scholarly journals Finite-temperature violation of the anomalous transverse Wiedemann-Franz law

2020 ◽  
Vol 6 (17) ◽  
pp. eaaz3522 ◽  
Author(s):  
Liangcai Xu ◽  
Xiaokang Li ◽  
Xiufang Lu ◽  
Clément Collignon ◽  
Huixia Fu ◽  
...  
Keyword(s):  
Wave Function ◽  
Inelastic Scattering ◽  
Finite Temperature ◽  
Room Temperature ◽  
Theoretical Calculations ◽  
Data Accuracy ◽  
Berry Curvature ◽  
Curvature Distribution ◽  
Open Question ◽  
Transverse Response

The Wiedemann-Franz (WF) law has been tested in numerous solids, but the extent of its relevance to the anomalous transverse transport and the topological nature of the wave function, remains an open question. Here, we present a study of anomalous transverse response in the noncollinear antiferromagnet Mn3Ge extended from room temperature down to sub-kelvin temperature and find that the anomalous Lorenz ratio remains close to the Sommerfeld value up to 100 K but not above. The finite-temperature violation of the WF correlation is caused by a mismatch between the thermal and electrical summations of the Berry curvature and not by inelastic scattering. This interpretation is backed by our theoretical calculations, which reveals a competition between the temperature and the Berry curvature distribution. The data accuracy is supported by verifying the anomalous Bridgman relation. The anomalous Lorenz ratio is thus an extremely sensitive probe of the Berry spectrum of a solid.

Positron Annihilation and the Band Structure in Molybdenum

1972 ◽  
Vol 50 (15) ◽  
pp. 1777-1781 ◽  
Author(s):  
S. M. Kim ◽  
W. J. L. Buyers
Keyword(s):  
Wave Function ◽  
Band Structure ◽  
Angular Correlation ◽  
Room Temperature ◽  
Theoretical Calculations ◽  
Plane Waves ◽  
Interpolation Scheme ◽  
Accurate Representation ◽  
Two Photon ◽  
Positron Wave Function

Measurements have been made of the two-photon angular correlation from positrons annihilating in single-crystal molybdenum at room temperature. By means of a combination of conventional slits and Soller slits the number of annihilations for which the momentum lies along a line in the momentum distribution is obtained, and results are presented for the [ζ,ζ,0], [0,0,ζ, and [ζ,ζ,0.71] directions. Theoretical calculations of the angular correlation have been made based on the interpolation or pseudopotential scheme with s–d interaction included. The parameters of the interpolation scheme have been chosen so that an accurate representation is obtained of the APW band structure of Mattheiss. The positron wave function has been obtained in terms of 141 plane waves. The width of the calculated two-photon angular correlation is found to be much broader than the experimental width unless the relative s and d enhancement is considered.

scholarly journals Large anomalous Hall effect driven by a nonvanishing Berry curvature in the noncolinear antiferromagnet Mn3Ge

2016 ◽  
Vol 2 (4) ◽  
pp. e1501870 ◽  
Author(s):  
Ajaya K. Nayak ◽  
Julia Erika Fischer ◽  
Yan Sun ◽  
Binghai Yan ◽  
Julie Karel ◽  
...  
Keyword(s):  
Hall Effect ◽  
Data Storage ◽  
Room Temperature ◽  
Theoretical Calculations ◽  
Anomalous Hall Effect ◽  
Spin Hall Effect ◽  
Storage Devices ◽  
Berry Curvature ◽  
Ferromagnetic Metals ◽  
Hall Effect Measurements

It is well established that the anomalous Hall effect displayed by a ferromagnet scales with its magnetization. Therefore, an antiferromagnet that has no net magnetization should exhibit no anomalous Hall effect. We show that the noncolinear triangular antiferromagnet Mn3Ge exhibits a large anomalous Hall effect comparable to that of ferromagnetic metals; the magnitude of the anomalous conductivity is ~500 (ohm·cm)−1 at 2 K and ~50 (ohm·cm)−1 at room temperature. The angular dependence of the anomalous Hall effect measurements confirms that the small residual in-plane magnetic moment has no role in the observed effect except to control the chirality of the spin triangular structure. Our theoretical calculations demonstrate that the large anomalous Hall effect in Mn3Ge originates from a nonvanishing Berry curvature that arises from the chiral spin structure, and that also results in a large spin Hall effect of 1100 (ħ/e) (ohm·cm)−1, comparable to that of platinum. The present results pave the way toward the realization of room temperature antiferromagnetic spintronics and spin Hall effect–based data storage devices.

scholarly journals Colossal anomalous Nernst effect in a correlated noncentrosymmetric kagome ferromagnet

2021 ◽  
Vol 7 (13) ◽  
pp. eabf1467
Author(s):  
T. Asaba ◽  
V. Ivanov ◽  
S. M. Thomas ◽  
S. Y. Savrasov ◽  
J. D. Thompson ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electronic Structure ◽  
Theoretical Calculations ◽  
Zero Magnetic Field ◽  
Nernst Effect ◽  
Nodal Lines ◽  
Transverse Response ◽  
Narrow Bands ◽  
Strong Spin ◽  
Anomalous Nernst Effect

The transverse voltage generated by a temperature gradient in a perpendicularly applied magnetic field, termed the Nernst effect, has promise for thermoelectric applications and for probing electronic structure. In magnetic materials, an anomalous Nernst effect (ANE) is possible in a zero magnetic field. We report a colossal ANE in the ferromagnetic metal UCo0.8Ru0.2Al, reaching 23 microvolts per kelvin. Uranium’s 5f electrons provide strong electronic correlations that lead to narrow bands, a known route to producing a large thermoelectric response. In addition, uranium’s strong spin-orbit coupling produces an intrinsic transverse response in this material due to the Berry curvature associated with the relativistic electronic structure. Theoretical calculations show that in UCo0.8Ru0.2Al at least 148 Weyl nodes, and two nodal lines, exist within 60 millielectron volt of the Fermi level. This work demonstrates that magnetic actinide materials can host strong Nernst and Hall responses due to their combined correlated and topological nature.

scholarly journals Nonreciprocal charge transport up to room temperature in bulk Rashba semiconductor α-GeTe

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yan Li ◽  
Yang Li ◽  
Peng Li ◽  
Bin Fang ◽  
Xu Yang ◽  
...  
Keyword(s):  
Charge Transport ◽  
Room Temperature ◽  
Theoretical Calculations ◽  
Ferromagnetic Layer ◽  
Spin Splitting ◽  
New Paradigm ◽  
Rashba Spin ◽  
Rashba Spin Splitting ◽  
Fundamental Insight ◽  
Insight Into

AbstractNonmagnetic Rashba systems with broken inversion symmetry are expected to exhibit nonreciprocal charge transport, a new paradigm of unidirectional magnetoresistance in the absence of ferromagnetic layer. So far, most work on nonreciprocal transport has been solely limited to cryogenic temperatures, which is a major obstacle for exploiting the room-temperature two-terminal devices based on such a nonreciprocal response. Here, we report a nonreciprocal charge transport behavior up to room temperature in semiconductor α-GeTe with coexisting the surface and bulk Rashba states. The combination of the band structure measurements and theoretical calculations strongly suggest that the nonreciprocal response is ascribed to the giant bulk Rashba spin splitting rather than the surface Rashba states. Remarkably, we find that the magnitude of the nonreciprocal response shows an unexpected non-monotonical dependence on temperature. The extended theoretical model based on the second-order spin–orbit coupled magnetotransport enables us to establish the correlation between the nonlinear magnetoresistance and the spin textures in the Rashba system. Our findings offer significant fundamental insight into the physics underlying the nonreciprocity and may pave a route for future rectification devices.

scholarly journals From lithium to sodium: cell chemistry of room temperature sodium–air and sodium–sulfur batteries

2015 ◽  
Vol 6 ◽  
pp. 1016-1055 ◽  
Author(s):  
Philipp Adelhelm ◽  
Pascal Hartmann ◽  
Conrad L Bender ◽  
Martin Busche ◽  
Christine Eufinger ◽  
...  
Keyword(s):  
Energy Density ◽  
Large Scale ◽  
Room Temperature ◽  
Low Cost ◽  
Strong Impact ◽  
Performance Improvements ◽  
Key Issues ◽  
Lithium Oxygen Batteries ◽  
Open Question ◽  
Lithium Sulfur

Research devoted to room temperature lithium–sulfur (Li/S8) and lithium–oxygen (Li/O2) batteries has significantly increased over the past ten years. The race to develop such cell systems is mainly motivated by the very high theoretical energy density and the abundance of sulfur and oxygen. The cell chemistry, however, is complex, and progress toward practical device development remains hampered by some fundamental key issues, which are currently being tackled by numerous approaches. Quite surprisingly, not much is known about the analogous sodium-based battery systems, although the already commercialized, high-temperature Na/S8 and Na/NiCl2 batteries suggest that a rechargeable battery based on sodium is feasible on a large scale. Moreover, the natural abundance of sodium is an attractive benefit for the development of batteries based on low cost components. This review provides a summary of the state-of-the-art knowledge on lithium–sulfur and lithium–oxygen batteries and a direct comparison with the analogous sodium systems. The general properties, major benefits and challenges, recent strategies for performance improvements and general guidelines for further development are summarized and critically discussed. In general, the substitution of lithium for sodium has a strong impact on the overall properties of the cell reaction and differences in ion transport, phase stability, electrode potential, energy density, etc. can be thus expected. Whether these differences will benefit a more reversible cell chemistry is still an open question, but some of the first reports on room temperature Na/S8 and Na/O2 cells already show some exciting differences as compared to the established Li/S8 and Li/O2 systems.

Analysis of 12C(α, α′) using α condensate model wave function

2006 ◽  
Vol 21 (31n33) ◽  
pp. 2341-2346
Author(s):  
M. Takashina ◽  
Y. Sakuragi
Keyword(s):  
Wave Function ◽  
Angular Distribution ◽  
Excited State ◽  
Inelastic Scattering ◽  
Transition Density ◽  
Nuclear Radius ◽  
Oscillation Pattern ◽  
Model Wave Function ◽  
Model Wave

We analyze the inelastic scattering of the α+12 C system leading to the [Formula: see text] state in 12 C at incident energies of E α=139 MeV ~ 240 MeV using α condensate model wave function, and investigate the affection of the large nuclear radius of [Formula: see text] on the inelastic angular distribution. It is found that the oscillation pattern in inelastic angular distribution is sensitive to the extent of transition density rather than the nuclear radius of the excited state.

Broadening and shifting of the depolarized component of the Raman Q branch in D2 at room temperature

1995 ◽  
Vol 73 (7-8) ◽  
pp. 530-536 ◽  
Author(s):  
P. M. Sinclair ◽  
P. Duggan ◽  
J. R. Drummond ◽  
A. D. May
Keyword(s):  
Spectral Data ◽  
Direct Measurement ◽  
Room Temperature ◽  
Theoretical Calculations

We report the first direct measurement of the broadening and shifting of the depolarized component of the Raman Q branch in D2. Spectral data were recorded from 1.5 to 12 amagat at 305.2 K. Both the measured broadening and shifting of the depolarized component are significantly different from that for the polarized Q branch. These results can be used as a check of theoretical calculations when they become available. Here they are used to correct previously reported values of the broadening of the polarized part of the Q-branch spectrum. Measured values of the ratio of the depolarized to polarized intensity for the Q-branch lines are also given.

scholarly journals InAs/InAsSb Strain-Balanced Superlattices for Longwave Infrared Detectors

Sensors ◽  
2019 ◽  
Vol 19 (8) ◽  
pp. 1907 ◽  
Author(s):  
Tetiana Manyk ◽  
Krystian Michalczewski ◽  
Krzysztof Murawski ◽  
Piotr Martyniuk ◽  
Jaroslaw Rutkowski
Keyword(s):  
Wave Function ◽  
Infrared Detectors ◽  
Theoretical Calculations ◽  
Spectral Response ◽  
Health Condition ◽  
Type Ii ◽  
Response Characteristics ◽  
Effective Masses ◽  
Gaas Substrates ◽  
The Stability

The InAs/InAsSb type-II superlattices (T2SLs) grown on a GaSb buffer layer and GaAs substrates were theoretically investigated. Due to the stability at high operating temperatures, T2SLs could be used for detectors operating in the longwave infrared (LWIR) range for different sensors to include, e.g., CH4 and C2H6 detection, which is very relevant for health condition monitoring. The theoretical calculations were carried out by the 8 × 8 k·p method. The estimated electrons and heavy holes probability distribution in a InAs/InAsSb superlattice (SL) shows that the wave function overlap increases while the thickness of the SL period decreases. The change in the effective masses for electrons and holes versus the SL period thickness for the kz-direction of the Brillouin zone is shown. The structures with a period lower than 15 nm are more optimal for the construction of LWIR detectors based on InAs/InAsSb SLs. The experimental results of InAs/InAsSb T2SLs energy bandgap were found to be comparable with the theoretical one. The proper fitting of theoretically calculated and experimentally measured spectral response characteristics in terms of a strain-balanced and unbalanced structures is shown.

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