arXiv subjects

Yi-De Chuang

Publications and source records attributed to Yi-De Chuang.

29 records · Page 2Linked to original sources

arXiv2017

Charge transfer excitations in VUV and soft X-ray resonant scattering spectroscopies

The utility of resonant scattering spectroscopies for identifying electronic symmetries and density distributions changes dramatically as a function of photon energy. In the hard X-ray regime, strong core hole monopole potentials tend to produce X-ray absorption features with well defined electron number on the scattering site. By contrast, in the vacuum ultraviolet (VUV), resonant scattering from Mott insulators tends to reveal spectra that are characteristic of only the nominal valence, and are insensitive to deviations from nominal valence brought on by metal-ligand hybridization. Here, atomic multiplet simulations are used to investigate the interplay of monopolar and mulitpolar Coulomb interactions in the VUV and soft X-ray regimes, to identify how charge transfer thresholds and other signatures of mixed valence can manifest in this low photon energy regime. The study focuses on the Mott insulator NiO as a well characterized model system, and extrapolates interactions into non-physical regimes to identify principles that shape the spectral features.

cond-mat.str-el↗

arXiv2017

Irreversible proliferation of magnetic moments at cleaved surfaces of the topological Kondo insulator SmB6

The compound SmB$_6$ is the best established realization of a topological Kondo insulator, in which a topological insulator state is obtained through Kondo coherence. Recent studies have found evidence that the surface of SmB$_6$ hosts ferromagnetic domains, creating an intrinsic platform for unidirectional ballistic transport at the domain boundaries. Here, surface-sensitive X-ray absorption (XAS) and bulk-sensitive resonant inelastic X-ray scattering (RIXS) spectra are measured at the Sm N$_{4,5}$-edge, and used to evaluate electronic symmetries, excitations and temperature dependence near the surface of cleaved samples. The XAS data show that the density of large-moment atomic multiplet states on a cleaved surface grows irreversibly over time, to a degree that likely exceeds a related change that has recently been observed in the surface 4f orbital occupation.

cond-mat.str-el↗

arXiv2016

Experimental signatures of phase interference and sub-femtosecond time dynamics on the incident energy axis of resonant inelastic X-ray scattering

Core hole resonance is used in X-ray spectroscopy to incisively probe the local electronic states of many-body systems. Here, resonant inelastic X-ray scattering (RIXS) is studied as a function of incident photon energy on Mott insulators SrCuO2 and NiO to examine how resonance states decay into different excitation symmetries at the transition metal M-, L- and K-edges. Quantum interference patterns characteristic of the two major RIXS mechanisms are identified within the data, and used to distinguish the attosecond scale scattering dynamics by which fundamental excitations of a many-body system are created. A function is proposed to experimentally evaluate whether a particular excitation has constructive or destructive interference in the RIXS cross-section, and corroborates other evidence that an anomalous excitation is present at the leading edge of the Mott gap in quasi-one dimensional SrCuO2.

cond-mat.str-el↗

arXiv2015

Selective Interface Control of Order Parameters in Complex Oxides

In complex materials observed electronic phases and transitions between them often involves coupling between many degrees of freedom whose entanglement convolutes understanding of the instigating mechanism. Metal-insulator transitions are one such problem where coupling to the structural, orbital, charge, and magnetic order parameters frequently obscures the underlying physics. Here, we demonstrate a way to unravel this conundrum by heterostructuring a prototypical multi-ordered complex oxide NdNiO3 in ultra thin geometry, which preserves the metal-to-insulator transition and bulk-like magnetic order parameter, but entirely suppresses the symmetry lowering and charge order parameter. These findings illustrate the utility of heterointerfaces as a powerful method for removing competing order parameters to gain greater insight into the nature of the transition, here revealing that the magnetic order generates the transition independently, leading to a purely electronic Mott metal-insulator transition.

cond-mat.str-el↗

arXiv2015

Response to Comment (arXiv:1506.02787v1) on Selective Interface Control of Order Parameters in Complex Oxides

In response to Lu et al, (arXiv:1506.02787v1), here we present a detailed writeup concerning the questions raised in their comment on our eprint (arXiv:1505.07451). The key question raised by Lu et al was if the bulk-like charge ordered state becomes indetectable with resonant scattering due to ultrathin film thickness. In this reply, we first detail the relation of our work to past work on the same compound by Staub et al to demonstrate that the presented data are indeed sufficient to support our claims of no charge order on ultra thin films of NdNiO3 (NNO) on NdGaO3 (NGO). Further, we demonstrate that if a well defined charge ordered phase exists in ultra thin films, it is indeed resolvable such as that in EuNiO3 (ENO).

cond-mat.str-el↗

arXiv2015

Spectroscopic determination of the atomic f-electron symmetry underlying hidden order in URu$_2$Si$_2$

The low temperature hidden order state of URu$_2$Si$_2$ has long been a subject of intense speculation, and is thought to represent an as yet undetermined many-body quantum state not realized by other known materials. Here, X-ray absorption spectroscopy (XAS) and high resolution resonant inelastic X-ray scattering (RIXS) are used to observe electronic excitation spectra of URu$_2$Si$_2$, as a means to identify the degrees of freedom available to constitute the hidden order wavefunction. Excitations are shown to have symmetries that derive from a correlated $5f^2$ atomic multiplet basis that is modified by itinerancy. The features, amplitude and temperature dependence of linear dichroism are in agreement with ground states that closely resemble the doublet $Γ_5$ crystal field state of uranium.

cond-mat.mtrl-sci↗

arXiv2014

Measurement of the spectral line shapes for orbital excitations in the Mott insulator CoO using high-resolution resonant inelastic x-ray scattering

We establish the spectral line shape of orbital excitations created by resonant inelastic X-ray scattering for the model Mott insulator CoO. Improved experimental energy resolution reveals that the line shapes are strikingly different from expectations in a first principles-based atomic multiplet model. Extended theoretical simulations are performed to identify the underlying physical origins, which include a pronounced thermal tail reminiscent of anti-Stokes scattering on the energy gain side of excitations, and an essential contribution from interatomic many-body dynamics on the energy loss side of excitations.

cond-mat.str-el↗

arXiv2013

Heterointerface engineered electronic and magnetic phases of NdNiO3 thin films

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 Néel 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.

cond-mat.str-el↗

arXiv2012

Multiplet resonance lifetimes in resonant inelastic X-ray scattering involving shallow core levels

Resonant inelastic X-ray scattering (RIXS) spectra of model copper- and nickel-based transition metal oxides are measured over a wide range of energies near the M-edge (h$ν$=60-80eV) to better understand the properties of resonant scattering involving shallow core levels. Standard multiplet RIXS calculations are found to deviate significantly from the observed spectra. However, by incorporating the self consistently calculated decay lifetime for each intermediate resonance state within a given resonance edge, we obtain dramatically improved agreement between data and theory. Our results suggest that these textured lifetime corrections can enable a quantitative correspondence between first principles predictions and RIXS data on model multiplet systems. This accurate model is also used to analyze resonant elastic scattering, which displays the elastic Fano effect and provides a rough upper bound for the core hole shake-up response time.

cond-mat.str-el↗

arXiv2012

Disentangling a quantum antiferromagnet with resonant inelastic X-ray scattering

Low-dimensional copper oxide lattices naturally manifest electronic states with strong short range quantum entanglement, which are known to lead to remarkable emergent material properties. However the nanometer scale many-body wavefunction is challenging to measure or manipulate in a simple way. In this study, X-ray induced $dd$ electronic transitions are used to suppress spin entanglement across a single lattice site in the spin-1/2 antiferromagnetic chain compound SrCuO$_2$, revealing a class of cuprate magnetic excitations that result from breaking the spin chain. These measurements are the first to employ two closely spaced X-ray resonances of copper (M$_2$ and M$_3$) as a form of natural 2-slit interferometer to distinguish between different types of electronic transition and resolve how they influence the dynamics of nearby spin-entangled electrons.

cond-mat.str-el↗

arXiv2011

Widespread spin polarization effects in photoemission from topological insulators

High resolution spin- and angle-resolved photoemission spectroscopy (spin-ARPES) was performed on the three-dimensional topological insulator Bi$_2$Se$_3$ using a recently developed high-efficiency spectrometer. The topological surface state's helical spin structure is observed, in agreement with theoretical prediction. Spin textures of both chiralities, at energies above and below the Dirac point, are observed, and the spin structure is found to persist at room temperature. The measurements reveal additional unexpected spin polarization effects, which also originate from the spin-orbit interaction, but are well differentiated from topological physics by contrasting momentum and photon energy and polarization dependencies. These observations demonstrate significant deviations of photoelectron and quasiparticle spin polarizations. Our findings illustrate the inherent complexity of spin-resolved ARPES and demonstrate key considerations for interpreting experimental results.

cond-mat.mtrl-sci↗