Interface-induced magnetism in perovskite quantum wells

We investigate the angular dependence of the magnetoresistance of thin (< 1 nm), metallic SrTiO3 quantum wells epitaxially embedded in insulating, ferrimagnetic GdTiO3 and insulating, antiferromagnetic SmTiO3, respectively. The SrTiO3 quantum wells contain a high density of mobile electrons (~7x10^14 cm^-2). We show that the longitudinal and transverse magnetoresistance in the structures with GdTiO3 are consistent with anisotropic magnetoresistance, and thus indicative of induced ferromagnetism in the SrTiO3, rather than a nonequilibrium proximity effect. Comparison with the structures with antiferromagnetic SmTiO3 shows that the properties of thin SrTiO3 quantum wells can be tuned to obtain magnetic states that do not exist in the bulk material.Comment: Accepted for publication as a Rapid Communication in Physical Review

Characterizing the Sample Complexity of Private Learners

In 2008, Kasiviswanathan et al. defined private learning as a combination of PAC learning and differential privacy. Informally, a private learner is applied to a collection of labeled individual information and outputs a hypothesis while preserving the privacy of each individual. Kasiviswanathan et al. gave a generic construction of private learners for (finite) concept classes, with sample complexity logarithmic in the size of the concept class. This sample complexity is higher than what is needed for non-private learners, hence leaving open the possibility that the sample complexity of private learning may be sometimes significantly higher than that of non-private learning. We give a combinatorial characterization of the sample size sufficient and necessary to privately learn a class of concepts. This characterization is analogous to the well known characterization of the sample complexity of non-private learning in terms of the VC dimension of the concept class. We introduce the notion of probabilistic representation of a concept class, and our new complexity measure RepDim corresponds to the size of the smallest probabilistic representation of the concept class. We show that any private learning algorithm for a concept class C with sample complexity m implies RepDim(C)=O(m), and that there exists a private learning algorithm with sample complexity m=O(RepDim(C)). We further demonstrate that a similar characterization holds for the database size needed for privately computing a large class of optimization problems and also for the well studied problem of private data release

Spontaneous Hall effects in the electron system at the SmTiO3/EuTiO3 interface

Magnetotransport and magnetism of epitaxial SmTiO3/EuTiO3 heterostructures grown by molecular beam epitaxy are investigated. It is shown that the polar discontinuity at the interface introduces ~ 3.9x10^14 cm^-2 carriers into the EuTiO3. The itinerant carriers exhibit two distinct contributions to the spontaneous Hall effect. The anomalous Hall effect appears despite a very small magnetization, indicating a non-collinear spin structure and the second contribution resembles a topological Hall effect. Qualitative differences exist in the temperature dependence of both Hall effects when compared to uniformly doped EuTiO3. In particular, the topological Hall effect contribution appears at higher temperatures and the anomalous Hall effect shows a sign change with temperature. The results suggest that interfaces can be used to tune topological phenomena in itinerant magnetic systems.Comment: Accepted in APL Material

THE MIND AND BRAIN SCHOLAR AS A HITCH-HIKER IN POST-GUTENBERG GALAXY: PUBLISHING AT 2000 AND BEYOND

Electronic journal (e-journal) publishing has started to change the ways we think about publish-ing. However, many scholars and scientists in the mind and brain sciences are still ignorant of the new possibilities and on-going debates. This paper will provide a summary of the issues in-volved, give an update of the current discussion, and supply practical information on issues re-lated to e- journal publishing and self-archiving relevant for the mind and brain sciences. Issues such as differences between traditional and e-journal publishing, open archive initiatives, world-wide conventions, quality control, costs involved in e-journal publishing, and copyright questions will be addressed. Practical hints on how to self-archive, how to submit to the e-journal Psycolo-quy, how to create an open research archive, and where to find information relevant to e-publishing will be supplied

Losing the error related negativity (ERN): an indicator for willed action

When people make errors in a discrimination task, a negative-going waveform can be observed in scalp-recorded EEG that has been coined the error-related negativity (ERN). We hypothesized that the ERN only occurs with slips, that is unwilled action errors, but not if an error is committed willingly and intentionally. We investigated the occurrence of the ERN in a choice reaction time task that has been shown to produce an ERN and in an error simulation task where subjects had to fake errors while the EEG was recorded. We observed a loss of the ERN when errors were committed in willed actions but not in unwilled actions thus supporting the idea that the production of the ERN is tied to slips in unwilled actions but not mistakes in willed actions

Disorder versus two transport lifetimes in a strongly correlated electron liquid

We report on angle-dependent measurements of the sheet resistances and Hall coefficients of electron liquids in SmTiO3/SrTiO3/SmTiO3 quantum well structures, which were grown by molecular beam epitaxy on (001) DyScO3. We compare their transport properties with those of similar structures grown on LSAT [(La0.3Sr0.7)(Al0.65Ta0.35)O3]. On DyScO3, planar defects normal to the quantum wells lead to a strong in-plane anisotropy in the transport properties. This allows for quantifying the role of defects in transport. In particular, we investigate differences in the longitudinal and Hall scattering rates, which is a non-Fermi liquid phenomenon known as lifetime separation. The residuals in both the longitudinal resistance and Hall angle were found to depend on the relative orientations of the transport direction to the planar defects. The Hall angle exhibited a robust T2 temperature dependence along all directions, whereas no simple power law could describe the temperature dependence of the longitudinal resistances. Remarkably, the degree of the carrier lifetime separation, as manifested in the distinctly different temperature dependences and diverging residuals near a critical quantum well thickness, was completely insensitive to disorder. The results allow for a clear distinction between disorder-induced contributions to the transport and intrinsic, non-Fermi liquid phenomena, which includes the lifetime separation.Comment: In press, Sci. Re