Guneeta Singh-Bhalla

Lawrence Berkeley National Laboratory | LBL · Materials Sciences Division

Polar crystals composed of charged ionic planes cannot exist in nature without acquiring surface changes to balance an ever-growing dipole. The necessary changes can manifest structurally or electronically. An electronic asymetry has long been observed in the LaAlO3/SrTiO3 system. Electron accumulation is observed near the LaAlO3/TiO2-SrTiO3 interf...

High Speed scanning probe microscopy (SPM) imaging is employed here,in which the local device state is simultaneously detected and manipulated in situ by biasing through a conducting atomic force microscopy (AFM) tip. This chapter shows that sufficient ionic compensation of bare (unelectroded) ferroelectric (FE) surfaces can occur such that ultrath...

Dipole screening mechanisms for polar crystals can manifest in a variety of ways depending on bandgaps, surface energies and environmental conditions. Here we study the polarity compensation process in LaAlO3 thin film grown on the two different surface terminations of [001] SrTiO3 crystals (SrO and TiO2). An electron gas that appears at the interf...

High quality epitaxial thin films of Jeff=1/2 Mott insulator Sr2IrO4 with increasing in-plane tensile strain have been grown on top of SrTiO3(001) substrates. Increasing the in-plane tensile strain up to ~0.3% was observed to drop the c/a tetragonality by 1.2 %. X-ray absorption spectroscopy detected a strong reduction of the linear dichroism upon...

The control of material interfaces at the atomic level has led to novel interfacial properties and functionalities. In particular, the study of polar discontinuities at interfaces between complex oxides lies at the frontier of modern condensed matter research. Here we employ a combination of experimental measurements and theoretical calculations to...

Domain walls in multiferroics can exhibit intriguing behaviors that are significantly different from the bulk of the material. We investigate strong magnetoresistance in domain walls of the model multiferroic BiFeO3 by probing ordered arrays of 109° domain walls with temperature- and magnetic-field-dependent transport. We observe temperature-depend...

In this article we provide an overview of phenomena involving domain walls in BiFeO3 as nanoscale functional elements. Because ferroelectric domain walls can be routinely modified using electric fields, our results suggest a new degree of flexibility for domain boundary engineering and oxide-based nanoelectronics.

We have grown epitaxial thin films of multiferroic BiMnO$_3$ using pulsed laser deposition. The films were grown on SrTiO$_3$ (001) substrates by ablating a Bi-rich target. Using x-ray diffraction we confirmed that the films were epitaxial and the stoichiometry of the films was confirmed using Auger electron spectroscopy. The films have a ferromagn...

We have grown epitaxial thin films of multiferroic BiMnO3 using pulsed laser deposition. The films were grown on SrTiO3 001 substrates by ablating a Bi-rich target. Using x-ray diffraction, we confirmed that the films were epitaxial and the stoichiometry of the films was confirmed using Auger electron spectroscopy. The films have a ferromagnetic Cu...

Ionic crystals terminated at oppositely charged polar surfaces are inherently unstable and expected to undergo surface reconstructions to maintain electrostatic stability. Essentially, an electric field that arises between oppositely charged atomic planes gives rise to a built-in potential that diverges with thickness. Here we present evidence of s...

The growth conditions for growing BiMnO3, with pulsed laser deposition, are optimized. The optimal oxygen pressure was found to be near 32 mTorr, and the optimal substrate temperature was found to be between 630 C and 635 C. The quality of the films was checked using x-ray diffraction, Auger electron spectroscopy, and atomic force microscopy. Magne...

The manganite (La,Pr,Ca)MnO3 is well known for its micrometer-scale phase separation into coexisting ferromagnetic metallic (FMM) and insulating regions. Fabrication of bridges with widths smaller than the phase-separation length scale has allowed us to probe the magnetic properties of individual phase-separated regions. At the onset of phase separ...

The manganite (La,Pr,Ca)MnO3 is well known for its micrometer scale phase separation into coexisting ferromagnetic metallic and antiferromagnetic insulating (AFI) regions. Fabricating bridges with widths smaller than the phase separation length scale has allowed us to probe the magnetic properties of individual phase separated regions. We observe t...

We present evidence of direct electron tunneling across intrinsic insulating regions in sub-micrometer wide bridges of the phase separated ferromagnet (La,Pr,Ca)MnO$_3$. Upon cooling below the Curie temperature, a predominantly ferromagnetic supercooled state persists where tunneling across the intrinsic tunnel barriers (ITBs) results in metastable...

The current-voltage (I-V) characteristics of manganite nanowires seen in an experiment closely resemble the hallmark I-V curves of the Coulomb blockade. Unlike normal Coulomb blockade curves, these curves have multiple lines instead of one, branching out from the zero current point. In order to discover an explanation for these I-V curves a simulat...

We have examined the electric field effect on the nanometer scale in the manganite (La,Pr,Ca)MnO{}&{slash;3&}slash;{}which is well known for its micrometer scale phase separation (PS) into coexisting metallic and insulating regions. When thin films of this material are patterned into micrometer and nanometer wide bridges, alternating insulating and...

Magnetocapacitance techniques[1] have been used in a study of (La1-yPry)1-xCaxMnO3 (LPCMO) thin films to determine the range of phase space, described by frequency (phi), temperature (T) and field (H), over which a dielectric response of the form, C"(phi,T,H) = [C'(phi,T,H) - C∞]^gamma , is found to hold. This power-law scaling collapse (PLSC) of t...

In magnetic oxides, such as hole-doped manganites the reduction of electrostatic and elastic energies in addition to the magnetostatic energy leads to coexisting regions of ferromagnetic metallic (FMM) and insulating phases. Such phase coexistence provides unique opportunities for understanding the interaction of spin-polarized currents with insula...

Thin films of strongly-correlated electron materials (SCEM) are often grown epitaxially on planar substrates and typically have anisotropic properties that are usually not captured by edge-mounted four-terminal electrical measurements, which are primarily sensitive to in-plane conduction paths. Accordingly, the correlated interactions in the out-of...

Resistance measurements on thin films of strongly correlated electronic materials that have anisotropic properties due to atomic layering and/or substrate induced strain are primarily sensitive to in-plane conduction paths and therefore fail to capture any information about perpendicular transport. We present an experimental technique in which the...

We present a systematic study of the dependence of breakdown voltages on oxide thickness d in Al-AlOx-Al thin-film capacitor structures. For sufficiently thin dielectrics, we find that a significant portion of the measured breakdown potential Vb occurs across the electrode interfaces, thereby leading to an overestimate (Vb/d) of the true breakdown...