The single-particle density matrix and the momentum distribution of dark "solitons" in a Tonks-Girardeau gas

We study the reduced single-particle density matrix (RSPDM), the momentum distribution, natural orbitals and their occupancies, of dark "soliton" (DS) states in a Tonks-Girardeau gas. DS states are specially tailored excited many-body eigenstates, which have a dark solitonic notch in their single-particle density. The momentum distribution of DS states has a characteristic shape with two sharp spikes. We find that the two spikes arise due to the high degree of correlation observed within the RSPDM between the mirror points ($x$ and $-x$) with respect to the dark notch at $x=0$; the correlations oscillate rather than decay as the points $x$ and $-x$ are being separated.Comment: 9 pages, 8 figure

Application of benchtop total-reflection X-ray fluorescence spectrometry and chemometrics in classification of origin and type of Croatian wines

The contents of selected metals (K, Ca, Fe, Cu, Zn, Mn, Sr, Rb, Ba, Pb, Ni, Cr and V) in 70 wine samples from Continental and Adriatic part of Croatia and different types of wine (red and white) were determined by TXRF. The aim of this study was to compare the elemental composition of wines from two different regions and to determine the discriminant ability of each variable and to indicate which variables discriminate between the four categories considered. Principal component analysis and cluster analysis showed that K, Mn, Ba and Ni can be considered as the most important characteristics to distinguish between Continental red and white wines, Rb, Ni and Ba for Continental red and Adriatic red wines while Sr is the only metal that completely distinguishes the samples of each category. Finally, linear discriminant analysis showed good recognition (100%) and prediction abilities (96.43%) using these selected elements

About loach in the Sava river

Porodica Cobitidae obuhvaća otprilike 160 vrsta, no rod Cobitis je još uvijek nedovoljno proučen. U rijeci Savi u blizini Zagreba zabilježene su dvije vrste iz roda Cobitis, C. elongata i C. elongatoides. Obje vrste žive na istom staništu u muljevitim i sporotekućim dijelovima rijeke. Nije pronađen niti jedan podatak literature o njihovoj biologiji pa su stoga su ciljevi ovog istraživanja bili utvrditi uvjete rasta vijuna iz gornjeg toka rijeke Save. Prikupljanje uzoraka vode, makrozoobentosa i riba izvršeno je 15. svibnja 2006. na lokaciji Medsave i 17. svibnja 2006. na lokacijama Lijevi Dubrovčak i Setuš. Kvaliteta vode rijeke Save pogodna je za rast, razmnožavanje i život C. elongata, a manje za C. elongatoides. Makrozoobentos je zastupljen sa 10 taksona na sve tri lokacije, a od toga na lokaciji Medsave najviše su zastupljeni Crustacea, na lokaciji Lijevi Dubrovčak Oligochaeta, a na lokaciji Setuš Diptera i Gastropoda. Morfometrijske vrijednosti pokazuju određena odstupanja uvjetovana razlikama u dimenzijama tijela ovih dviju vrsta vijuna. Izmjerene vrijednosti smještaja početka i kraja prsne peraje, te početka trbušne peraje na tijelu obje vrste vijuna najviše su se i razlikovale od ostalih izmjera. Faktor kondicije ukazuje da C. elongatoides ima veću tjelesnu masu, te da je bolje uhranjen, budući da njegov CF iznosi 0,81, dok kod C. elongata iznosi 0,61. Rezultati dužinsko masenih odnosa C. elongata mogu se prikazati formulom W= 0,0039 * SL3,2063, a C. elongatoides W= 0,0057 * SL 3,1872.Cobitidae family contains cca 160 species but there isn\u27t enough data on the genus Cobitis. In the Sava river near Zagreb, two species of the genus Cobitis were recorded C. elongata and C. elongatoides. Both species live together in the mud covered slow flowing sections of the river. As no data on the biology of these two loach were found in literature, the aim of this study was to research the conditions of the loach from the Sava river. The fish were caught by electric gear on three locations in May 2006. Also, macroinvertebrates were collected and physical and chemical analyses of water were performed. Quality of water of the Sava river is sufficient for growth, reproduction and presence of C. elongata, it is less so for C. elongatoides. Macroinvertebrates are present with 10 taxa at three investigated sites. Crustacea was dominant at Medsave site, Oligochaeta at Lijevi Dubrovčak site and Diptera and Gastropoda at Setuš site. There are some differences in morphometric parameters of both species, due to the differences in the body dimensions. Main differences occurred when measuring the value of prepectoral distance, the end of prepectoral distance and preventral distance of the fin. Condition factor of C elongata was lower (0,61) than that of C. elongatoides (0,81). Length-mass relationships of C. elongata could be expressed by the following formula: W= 0,0039 * SL3,2063, and C. elongatoides W= 0,0057 * SL 3,187

Mid-infrared plasmons in scaled graphene nanostructures

Plasmonics takes advantage of the collective response of electrons to electromagnetic waves, enabling dramatic scaling of optical devices beyond the diffraction limit. Here, we demonstrate the mid-infrared (4 to 15 microns) plasmons in deeply scaled graphene nanostructures down to 50 nm, more than 100 times smaller than the on-resonance light wavelength in free space. We reveal, for the first time, the crucial damping channels of graphene plasmons via its intrinsic optical phonons and scattering from the edges. A plasmon lifetime of 20 femto-seconds and smaller is observed, when damping through the emission of an optical phonon is allowed. Furthermore, the surface polar phonons in SiO2 substrate underneath the graphene nanostructures lead to a significantly modified plasmon dispersion and damping, in contrast to a non-polar diamond-like-carbon (DLC) substrate. Much reduced damping is realized when the plasmon resonance frequencies are close to the polar phonon frequencies. Our study paves the way for applications of graphene in plasmonic waveguides, modulators and detectors in an unprecedentedly broad wavelength range from sub-terahertz to mid-infrared.Comment: submitte

Graphene-based photovoltaic cells for near-field thermal energy conversion

Thermophotovoltaic devices are energy-conversion systems generating an electric current from the thermal photons radiated by a hot body. In far field, the efficiency of these systems is limited by the thermodynamic Schockley-Queisser limit corresponding to the case where the source is a black body. On the other hand, in near field, the heat flux which can be transferred to a photovoltaic cell can be several orders of magnitude larger because of the contribution of evanescent photons. This is particularly true when the source supports surface polaritons. Unfortunately, in the infrared where these systems operate, the mismatch between the surface-mode frequency and the semiconductor gap reduces drastically the potential of this technology. Here we show that graphene-based hybrid photovoltaic cells can significantly enhance the generated power paving the way to a promising technology for an intensive production of electricity from waste heat.Comment: 5 pages, 4 figure

Tunable hybrid surface waves supported by a graphene layer

We study surface waves localized near a surface of a semi-infinite dielectric medium covered by a layer of graphene in the presence of a strong external magnetic field. We demonstrate that both TE-TM hybrid surface plasmons can propagate along the graphene surface. We analyze the effect of the Hall conductivity on the disper- sion of hybrid surface waves and suggest a possibility to tune the plasmon dispersion by the magnetic field.Comment: 3 pages, 3 figure

Real-space mapping of tailored sheet and edge plasmons in graphene nanoresonators

Plasmons in graphene nanoresonators have many potential applications in photonics and optoelectronics, including room-temperature infrared and terahertz photodetectors, sensors, reflect arrays or modulators1, 2, 3, 4, 5, 6, 7. The development of efficient devices will critically depend on precise knowledge and control of the plasmonic modes. Here, we use near-field microscopy8, 9, 10, 11 between λ0 = 10–12 μm to excite and image plasmons in tailored disk and rectangular graphene nanoresonators, and observe a rich variety of coexisting Fabry–Perot modes. Disentangling them by a theoretical analysis allows the identification of sheet and edge plasmons, the latter exhibiting mode volumes as small as 10−8λ03. By measuring the dispersion of the edge plasmons we corroborate their superior confinement compared with sheet plasmons, which among others could be applied for efficient 1D coupling of quantum emitters12. Our understanding of graphene plasmon images is a key to unprecedented in-depth analysis and verification of plasmonic functionalities in future flatland technologies.Peer ReviewedPostprint (author's final draft

Intrinsic Terahertz Plasmons and Magnetoplasmons in Large Scale Monolayer Graphene

We show that in graphene epitaxially grown on SiC the Drude absorption is transformed into a strong terahertz plasmonic peak due to natural nanoscale inhomogeneities, such as substrate terraces and wrinkles. The excitation of the plasmon modifies dramatically the magneto-optical response and in particular the Faraday rotation. This makes graphene a unique playground for plasmon-controlled magneto-optical phenomena thanks to a cyclotron mass 2 orders of magnitude smaller than in conventional plasmonic materials such as noble metals.Comment: to appear in Nano Letter

Optical Excitations and Field Enhancement in Short Graphene Nanoribbons

The optical excitations of elongated graphene nanoflakes of finite length are investigated theoretically through quantum chemistry semi-empirical approaches. The spectra and the resulting dipole fields are analyzed, accounting in full atomistic details for quantum confinement effects, which are crucial in the nanoscale regime. We find that the optical spectra of these nanostructures are dominated at low energy by excitations with strong intensity, comprised of characteristic coherent combinations of a few single-particle transitions with comparable weight. They give rise to stationary collective oscillations of the photoexcited carrier density extending throughout the flake, and to a strong dipole and field enhancement. This behavior is robust with respect to width and length variations, thus ensuring tunability in a large frequency range. The implications for nanoantennas and other nanoplasmonic applications are discussed for realistic geometries

Infrared nanoscopy of Dirac plasmons at the graphene-SiO2 interface

We report on infrared (IR) nanoscopy of 2D plasmon excitations of Dirac fermions in graphene. This is achieved by confining mid-IR radiation at the apex of a nanoscale tip: an approach yielding two orders of magnitude increase in the value of in-plane component of incident wavevector q compared to free space propagation. At these high wavevectors, the Dirac plasmon is found to dramatically enhance the near-field interaction with mid-IR surface phonons of SiO2 substrate. Our data augmented by detailed modeling establish graphene as a new medium supporting plasmonic effects that can be controlled by gate voltage.Comment: 12 pages, 4 figure