Instability of a gapless color superconductor with respect to inhomogeneous fluctuations

We systematically apply density functional theory to determine the kind of inhomogeneities that spontaneously develop in a homogeneous gapless phase of neutral two-flavor superfluid quark matter. We consider inhomogeneities in the quark and electron densities and in the phases and amplitude of the order parameter. These inhomogeneities are expected to lead the gapless phase to a BCS-normal coexisting phase, a Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) state with phase oscillations alone, and a LOFF state with amplitude oscillations. We find that which of them the homogeneous system tends towards depends sensitively on the chemical potential separation between up and down quarks and the gradient energies.Comment: 15 pages, 3 figures; corrected Eq. (36) and changed content associated with d quark clustering instabilit

Thermal fluctuations of gauge fields and first order phase transitions in color superconductivity

We study the effects of thermal fluctuations of gluons and the diquark pairing field on the superconducting-to-normal state phase transition in a three-flavor color superconductor, using the Ginzburg-Landau free energy. At high baryon densities, where the system is a type I superconductor, gluonic fluctuations, which dominate over diquark fluctuations, induce a cubic term in the Ginzburg-Landau free energy, as well as large corrections to quadratic and quartic terms of the order parameter. The cubic term leads to a relatively strong first order transition, in contrast with the very weak first order transitions in metallic type I superconductors. The strength of the first order transition decreases with increasing baryon density. In addition gluonic fluctuations lower the critical temperature of the first order transition. We derive explicit formulas for the critical temperature and the discontinuity of the order parameter at the critical point. The validity of the first order transition obtained in the one-loop approximation is also examined by estimating the size of the critical region.Comment: 12 pages, 4 figures, final version published in Phys. Rev.

Doping and critical-temperature dependence of the energy gaps in Ba(Fe_{1-x}Co_x)_2As_2 thin films

The dependence of the superconducting gaps in epitaxial Ba(Fe_{1-x}Co_{x})_2As_2 thin films on the nominal doping x (0.04 \leq x \leq 0.15) was studied by means of point-contact Andreev-reflection spectroscopy. The normalized conductance curves were well fitted by using the 2D Blonder-Tinkham-Klapwijk model with two nodeless, isotropic gaps -- although the possible presence of gap anisotropies cannot be completely excluded. The amplitudes of the two gaps \Delta_{S} and \Delta_{L} show similar monotonic trends as a function of the local critical temperature T_{c}^{A} (measured in the same point contacts) from 25 K down to 8 K. The dependence of the gaps on x is well correlated to the trend of the critical temperature, i.e. to the shape of the superconducting region in the phase diagram. When analyzed within a simple three-band Eliashberg model, this trend turns out to be compatible with a mechanism of superconducting coupling mediated by spin fluctuations, whose characteristic energy scales with T_{c} according to the empirical law \Omega_{0}= 4.65*k_{B}*T_{c}, and with a total electron-boson coupling strength \lambda_{tot}= 2.22 for x \leq 0.10 (i.e. up to optimal doping) that slightly decreases to \lambda_{tot}= 1.82 in the overdoped samples (x = 0.15).Comment: 8 pages, 5 color figure

Student voices on multiculturality:a qualitative study with fifth and sixth graders in two finnish classrooms

Abstract. This thesis examines student voice on multiculturality in a qualitative study through the voices of students from two Finnish classrooms of fifth and sixth graders. The missing perspective of students and children in educational research on multiculturality motivated us to set out to answer the research questions of “How do students perceive multicultural situations?” and “What observations do students have about multiculturality in Finnish schools?. Our aim is to give a voice to the ones who experience and perceive the implementation of multicultural education in schools firsthand. Student voice offers a unique view of education and should be given the space to bring forth student ideas and opinions in assessing, evaluating, and developing multicultural education. Multicultural education in this thesis is examined from a critical perspective as education that aims for equity. By using vignette stories and a written task, the participants expressed their perceptions and observations related to multiculturality, which were then analyzed using the method of qualitative content analysis. It was discovered that students perceive multicultural situations through compassionate feelings, through a sense of justice, and perceive the effects of one’s cultural background in these situations. The participant’s observations of their own schools showed that the students observed diversity in their schools and classrooms to be related to language, nationality, and other visible diversity, such as one’s skin color. The students also observed multiculturality in the actions of the school through discussions of diversity, use of languages, and the values of acceptance, equality, and respect. The findings of our thesis illustrate the need for listening and giving a platform to student voice on educational issues. Through the analysis, we found that the data received from the students provided significant viewpoints to begin a larger discussion on insights student voice can offer to research on multicultural education.Oppilaiden näkemyksiä monikulttuurisuudesta : kvalitatiivinen tutkimus suomalaisen viides- ja kuudesluokan kanssa. Tiivistelmä. Tämä kvalitatiivinen pro-gradu tutkielma pyrkii nostamaan esiin oppilaiden äänen monikulttuurisuutta tutkittaessa. Tutkielma toteutettiin kahdessa suomalaisessa luokassa viides- ja kuudesluokkalaisten kanssa. Aiempi kasvatustieteellinen tutkimus ei ole juurikaan huomioinut oppilaiden näkökulmaa monikulttuurisuudesta, mikä motivoi meitä etsimään vastauksia tutkimuskysymyksiimme: ”Kuinka oppilaat käsittävät monikulttuurisia tilanteita?” sekä ”Minkälaisia havaintoja oppilailla on monikulttuurisuudesta suomalaisissa kouluissa?”. Tavoitteenamme on antaa ääni niille henkilöille, jotka ensisijaisesti kokevat ja havaitsevat monikulttuurisuuskasvatuksen toteutuksen kouluissa. Oppilaan ääni tarjoaa uniikin näkökulman kasvatukseen, ja sille tulisi antaa tilaa arvioitaessa ja kehitettäessä monikulttuurisuuskasvatusta koulussa. Monikulttuurisuuskasvatusta käsitellään tässä tutkielmassa kriittisestä näkökulmasta kasvatuksena, joka tavoittelee oikeudenmukaisuutta. Tutkimuksen aineisto koostuu oppilaiden kirjoitelmista. Tutkimukseen osallistuville oppilaille annettiin kuvauksia erilaisista koulun monikulttuurisista tilanteista. Näiden kuvasten pohjalta osallistujat kirjoittivat käsityksistään ja näkemyksistään monikulttuurisuudesta. Vastaukset analysoitiin kvalitatiivisen sisällönanalyysin keinoin. Tulokset osoittavat, että oppilaat liittävät monikulttuurisiin tilanteisiin myötätunnon, oikeudenmukaisuuden sekä kulttuuritaustan merkityksiä. Osallistujien havainnot heidän omista kouluistaan osoittivat, että oppilaat havaitsivat kouluissaan moninaisuutta kielen, kansallisuuden sekä muun näkyvän moninaisuuden, kuten ihon värin kautta. Oppilaat havaitsivat monikulttuurisuutta myös heidän koulujensa käytänteissä, kuten keskusteluissa moninaisuudesta, kielten käytössä sekä koulun arvoissa. Tutkimuksen tulokset kuvaavat tarvetta kuunnella oppilaita ja antaa tilaa oppilaan äänille monikulttuurisuuskasvatuksessa. Analyysin myötä havaitsimme oppilailta saadun aineiston tuovan ilmi näkökantoja, jotka ovat merkityksellisiä käynnistettäessä keskustelua oppilaiden äänestä monikulttuurisuuskasvatuksessa

Resistivity in Co-doped Ba-122: comparison of thin films and single crystals

The temperature dependence of the resistivity of epitaxial Ba(Fe_(1-x)Co_x)2As2 thin films (with nominal doping x = 0.08, 0.10 and 0.15) has been analyzed and compared with analogous measurements on single crystals taken from literature. The rho(T) of thin films looks different from that of single crystals, even when the cobalt content is the same. All rho(T) curves can be fitted by considering an effective two-band model (with holes and electrons bands) in which the electrons are more strongly coupled with the bosons (spin fluctuations) than holes, while the effect of impurities is mainly concentrated in the hole band. Within this model the mediating boson has the same characteristic energy in single crystals and thin films, but the shape of the transport spectral function at low energy has to be very different, leading to a "hardening" of the electron-boson spectral function in thin films, associated with the strain induced by the substrate.Comment: 13 pages, 4 figure