The interactions between delocalized and localized charges play important roles in correlated electron systems. Here, using a combination of transport measurements, spectroscopic ellipsometry (SE), and X-ray absorption spectroscopy (XAS) supported by theoretical calculations, we reveal the important role of interfacial localized charges and their screening effects in determining the mobility of (La0.3 Sr0.7 )(Al0.65 Ta0.35 )O3 /SrTiO3 (LSAT/SrTiO3 ) interfaces. When the LSAT layer thickness reaches the critical value of 5 uc, the insulating interface abruptly becomes conducting, accompanied by the appearance of a new midgap state. This midgap state emerges at ≈1 eV below the Ti t2g band and shows a strong character of Ti 3dxy - O 2p hybridization. Increasing the LSAT layer from 5 to 18 uc, the number of localized charges increases, resulting in an enhanced screening effect and higher mobile electron mobility. This observation contradicts the traditional semiconductor interface where the localized charges always suppress the carrier mobility. These results demonstrate a new strategy to probe localized charges and mobile electrons in correlated electronic systems and highlight the important role of screening effects from localized charges in improving the mobile electron mobility at complex oxide interfaces.

Large Enhancement of 2D Electron Gases Mobility Induced by Interfacial Localized Electron Screening Effect.

Local phenomena at grain boundaries: An alternative approach to grasp the role of oxygen vacancies in metallization of VO2

VO2 thin films were prepared on quartz glass substrates by using high power impulse magnetron sputtering with different pulsed bias voltages. X-ray diffraction patterns revealed that all as-deposited films were polycrystalline monoclinic VO2 and the preferred crystalline orientation of the as-deposited films varied with the magnitude of the bias voltage. Scanning electron microscopy images exhibited that the crystalline size of the VO2 thin films reduced with the magnitude of the bias voltage. X-ray photoelectron spectroscopy results revealed that oxygen vacancies were formed in all films and their quantities were similar. UV–visible-near IR spectra of the VO2 thin films at different temperatures confirmed that all films possessed typical metal–insulator transition properties. Four-point probes resistivity results exhibited that the phase transition temperature was reduced from 54 to 31.5°C when the magnitude of the bias voltage was increased from − 50 to − 250 V.

Influence of bias voltage on microstructure and phase transition properties of VO2 thin film synthesized by HiPIMS

Hydrogenated amorphous silicon (a-Si: H) has received great attention for rich fundamental physics and potentially inexpensive solar cells. Here, we observe new resonant excitons and correlated plasmons tunable via hydrogen content in a-Si: H films on Indium Tin Oxide (ITO) substrate. Spectroscopic ellipsometry supported with High Resolution-Transmission Electron Microscopy (HR-TEM) is used to probe optical properties and the density of electronic states in the various crystallinity from nano-size crystals to amorphous a-Si: H films. The observed optical and electronic structures are analyzed by the second derivative with analytic critical-point line shapes. The complex dielectric function shows good agreement with microscopic calculations for the energy shift and the broadening inter-band transitions based on the electron-hole interaction. Interestingly, we observe an unusual spectral weight transfer over a broad energy range revealing electronic correlations that cause a drastic change in the charge carrier density and determine the photovoltaic performance. Furthermore, the interplay of resonant excitons and correlated plasmons is discussed in term of a correlated plexciton. Our result shows the important role of hydrogen in determining the coupling of excitons and plasmons in a-Si: H film for photovoltaic devices. 

/pdf/observation-of-resonant-exciton-and-correlated-plasmon-1kgcmeq7.pdf

Observation of resonant exciton and correlated plasmon yielding correlated plexciton in amorphous silicon with various hydrogen content

Characteristic first‐order insulator–metal transition (IMT) in VO2 (M1) phase finds a place in ample practical applications such as switches, transistors, memory devices, and energy‐saving windows. A polymorph VO2 (B) phase which may appear as an additional phase can strongly influence IMT in VO2 (M1) and not much is known about it. Here, the electrical conductivity and the electronic structure studies on the VO2 thin films on R‐ and C‐cut sapphire and silicon (Si) substrates are reported. X‐ray diffraction (XRD) and Raman spectra confirm the growth of VO2 (B) as well as VO2 (M1) polymorphs on the sapphire substrates and the pure VO2 (M1) phase on the Si substrate. The first‐order IMT is observed in all the thin films, however, due to the presence of the semimetallic VO2 (B) phase in the thin film on sapphire substrate, a decrease in the IMT strength and higher electrical conductivity have been observed. The electronic structure studies, by utilizing soft X‐ray absorption spectroscopy (SXAS) measurements, reveal that the presence of VO2 (B) phase not only causes an overall increase in the crystal field energy but also significantly affects the orbital occupancies around the Fermi level.

Unveiling the Role of VO2 (B) Polymorph in the Insulator–Metal Transition of VO2 (M1) Thin Films

Vanadium dioxide $({\mathrm{VO}}_{2})$ undergoes an unusual insulator-metal transition (IMT), and after decades of study, the origin of the IMT remains hotly debated. Here, by analyzing spectral-weight transfers (SWTs) of x-ray absorption spectroscopy at the $\mathrm{V}\phantom{\rule{0.28em}{0ex}}{L}_{3,2}$ and O K edges on specially designed ${\mathrm{VO}}_{2}$ films, we observe ${d}_{||}\phantom{\rule{0.28em}{0ex}}({d}_{{x}^{2}\ensuremath{-}{y}^{2}})$ band splitting at the $\mathrm{V}\phantom{\rule{0.28em}{0ex}}{L}_{3,2}$ edges across the IMT, accompanied by anomalous SWTs as high as $\ensuremath{\sim}12\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$ at the $\mathrm{O}\phantom{\rule{0.28em}{0ex}}K$ edge, indicating strong electronic correlations. Surprisingly, a few oxygen vacancies induce dramatic SWTs at the $\mathrm{O}\phantom{\rule{0.28em}{0ex}}K$ edge, but the sample remains conducting. Supported by theoretical calculations, we find that in the metallic state, direct $\mathrm{V}(3{d}_{\ensuremath{\parallel}})\text{-V}(3{d}_{\ensuremath{\parallel}})$ and $\text{O}(2p)\text{-V}(3{d}_{\ensuremath{\parallel}})$ hybridized orbital correlations are screened by $\text{O}(2p)\text{-V}(3{d}_{\ensuremath{\pi}})$ hybridized orbitals, while in the insulating state they are strongly correlated due to changes in the oxygen orbital occupancy. Our result shows the importance of screenings and electronic correlations for IMTs in ${\mathrm{VO}}_{2}$.

Anomalous spectral-weight transfers unraveling oxygen screening and electronic correlations in the insulator-metal transition of VO 2

In this paper we discussed the propagation of blast waves generated by intense flares in stellar atmosphere. The effects due topressure of magnetic field, self-gravitation and radiation heat flux are discussed. The numerical solutions for the flow behind the shock have been obtained in presence of self-gravitation, weak and strong magnetic field separately.

Propagation of Blast Waves Generated by Intense Flares

The effects of an interplanetary magnetic field on the propagation of the flare generated shock wave in a non-uniformly distributed solar self-gravitating atmosphere are investigated by using an approximate analytic method of Whitham. The expressions for the velocity of shock wave and for the other flow variables behind weak and strong shocks are derived and discussed.

The Propagation of Flare Generated Shockwaves in Self-Gravitating Solar Atmosphere

The problem of propagation of explosion waves in a gas containing small solid particles has been discussed by using the method developed by Whitham 1 , including the effects due to gravitational force. The analytical solutions of the shock strength, shock velocity and flow variables for weak and strong shocks have been obtained and particular cases are discussed.

Propagation of Spherical Shock Waves in a Dusty Gas under Influence of Gravitation

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Papers

Anomalous spectral-weight transfers unraveling oxygen screening and electronic correlations in the insulator-metal transition of VO 2

Propagation of Blast Waves Generated by Intense Flares

The Propagation of Flare Generated Shockwaves in Self-Gravitating Solar Atmosphere

Propagation of Spherical Shock Waves in a Dusty Gas under Influence of Gravitation