Search results for "MT"
showing 10 items of 2759 documents
Cross-sublattice Spin Pumping and Magnon Level Attraction in van der Waals Antiferromagnets
2020
We theoretically study spin pumping from a layered van der Waals antiferromagnet in its canted ground state into an adjacent normal metal. We find that the resulting dc spin pumping current bears contributions along all spin directions. Our analysis allows for detecting intra- and cross-sublattice spin-mixing conductances via measuring the two in-plane spin current components. We further show that sublattice symmetry-breaking Gilbert damping can be realized via interface engineering and induces a dissipative coupling between the optical and acoustic magnon modes. This realizes magnon level attraction and exceptional points in the system. Furthermore, the dissipative coupling and cross-subla…
Orbital Rotations induced by Charges of Polarons and Defects in Doped Vanadates
2020
We explore the competiton of doped holes and defects that leads to the loss of orbital order in vanadate perovskites. In compounds such as La$_{1-{\sf x}}$Ca$_{\,\sf x}$VO$_3$ spin and orbital order result from super-exchange interactions described by an extended three-orbital degenerate Hubbard-Hund model for the vanadium $t_{2g}$ electrons. Long-range Coulomb potentials of charged Ca$^{2+}$ defects and $e$-$e$ interactions control the emergence of defect states inside the Mott gap. The quadrupolar components of the Coulomb fields of doped holes induce anisotropic orbital rotations of degenerate orbitals. These rotations modify the spin-orbital polaron clouds and compete with orbital rotat…
Magnetic and electronic properties of double perovskites and estimation of their Curie temperatures byab initiocalculations
2008
First principles electronic structure calculations have been carried out on ordered double perovskites Sr_2B'B"O_6 (for B' = Cr or Fe and B" 4d and 5d transition metal elements) with increasing number of valence electrons at the B-sites, and on Ba_2MnReO_6 as well as Ba_2FeMoO_6. The Curie temperatures are estimated ab initio from the electronic structures obtained with the local spin-density functional approximation, full-potential generalized gradient approximation and/or the LDA+U method (U - Hubbard parameter). Frozen spin-spirals are used to model the excited states needed to evaluate the spherical approximation for the Curie temperatures. In cases, where the induced moments on the oxy…
Quantum Phases and Spin Liquid Properties of 1T-TaS2
2021
Quantum materials exhibiting magnetic frustration are connected to diverse phenomena including high-Tc superconductivity, topological order and quantum spin liquids (QSLs). A QSL is a quantum phase (QP) related to a quantum-entangled fluid-like state of matter. Previous experiments on QSL candidate materials are usually interpreted in terms of a single QP, although theories indicate that many distinct QPs are closely competing in typical frustrated spin models. Here we report on combined temperature-dependent muon spin relaxation and specific heat measurements for the triangular-lattice QSL candidate material 1T-TaS2 that provide evidence for competing QPs. The measured properties are assig…
Defects, Disorder, and Strong Electron Correlations in Orbital Degenerate, Doped Mott Insulators.
2015
We elucidate the effects of defect disorder and $e$-$e$ interaction on the spectral density of the defect states emerging in the Mott-Hubbard gap of doped transition-metal oxides, such as Y$_{1-x}$Ca$_{x}$VO$_{3}$. A soft gap of kinetic origin develops in the defect band and survives defect disorder for $e$-$e$ interaction strengths comparable to the defect potential and hopping integral values above a doping dependent threshold, otherwise only a pseudogap persists. These two regimes naturally emerge in the statistical distribution of gaps among different defect realizations, which turns out to be of Weibull type. Its shape parameter $k$ determines the exponent of the power-law dependence o…
Optimized substrates and measurement approaches for Raman spectroscopy of graphene nanoribbons
2019
The on-surface synthesis of graphene nanoribbons (GNRs) allows for the fabrication of atomically precise narrow GNRs. Despite their exceptional properties which can be tuned by ribbon width and edge structure, significant challenges remain for GNR processing and characterization. In this contribution, we use Raman spectroscopy to characterize different types of GNRs on their growth substrate and to track their quality upon substrate transfer. We present a Raman-optimized (RO) device substrate and an optimized mapping approach that allows for acquisition of high-resolution Raman spectra, achieving enhancement factors as high as 120 with respect to signals measured on standard SiO2/Si substra…
Mode cleaning in graphene oxide-doped polymeric whispering gallery mode microresonators
2020
The strategy to incorporate graphene oxide (GO) in a composite material offers significant opportunities to realize compact photonic devices, such as saturable absorbers and polarization selective devices. However, the processing of GO-based composites by direct laser writing, which would afford vast patterning and material flexibility in a single step process, has been little addressed. In this work, we investigated the mechanisms underlying a mode cleaning effect in polymeric whispering gallery mode microresonators containing GO, aiming at the development of on-chip integrable photonic devices. We fabricated the microresonators (cavity loaded Q-factor of 20 000 at 1550 nm) in a single ste…
Growth of two-dimensional Au patches in graphene pores: A density-functional study
2017
Inspired by recent studies of various two-dimensional (2D) metals such as Au, Fe and Ag, we study the growth of two-dimensional gold patches in graphene pores by density-functional theory. We find that at room temperature gold atoms diffuse readily on top of both graphene and two-dimensional gold with energy barriers less than $0.5$ eV. Furthermore, gold atoms move without barriers from the top of graphene to its edge and from the top of 2D gold to its edge. The energy barriers are absent even at the interface of 2D gold and graphene, so that the gold atoms move effortlessly across the interface. We hope our demonstration for the propensity of diffusing gold atoms to grow 2D gold patches in…
Latvijas valsts simtgades svinības: dienas kārtība Latvijas simtgades biroja "Facebook" lapā "LV100" (2017. gada janvāris - 2018. gada marts)
2018
Bakalaura darba nosaukums ir “Latvijas valsts simtgades svinības: dienas kārtība Latvijas simtgades biroja "Facebook" lapā "LV100" (2017. gada janvāris - 2018. gada marts)”. Pētījuma mērķis ir noskaidrot, kuri komunikācijas temati un to aspekti veido prioritāšu sarakstu Latvijas valsts simtgades biroja “Facebook” lapas «LV100» dienas kārtībā no 2017.gada janvāra līdz 2018.gada martam, kā veidota «Facebook» lapas pirmā un otrā līmeņa dienas kārtība un kāda ir «LV100» dienas kārtības ietekme un mijiedarbība ar lietotāju. Darba teorētisko pamatu veido Maksvela Makkomba (Maxwell McCombs) un Donalda Šava (Donald Shaw) pirmā un otrā līmeņa dienas kārtības teorija, kā arī teorētiskais apskats par …
MicroRNAs Associated With Biological Pathways of Left- and Right-sided Colorectal Cancer.
2020
BACKGROUND/AIM MicroRNAs (miRNAs) regulate the development of colorectal cancer (CRC). We aimed to investigate miRNAs and their relation to cancer-related signaling pathways in site-specific CRC. MATERIALS AND METHODS We used a total of 24 left- and right-sided Finnish CRC samples (discovery cohort) and The Cancer Genome Atlas public mature miRSeq dataset of 201 CRC samples (validation cohort). MiRNA differential expression and biological pathway analyses were performed using DESeq2 and the DIANA/mirPath tool, respectively. RESULTS We found 17 significantly differentially up-regulated [false discovery rate (FDR) <0.05] miRNAs in left-sided CRC ("left miRNAs"), and 15 in right-sided CRC ("ri…