Electronic reconstruction at SrMnO3-LaMnO3 superlattice interfaces

We use resonant soft x-ray scattering to study electronic reconstruction at the interface between the Mott insulator LaMnO3 and the "band" insulator SrMnO3. Superlattices of these two insulators were shown previously to have both ferromagnetism and metallic tendencies [Koida et al., Phys. Rev. B 66, 144418 (2002)]. By studying a judiciously chosen superlattice reflection we show that the interface density of states exhibits a pronounced peak at the Fermi level, similar to that predicted by Okamoto et al. [Phys. Rev. B 70, 241104(R) (2004)]. The intensity of this peak correlates with the conductivity and magnetization, suggesting it is the driver of metallic behavior. Our study demonstrates a general strategy for using RSXS to probe the electronic properties of heterostructure interfaces.Comment: 4.2 pages, 4 figure

Probing Interface of Perovskite Oxide Using Surface-specific Terahertz Spectroscopy

The surface/interface species in perovskite oxides play an essential role in many novel emergent physical phenomena and chemical processes. With low eigen-energy in the terahertz region, such species at buried interfaces remain poorly understood due to the lack of feasible experimental techniques. Here, we show that vibrational resonances and two-dimensional electron gas at the interface can be characterized using surface-specific nonlinear spectroscopy in the terahertz range. This technique uses intra-pulse difference frequency mixing (DFM) process, which is allowed only at surface/interface of a medium with inversion symmetry. Sub-monolayer sensitivity can be achieved using the state-of-the-art detection scheme for the terahertz emission from surface/interface. As a demonstration, Drude-like nonlinear response from the two-dimensional electron gas emerging at LaAlO3/SrTiO3 or Al2O3/ SrTiO3 interface was successfully observed. Meanwhile, the interfacial vibrational spectrum of the ferroelectric soft mode of SrTiO3 at 2.8 THz was also obtained that was polarized by the surface field in the interfacial region. The corresponding surface/interface potential, which is a key parameter for SrTiO3-based interface superconductivity and photocatalysis, can now be determined optically via quantitative analysis on the polarized phonon spectrum. The interfacial species with resonant frequencies in the THz region revealed by our method provide more insights into the understanding of physical properties of complex oxides.Comment: arXiv admin note: substantial text overlap with arXiv:2207.1461

Atomic structure, energetics, and dynamics of topological solitons in Indium chains on Si(111) surfaces

Based on scanning tunneling microscopy and first-principles theoretical studies, we characterize the precise atomic structure of a topological soliton in In chains grown on Si(111) surfaces. Variable-temperature measurements of the soliton population allow us to determine the soliton formation energy to be ~60 meV, smaller than one half of the band gap of ~200 meV. Once created, these solitons have very low mobility, even though the activation energy is only about 20 meV; the sluggish nature is attributed to the exceptionally low attempt frequency for soliton migration. We further demonstrate local electric field-enhanced soliton dynamics.Comment: 5 pages, 3 figure

Correlation-driven eightfold magnetic anisotropy in a two-dimensional oxide monolayer.

Engineering magnetic anisotropy in two-dimensional systems has enormous scientific and technological implications. The uniaxial anisotropy universally exhibited by two-dimensional magnets has only two stable spin directions, demanding 180° spin switching between states. We demonstrate a previously unobserved eightfold anisotropy in magnetic SrRuO3 monolayers by inducing a spin reorientation in (SrRuO3)1/(SrTiO3) N superlattices, in which the magnetic easy axis of Ru spins is transformed from uniaxial 〈001〉 direction (N < 3) to eightfold 〈111〉 directions (N ≥ 3). This eightfold anisotropy enables 71° and 109° spin switching in SrRuO3 monolayers, analogous to 71° and 109° polarization switching in ferroelectric BiFeO3. First-principle calculations reveal that increasing the SrTiO3 layer thickness induces an emergent correlation-driven orbital ordering, tuning spin-orbit interactions and reorienting the SrRuO3 monolayer easy axis. Our work demonstrates that correlation effects can be exploited to substantially change spin-orbit interactions, stabilizing unprecedented properties in two-dimensional magnets and opening rich opportunities for low-power, multistate device applications

The (p)ppGpp synthetase Rsh promotes rifampicin tolerant persister cell formation in Brucella abortus by regulating the type II toxin-antitoxin module mbcTA

Persister cells are transiently tolerant to antibiotics and are associated with recalcitrant chronic infections due to recolonization of host cells after antibiotic removal. Brucella spp. are facultative pathogens that establish intracellular infection cycles in host cells which results in chronic persistent infections. Brucella abortus forms multi-drug persister cells which are promoted by the (p)ppGpp synthetase Rsh during rifampicin exposure. Here, we confirmed that Rsh promoted persister cells formation in B. abortus stationary phase treated with rifampicin and enrofloxacin. Deletion of the gene for Rsh decreased persister cells level in the presence of these drugs in different growth phases. However, persister cells formation by deletion strain varied in different growth phases in the presence of other antibiotics. Rsh also was involved in persister cells formation during rifampicin treatment under certain stress conditions, including acidic conditions, exposure to PBS, and heat stress. Moreover, Rsh impacted persister cell levels during rifampicin or enrofloxacin treatment in RAW264.7 macrophages. Certain typeIItoxin-antitoxin modules were upregulated under various stress conditions in B. abortus. We established that Rsh positively regulated the type II toxin-antitoxin mbcTA. Moreover, rifampicin-tolerant persister cells formation was elevated and ATP levels were decreased when mbcTA promoter was overexpressed in Rsh deletion background in stationary phase. Our results establish that (p)ppGpp synthetase Rsh plays a key role in B. abortus persistence and may serve as a potent novel target in combination with rifampicin in the development of new therapeutic approaches and prevention strategies to treat chronic infections of Brucella