Temperature study of the giant spin Hall effect in the bulk limit of 
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Chen, Wenzhe; Xiao, Gang; Zhang, Qiang; Zhang, Xixiang

doi:10.1103/physrevb.98.134411

Cited by 32 publications

(16 citation statements)

References 38 publications

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“…Using the calculated intrinsic spin Hall conductivity for pristine β-W and the calculated electrical resistivity due to scattering from O impurities, the intrinsic SHA is estimated to be θ int β = −37%. For β-W, the experimental SHAs have been reported between −30% and −64% 4,5,37,42,50 in good agreement with our estimated values. This finding suggests that the stabilizing impurities do not have a significant effect on the spin Hall conductivity.…”

Section: Discussionsupporting

confidence: 90%

“…Using a slow deposition procedure, Chen et al 42 (blue inverted triangle) were able to grow β-W films up to 18 nm and the extracted SHC is close to our predicted range for pristine β-W intrinsic SHC. Some other studies 5,42,50,51 have measured SHC values higher than our upper limit for the intrinsic SHC. One possible explanation for these high values could be due to the ferromagnetic/heavy metal interface spin transmission factor used to determine the intrinsic spin Hall angle.…”

Section: E Total Spin Hall Conductivitysupporting

confidence: 80%

“…The magnitude of the Spin Hall conductivity as a function of tungsten film thickness is shown for a variety of experimental measurements 4,5,37,41,42,[50][51][52][53][54] and theoretical predictions 6,47 . The calculated bulk intrinsic SHC for pristine β-W is shown at the Fermi energy (red dashed line) and for maximum possible value with p-type doping (black dashed line).…”

Section: Figmentioning

confidence: 99%

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Impact of impurities on the spin Hall conductivity in β -W

McHugh

Goh

Gradhand

et al. 2020

Phys. Rev. Materials

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While the metastable β (A15) phase of tungsten has one of the largest spin Hall angles measured, the origin of this high spin Hall conductivity is still unclear. Since large concentrations of oxygen and nitrogen are often used to stabilize β tungsten, it is not obvious whether the high spin Hall conductivity is due to an intrinsic or extrinsic effect. In this work, we have examined the influence of O and N dopants on the spin Hall conductivity and spin Hall angle of β-W. Using multiple first principles approaches, we examine both the intrinsic and extrinsic (skew scattering) contributions to spin Hall conductivity. We find that intrinsic spin Hall conductivity calculations for pristine β-W are in excellent agreement with experiment. However, when the effect of high concentrations (11 at.%) of O or N interstitials on the electronic structures is taken into account, the predicted intrinsic spin Hall conductivity is significantly reduced. Skew scattering calculations for O and N interstitials in β-W indicate that extrinsic contributions have a limited impact on the total spin Hall conductivity. However, we find that the spin-flip scattering at O and N impurities can well explain the experimentally found spin-diffusion length within the range of 1-5 nm. To explain these findings, we propose that dopants (O and N) help to stabilize β-W grains during film deposition and afterwards segregate to the grain boundaries. This process leads to films of relatively pristine small β-W grains and grain boundaries with high concentrations of O or N scattering sites. This combination provides high spin Hall conductivity and large electrical resistance, leading to high spin Hall angles. This work shows that engineering grain boundary properties in other high spin Hall conductivity materials could provide an effective way to boost the spin Hall angle.

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Section: Discussionsupporting

confidence: 90%

Section: E Total Spin Hall Conductivitysupporting

confidence: 80%

Section: Figmentioning

confidence: 99%

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Impact of impurities on the spin Hall conductivity in β -W

McHugh

Goh

Gradhand

et al. 2020

Phys. Rev. Materials

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“…Beyond conventional electronics where electron charges play a dominant role, spintronics has been developed by relying on the electron spins as a memory and logic agent with their distinctive "spin-up" and "spin-down" binary states [1][2][3][4][5][6][7][8]. Among spintronic devices [1], magnetic domain walls (DWs) have been proposed as device elements, for example, in the innovative domain-wall racetrack memory design [9,10].…”

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confidence: 99%

Resistance of domain-wall states in half-metallic CrO2

2018

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The half-metallic CrO 2 with nearly 100% spin polarization is an ideal system to study magnetic domain wall resistance, which differs from the resistance (or resistivity) inside a single-domain. To experimentally measure the domain wall resistance, we design and prepare a special CrO 2 epitaxial nanostructure with an asymmetrical weak link to localize a single domain wall, by using the techniques of chemical vapor deposition and selective-area growth. This structure provides a capability to generate and annihilate a domain wall near the weak link. By contrasting the resistance between a single-domain state and a domain state, we observe a repeatable and reversible resistance jump, namely domain wall resistance, in half metallic CrO 2. Using the Levy-Zhang model, we further obtain the spin asymmetry ratio / between resistivities in the two spin channels. The ratio, 4256 ± 388 at 5.0 K, is much larger than that of conventional ferromagnetic metals, attesting the half-metallicity of CrO 2 .

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“…For ρ 0 a pure state, this distribution is also known as that of 'Haar states' [31]. Entanglement spectrum of reduced density matrices of Haar states has been studied in [34][35][36] by using Wishart ensembles [32,33] (See the Supplementary Material for a brief discussion). Indeed, the U (H V )-invariance means that, for any unitary V , the density matrices ρ and V ρV † are identi-cally distributed.…”

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confidence: 99%

Universal fluctuations around typicality for quantum ergodic systems

2020

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For a quantum system in a macroscopically large volume V , prepared in a pure state and subject to maximally noisy or ergodic unitary dynamics, the reduced density matrix of any sub-system v ≪ V is almost surely totally mixed. We show that the fluctuations around this limiting value, evaluated according to the invariant measure of these unitary flows, are captured by the Gaussian unitary ensemble (GUE) of random matrix theory. An extension of this statement, applicable when the unitary transformations conserve the energy but are maximally noisy or ergodic on any energy shell, allows to decipher the fluctuations around canonical typicality. According to typicality, if the large system is prepared in a generic pure state in a given energy shell, the reduced density matrix of the sub-system is almost surely the canonical Gibbs state of that sub-system. We show that the fluctuations around the Gibbs state are encoded in a deformation of the GUE whose covariance is specified by the Gibbs state. Contact with the eigenstate thermalisation hypothesis (ETH) is discussed.Introduction.-Understanding how isolated quantum systems relax towards thermal equilibrium is a central question in quantum statistical physics. There are essentially two lines of thought in the literature: an ensemblist point of view, according to which a system in thermal equilibrium is represented by a statistical ensemble of states close to the canonical or micro-canonical mixed state, and a purist perspective, according to which a large system in a single pure state may behave as thermal for any local measurement. See [1][2][3] for thorough discussions. These understandings led to the related notions of typicality [4][5][6], partially present in Von Neumanns work [7], and of eigen-state thermal hypothesis (ETH) [8][9][10], formalising under which conditions a pure state can describe thermal equilibrium locally.Thermalisation occurs via entanglement which allows information to spread over the system. Recent studies of random quantum circuits [11][12][13][14] gave detailed hints on this mechanism. Thermalisation may be quantified by looking at properties of the system state reduced to small sub-systems, such as the entanglement spectrum [15]. It is now believed that there is a link between thermalisation and the distribution of the entanglement spectrum [16,17], e.g. whether it is Poisson or Wigner-Dyson like. For instance, entanglement spectrum statistics have been used as diagnosis for thermalisation, distinguishing Clifford circuits from universal quantum circuits [18]. This establishes a link between thermalisation, which is a statement about typical behaviour, and fluctuations, which goes beyond typical behaviours.This letter aims at making this link more precise, and possibly rigorous. Under the assumption of some form of ergodicity, we present a simple derivation and characterisation of the fluctuations of density matrices reduced to small sub-systems embedded in a large system prepared in a pure state. The form of these fluctuations makes contac...

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Temperature study of the giant spin Hall effect in the bulk limit of β−W

Cited by 32 publications

References 38 publications

Impact of impurities on the spin Hall conductivity in β -W

Impact of impurities on the spin Hall conductivity in β -W

Resistance of domain-wall states in half-metallic CrO2

Universal fluctuations around typicality for quantum ergodic systems

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