15 research outputs found
Quasi Two-dimensional Vortex Matter in ThH Superhydride
A comprehensive study of the vortex phases and vortex dynamics is presented
for a recently discovered high-temperature superconductor ThH with
= 153 K at 170 GPa. The obtained results strongly suggest a
quasi two-dimensional (2D) character of the vortex glass phase transition in
ThH. The activation energy yields a logarithmic dependence
ln() on magnetic field in a low field
region and a power law dependence ~ in a
high field region, signaling a crossover from 2D regime to 3D collective
pinning regime, respectively. Additionally, a pinning force field dependence
showcases dominance of surface-type pinning in the vicinity of
. Thermal activation energy (), derived within
thermally activated flux flow (TAFF) theory, takes very high values above
210 K together with the Ginzburg number = 0.039 -
0.085, which is lower only than those of BiSrCaCuO cuprates and 10-3-8 family
of iron based superconductor. This indicates the enormous role of thermal
fluctuations in the dynamics of the vortex lattice of superhydrides, the
physics of which is similar to the physics of unconventional high-temperature
superconductors
Anatomy of the band structure of the newest apparent near-ambient superconductor LuHN
Recently it was claimed that nitrogen-doped lutetium hydride exhibited a
near-ambient superconducting transition with a temperature of 294 K at a
pressure of only 10 kbar, this pressure being several orders of magnitude lower
than previously demonstrated for hydrides under pressure. In this paper, we
investigate within DFT+U the electronic structure of both parent lutetium
hydride LuH and nitrogen doped lutetium hydride LuHN. We
calculated corresponding bands, density of states and Fermi surfaces. It is
shown that in the stoichiometric system the Lu-5d states cross the Fermi level
while the H-1s states make almost no contribution at the Fermi level. However,
with nitrogen doping, the N-2p states enter the Fermi level in large quantities
and bring together a significant contribution from the H-1s states. The
presence of N-2p and H-1s states at the Fermi level in a doped compound can
facilitate the emergence of superconductivity. For instance, nitrogen doping
almost doubles the value of DOS at the Fermi level. Simple BCS analysis shows
that the nitrogen doping of LuH can provide T more than 100K and even
increase it with further hole doping.Comment: 7 pages, 5 figure
Non-Fermi-Liquid Behavior of Superconducting SnH
We studied chemical interaction of Sn with H by X-ray diffraction methods
at pressures of 180-210 GPa. A previously unknown tetrahydride SnH with a
cubic structure () exhibiting superconducting properties below
= 72 K was obtained; the formation of a high molecular -SnH
superhydride and several lower hydrides, SnH and
-SnH, was also detected. The temperature dependence of
critical current density (T) in SnH yields the superconducting gap
2(0) = 20-22 meV at 180 GPa. The SnH superconductor has unusual
behavior in strong magnetic fields: linear temperature dependences of
magnetoresistance and the upper critical magnetic field (T)
( - ). The latter contradicts the
Wertheimer-Helfand-Hohenberg model developed for conventional superconductors.
Along with this, the temperature dependence of electrical resistance of
SnH in normal resistivity state exhibits a deviation from what is expected
for phonon-mediated scattering described by the Bloch-Gr\"uneisen model, and is
beyond the framework of the Fermi liquid theory. Such anomalies occur for many
superhydrides, making them much closer to cuprates than previously believed
Electronic Structure and Coexistence of Superconductivity with Magnetism in RbEuFe4As4
In the novel stoichiometric iron-based material RbEuFe4As4, superconductivity coexists with a peculiar long-range magnetic order of Eu 4f states. Using angle-resolved photoemission spectroscopy, we reveal a complex three-dimensional electronic structure and compare it with density functional theory calculations. Multiple super-conducting gaps were measured on various sheets of the Fermi surface. High-resolution resonant photoemission spectroscopy reveals magnetic order of the Eu 4f states deep into the superconducting phase. Both the absolute values and the anisotropy of the superconducting gaps are remarkably similar to the sibling compound without Eu, indicating that Eu magnetism does not affect the pairing of electrons. A complete decoupling between Fe-and Eu-derived states was established from their evolution with temperature, thus unambiguously demonstrating that superconducting and a long-range magnetic orders exist independently from each other. The established electronic structure of RbEuFe4As4 opens opportunities for the future studies of the highly unorthodox electron pairing and phase competition in this family of iron-based superconductors with doping.We thank Matthew Watson for his critical reading of the manuscript. We thank Diamond Light Source for access to beamline I05 (Proposal No. SI15074 and No. SI19041) that contributed to the results presented here. Work was done using equipment from the LPI Shared Facility Center. K.S.P. and V.M.P. acknowledge support by the Russian Scientific Foundation (RSF Project No. 21-12-00394). A.V.S. and A.S.U. acknowledge support by the Russian Foundation for Basic Research (Project No. 21-52-12043). E.V.C. acknowledges funding by Saint Petersburg State University project for scientific investigations (ID No. 73028629). S.V.E. acknowledges support from the government research assignment for ISPMS SB RAS (Project FWRW-2019-0032). R.V. acknowledges funding by the Deutsche Forschungsgemeinschaft (DFG) TRR 288 (Project A05). V.B. thanks the Goethe University Frankfurt for computational resources and Daniel Guterding for providing the FS plotting software. K.K. thanks M. Valvidares, J. Herrero, H. B. Vasili, S. Agrestini, and N. Brookes for their support during the XMCD experiment at ALBA via IHR Proposal 2019063615. D.V.V. also acknowledges support from the Spanish Ministry of Economy (MAT-2017-88374-P
Anomalous high-temperature superconductivity in YH
Pressure-stabilized hydrides are a new rapidly growing class of
high-temperature superconductors which is believed to be described within the
conventional phonon-mediated mechanism of coupling. Here we report the
synthesis of yttrium hexahydride Im3m-YH that demonstrates the
superconducting transition with T = 224 K at 166 GPa, much lower than the
theoretically predicted (>270 K). The measured upper critical magnetic field
B(0) of YH was found to be 116-158 T, which is 2-2.5 times larger
than the calculated value. A pronounced shift of T in yttrium deuteride
YD with the isotope coefficient 0.4 supports the phonon-assisted
superconductivity. Current-voltage measurements showed that the critical
current I and its density J may exceed 1.75 A and 3500 A/mm at 0 K,
respectively, which is comparable with the parameters of commercial
superconductors, such as NbTi and YBCO. The superconducting density functional
theory (SCDFT) and anharmonic calculations suggest unusually large impact of
the Coulomb repulsion in this compound. The results indicate notable departures
of the superconducting properties of the discovered YH from the
conventional Migdal-Eliashberg and Bardeen-Cooper-Schrieffer theories.Comment: arXiv admin note: text overlap with arXiv:1902.1020
On the structure of the superconducting order parameter in high-temperature Fe-based superconductors
Vortex Phase Dynamics in Yttrium Superhydride YH<sub>6</sub> at Megabar Pressures
A comprehensive study of vortex phases and vortex dynamics
is
presented for a recently discovered high-temperature superconductor
YH6 with Tc(onset) of 215 K
under a pressure of 200 GPa. The thermal activation energy (U0) is derived within the framework of the thermally
activated flux flow (TAFF) theory. The activation energy yields a
power law dependence U0 ∝ Hα on magnetic field with a possible crossover
at a field around 8–10 T. Furthermore, we have depicted the
vortex phase transition from the vortex-glass to vortex-liquid state
according to the vortex-glass theory. Finally, vortex phase diagram
is constructed for the first time for superhydrides. Very high estimated
values of flux flow barriers U0(H) = (1.5–7) × 104 K together with
high crossover fields make YH6 a rather outstanding superconductor
as compared to most cuprates and iron-based systems. The Ginzburg
number for YH6 Gi = (3–7) ×
10–3 indicates that thermal fluctuations are not
so strong and cannot broaden superconducting transitions in weak magnetic
fields
Vortex Phase Dynamics in Yttrium Superhydride YH<sub>6</sub> at Megabar Pressures
A comprehensive study of vortex phases and vortex dynamics
is
presented for a recently discovered high-temperature superconductor
YH6 with Tc(onset) of 215 K
under a pressure of 200 GPa. The thermal activation energy (U0) is derived within the framework of the thermally
activated flux flow (TAFF) theory. The activation energy yields a
power law dependence U0 ∝ Hα on magnetic field with a possible crossover
at a field around 8–10 T. Furthermore, we have depicted the
vortex phase transition from the vortex-glass to vortex-liquid state
according to the vortex-glass theory. Finally, vortex phase diagram
is constructed for the first time for superhydrides. Very high estimated
values of flux flow barriers U0(H) = (1.5–7) × 104 K together with
high crossover fields make YH6 a rather outstanding superconductor
as compared to most cuprates and iron-based systems. The Ginzburg
number for YH6 Gi = (3–7) ×
10–3 indicates that thermal fluctuations are not
so strong and cannot broaden superconducting transitions in weak magnetic
fields