1,920 research outputs found
Electronic Raman scattering in Tl2Ba2CuO6+x: symmetry of the order parameter, oxygen doping effects, and normal state scattering
Single crystals of the optimally doped, moderately and strongly overdoped
high temperature superconductor Tl2Ba2CuO6+x (Tl-2201) with Tc=80, 56 and 30K,
respectively, have been investigated by polarized Raman scattering. By taking
the peak position of the B_1g component of electronic Raman scattering as
2Delta_0 we found that the reduced gap value (2Delta_0/k_BT_c) strongly
decreases with increasing doping. The behavior of the low frequency scattering
for the B_1g and B_2g scattering components is similar for optimally doped and
overdoped crystals and can be described by a w^3 - and w -law, respectively,
which is consistent with a d-wave symmetry of the order parameter. In contrast
to the optimally doped Tl-2201 in both, moderately and strongly overdoped
Tl-2201, the relative (compared to the B_1g) intensity of the A_1g scattering
component is suppressed. We suggest that the van Hove singularity is
responsible for the observed changes of Raman intensity and reduced gap value
with doping. Electronic Raman scattering in the normal state is discussed in
the context of the scattering from impurities and compared to the existing
infrared data. The scattering rate evaluated from the Raman measurements is
smaller for the overdoped samples, compared to the moderately overdoped
samples.Comment: 7 pages, 7 figure
Multiple magnon modes in the CoSnS Weyl semimetal candidate
We experimentally investigate electron transport in kagome-lattice
ferromagnet CoSnS, which is regarded as a time-reversal symmetry
broken Weyl semimetal candidate. We demonstrate curves with
pronounced asymmetric spikes, similar to those attributed to
current-induced spin-wave excitations in ferromagnetic multilayers. In contrast
to multilayers, we observe several spikes' sequences at low,
10 A/cm, current densities for a thick single-crystal
CoSnS flake in the regime of fully spin-polarized bulk. The spikes
at low current densities can be attributed to novel magnon branches in magnetic
Weyl semimetals, which are predicted due to the coupling between two magnetic
moments mediated by Weyl fermions. Presence of spin-transfer effects at low
current densities in CoSnS makes the material attractive for
applications in spintronics.Comment: final versio
Multivalued current-phase relationship in a.c. Josephson effect for a three-dimensional Weyl semimetal WTe
We experimentally study electron transport between two superconducting indium
leads, coupled to a single WTe crystal, which is a three-dimensional Weyl
semimetal. We demonstrate Josephson current in long 5~m In-WTe-In
junctions, as confirmed by the observation of integer (1,2,3) and fractional
(1/3, 1/2, 2/3) Shapiro steps under microwave irradiation. Demonstration of
fractional a.c. Josephson effect indicates multivalued character of the
current-phase relationship, which we connect with Weyl topological surface
states contribution to Josephson current. In contrast to topological insulators
and Dirac semimetals, we do not observe periodicity in a.c. Josephson
effect for WTe at different frequencies and power, which might reflect
chiral character of the Fermi arc surface states in Weyl semimetal.Comment: the text is seriously corrected. arXiv admin note: text overlap with
arXiv:1801.0955
Signature of Fermi arc surface states in Andreev reflection at the WTe Weyl semimetal surface
We experimentally investigate charge transport through the interface between
a niobium superconductor and a three-dimensional WTe Weyl semimetal. In
addition to classical Andreev reflection, we observe sharp non-periodic subgap
resistance resonances. From an analysis of their positions, magnetic field and
temperature dependencies, we can interpret them as an analog of Tomasch
oscillations for transport along the topological surface state across the
region of proximity-induced superconductivity at the Nb-WTe interface.
Observation of distinct geometrical resonances implies a specific transmission
direction for carriers, which is a hallmark of the Fermi arc surface states.Comment: 5 pages, some misprints has been correcte
Revisión de la edad del Grupo de Asha en los Urales meridionales
The Asha Group of the South Urals, initially erected by Albert Olli as Palaeozoic sedimentary complex, more than half a century ago was considered as a key section for the Vendian (Ediacaran) of the western slope of the South Urals. However, the ca. 1700 m-thick terrigenous sedimentary sequence is characterised by unusual low biodiversity of Ediacaran macrofossils, which might be explained by relatively young age of the Asha Group and possible mass extinction event in the end of Ediacaran Period. The relatively young age was confirmed by the U-Pb zircon date of 547.6±3.8 Ma obtained from the tuff in the lower part of the Basa Formation as well as finding of ichnospecies Didymaulichnus tirasensis in the upper part of Zigan formation. However, in 2018 it has been documented there the mass appearing of D. tirasensis in the lowermost part of the Basa Formation. Therefore, the Vendian (Ediacaran) age of the Asha Group of the South Urals can be revisited in favour to terminal Ediacaran- Cambrian or even early Cambrian.El Grupo de Asha de los Urales meridionales, inicialmente definido por Albert Olli como complejo sedimentario paleozoico, hace más de medio siglo, fue considerado como una sección clave para el Véndico (Ediacárico) de la vertiente occidental de los Urales meridionales. Sin embargo, secuencia sedimentaria terrÃgena de unos 1.700 m de espesor se caracteriza por una biodiversidad inusualmente baja de macrofósiles ediacaranos, lo que podrÃa explicarse por la edad relativamente temprana del grupo y el posible evento de extinción masiva que marca el final del perÃodo Ediacárico. La edad relativamente temprana fue confirmada por la datación de 547.6±3.8 Ma obtenida de una toba en la parte inferior de la Formación de Basa, asà como por el hallazgo de la iconospecie Didymaulichnus tirasensis en la parte superior de la Formación de Zigan. Sin embargo, en 2018 se ha documentó la aparición masiva de D. tirasensis en la parte más baja de la Formación de Basa. Por lo tanto, la edad Véndico (Ediacárico) del Grupo de Asha de los Urales meridionales puede ser reconsiderada en favor del Ediacárico terminal-Cámbrico o incluso del Cambrian temprano
Gate-dependent non-linear Hall effect at room temperature in topological semimetal GeTe
We experimentally investigate non-linear Hall effect as zero-frequency and
second-harmonic transverse voltage responses to ac electric current for
topological semimetal GeTe. A thick single-crystal GeTe flake is placed on the
Si/SiO substrate, where the p-doped Si layer serves as a gate electrode. We
confirm, that electron concentration is not gate-sensitive in thick GeTe flakes
due to the gate field screening by bulk carriers. In contrast, by transverse
voltage measurements, we demonstrate that the non-linear Hall effect shows
pronounced dependence on the gate electric field at room temperature. Since the
non-linear Hall effect is a direct consequence of a Berry curvature dipole in
topological media, our observations indicate that Berry curvature can be
controlled by the gate electric field. This experimental observation can be
understood as a result of the known dependence of giant Rashba splitting on the
external electric field in GeTe. For possible applications, the zero-frequency
gate-controlled non-linear Hall effect can be used for the efficient broad-band
rectification
Current-induced control of the polarization state in a polar metal based heterostructure SnSe/WTe
The concept of a polar metal proposes new approach of current-induced
polarization control for ferroelectrics. We fabricate SnSe/WTe
heterostructure to experimentally investigate charge transport between two
ferroelectric van der Waals materials with different polarization directions.
WTe is a polar metal with out-of-plane ferroelectric polarization, while
SnSe ferroelectric semiconductor is polarized in-plane, so one should expect
complicated polarization structure at the SnSe/WTe interface. We study
curves, which demonstrate sharp symmetric drop to zero
differential conductance at some threshold bias voltages , which
are nearly symmetric in respect to the bias sign. While the gate electric field
is too small to noticeably affect the carrier concentration, the positive and
negative threshold positions are sensitive to the gate voltage. Also,
SnSe/WTe heterostructure shows re-entrant transition to the low-conductive
state for abrupt change of the bias voltage even below the threshold
values. This behavior can not be observed for single SnSe or WTe flakes, so
we interpret it as a result of the SnSe/WTe interface coupling. In this
case, some threshold value of the electric field at the SnSe/WTe interface
is enough to drive 90 change of the initial SnSe in-plane polarization
in the overlap region. The polarization mismatch leads to the significant
interface resistance contribution, analogously to the scattering of the charge
carriers on the domain walls. Thus, we demonstrate polarization state control
by electron transport through the SnSe/WTe interface
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