Wavefunction Is an Observable Physical Field

Topological Defects Induced High-Spin Quartet State in Truxene-Based Molecular Graphenoids

STM and DFT studies of CO2 adsorption on O-Cu(100) surface

Atomic imaging with a 12 T magnetic field perpendicular or parallel to the sample surface by an ultra-stable scanning tunneling microscope

Learning advanced physics, in general, is challenging not only due to the\nincreased mathematical sophistication but also because one must continue to\nbuild on all of the prior knowledge acquired at the introductory and\nintermediate levels. In addition, learning quantum mechanics can be especially\nchallenging because the paradigms of classical mechanics and quantum mechanics\nare very different. Here, we review research on student reasoning difficulties\nin learning upper-level quantum mechanics and research on students'\nproblem-solving and metacognitive skills in these courses. Some of these\nstudies were multi-university investigations. The investigations suggest that\nthere is large diversity in student performance in upper-level quantum\nmechanics regardless of the university, textbook, or instructor and many\nstudents in these courses have not acquired a functional understanding of the\nfundamental concepts. The nature of reasoning difficulties in learning quantum\nmechanics is analogous to reasoning difficulties found via research in\nintroductory physics courses. The reasoning difficulties were often due to\nover-generalizations of concepts learned in one context to another context\nwhere they are not directly applicable. Reasoning difficulties in\ndistinguishing between closely related concepts and in making sense of the\nformalism of quantum mechanics were common. We conclude with a brief summary of\nthe research-based approached that take advantage of research on student\ndifficulties in order to improve teaching and learning of quantum mechanics.\n

We report on the first successful lateral manipulation of molecules and controlled formation of nanostructures with the Scanning Tunneling Microscope (STM) at temperatures above 4 K as used by Eigler and collaborators. Among the first structures, we built the letters F and U forming the logo of our university at 30 K with CO molecules on a Cu(211) substrate. Our method to manipulate the molecules is analogous to that employed successfully up to now only by Eigler and co-workers. First experiences concerning the manipulation of the CO molecules on the highly anisotropic substrate are presented and the crucial role of the tip composition in imaging the CO molecules is demonstrated.

Scanning tunnelling microscope (STM) images of the c(2√3×4)rect layer of benzene and carbon monoxide co-adsorbed on the Rh(111) surface are shown. For the first time, individual CO molecules have been resolved, as well as ring-like benzene structures.

Quantum mechanics is often credited for having clearly shown that the whole is something over and above the sum of its parts. We want to assess whether this is really the case, and if so, in what sense. We argue that there is indeed a sense in which this is true. Our argument is that even a weak realistic interpretation of quantum mechanics renders a particular metaphysical principle about property instantiation, that we label Property Compositional Determinateness, untenable. Yet there is another metaphysical principle about composition that is usually maintained to imply that composition of parts exhausts the whole they are part of, namely Mereological Extensionalism. In this case, contrary to widespread agreement, we argue that quantum mechanics does not provide any reason, either direct or indirect, to abandon such principle.

The Scanning Tunneling Microscope (STM) is a powerful instrument to measure electronic density of states at surfaces down to atomic scale. Many systems of interest require studying variations as a function of the magnetic field, which is most often applied perpendicular to the surface. Conventional STM setups make it challenging to perform measurements when the magnetic field must be applied in other directions. Here, we describe a new STM, which is small enough to allow for full rotation on a space with a diameter of 37mm, well below the available space within many magnets. We have installed the STM on a rotatable platform. We show that the new rotatable STM setup preserves the performance of state-of-the-art setups in terms of noise and accuracy. Our new approach significantly enhances control over the direction of the applied magnetic field for STM and opens exciting new possibilities to study quantum materials.

Teaching and learning quantum mechanics is one of the most demanding educational and conceptual challenges, in particular in secondary schools where students do not possess an adequate mathematical background to effectively support the description of quantum behaviour. Educational research shows that traditional approaches, generally based on historical and narrative perspectives, are only partially effective. The reason is that they do not address in depth those basic quantum concepts that radically question the fundamentals of classical physics. A research-based educational program has been proposed to two final-year classes of an Italian scientific high school. In order to build the main concepts of quantum mechanics and their formal basic representation via real and simulated experiments, the program uses the light polarization as a context. A quantum game was then integrated in the educational program, to support students’ learning. Their conceptual paths, monitored by means of tutorials and questionnaires, show significant student learning especially on the concept of state and on appropriating the formalism meaning, whereas students more frequently referred to the geometrical vector representation instead of the algebraic-analytic formula. The quantum game has emerged to support intuition and operative experience in distinguishing the foundational concepts of superposition and entanglement.

Fe, Cu atoms and CO molecules were manipulated with a scanning tunneling microscope (STM) on a Ag(110) surface, and one or two CO can transfer from the surface and bond with a metal atom through the STM tip [H. J. Lee and W. Ho, Science 286, 1719 (1999); Phys. Rev. B 61, R16347 (2000)]. We perform a density-functional cluster model investigation for the systems. The experimental geometries are validated and understood using the frontier orbital theory. The STM topographic images are reproduced. The vibrational frequencies of the adsorbate systems are obtained by diagonalizing the second-derivative matrices and are in excellent agreement with the experimental measurements. The geometries and C-O stretch frequencies are predicted for systems with the adsorbate metal atom being Co, Ni, Zn, and Ag. These systems can be divided to two classes, and each class exhibits a different set of properties.

An intriguing corrugation reversal in scanning tunneling microscopy (STM) images has been observed on several metal surfaces as well as on graphite. With a sudden change of tip condition, under the same tunneling conditions, the STM image can switch from positive (atoms being protrusions) to negative (atoms being depressions) and vice versa. In both cases, the absolute values of corrugation amplitude can be one order of magnitude greater than what is expected from the electron charge density near the Fermi level. We explain this effect as a manifestation of tip electronic states. If m≠0 states dominate the tip electronic states near the Fermi level, images with inverted atomic corrugation are expected. For an m=0, l≠0 tip state, noninverted images with large corrugation amplitude are expected. The type of image (i.e., inverted or noninverted) is expected to be independent of the tip–sample distance. The absolute values and the distance dependence of corrugation amplitudes expected from the tip–state effect are in agreement with experimental observations. Alternative explanations are discussed in conjunction with experimental observations.

Atomic Scale STM Imaging of Alloy Surfaces With Chemical Resolution

STM study of the Ni(110)-(2 × 1)-2CO system: structure and bonding-site determination

Motivated by a recent experiment in which zero-bias peaks have been observed in scanning tunneling microscopy (STM) experiments performed on chains of magnetic atoms on a superconductor, we show, by generalizing earlier work, that a multichannel ferromagnetic wire deposited on a spin-orbit coupled superconducting substrate can realize a non-trivial chiral topological superconducting state with Majorana bound states localized at the wire ends. The non-trivial topological state occurs for generic parameters requiring no fine tuning, at least for very large exchange spin splitting in the wire. We theoretically obtain the signatures which appear in the presence of an arbitrary number of Majorana modes in multi-wire systems incorporating the role of finite temperature, finite potential barrier at the STM tip, and finite wire length. These signatures are presented in terms of spatial profiles of STM differential conductance which clearly reveal zero energy Majorana end modes and the prediction of a multiple Majorana based fractional Josephson effect. A substantial part of this work is devoted to a detailed critical comparison between our theory and the recent STM experiment claiming the observation of Majorana fermions. The conclusion of this detailed comparison is that although the experimental observations are not manifestly inconsistent with our theoretical findings, the very small topological superconducting gap and the very high temperature of the experiment make it impossible to decisively verify the existence of a localized Majorana zero mode, as the spectral weight of the Majorana mode is necessarily spread over a very broad energy regime exceeding the size of the gap. Thus, although the experimental findings are indeed consistent with a highly broadened and weakened Majorana zero bias peak, much lower experimental temperatures are necessary for any definitive conclusion.

We present the design and performance of a cryogenic scanning tunneling microscope (STM) which operates inside a water-cooled Bitter magnet, which can attain a magnetic field of up to 38 T. Due to the high vibration environment generated by the magnet cooling water, a uniquely designed STM and a vibration damping system are required. The STM scan head is designed to be as compact and rigid as possible, to minimize the effect of vibrational noise as well as fit the size constraints of the Bitter magnet. The STM uses a differential screw mechanism for coarse tip-sample approach, and operates in helium exchange gas at cryogenic temperatures. The reliability and performance of the STM are demonstrated through topographic imaging and scanning tunneling spectroscopy on highly oriented pyrolytic graphite at T = 4.2 K and in magnetic fields up to 34 T.