Insulator-metal transition and valence instability in EuO near 130 kbar

Zimmer, H.-G.; Takemura, Keiji; Syassen, K.; Fischer, K.

doi:10.1103/physrevb.29.2350

Cited by 73 publications

(50 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This compares well with the appearance of a drudelike peak in the optical reflectivity and a jump in the room temperature resistivity at a pressure of ≈ 130 kbar, or a/a 0 = 0.96. [10,26] As seen in Figure 2, a saturation of the experimental parameter T I , which is thought to track T c , is also found around a/a 0 = 0.96. If T I does in fact track T c , then this saturation may be connected to the filled spin up 4f and empty 5d bands starting to overlap causing a mixed configuration of the J=7/2 magnetic Eu 4f 7 configuration and the J=0 non-magnetic Eu 4f 6 configuration.…”

mentioning

confidence: 69%

“…Our exchange parameters for the optimized bulk lattice parameter (J 1 = 0.66, J 2 = 0.19) are in good agreement with neutron measurements, and previous calculations. [23,24] Previous experimental studies have looked at the effect of hydrostatic pressure on T c [10,25] and the unit cell volume [26] in EuO. In Figure 2b we combine that data to plot the experimental change in T c as a function of lattice parameter.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Influence of epitaxial strain on the ferromagnetic semiconductorEuO: First-principles calculations

2008

View full text Add to dashboard Cite

From first principles calculations we investigate the electronic structure and the magnetic properties of EuO under hydrostatic and epitaxial forces. There is a complex interdependence of the O 2p and Eu 4f and 5d bands on the magnetism in EuO, and decreasing lattice parameters is an ideal method to increase the Curie temperature, Tc. Compared to hydrostatic pressure, the out-of-plane compensation that is available to epitaxial films influences this increase in Tc, although it is minimized by the small value of poisson's ratio for EuO. We find the semiconducting gap closes at a 6% in-plane lattice compression for epitaxy, at which point a significant conceptual change must occur in the active exchange mechanisms.

show abstract

mentioning

confidence: 69%

mentioning

confidence: 99%

Influence of epitaxial strain on the ferromagnetic semiconductorEuO: First-principles calculations

2008

View full text Add to dashboard Cite

show abstract

“…Consequently, the Mössbauer experiment sees a fast fluctuating valence [1] as a static average of both states while the XANES process is fast enough to separately probe both states. Interestingly, the proximity in the lifetime of the fluctuating valence state and lattice fluctuations (≈ 10 −13 ) may influence how the magnetism [9,18,19,23,25] and conductivity [17,25,26] of EuO respond to pressure as the 4f electronic bandwidth changes with lattice contraction. The general approximation "bond length is a unique function of bond valence" [11] is widely used to determine a material's valence based on crystal structure.…”

Section: +mentioning

confidence: 99%

“…After reaching about 92 GPa, the pressure was released and the structural changes were observed to be reversible. XRD results were previously used to argue, based on bondvalence sum rules [11,12], that the valence of Eu in EuO dramatically increases as a function of pressure with a first order valence transition towards a Eu 3+ state taking place at the modest isostructural volume collapse resulting in a 2.5+ valence at about 35 GPa [10,17]. While a volume collapse could in principle be a signature of a sizable increase in valence, just the opposite takes place at the structural phase transition in EuO, as discussed below.…”

Section: +mentioning

confidence: 99%

Reentrant Valence Transition in EuO at High Pressures: Beyond the Bond-Valence Model

Souza-Neto

Zhao

et al. 2012

Phys. Rev. Lett.

View full text Add to dashboard Cite

The pressure-dependent relation between Eu valence and lattice structure in model compound EuO is studied with synchrotron-based x-ray spectroscopic and diffraction techniques. Contrary to expectation, a 7% volume collapse at ≈ 45 GPa is accompanied by a reentrant Eu valence transition into a lower valence state. In addition to highlighting the need for probing both structure and electronic states directly when valence information is sought in mixed-valent systems, the results also show that widely used bond-valence methods fail to quantitatively describe the complex electronic valence behavior of EuO under pressure.The phenomenon of mixed-valency in f -electron systems occurs when otherwise localized f -orbitals of RareEarth or Actinide elements hybridize in the solid with s,p,d electrons. A quantum superposition of differently occupied (valence) f -states emerges when the energy difference between competing single-valent states is smaller than the f -electron bandwidth, usually termed fluctuating valence state [1]. The onset of mixed-valency under applied pressure, chemical substitutions, or finite temperature has dramatic consequences on the macroscopic properties of f -electron systems including volume collapse [2], quenched magnetism [3], onset of superconductivity [4,5], Kondo physics [6], and quantum criticality [4,5]. Despite mixed-valency being central to f -electron physics, our ability to directly probe this peculiar quantum electronic state at high pressures is limited.EuO with its simple NaCl (B1) crystal structure is a model system to study valence effects upon lattice compression [7]. Eu-containing compounds are prototypical mixed-valent systems because Eu can display both trivalent (as most Rare-Earths ions do) and divalent electronic states at ambient conditions, the latter stabilized by a half-filled 4f orbital occupation ([Xe]4f 7 5d 0 6 sAdditionally, the ferromagneticsemiconductor character of EuO [7] coupled with perfect spin-polarization of electronic states near the Fermi level generated interest for possible applications of EuO in Spintronics [8]. A dramatic, three-fold increase in magnetic ordering temperature is observed under applied pressures of up to ≈14 GPa (or at strained interfaces), reaching a maximum T C ≈ 200 K but decreasing at higher pressures [9]. The relationship between crystal structure, electronic structure and magnetic ordering temperature has fueled much of the research in EuO over the last two decades, with the question of Eu valency remaining key for a complete understanding of this and other f -electron mixed-valent systems. In this Letter we report direct measurements of electronic valence and crystal structure in Europium monoxide (EuO) at pressures up to 90 GPa using x-ray absorption spectroscopy, nuclear forward scattering and x-ray diffraction techniques. Below 40 GPa a complex, pressuredependent valence is observed to fluctuate between Eu 2+and Eu 3+ states at a frequency f > ∼ ∆E/h ∼ 0.15 PetaHertz where ∆E is the 4f bandwidth. At higher pressures we obse...

show abstract

“…For example, in the early 1980s, Syassen and Sonnenschein developed a high-pressure optical spectroscopy apparatus that covered the near IR to UV ranges (0.5-4 eV). 127) Syassen and coworkers studied various materials under high pressure such as K (potassium), 128) EuO, 129) YbS and YbO, 119) and Si. 92) At present, commercially available FTIR instruments coupled with a microscope (micro-FTIRs) generally cover a wide spectral range with a high spatial resolution and a high signal-to-noise ratio.…”

Section: High-pressure Ir Studies Without Using Ir-srmentioning

confidence: 99%

Infrared and Terahertz Spectroscopy of Strongly Correlated Electron Systems under Extreme Conditions

Kimura

Okamura

2013

J. Phys. Soc. Jpn.

View full text Add to dashboard Cite

Owing to its high brilliance, infrared and terahertz synchrotron radiation (IR/THz-SR) has emerged as a powerful tool for spectroscopy under extreme (i.e., technically more difficult) experimental conditions such as high pressure, high magnetic field, high spatial resolution, and a combination of these. The methodologies for pressure-and magneticfield-dependent spectroscopy and microscopy using IR/THz-SR have advanced rapidly worldwide. By applying them to strongly correlated electron systems (SCESs), many experimental studies have been performed on their electronic structures and phonon/molecular vibration modes under extreme conditions. Here, we review the recent progress of methodologies of IR/THz-SR spectroscopy and microscopy, and the experimental results on SCESs and other systems obtained under extreme conditions.

show abstract

Insulator-metal transition and valence instability in EuO near 130 kbar

Cited by 73 publications

References 19 publications

Influence of epitaxial strain on the ferromagnetic semiconductorEuO: First-principles calculations

Influence of epitaxial strain on the ferromagnetic semiconductorEuO: First-principles calculations

Reentrant Valence Transition in EuO at High Pressures: Beyond the Bond-Valence Model

Infrared and Terahertz Spectroscopy of Strongly Correlated Electron Systems under Extreme Conditions

Contact Info

Product

Resources

About