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Probing the metal-insulator transition of NdNiO3 by electrostatic doping  [PDF]
Junwoo Son,Bharat Jalan,Adam P. Kajdos,Leon Balents,S. James Allen,Susanne Stemmer
Physics , 2011, DOI: 10.1063/1.3659310
Abstract: Modulation of the charge carrier density in a Mott material by remote doping from a highly doped conventional band insulator is proposed to test theoretical predictions of band filling control of the Mott metal-insulator transition without introducing lattice distortions or disorder, as is the case for chemical doping. The approach is experimentally tested using ultrathin (2.5 nm) NdNiO3 films that are epitaxially grown on La-doped SrTiO3 films. We show that remote doping systematically changes the charge carrier density in the NdNiO3 film and causes a moderate shift in the metal-insulator transition temperature. These results are discussed in the context of theoretical models of this class of materials exhibiting a metal-insulator transition.
Role of magnetic and orbital ordering at the metal-insulator transition in NdNiO3  [PDF]
V. Scagnoli,U. Staub,A. M. Mulders,M. Janousch,G. I. Meijer,G. Hammerl,J. M. Tonnerre,N. Stojic
Physics , 2006, DOI: 10.1103/PhysRevB.73.100409
Abstract: Soft x-ray resonant scattering at the Ni L2,3 edges is used to test models of magnetic and orbital-ordering below the metal-insulator transition in NdNiO3. The large branching ratio of the L3 to L2 intensities of the (1/2,0,1/2) reflection and the observed azimuthal angle and polarization dependence originates from a non collinear magnetic structure. The absence of an orbital signal and the non collinear magnetic structure show that the nickelates are materials for which orbital ordering is absent at the metal-insulator transition.
Strain-mediated metal-insulator transition in epitaxial ultra-thin films of NdNiO3  [PDF]
Jian Liu,M. Kareev,B. Gray,J. W. Kim,P. Ryan,B. Dabrowski,J. W. Freeland,J. Chakhalian
Physics , 2010, DOI: 10.1063/1.3451462
Abstract: We have synthesized epitaxial NdNiO$_{3}$ ultra-thin films in a layer-by-layer growth mode under tensile and compressive strain on SrTiO$_{3}$ (001) and LaAlO$_3$ (001), respectively. A combination of X-ray diffraction, temperature dependent resistivity, and soft X-ray absorption spectroscopy has been applied to elucidate electronic and structural properties of the samples. In contrast to the bulk NdNiO$_{3}$, the metal-insulator transition under compressive strain is found to be completely quenched, while the transition remains under the tensile strain albeit modified from the bulk behavior.
Tuning the metal-insulator transition in NdNiO3 heterostructures via Fermi surface instability and spin-fluctuations  [PDF]
R. S. Dhaka,Tanmoy Das,N. C. Plumb,Z. Ristic,W. Kong,C. E. Matt,N. Xu,K. Dolui,E. Razzoli,M. Medarde,L. Patthey,M. Shi,M. Radovic,Joel Mesot
Physics , 2015, DOI: 10.1103/PhysRevB.92.035127
Abstract: We employed {\it in-situ} pulsed laser deposition (PLD) and angle-resolved photoemission spectroscopy (ARPES) to investigate the mechanism of the metal-insulator transition (MIT) in NdNiO$_3$ (NNO) thin films, grown on NdGaO$_3$(110) and LaAlO$_3$(100) substrates. In the metallic phase, we observe three dimensional hole and electron Fermi surface (FS) pockets formed from strongly renormalized bands with well-defined quasiparticles. Upon cooling across the MIT in NNO/NGO sample, the quasiparticles lose coherence via a spectral weight transfer from near the Fermi level to localized states forming at higher binding energies. In the case of NNO/LAO, the bands are apparently shifted upward with an additional holelike pocket forming at the corner of the Brillouin zone. We find that the renormalization effects are strongly anisotropic and are stronger in NNO/NGO than NNO/LAO. Our study reveals that substrate-induced strain tunes the crystal field splitting, which changes the FS properties, nesting conditions, and spin-fluctuation strength, and thereby controls the MIT via the formation of an electronic order parameter with Q$_{AF}\sim$(1/4, 1/4, 1/4$\pm$$\delta$).
The possibility of a metal insulator transition in antidot arrays induced by an external driving  [PDF]
A. Iomin,S. Fishman
Physics , 1999, DOI: 10.1103/PhysRevB.61.2085
Abstract: It is shown that a family of models associated with the kicked Harper model is relevant for cyclotron resonance experiments in an antidot array. For this purpose a simplified model for electronic motion in a related model system in presence of a magnetic field and an AC electric field is developed. In the limit of strong magnetic field it reduces to a model similar to the kicked Harper model. This model is studied numerically and is found to be extremely sensitive to the strength of the electric field. In particular, as the strength of the electric field is varied a metal -- insulator transition may be found. The experimental conditions required for this transition are discussed.
Metal-insulator transition in the In/Si(111) surface  [PDF]
Sampsa Riikonen,Andres Ayuela,Daniel Sanchez-Portal
Physics , 2005, DOI: 10.1016/j.susc.2006.01.092
Abstract: The metal-insulator transition observed in the In/Si(111)-4x1 reconstruction is studied by means of ab initio calculations of a simplified model of the surface. Different surface bands are identified and classified according to their origin and their response to several structural distortions. We support the, recently proposed [New J. of Phys. 7 (2005) 100], combination of a shear and a Peierls distortions as the origin of the metal-insulator transition. Our results also seem to favor an electronic driving force for the transition.
Electronic Structure of Pyrochlore Iridates: From Topological Dirac Metal to Mott Insulator  [PDF]
Xiangang Wan,Ari Turner,Ashvin Vishwanath,Sergey Y. Savrasov
Physics , 2010, DOI: 10.1103/PhysRevB.83.205101
Abstract: In 5d transition metal oxides such as the iridates, novel properties arise from the interplay of electron correlations and spin-orbit interactions. We investigate the electronic structure of the pyrochlore iridates, (such as Y$_{2}$Ir$_{2}$O$_{7}$) using density functional theory, LDA+U method, and effective low energy models. A remarkably rich phase diagram emerges on tuning the correlation strength U. The Ir magnetic moment are always found to be non-collinearly ordered. However, the ground state changes from a magnetic metal at weak U, to a Mott insulator at large U. Most interestingly, the intermediate U regime is found to be a Dirac semi-metal, with vanishing density of states at the Fermi energy. It also exhibits topological properties - manifested by special surface states in the form of Fermi arcs, that connect the bulk Dirac points. This Dirac phase, a three dimensional analog of graphene, is proposed as the ground state of Y$_{2}$Ir$_{2}$O$_{7}$ and related compounds. A narrow window of magnetic `axion' insulator, with axion parameter $\theta=\pi$, may also be present at intermediate U. An applied magnetic field induces ferromagnetic order and a metallic ground state.
Heterointerface engineered electronic and magnetic phases of NdNiO3 thin films  [PDF]
Jian Liu,Mehdi Kargarian,Mikhail Kareev,Ben Gray,Phil J. Ryan,Alejandro Cruz,Nadeem Tahir,Yi-De Chuang,Jinghua Guo,James M. Rondinelli,John W. Freeland,Gregory A. Fiete,Jak Chakhalian
Physics , 2013, DOI: 10.1038/ncomms3714
Abstract: Mott physics is characterized by an interaction-driven metal-to-insulator transition in a partially filled band. In the resulting insulating state, antiferromagnetic orders of the local moments typically develop, but in rare situations no long-range magnetic order appears, even at zero temperature, rendering the system a quantum spin liquid. A fundamental and technologically critical question is whether one can tune the underlying energetic landscape to control both metal-to-insulator and N\'eel transitions, and even stabilize latent metastable phases, ideally on a platform suitable for applications. Here we demonstrate how to achieve this in ultrathin films of NdNiO3 with various degrees of lattice mismatch, and report on the quantum critical behaviours not reported in the bulk by transport measurements and resonant X-ray spectroscopy/scattering. In particular, on the decay of the antiferromagnetic Mott insulating state into a non-Fermi liquid, we find evidence of a quantum metal-to-insulator transition that spans a non-magnetic insulating phase.
Correlation-driven insulator-metal transition in near-ideal vanadium dioxide films  [PDF]
A. X. Gray,J. Jeong,N. P. Aetukuri,P. Granitzka,Z. Chen,R. Kukreja,D. Higley,T. Chase,A. H. Reid,H. Ohldag,M. A. Marcus,A. Scholl,A. T. Young,A. Doran,C. A. Jenkins,P. Shafer,E. Arenholz,M. G. Samant,S. S. P. Parkin,H. A. Dürr
Physics , 2015,
Abstract: We use polarization- and temperature-dependent x-ray absorption spectroscopy, in combination with photoelectron microscopy, x-ray diffraction and electronic transport measurements, to study the driving force behind the insulator-metal transition in VO2. We show that both the collapse of the insulating gap and the concomitant change in crystal symmetry in homogeneously strained single-crystalline VO2 films are preceded by the purely-electronic softening of Coulomb correlations within V-V singlet dimers. This process starts 7 K (+/- 0.3 K) below the transition temperature, as conventionally defined by electronic transport and x-ray diffraction measurements, and sets the energy scale for driving the near-room-temperature insulator-metal transition in this technologically-promising material.
Complementarity of perturbations driving insulator-to-metal transition in a charge ordered manganite  [PDF]
S. Chaudhuri,R. C. Budhani
Physics , 2007, DOI: 10.1209/0295-5075/81/17002
Abstract: Modulation of charge carrier dynamics and hence electrical conductivity of solids by photoexcitation has been a rich field of research with numerous applications. Similarly, electric and magnetic field assisted enhancement of conductivity are of fundamental importance and technological use. Hole doped manganites of the type (A$_{1-x}$B$_{x})$MnO$_{3}$, where A and B are rare and alkaline earth metals respectively have the distinction of showing all three effects. Here we establish the complementarity of the electric, magnetic and photon fields in driving an insulator-metal transition in epitaxial thin films of La$_{0.175}$Pr$_{0.45}$Ca$_{0.375}$MnO$_{3}$ whose electrical ground state is insulating. Both pulsed and CW lasers cause a giant photon flux dependent enhancement of conductivity. It is further observed that electric and magnetic fields trigger the persistent enhancement of conductivity whose magnitude can be accentuated by application of these fields in parallel.
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