28 research outputs found
Kubo formula for Floquet states and photoconductivity oscillations in a 2D electron gas
The recent discovery of the microwave induced vanishing resistance states in
a two dimensional electron system (2DES) is an unexpected and surprising
phenomena. In these experiments the magnetoresistance of a high mobility 2DES
under the influence of microwave radiation of frequency at moderate
values of the magnetic field, exhibits strong oscillations with zero-resistance
states (ZRS) governed by the ratio , where is the
cyclotron frequency. In this work we present a model for the photoconductivity
of a two dimensional electron system (2DES) subjected to a magnetic field. The
model includes the microwave and Landau contributions in a non-perturbative
exact way, impurity scattering effects are treated perturbatively. In our
model, the Landau-Floquet states act coherently with respect to the oscillating
field of the impurities, that in turn induces transitions between these levels.
Based on this formalism, we provide a Kubo-like formula that takes into account
the oscillatory Floquet structure of the problem. We study the effects of both
short-range and long-range disorder on the photoconductivity. Our calculation
yields a magnetoresistance oscillatory behavior with the correct period and
phase. It is found that, in agreement with experiment, negative dissipation can
only be induced in very high mobility samples. We analyze the dependence of the
results on the microwave power and polarization. For high-intensity radiation
multi-photon processes take place predicting new negative-resistance states
centered at , and .Comment: Final version, accepted for publication in Phys. Rev.
Preclinical efficacy of azacitidine and venetoclax for infant KMT2A-rearranged acute lymphoblastic leukemia reveals a new therapeutic strategy
Infants with KMT2A-rearranged B-cell acute lymphoblastic leukemia (ALL) have a dismal prognosis. Survival outcomes have remained static in recent decades despite treatment intensification and novel therapies are urgently required. KMT2A-rearranged infant ALL cells are characterized by an abundance of promoter hypermethylation and exhibit high BCL-2 expression, highlighting potential for therapeutic targeting. Here, we show that hypomethylating agents exhibit in vitro additivity when combined with most conventional chemotherapeutic agents. However, in a subset of samples an antagonistic effect was seen between several agents. This was most evident when hypomethylating agents were combined with methotrexate, with upregulation of ATP-binding cassette transporters identified as a potential mechanism. Single agent treatment with azacitidine and decitabine significantly prolonged in vivo survival in KMT2A-rearranged infant ALL xenografts. Treatment of KMT2A-rearranged infant ALL cell lines with azacitidine and decitabine led to differential genome-wide DNA methylation, changes in gene expression and thermal proteome profiling revealed the target protein-binding landscape of these agents. The selective BCL-2 inhibitor, venetoclax, exhibited in vitro additivity in combination with hypomethylating or conventional chemotherapeutic agents. The addition of venetoclax to azacitidine resulted in a significant in vivo survival advantage indicating the therapeutic potential of this combination to improve outcome for infants with KMT2A-rearranged ALL
Electron-nuclear coherent spin oscillations probed by spin-dependent recombination
International audienceWe demonstrate the triggering and detection of coherent electron-nuclear spin oscillations related to the hyperfine interaction in Ga deep paramagnetic centers in GaAsN by band-to-band photoluminescence without an external magnetic field. In contrast to other point defects such as Cr4+ in SiC, Ce3+ in yttrium aluminum garnet crystals, nitrogen-vacancy centers in diamond, and P atoms in silicon, the bound-electron spin in Ga centers is not directly coupled to the electromagnetic field via the spin-orbit interaction. However, this apparent drawback can be turned into an advantage by exploiting the spin-selective capture of conduction band electrons to the Ga centers. On the basis of a pump-probe photoluminescence experiment we measure directly in the temporal domain the hyperfine constant of an electron coupled to a gallium defect in GaAsN by tracing the dynamical behavior of the conduction electron spin-dependent recombination to the defect site. The hyperfine constants and the relative abundance of the nuclei isotopes involved can be determined without the need of an electron spin resonance technique and in the absence of any magnetic field. Information on the nuclear and electron spin relaxation damping parameters can also be estimated from the oscillation amplitude decay and the long-time-delay behavior
Electron-nuclear coherent spin oscillations probed by spin-dependent recombination
International audienceWe demonstrate the triggering and detection of coherent electron-nuclear spin oscillations related to the hyperfine interaction in Ga deep paramagnetic centers in GaAsN by band-to-band photoluminescence without an external magnetic field. In contrast to other point defects such as Cr4+ in SiC, Ce3+ in yttrium aluminum garnet crystals, nitrogen-vacancy centers in diamond, and P atoms in silicon, the bound-electron spin in Ga centers is not directly coupled to the electromagnetic field via the spin-orbit interaction. However, this apparent drawback can be turned into an advantage by exploiting the spin-selective capture of conduction band electrons to the Ga centers. On the basis of a pump-probe photoluminescence experiment we measure directly in the temporal domain the hyperfine constant of an electron coupled to a gallium defect in GaAsN by tracing the dynamical behavior of the conduction electron spin-dependent recombination to the defect site. The hyperfine constants and the relative abundance of the nuclei isotopes involved can be determined without the need of an electron spin resonance technique and in the absence of any magnetic field. Information on the nuclear and electron spin relaxation damping parameters can also be estimated from the oscillation amplitude decay and the long-time-delay behavior