Condensed Matter and Quantum Physics
- Two-dimensional Josephson-junction arrays: quantum phase diagram and its modifications for resistive dissipation.
- Quantum Monte Carlo algorithm for a dissipative system and low-temperature phase diagram of two-dimensional Josephson-junction arrays with resistive shunts.
- Quantum-phase transitions: comparison of the finite-temperature behaviors of the quantum and the classical transverse-field XY model.
Propagative or localized surface plasmons supported by metal-dielectric interfaces are collective oscillations of the free electrons of the metal which can resonantly couple to an incident electromagnetic wave. They are responsible for the characteristic brilliant colors of coinage metal nanoparticles and enhance significantly both the extinction cross section (absorption and scattering) of metal-organic complexes and the local electromagnetic field in the vicinity of the metal dielectric interface. The evanescent nature of the electromagnetic field associated with the plasmon helps to concentrate the light beyond the limit of diffraction and is responsible for the deep changes observed in the local density of photonic modes. The light concentration makes a planar (or slightly modulated) metal-dielectric interface very sensitive to physical-chemical changes due for example to receptor-ligand binding reactions, and is widely used in the development and implementation of a class of label-free sensors (Surface Plasmon Resonance sensors). Moreover, the proximity of a metal nanostructure to an optically active moiety changes the strength, the spectrum and the pattern of its emission, with a behaviour depending on the relation between the amplification of its radiative and non-radiative decay rates. These changes can be used to manipulate the scattering and luminescent properties of molecular moieties adsorbed on the metal nanostructure and to develop new diagnostics related to the enhancements of such emission phenomena, namely the surface enhanced spectroscopies (SERS, SEF, SPFS). Thanks to the huge development of nanofabrication techniques, these alterations have been observed on a variety of silver and gold nanostructures (nanoparticles like nanostars, nanocages, nanoshells, nanoprisms or metal thin films, metal or glassy planar surfaces with 1D or 2D relief random or regular modulations obtained with nanoparticles functionalization or via nano-carving techniques) and the resonant absorption and/or the induced enhancement of light emission has led to their exploitation in several fields like the ultrahigh resolution sensing (detection of analytes concentrations down to zeptomolar, 10-21, levels), bioimaging, selective drug delivery. Beyond their interest related with the possibility of plasmonic excitation (and hence all the associated applications and fundamental issues), nanoparticles of coinage metals are employed in many other fields, such as catalysis (due to the high surface/volume ratio with respect to bulk materials) or biology and medicine (theragnostic and drug delivery, in the case of Au; bactericide and fungicide applications in the case of Ag and Cu). Many of the previous applications can also involve nanoparticles of different metals (Pd, Pt, Ru), or ceramic nanoparticles (Cu, Ti, Fe and Ni oxides). Although most nanoparticles synthesis protocols are based onto chemical reduction, an efficient green method for the preparation of such nanostructures is by pulsed laser ablation in liquid environment, which permits to obtain a wide range of colloidal suspensions of metal, ceramic and metal/ceramic nanoparticles in pure solvents, including pure water, thus favouring the biocompatibility of the final products.
The field of low dimensional magnetism dates back to 1925, when the one-dimensional (1D) Ising model was first proposed, in the - unsuccessful - effort to provide a microscopic justification for cooperative behavior in magnets. Some decades of purely theoretical research followed. Onsager provided the exact solution of the 2D Ising model (1949), which /does/ exhibit long range magnetic order, while Mermin and Wagner in their famous theorem (1966) stated the absence of long range order in 1D and 2D magnetic models /with a continuous symmetry/ at any finite temperature. Around 1970, magnets in restricted dimensions started being investigated also experimentally, since real bulk crystals were synthesized with magnetic coupling much stronger in one or two spatial directions than in the remaining ones. Since then, new phenomena and new materials have appeared. In addition to ultrathin magnetic films and multilayers (2D magnets) and magnetic chains (1D magnets), the important class of molecular magnetic clusters (0D magnets) has attracted increasing attention thanks to interesting basic properties (e.g. magnetic quantum tunneling) as well as possible technical applications (e.g. in quantum computing).
- Effective potential for dissipative quantum systems.
- Systems with anomalous quantum dissipation: bath-momentum coupling.
- General path-integral theory of environmental coupling and reentrant enhancement of quantum fluctuations.
- Interaction of quantum spin systems with the crystal lattice treated as environmental effect.
- Quantum information transfer through quantum channels.
- Ballistic quantum-state transfer mechanism over a spin-1/2 chain.
- Analysis of the conditions for minimal dispersion in a quasi-uniform transmission channel.
- Quasi-perfect quantum-state transfer in an unmodulated channel of arbitrary length.
Every primary school pupil knows that matter can be broadly divided into three basic categories: gas, liquid, and solid, corresponding, broadly speaking, to the air we breathe, the water we drink, and the ground we walk on. In a scientifically more proper language, solids are better identified with matter spatially organized in regular lattices, while fluids (i.e. liquids and gases) tend to assume the shape of their (solid) container, with gases totally filling the available space, and liquids distributing on the bottom of it (thanks to the effect of gravity).
Chemistry, at the most elementary level, teaches us how to deal with ideal gas, which models the behavior of any real gas at sufficiently low pressure. However, as pressure (and density) increases the ideal gas model breaks down and a more complex approach should be devised. Nonetheless, chemistry still teaches us that matter can be defined to be in its gas state if it is not possible to transform it into a liquid by any compression.
The temperature below which a gas can be converted into a liquid is called the critical temperature. When temperature is lower than this value, a gas (which is now more properly called vapour) can be transformed into a liquid simply by applying some pressure. Differently from the gaseous state, where the driving rule is a total kinematic disorder with particles (atoms or molecules) traveling in all directions and colliding among themselves, as well as with the container wall (and producing pressure), the solid state resembles a more quit situation where particles sit in the vicinity of their assigned site, orderly surrounded by their neighbors, and obeying long-range periodicity. Liquid state is the logical intermediate between the two extreme limits of long-range order and full chaotic disorder. Here the periodic order of the solid state is lost, and the particles are randomly distributed in space, even though a residual short-range order is maintained which makes the liquid behavior different from that of an ideal gas. Physics of Fluids studies the structure and dynamics of this intermediate state of matter trying to establish a relationship between the properties measured at the microscopic and the macroscopic level and the characteristic of the component particles (atoms or molecules).
Thermodynamics is a powerful technique, which allows to accurately predict the macroscopic behavior of a statistical ensemble starting from the basic characteristics of its microscopic components. However, one of the fundamental assumptions of thermodynamics resides in the asymptotic limit for both N (number of particles) and V (sample volume), though their ratio remains finite and defines the sample density. Thus, when the number of interacting particles becomes finite (and small), thermodynamics does not apply any more and a totally new wealth of science opens for the scientific investigation (nanoscience). Nanoscience can be investigated using novel techniques whose most important examples are modern electron and atomic-force microscopies, which are able to probe matter at the atomic level. Nevertheless, it would be not wise to give-up, a priori, the well-established spectroscopy techniques which have allowed, in the last century, such a great abundance of discoveries in almost every field of science. However, as the detected spectroscopic signal is proportional to the number of probed particles, nanoscience and spectroscopy would appear, at first sight, incompatible to each other.
Luckily enough, a certain class of materials exists, which allows overcoming this apparent difficulty. Nanoporous materials, in fact, can be used to confine a finite number of particles in a small volume, so that neighboring cavities do not interact to each other. Thus, each individual nanosample can be replicated for an extremely high number of times, so that a macroscopic sample can be measured. Carbon nanotubes, single- and multi-walled, represent the prototype of a nanoporous material but they are not the only ones. Other carbon-based materials are currently used, like fullerenes, carbon nanofibers, zeolites, silicon nanotubes, amorphous nanoporous glasses (e.g.: vycor), and MOF (metal organic frameworks). Last, but not least, it is possible to prepare macroscopic samples made of nanocages composed by water and containing guest molecules (clathrates hydrates). These nanoporous materials can be used to prepare a wealth of samples where classical thermodynamics does not apply and a new scientific approach is necessary. It is important to point out that this possibility opens a research field which is not only interesting for academic curiosity but it can mimic, in well defined experimental conditions, the behavior of important biological systems and processes.
Material investigation, at a microscopic level, can be carried out using spectroscopic techniques like neutron or light scattering. Optical spectroscopic techniques (e.g. Raman scattering) are sensitive to the vibrational dynamics and are generally used to probe optically transparent media. In the case of optically dense specimens, or metals, only the surface can be accessed, with a substantial decrease in the detection efficiency. This problem does not affect thermal neutrons, for which almost all materials are basically transparent. In addition, due to the exceptionally high neutron scattering cross section for protons, neutron scattering techniques are extremely useful to investigate bulk microscopic properties of materials that are promising for hydrogen storage, such as complex hydrides, nanostructured carbon and MOF's.View items...