Spatially-modulated Superfluid States in Fermionic Optical Ladder Systems with Repulsive Interactions

We investigate two-component ultracold fermionic atoms with repulsive interactions trapped in an optical lattice with a ladder structure. By applying the Bogoliubov-de Gennes equations to an effective t-J model in the strong correlation limit, we discuss how the spatially-modulated spin-singlet pairs with d-wave like symmetry are formed in the systems with trapping potentials. Furthermore, a close examination of the condensation energy as well as the local average of potential, kinetic and exchange energies by means of the variational Monte Carlo method elucidates that local particle correlations enhance the stability of the superfluid state via substantial energy gain due to singlet pairing in the high particle density region.Comment: 8 pages, 5 figure

Low temperature properties of the infinite-dimensional attractive Hubbard model

We investigate the attractive Hubbard model in infinite spatial dimensions by combining dynamical mean-field theory with a strong-coupling continuous-time quantum Monte Carlo method. By calculating the superfluid order parameter and the density of states, we discuss the stability of the superfluid state. In the intermediate coupling region above the critical temperature, the density of states exhibits a heavy fermion behavior with a quasi-particle peak in the dense system, while a dip structure appears in the dilute system. The formation of the superfluid gap is also addressed.Comment: 8 pages, 9 figure

Competition between Spin-Orbit Interaction and Zeeman Coupling in Rashba 2DEGs

We investigate systematically how the interplay between Rashba spin-orbit interaction and Zeeman coupling affects the electron transport and the spin dynamics in InGaAs-based 2D electron gases. From the quantitative analysis of the magnetoconductance, measured in the presence of an in-plane magnetic field, we conclude that this interplay results in a spin-induced breaking of time reversal symmetry and in an enhancement of the spin relaxation time. Both effects, due to a partial alignment of the electron spin along the applied magnetic field, are found to be in excellent agreement with recent theoretical predictions.Comment: 4 figures and 4 page

Spin, charge and orbital fluctuations in a multi-orbital Mott insulator

The two-orbital degenerate Hubbard model with distinct hopping integrals is studied by combining dynamical mean-field theory with quantum Monte Carlo simulations. The role of orbital fluctuations for the nature of the Mott transition is elucidated by examining the temperature dependence of spin, charge and orbital susceptibilities as well as the one-particle spectral function. We also consider the effect of the hybridization between the two orbitals, which is important particularly close to the Mott transition points. The introduction of the hybridization induces orbital fluctuations, resulting in the formation of a Kondo-like heavy-fermion behavior, similarly to $f$ electron systems, but involving electrons in bands of comparable width.Comment: 8 pages, 9 figure

Venäjänkielisten lasten äidinkielen tukeminen varhaiskasvatuksessa

Toiminnallinen opinnäytetyön tarkoitus on tukea venäläisten lasten äidinkielen kehittymistä. Tekijän oma äidinkieli on myös venäjä. Toiminnallisen osan menetelmänä käytin kerhoa nimellä Sadun parissa, jonka pohjana oli lasten kirjallisuus. Tuokiot toteutuivat lapsiryhmässä, jossa oli viisi kuusivuotiaita lasta. Kerhon tavoitteena oli rohkaista lapsia puhumaan äidinkieltä ja saada lapsia kiinnostumaan lasten kirjallisuudesta. Opinnäytetyön tietoperusta muodostaa viitekehityksen toteutukselle. Se auttaa lukijaa ymmärtämään äidinkielen merkitys maahanmuuttajille ja lasten äidinkielen tukemisen tärkeyttä. Teoriatausta käsittelee kielen keskeinen merkitystä ja sen yhteyttä kulttuuriin, maahanmuuttajataustaisten lasten kielikasvatusta varhaiskasvatuksessa ja kasvattajan roolia äidinkielen tukemisessa. Opinnäytetyöni onnistui hyvin. Lapset osallistuivat toimintaan innokkaasti. Sain hyviä palautteita vanhemmilta ja lastentarhanopettajalta, joita kertoivat lasten ja vanhempien tyytyväisyydestä kerhon toiminnastaЦелью дипломной работы является поддержка развития родного языка русскоязычных детей. Родной язык автора тоже русский. Практической частью работы является кружок В гостях у сказки, за основу которого взята детская литература. Занятия проводились с группой детей, в которой пять шестилеток. Целью кружка было поощрение общения на родном языке, а также пробуждение у детей интереса к детской литературе. Теоретическая часть работы представляет собой основу для выполнения практической части. Теория помогает читателю понять значение родного языка для иммигрантов и значимость поддержки родного языка ребенка. Tеоретическая часть содержит следующие понятия: общее значение языка и его связь с культурой, дошкольное языковое воспитание детей иммигрантов и роль воспитателя в поддержке родного языка. Практическая часть работы удалась хорошо. Дети принимали участие в деятельности кружка с воодушевлением. Я получила хорошие отзывы от родителей и воспитателя детского сада, которые говорят об удовлетворенности детей и их родителей деятельностью кружк

Anti-crossings of spin-split Landau levels in an InAs two-dimensional electron gas with spin-orbit coupling

We report tilted-field transport measurements in the quantum-Hall regime in an InAs/In_0.75Ga_0.25As/In_0.75Al_0.25As quantum well. We observe anti-crossings of spin-split Landau levels, which suggest a mixing of spin states at Landau level coincidence. We propose that the level repulsion is due to the presence of spin-orbit and of band-non-parabolicity terms which are relevant in narrow-gap systems. Furthermore, electron-electron interaction is significant in our structure, as demonstrated by the large values of the interaction-induced enhancement of the electronic g-factor.Comment: 4 pages, 3 figure

Statistical significance of fine structure in the frequency spectrum of Aharonov-Bohm conductance oscillations

We discuss a statistical analysis of Aharonov-Bohm conductance oscillations measured in a two-dimensional ring, in the presence of Rashba spin-orbit interaction. Measurements performed at different values of gate voltage are used to calculate the ensemble-averaged modulus of the Fourier spectrum and, at each frequency, the standard deviation associated to the average. This allows us to prove the statistical significance of a splitting that we observe in the h/e peak of the averaged spectrum. Our work illustrates in detail the role of sample specific effects on the frequency spectrum of Aharonov-Bohm conductance oscillations and it demonstrates how fine structures of a different physical origin can be discriminated from sample specific features.Comment: accepted for publication in PR

Finite-temperature Mott transitions in multi-orbital Hubbard model

We investigate the Mott transitions in the multi-orbital Hubbard model at half-filling by means of the self-energy functional approach. The phase diagrams are obtained at finite temperatures for the Hubbard model with up to four-fold degenerate bands. We discuss how the first-order Mott transition points $U_{c1}$ and $U_{c2}$ as well as the critical temperature $T_c$ depend on the orbital degeneracy. It is elucidated that enhanced orbital fluctuations play a key role to control the Mott transitions in the multi-orbital Hubbard model.Comment: 8 pages, 7 figure

Orbital-selective Mott transitions in the anisotropic two-band Hubbard model at finite temperatures

The anisotropic degenerate two-orbital Hubbard model is studied within dynamical mean-field theory at low temperatures. High-precision calculations on the basis of a refined quantum Monte Carlo (QMC) method reveal that two distinct orbital-selective Mott transitions occur for a bandwidth ratio of 2 even in the absence of spin-flip contributions to the Hund exchange. The second transition -- not seen in earlier studies using QMC, iterative perturbation theory, and exact diagonalization -- is clearly exposed in a low-frequency analysis of the self-energy and in local spectra.Comment: 4 pages, 5 figure

Orbital-selective Mott transitions in the degenerate Hubbard model

We investigate the Mott transitions in two-band Hubbard models with different bandwidths. Applying dynamical mean field theory, we discuss the stability of itinerant quasi-particle states in each band. We demonstrate that separate Mott transitions occur at different Coulomb interaction strengths in general, which merge to a single transition only under special conditions. This kind of behavior may be relevant for the physics of the single-layer ruthenates, Ca$_{2-x}$Sr$_x$RuO$_4$.Comment: 4 pages, 4 figure