168 research outputs found
Finite-temperature violation of the anomalous transverse Wiedemann-Franz law
The Wiedemann-Franz (WF) law links the ratio of electronic charge and heat
conductivity to fundamental constants. It has been tested in numerous solids,
but the extent of its relevance to the anomalous transverse transport, which
represents the topological nature of the wave function, remains an open
question. Here we present a study of anomalous transverse response in the
noncollinear antiferromagnet MnGe 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, rather than the inelastic
scattering as observed in ordinary metals. This interpretation is backed by our
theoretical calculations, which reveals a competition between the temperature
and the Berry curvature distribution. The accuracy of the experiment is
supported by the verification of the Bridgman relation between the anomalous
Ettingshausen and Nernst effects. Our results identify the anomalous Lorenz
ratio as an extremely sensitive probe of Berry spectrum near the chemical
potential.Comment: 9 pages,6 figures, Supplemental Material include
Tuning the anomalous Nernst and Hall effects with shifting the chemical potential in Fe-doped and Ni-doped CoSnS
CoSnS is believed to be a magnetic Weyl semimetal. It displays
large anomalous Hall, Nernst and thermal Hall effects with a remarkably large
anomalous Hall angle. Here, we present a comprehensive study of how
substituting Co by Fe or Ni affects the electrical and thermoelectric
transport. We find that doping alters the amplitude of the anomalous transverse
coefficients. The maximum decrease in the amplitude of the low-temperature
anomalous Hall conductivity is twofold. Comparing our results
with theoretical calculations of the Berry spectrum assuming a rigid shift of
the Fermi level, we find that given the modest shift in the position of the
chemical potential induced by doping, the experimentally observed variation
occurs five times faster than expected. Doping affects the amplitude and the
sign of the anomalous Nernst coefficient. Despite these drastic changes, the
amplitude of the ratio at the Curie temperature
remains close to , in agreement with the scaling
relationship observed across many topological magnets.Comment: 8 pages, 9 figure
Enhanced thermal stability and electrical behavior of Zn-doped Sb2Te films for phase change memory application
Zn-doped Sb₂Te films are proposed to present the feasibility for phase-change memory application. Zn atoms are found to significantly increase crystallization temperature of Zn x (Sb₂Te)1−x films and be almost linearly with the wide range of Zn-doping concentration from x = 0 to 29.67 at.%. Crystalline resistances are enhanced by Zn-doping, while keeping the large amorphous/crystalline resistance ratio almost constant at ∼10⁵. Especially, the Zn 26.07 (Sb₂Te)73.93 and Zn 29.67 (Sb₂Te)70.33 films exhibit a larger resistance change, faster crystallization speed, and better thermal stability due to the formation of amorphous Zn-Sb and Zn-Te phases as well as uniform distribution of Sb₂Te crystalline grains
Phase change behaviors of Zn-doped Ge2Sb2Te5 films
This work was financially supported by the Program for
New Century Excellent Talents in University (Grant No.
NCET-10-0976), the International Science & Technology
Cooperation Program of China (Grant No. 2011DFA12040),
the National Program on Key Basic Research Project (973
Program) (Grant No. 2012CB722703), the Natural Science
Foundation of China (Grant Nos. 61008041 and 60978058),
the Natural Science Foundation of Zhejiang Province, China
(Grant No. Y1090996), the Natural Science Foundation of
Ningbo City, China (Grant No. 2011A610092), the Program
for Innovative Research Team of Ningbo city (Grant No.
2009B21007), and sponsored by K. C. Wong Magna Fund in
Ningbo University
Anomalous transverse response of CoMnGa and universality of the room-temperature ratio across topological magnets
The off-diagonal (electric, thermal and thermoelectric) transport
coefficients of a solid can acquire an anomalous component due to the
non-trivial topology of the Bloch waves. We present a study of the anomalous
Hall (AHE), Nernst (ANE) and thermal Hall effects (ATHE) in the Heusler Weyl
ferromagnet CoMnGa. The Anomalous Wiedemann-Franz law, linking electric and
thermal responses, was found to be valid over the whole temperature window.
This indicates that the AHE has an intrinsic origin and the Berry spectrum is
smooth in the immediate vicinity of the Fermi level. From the ANE data, we
extract the magnitude and temperature dependence of and put
under scrutiny the ratio, which approaches
k/e at room temperature. We show that in various topological magnets the
room-temperature magnitude of this ratio is a sizeable fraction of k/e and
argue that the two anomalous transverse coefficients depend on universal
constants, the Berry curvature averaged over a window set by either the Fermi
wavelength (for Hall) or the de Broglie thermal length (for Nernst). Since the
ratio of the latter two is close to unity at room temperature, such a universal
scaling finds a natural explanation in the intrinsic picture of anomalous
transverse coefficients.Comment: 5 pages, 4 figures, supplemental material include
Improved phase-change characteristics of Zn-doped amorphous Sb₇Te₃ films for high-speed and low-power phase change memory
The superior performance of Zn-doped Sb₇Te₃ films might be favorable for the application in phase change memory. It was found that Zn dopants were able to suppress phase separation and form single stable Sb2Te crystal grain, diminish the grain size, and enhance the amorphous thermal stability of Sb₇Te₃ film. Especially, Zn 30.19(Sb₇Te₃)69.81 film has higher crystallization temperature (∼258 °C), larger crystallization activation energy (∼4.15 eV), better data retention (∼170.6 °C for 10 yr), wider band gap (∼0.73 eV), and higher crystalline resistance. The minimum times for crystallization of Zn 30.19(Sb₇Te₃)69.81 were revealed to be as short as ∼10 ns at a given proper laser power of 70 mW.This work was financially supported by the International
Science & Technology Cooperation Program of China
(Grant No. 2011DFA12040), the National Program on Key
Basic Research Project (973 Program) (Grant No.
2012CB722703), the Natural Science Foundation of China
(Grant Nos. 61008041 and 60978058), the CAS Special
Grant for Postgraduate Research, Innovation and Practice,
the Program for Innovative Research Team of Ningbo city
(Grant No. 2009B21007), and sponsored by K. C. Wong
Magna Fund in Ningbo University
- …