediate wave vectors along the [100] direction. In addition, we find evidence for a similar double-peak structure in the spectral function along the [111] direction.Comment: 16 pages, 11 figures, 5 table

College admissions with entrance exams: Centralized versus decentralized

© 2018 Elsevier Inc. We study a college admissions problem in which colleges accept students by ranking students’ efforts in entrance exams. Students’ ability levels affect the cost of their efforts. We solve and compare equilibria of “centralized college admissions” (CCA) where students apply to all colleges and “decentralized college admissions” (DCA) where students only apply to one college. We show that lower ability students prefer DCA whereas higher ability students prefer CCA. Many predictions of the theory are supported by a lab experiment designed to test the theory, yet we find a number of differences that render DCA less attractive than CCA compared to the equilibrium benchmark

Ultrafast Insulator-Metal Phase Transition in VO2 Studied by Multiterahertz Spectroscopy

The ultrafast photoinduced insulator-metal transition in VO2 is studied at different temperatures and excitation fluences using multi-THz probe pulses. The spectrally resolved mid-infrared response allows us to trace separately the dynamics of lattice and electronic degrees of freedom with a time resolution of 40 fs. The critical fluence of the optical pump pulse which drives the system into a long-lived metallic state is found to increase with decreasing temperature. Under all measurement conditions we observe a modulation of the eigenfrequencies of the optical phonon modes induced by their anharmonic coupling to the coherent wave packet motion of V-V dimers at 6.1 THz. Furthermore, we find a weak quadratic coupling of the electronic response to the coherent dimer oscillation resulting in a modulation of the electronic conductivity at twice the frequency of the wave packet motion. The findings are discussed in the framework of a qualitative model based on an approximation of local photoexcitation of the vanadium dimers from the insulating state.Comment: 10 pages, 8 figures submitted to Physical Review

Itinerant magnetic multipole moments of rank five, triakontadipoles, as the hidden order in URu2_{2}Si2_{2}

A broken symmetry ground state without any magnetic moments has been calculated by means of local-density-approximation to density functional theory plus a local exchange term, the so-called LDA+$U$ approach, for URu$_{2}$Si$_{2}$. The solution is analysed in terms of a multipole tensor expansion of the itinerant density matrix and is found to be a non-trivial magnetic multipole. Analysis and further calculations show that this type of multipole enters naturally in time reversal breaking in presence of large effective spin-orbit coupling and co-exists with magnetic moments for most magnetic actinidesComment: 5 pages, 3 figure