arXiv subjects

J. W. Lu

Publications and source records attributed to J. W. Lu.

7 recordsLinked to original sources

arXiv2019

Nano-engineering of electron correlation in oxide superlattices

Oxide heterostructures and superlattices have attracted a great deal of attention in recent years owing to the rich exotic properties encountered at their interfaces. We focus on the potential of tunable correlated oxides by investigating the spectral function of the prototypical correlated metal SrVO3, using soft x-ray absorption spectroscopy (XAS) and resonant inelastic soft x-ray scattering (RIXS) to access both unoccupied and occupied electronic states, respectively. We demonstrate a remarkable level of tunability in the spectral function of SrVO3 by varying its thickness within the SrVO3/SrTiO3 superlattice, showing that the effects of electron correlation can be tuned from dominating the energy spectrum in a strongly correlated Mott-Hubbard insulator, towards a correlated metal. We show that the effects of dimensionality on the correlated properties of SrVO3 are augmented by interlayer coupling, yielding a highly flexible correlated oxide that may be readily married with other oxide systems.

cond-mat.str-el↗

arXiv2019

Observation of weakened V-V dimers in the monoclinic metallic phase of strained VO2

Emergent order at mesoscopic length scales in condensed matter can provide fundamental insight into the underlying competing interactions and their relationship with the order parameter. Using spectromicroscopy, we show that mesoscopic stripe order near the metal-insulator transition (MIT) of strained VO2 represent periodic modulations in both crystal symmetry and V-V dimerization. Above the MIT, we unexpectedly find the long range order of V-V dimer strength and crystal symmetry become dissociated beyond ~ 200 nm, whereas the conductivity transition proceeds homogeneously in a narrow temperature range.

cond-mat.str-el↗

arXiv2015

Half-metallic state and magnetic properties versus the lattice constant in Zr2RhZ (Z = Al, Ga, In) Heusler alloys

The half metallic and magnetic properties of Zr2RhZ (Z = Al, Ga, In) alloys with an Hg2CuTi-type structure were systematically investigated using the first-principle calculations. Zr2RhZ (Z = Al, Ga, In) alloys are predicted to be half-metallic ferrimagnets at their equilibrium lattice constants. The Zr2Rh-based alloys have Mt (the total magnetic moment per unit cell) and Zt (the valence concentration) values that in agreement with Slater-Pauling rule Mt = Zt -18. The half-metallic properties and the magnetic properties at different lattice constants are discussed in detail. We expect that our results may trigger Zr2RhZ (Z = Al, Ga, In) applying in the future spintronics field.

cond-mat.mtrl-sci↗

arXiv2014

Direct Observation of Decoupled Structural and Electronic Transitions and an Ambient Pressure Monoclinic-Like Metallic Phase of VO$_2$

We report the simultaneous measurement of the structural and electronic components of the metal-insulator transition of VO$_2$ using electron and photoelectron spectroscopies and microscopies. We show that these evolve over different temperature scales, and are separated by an unusual monoclinic-like metallic phase. Our results provide conclusive evidence that the new monoclinic-like metallic phase, recently identified in high-pressure and nonequilibrium measurements, is accessible in the thermodynamic transition at ambient pressure, and we discuss the implications of these observations on the nature of the MIT in VO$_2$.

cond-mat.str-el↗

arXiv2013

Resonant soft x-ray emission as a bulk probe of correlated electron behavior in metallic Sr$_x$Ca$_{1-x}$VO$_3$

The evolution of electron correlation in Sr$_{x}$Ca$_{1-x}$VO$_3$ has been studied using a combination of bulk-sensitive resonant soft x-ray emission spectroscopy (RXES), surface-sensitive photoemission spectroscopy (PES), and ab initio band structure calculations. We show that the effect of electron correlation is enhanced at the surface. Strong incoherent Hubbard subbands are found to lie ~ 20% closer in energy to the coherent quasiparticle features in surface-sensitive PES measurements compared with those from bulk-sensitive RXES, and a ~ 10% narrowing of the overall bandwidth at the surface is also observed.

cond-mat.str-el↗

arXiv2012

Photoemission evidence for crossover from Peierls-like to Mott-like transition in highly strained VO$_2$

We present a spectroscopic study that reveals that the metal-insulator transition of strained VO$_2$ thin films may be driven towards a purely electronic transition, which does not rely on the Peierls dimerization, by the application of mechanical strain. Comparison with a moderately strained system, which does involve the lattice, demonstrates the crossover from Peierls- to Mott-like transitions.

cond-mat.str-el↗

arXiv2012

Strain dependence of bonding and hybridization across the metal-insulator transition of VO2

Soft x-ray spectroscopy is used to investigate the strain dependence of the metal-insulator transition of VO2. Changes in the strength of the V 3d - O 2p hybridization are observed across the transition, and are linked to the structural distortion. Furthermore, although the V-V dimerization is well-described by dynamical mean-field theory, the V-O hybridization is found to have an unexpectedly strong dependence on strain that is not predicted by band theory, emphasizing the relevance of the O ion to the physics of VO2.

cond-mat.str-el↗