1,106 research outputs found
Nanoscale spin-polarization in dilute magnetic semiconductor (In,Mn)Sb
Results of point contact Andreev reflection (PCAR) experiments on (In,Mn)Sb
are presented and analyzed in terms of current models of charge conversion at a
superconductor-ferromagnet interface. We investigate the influence of surface
transparency, and study the crossover from ballistic to diffusive transport
regime as contact size is varied. Application of a Nb tip to a (In,Mn)Sb sample
with Curie temperature Tc of 5.4 K allowed the determination of
spin-polarization when the ferromagnetic phase transition temperature is
crossed. We find a striking difference between the temperature dependence of
the local spin polarization and of the macroscopic magnetization, and
demonstrate that nanoscale clusters with magnetization close to the saturated
value are present even well above the magnetic phase transition temperature.Comment: 4 page
Engineering of spin-lattice relaxation dynamics by digital growth of diluted magnetic semiconductor CdMnTe
The technological concept of "digital alloying" offered by molecular-beam
epitaxy is demonstrated to be a very effective tool for tailoring static and
dynamic magnetic properties of diluted magnetic semiconductors. Compared to
common "disordered alloys" with the same Mn concentration, the spin-lattice
relaxation dynamics of magnetic Mn ions has been accelerated by an order of
magnitude in (Cd,Mn)Te digital alloys, without any noticeable change in the
giant Zeeman spin splitting of excitonic states, i.e. without effect on the
static magnetization. The strong sensitivity of the magnetization dynamics to
clustering of the Mn ions opens a new degree of freedom for spin engineering.Comment: 9 pages, 3 figure
Evidence for Charging Effects in CdTe/CdMgTe Quantum Point Contacts
Here we report on fabrication and low temperature magnetotransport
measurements of quantum point contacts patterned from a novel two-dimensional
electron system - CdTe/CdMgTe modulation doped heterostructure. From the
temperature and bias dependence we ascribe the reported data to evidence for a
weakly bound state which is naturally formed inside a CdTe quantum
constrictions due to charging effects. We argue that the spontaneous
introduction of an open dot is responsible for the replacement of flat
conductance plateaus by quasi-periodic resonances with amplitude less than
2e^{2}/h, as found in our system. Additionally, below 1 K a pattern of weaker
conductance peaks, superimposed upon wider resonances, is also observed.Comment: 4 pages, 4 figure
Interacting many-body systems in quantum wells: Evidence for exciton-trion-electron correlations
We report on the nonlinear optical dynamical properties of excitonic
complexes in CdTe modulation-doped quantum wells, due to many-body interactions
among excitons, trions and electrons. These were studied by time and spectrally
resolved pump-probe experiments. The results reveal that the nonlinearities
induced by trions differ from those induced by excitons, and in addition they
are mutually correlated. We propose that the main source of these subtle
differences comes from the Pauli exclusion-principle through phase-space
filling and short-range fermion exchange.Comment: 5 pages, 4 figures. accepted for publications in Phys. Rev.
BeWith: A Between-Within Method to Discover Relationships between Cancer Modules via Integrated Analysis of Mutual Exclusivity, Co-occurrence and Functional Interactions
The analysis of the mutational landscape of cancer, including mutual
exclusivity and co-occurrence of mutations, has been instrumental in studying
the disease. We hypothesized that exploring the interplay between
co-occurrence, mutual exclusivity, and functional interactions between genes
will further improve our understanding of the disease and help to uncover new
relations between cancer driving genes and pathways. To this end, we designed a
general framework, BeWith, for identifying modules with different combinations
of mutation and interaction patterns. We focused on three different settings of
the BeWith schema: (i) BeME-WithFun in which the relations between modules are
enriched with mutual exclusivity while genes within each module are
functionally related; (ii) BeME-WithCo which combines mutual exclusivity
between modules with co-occurrence within modules; and (iii) BeCo-WithMEFun
which ensures co-occurrence between modules while the within module relations
combine mutual exclusivity and functional interactions. We formulated the
BeWith framework using Integer Linear Programming (ILP), enabling us to find
optimally scoring sets of modules. Our results demonstrate the utility of
BeWith in providing novel information about mutational patterns, driver genes,
and pathways. In particular, BeME-WithFun helped identify functionally coherent
modules that might be relevant for cancer progression. In addition to finding
previously well-known drivers, the identified modules pointed to the importance
of the interaction between NCOR and NCOA3 in breast cancer. Additionally, an
application of the BeME-WithCo setting revealed that gene groups differ with
respect to their vulnerability to different mutagenic processes, and helped us
to uncover pairs of genes with potentially synergetic effects, including a
potential synergy between mutations in TP53 and metastasis related DCC gene
Spin diffusion in the Mn2+ ion system of II-VI diluted magnetic semiconductor heterostructures
The magnetization dynamics in diluted magnetic semiconductor heterostructures
based on (Zn,Mn)Se and (Cd,Mn)Te has been studied experimentally by optical
methods and simulated numerically. In the samples with nonhomogeneous magnetic
ion distribution this dynamics is contributed by spin-lattice relaxation and
spin diffusion in the Mn spin system. The spin diffusion coefficient of
7x10^(-8) cm^2/s has been evaluated for Zn(0.99)Mn(0.01)Se from comparison of
experimental and numerical results. Calculations of the giant Zeeman splitting
of the exciton states and the magnetization dynamics in the ordered alloys and
parabolic quantum wells fabricated by the digital growth technique show perfect
agreement with the experimental data. In both structure types the spin
diffusion has an essential contribution to the magnetization dynamics.Comment: 12 pages, 11 figure
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