Inherited mtDNA diseases transmit maternally and cause severe phenotypes. Currently, there is no effective therapy or genetic screens for these diseases; however, nuclear genome transfer between patients' and healthy eggs to replace mutant mtDNAs holds promises. Considering that a polar body contains few mitochondria and shares the same genomic material as an oocyte, we perform polar body transfer to prevent the transmission of mtDNA variants. We compare the effects of different types of germline genome transfer, including spindle-chromosome transfer, pronuclear transfer, and first and second polar body transfer, in mice. Reconstructed embryos support normal fertilization and produce live offspring. Importantly, genetic analysis confirms that the F1 generation from polar body transfer possesses minimal donor mtDNA carryover compared to the F1 generation from other procedures. Moreover, the mtDNA genotype remains stable in F2 progeny after polar body transfer. Our preclinical model demonstrates polar body transfer has great potential to prevent inherited mtDNA diseases.

Neutron scattering results are presented for spin-wave excitations of three ferromagnetic metallic A1−xA ′ x MnO3 manganites (where A and A ′ are rare-and alkaline-earth ions), which when combined with previous work elucidate the systematics of the interactions as a function of carrier concentration x, on-site disorder, and strength of the lattice distortion. The long wavelength spin dynamics show only a very weak dependence across the series. The ratio of fourth to first neighbor exchange (J4/J1) that controls the zone boundary magnon softening changes systematically with x, but does not depend on the other parameters. None of the prevailing models can account for these behaviors.Determining the evolution of the elementary magnetic excitations in A 1−x A ′ x MnO 3 (where A and A ′ are rareand alkaline-earth ions respectively) is the first step in understanding the magnetic interactions in these doped perovskite manganites. According to the conventional double-exchange (DE) mechanism [1], the motion of charge carriers in the metallic state of A 1−x A ′ x MnO 3 establishes a ferromagnetic (FM) interaction between spins on adjacent Mn 3+ and Mn 4+ sites. In the strong Hundcoupling limit, spin-wave excitations of a DE ferromagnet below the Curie temperature T C can be described by a Heisenberg Hamiltonian with only the nearest neighbor exchange coupling [2]. At the long wavelength (small wavevector q), spin-wave stiffness D measures the average kinetic energy of charge carriers and therefore should increase with increasing x [2, 3]. While spin dynamics of some manganites initially studied appeared to follow these predictions [4,5], later measurements revealed anomalous zone boundary magnon softening deviating from the nearest neighbor Heisenberg Hamiltonian for other materials with x ∼ 0.3 [6,7,8,9,10]. Three classes of models have been proposed to explain the origin of such deviations. The first is based on the DE mechanism, considering the effect of the on-site Coulomb repulsion [3] or the conducting electron band (e g ) filling dependence of the DE and superexchange interactions [11]. The second suggests that magnon-phonon coupling [8,12] or the effects of disorder on the spin excitations of DE systems [13] is the origin for the zone boundary magnon softening. Finally, quantum fluctuations of the planar (x 2 −y 2 )-type orbital associated with the A-type antiferromagnetic (AF) ordering may induce magnon softening as the precursor of such AF order [14]. Although all these models appear to be reasonable in explaining the zone boundary magnon softening near x = 0.3, the lack of complete spinwave dispersion data for A 1−x A ′ x MnO 3 with x < 0.3 and x > 0.4 means that one cannot test the doping dependence of different mechanisms and, therefore, the origin of the magnon softening is still unsettled.Very recently, Endoh et al.[15] measured spinwave excitations in the FM phase of Sm 0.55 Sr 0.45 MnO 3 (SSMO45) and found that the dispersion can be described phenomenologically by the Heisenberg model with the nearest ne...

We have studied conductance quantization in metallic nanowires upon adsorption of molecules with different adsorption strengths. The conductance still changes in a step-wise fashion even in the presence of strong adsorption, and the average sharpness, length, and number of the conductance steps remain unchanged. However, the step positions deviate significantly from the integer values of the conductance quantum, 2e 2 /h. While the deviation may be attributed to the scattering of the ballistic electrons by the adsorbates, evidence shows that the adsorbates also affect conductance by changing the atomic configurations of the nanowires.It has been found for many years that the electrical conductivity of metals decreases upon adsorption of atoms and molecules because of the scattering of the conducting electrons by the adsorbates. 1-3 The studies, however, have been largely limited to nonballistic electron transport in which the electron mean free path is much smaller than the dimension of the metals. In the present paper, we study the adsorbate effect on ballistic electron transport in metallic nanowires. The conductance of the nanowires has been observed to vary in a stepwise fashion in which the steps occur at the integer values of conductance quantum, G 0 ϭ2e 2 /h, when the wire width is decreased to the atomic scale. 4-11 We find that upon adsorption of molecules at the nanowires, the conductance steps are still well defined but the step positions deviate significantly from the integer values of G 0 .Metallic nanowires, in which electron transport ballistically, have been created by mechanically breaking a fine metal wire, 4 by separating a tip and a flat substrate, 5-10 or two macroscopic electrodes in contact, 11 by anodizing Al nanowires with an atomic force microscope, 12 and by electrochemical deposition. 13 In this paper, we use the tip-flat substrate setup in which a gold tip is placed over a gold film epitaxially grown on mica. Instead of vertically driving the tip into and out of the substrate, 5-10 we create the nanowires by sweeping the tip horizontally across the substrate surface with a modified scanning tunneling microscope ͑STM͒. The substrate is first roughened by scanning an area with a large tunneling current. A contact is made when the tip moves into a bump on the substrate, and pulling out of the contact results in the formation of a nanowire ͑Fig. 1͒. This method allows us to rapidly sample the conductance of the nanowires formed in different surface areas. The tip is swept at a rate of 100 nm/s and the bias voltage is typically set at 26 mV. The preamplifier was modified such that it could sustain a current load of tens of A without affecting the bias voltage. We note that simply reducing the gain of a standard STM preamplifier usually results in a smaller bias voltage at large current, which shifts the conductance peaks in the histograms towards lower conductance values. The conductance vs time traces are recorded using a 200-MHz digital oscilloscope ͑Yokogawa͒ interfaced to a personal com...

Ferromagnetic (FM) manganites, a group of likely half-metallic oxides, are of special interest not only because they are a testing ground for the classical double-exchange interaction mechanism for the 'colossal' magnetoresistance, but also because they exhibit an extraordinary arena of emergent phenomena. These emergent phenomena are related to the complexity associated with strong interplay between charge, spin, orbital, and lattice. In this review, we focus on the use of inelastic neutron scattering to study the spin dynamics, mainly the magnon excitations in this class of FM metallic materials. In particular, we discuss the unusual magnon softening and damping near the Brillouin zone boundary in relatively narrow-band compounds with strong Jahn-Teller lattice distortion and charge-orbital correlations. The anomalous behaviours of magnons in these compounds indicate the likelihood of cooperative excitations involving spin and lattice as well as orbital degrees of freedom.