Low energy states with different symmetries in the t-J model with two holes on a 32-site lattice

We study the low energy states of the t-J model with two holes on a 32-site lattice with periodic boundary conditions. In contrary to common belief, we find that the state with d_{x^2-y^2} symmetry is not always the ground state in the realistic parameter range 0.2\le J/t\le 0.4. There exist low-lying finite-momentum p-states whose energies are lower than the d_{x^2-y^2} state when J/t is small enough. We compare various properties of these low energy states at J/t=0.3 where they are almost degenerate, and find that those properties associated with the holes (such as the hole-hole correlation and the electron momentum distribution function) are very different between the d_{x^2-y^2} and p states, while their spin properties are very similar. Finally, we demonstrate that by adding ``realistic'' terms to the t-J model Hamiltonian, we can easily destroy the d_{x^2-y^2} ground state. This casts doubt on the robustness of the d_{x^2-y^2} state as the ground state in a microscopic model for the high temperature superconductors

The hardening in alloys and composites and its examination with a diffraction and self-consistent model

The paper presents the results of diffraction stress measurement in Al/SiC composite and in 2124T6 aluminum alloy during the in situ tensile test. The main aim of the work is to observe the stress values for different stages of tensile test for the composite after applying two types of thermal treatment and for the alloy used as a matrix in this composite, to identify the type of hardening process. The experimental results were compared against the calculations results obtained from the self-consistent model developed by Baczmański [1] - [3] to gain the information about the micromechanical properties (critical resolved shear stress τ$_{cr}$ and hardening parameter H) of the examined materials. This comparison allowed researchers to determine the role of reinforcement in the composite as well as the impact of the heat treatment on the hardening of the material

A spin field effect transistor for low leakage current

In a spin field effect transistor, a magnetic field is inevitably present in the channel because of the ferromagnetic source and drain contacts. This field causes random unwanted spin precession when carriers interact with non-magnetic impurities. The randomized spins lead to a large leakage current when the transistor is in the ``off''-state, resulting in significant standby power dissipation. We can counter this effect of the magnetic field by engineering the Dresselhaus spin-orbit interaction in the channel with a backgate. For realistic device parameters, a nearly perfect cancellation is possible, which should result in a low leakage current.Comment: To appear in Physica E. The revised version has additional material which addresses the issue of which way the contacts should be magnetized in a Spin Field Effect Transistor. This was neither addressed in the previous version, nor in the upcoming journal pape

Relation between flux formation and pairing in doped antiferromagnets

We demonstrate that patterns formed by the current-current correlation function are landmarks which indicate that spin bipolarons form in doped antiferromagnets. Holes which constitute a spin bipolaron reside at opposite ends of a line (string) formed by the defects in the antiferromagnetic spin background. The string is relatively highly mobile, because the motion of a hole at its end does not raise extensively the number of defects, provided that the hole at the other end of the line follows along the same track. Appropriate coherent combinations of string states realize some irreducible representations of the point group C_4v. Creep of strings favors d- and p-wave states. Some more subtle processes decide the symmetry of pairing. The pattern of the current correlation function, that defines the structure of flux, emerges from motion of holes at string ends and coherence factors with which string states appear in the wave function of the bound state. Condensation of bipolarons and phase coherence between them puts to infinity the correlation length of the current correlation function and establishes the flux in the system.Comment: 5 pages, 6 figure

Large cell anaplastic lypmhoma versus Hodgkin's disease – difficulties in the diagnosis

AbstractDuring the last 5 years in the Polish Children's Leukemia/Lymphoma Study Group (7 centers) 241 children with Hodgkin's Disease and 14 children with Large Cell Anaplastic Lymphoma were treated.In 5 of them we had problems with differential diagnosis.Immunohistochemical tests:–CD30 positive, CD15 positive, LCA negative allowed us to change the diagnosis from Large Cell Anaplastic Lymphoma to Hodgkin's Disease (one child) and–CD30 positive, CD15 negative from Hodgkin's Disease to Large Cell Anaplastic Lymphoma (four children).All children achieved remission after changing the protocol of chemotherapy

Nonlocal resistance and its fluctuations in microstructures of band-inverted HgTe/(Hg,Cd)Te quantum wells

We investigate experimentally transport in gated microsctructures containing a band-inverted HgTe/Hg_{0.3}Cd_{0.7}Te quantum well. Measurements of nonlocal resistances using many contacts prove that in the depletion regime the current is carried by the edge channels, as expected for a two-dimensional topological insulator. However, high and non-quantized values of channel resistances show that the topological protection length (i.e. the distance on which the carriers in helical edge channels propagate without backscattering) is much shorter than the channel length, which is ~100 micrometers. The weak temperature dependence of the resistance and the presence of temperature dependent reproducible quasi-periodic resistance fluctuations can be qualitatively explained by the presence of charge puddles in the well, to which the electrons from the edge channels are tunnel-coupled.Comment: 8 pages, 4 figures, published versio

New results for the t-J model in ladders: Changes in the spin liquid state with applied magnetic field. Implications for the cuprates

Exact Diagonalization calculations are presented for the t-J model in the presence of a uniform magnetic field. Results for 2xL ladders (L=8,10,12) and 4x4 square clusters with 1 and 2 holes indicate that the diamagnetic response to a perpendicular magnetic field tends to induce a spin liquid state in the spin background. The zero-field spin liquid state of a two-leg ladder is reinforced by the magnetic field: a considerable increase of rung antiferromagnetic correlations is observed for J/t up to 0.6, for 1 and 2 holes. Pair-breaking is also clearly observed in the ladders and seems to be associated in part with changes promoted by the field in the spin correlations around the zero-field pair. In the 4x4 cluster, the numerical results seem to indicate that the field-induced spin liquid state competes with the zero-field antiferromagnetic short-range-order, the spin liquid state being favored by higher doping and smaller values of J/t. It is interesting to note that the field-effect can also be observed in a 2x2 plaquette with 1 and 2 holes. This opens up the possibility of gaining a qualitative understanding of the effect.Comment: 16 pages, 7 figures, latex New results adde

Studies of new antiferroelectric liquid crystal based on quantum-chemical model

Physical properties of new thermotropic antiferroelectric liquid crystal have been studied. Experiments were done by use of complementary methods such as differential scanning calorimetry, polarizing optical microscopy and X-ray powder diffractometry. Acquired data from X-ray powder diffractometry was examined under application of quantum chemical approach. It has been found that compound studied exhibits stable enantiotropic antiferroelectric SmC_{A}^{*} phase in the wide temperature range while ferroelectric phase SmC^{*} is very narrow

63. Raki Płaskonabłonkowe głowy i szyi u młodych dorosłych – retrospektywna wieloczynnikowa analiza oraz wstępne wyniki badań nad rolą czynnika genetycznego w ich etiopatogenezie

Celem pracy jest analiza cech klinicznych raków płaskonabłonkowych głowy i szyi u chorych poniżej 45 roku życia („young adult”) oraz ocena udziału czynnika genetycznego w ich etiopatogenezie. W ocenie klinicznej uwzględniono dane dotyczące: A.- pacjentów: wiek (średnia 40.9 lat), płeć (mężczyźni 85%, kobiety 15%) oraz ekspozycja na typowe czynniki ryzyka (palący papierosy −96.8%, spożywający alkohol −96.7%), B.- guza: lokalizacja (krtań 69%, jama ustna i gardło 28%), stopień zaawansowania klinicznego (głównie stadium IV −58.7%), typ histologiczny (ca planoepitheliale keratodes 71.2%, akeratodes 28.8%) i stopień zróżnicowania histologicznego (głownie G1+G2 −94.3%), C.- zastosowanego leczenia: metoda (głównie skojarzone: operacja + radioterapia −61.3%) oraz wyniki (wznowa miejscowa −15.9%, wznowa węzłowa −18.5%, przeżycia 3-letnie 46%, przeżycia 5-letnie 35%). W ocenie roli czynnika genetycznego zastosowano 3 techniki: genotypowanie, test bleomycynowy i test kometkowy. U 24 chorych oznaczono polimorfizm genów metabolizmu kancerogenów oraz genów związanych z naprawą DNA. Stwierdzono częstsze niż w grupie pacjentów starszych występowanie następujących genotypów ryzyka: GSTM1 (-) współwystępujący z NAT2 4/6A oraz NAT2 4/6A oraz allelu ryzyka: NAT2 4; allel ryzyka CYP 1A1 4 występował rzadziej niż w grupie starszych, natomiast częstość występowania genotypu ryzyka XPD 35931AA w obu grupach była zbliżona. U 5 pacjentów oznaczono poziom niestabilności chromosomowej za pomocą testu bleomycynowego – stwierdzono zbliżone wartości współczynnika b/c w grupie pacjentów młodszych i starszych przy jednocześnie wyraźnie większym odsetku uszkodzonych komórek w grupie młodych dorosłych. W obu grupach zarówno wartość współczynnika b/c jak i procent uszkodzonych komórek były wyrażnie większe niż w grupie osób zdrowych. W grupie 7 pacjentów za pomocą techniki comet assay określono uszkodzenia spontaniczne i indukowane oraz zdolności naprawy DNA – stwierdzono wysoki i zbliżony w grupie pacjentów młodych i starszych poziom uszkodzeń DNA – zarówno spontanicznych i indukowanych oraz zbliżone zdolności naprawy DNA

Disorder suppression and precise conductance quantization in constrictions of PbTe quantum wells

Conductance quantization was measured in submicron constrictions of PbTe, patterned into narrow,12 nm wide quantum wells deposited between Pb$_{0.92}$Eu$_{0.08}$Te barriers. Because the quantum confinement imposed by the barriers is much stronger than the lateral one, the one-dimensional electron energy level structure is very similar to that usually met in constrictions of AlGaAs/GaAs heterostructures. However, in contrast to any other system studied so far, we observe precise conductance quantization in $2e^2/h$ units, {\it despite of significant amount of charged defects in the vicinity of the constriction}. We show that such extraordinary results is a consequence of the paraelectric properties of PbTe, namely, the suppression of long-range tails of the Coulomb potentials due to the huge dielectric constant.Comment: 7 pages, 6 figures, submitted to Phys. Rev.