74 research outputs found
Huge linear magnetoresistance due to open orbits in -PtBi
Some single-crystalline materials present an electrical resistivity which
decreases between room temperature and low temperatures at zero magnetic field
as in a good metal and switches to a nearly semiconductinglike behavior at low
temperatures with the application of a magnetic field. Often, this is
accompanied by a huge and nonsaturating linear magnetoresistance which remains
difficult to explain. Here we present a systematic study of the
magnetoresistance in single-crystal -PtBi. We observe that the
angle between the magnetic field and the crystalline axis fundamentally
changes the magnetoresistance, going from a saturating to a nonsaturating
magnetic field dependence. In between, there is one specific angle where the
magnetoresistance is perfectly linear with the magnetic field. We show that the
linear dependence of the nonsaturating magnetoresistance is due to the
formation of open orbits in the Fermi surface of -PtBi.Comment: 12 pages, 8 figures including Supplementary Materia
Scanning tunneling spectroscopy with superconducting tips of Al
International audienceWe present scanning tunneling spectroscopy measurements at 0.1 K using tips made of Al. At zero field, the atomic lattice and charge density wave of 2H-NbSe2 are observed, and under magnetic fields the peculiar electronic properties of vortices are precisely resolved. The tip density of states is influenced by the local magnetic field of the vortex, providing a new probe for the magnetic field at nanometric sizes
Metastable inhomogeneous vortex configuration with non-uniform filling fraction inside a blind hole array patterned in a BSCCO single crystal and concentrating magnetic flux inside it
Using magneto-optical imaging technique, we map local magnetic field
distribution inside a hexagonally ordered array of blind holes patterned in
BSCCO single crystals. The nature of the spatial distribution of local magnetic
field and shielding currents across the array reveals the presence of a
non-uniform vortex configuration partially matched with the blind holes at
sub-matching fields. We observe that the filling fraction is different in two
different regions of the array. The mean vortex configuration within the array
is described as a patchy vortex configuration with the patches having different
mean filling fraction. The patchy nature of the vortex configuration is more
pronounced at partial filling of the array at low fields while the
configuration becomes more uniform with a unique filling fraction at higher
fields. The metastable nature of this patchy vortex configuration is revealed
by the application of magnetic field pulses of fixed height or individual
pulses of varying height to the array. The metastability of the vortex
configuration allows for a relatively easy way of producing flux reorganization
and flux focusing effects within the blind hole array. Effect of the magnetic
field pulses modifies the vortex configuration within the array and produces a
uniform enhancement in the shielding current around the patterned array edges.
The enhanced shielding current concentrates magnetic flux within the array by
driving vortices away from the edges and towards the center of the array. The
enhanced shielding current also prevents the uninhibited entry of vortices into
the array. We propose that the metastable patchy vortex configuration within
the blind hole array is due to a non-uniform pinning landscape leading to
non-uniform filling of individual blind holes.Comment: 15 pages, 6 figure
Low temperature magnetic transitions of single crystal HoBi
We present resistivity, specific heat and magnetization measurements in high
quality single crystals of HoBi, with a residual resistivity ratio of 126. We
find, from the temperature and field dependence of the magnetization, an
antiferromagnetic transition at 5.7 K, which evolves, under magnetic fields,
into a series of up to five metamagnetic phases.Comment: 5 pages, 5 figure
Generating strong magnetic flux shielding regions in a single crystal of Bi2Sr2CaCu2O8 using a blind hole array
Magneto-optical imaging studies in a single crystal of Bi2Sr2CaCu2O8
partially patterned with a hexagonal array of pinning centers (blind holes)
reveals local features in the patterned region which are distinct compared to
the pristine unpatterned regions in the sample. The patterned area exhibits a
strongly diamagnetic local magnetization response and is characterized by a
local penetration field enhanced by a factor of three. We show that strong
shielding currents around the periphery of the nanopatterned region create a
barrier which prevents vortex entry into the patterned region thus sustaining
an effectively flux-free state upto the enhanced penetration field.Comment: 11 pages, 4 figure
Low-Frequency Imaginary Impedance at the Superconducting Transition of 2H-NbSe2
The superconducting transition leads to a sharp resistance drop in a temperature interval that can be a small fraction of the critical temperature Tc. A superconductor exactly at Tc is thus very sensitive to all kinds of thermal perturbation, including the heat dissipated by the measurement current. We show that the interaction between electrical and thermal currents leads to a sizable imaginary impedance at frequencies of the order of tens of hertz at the resistive transition of single crystals of the layered material 2H-NbSe2.We explain the result using models developed for transition-edge sensors. By measuring under magnetic fields and at high currents, we find that the imaginary impedance is strongly influenced by the heat associated with vortex motion and out-of-equilibrium quasiparticles
Linear nonsaturating magnetoresistance in the Nowotny chimney ladder compound Ru2Sn3
We present magnetoresistivity measurements in high-quality single crystals of the Nowotny chimney ladder compound
Ru2Sn3. We find a linear and nonsaturating magnetoresistance up to 20 T. The magnetoresistance changes with the magnetic field orientation at small magnetic fields, from a positive to a negative curvature. Above 5 T, the magnetoresistance shows no sign of saturation up to 20 T for any measured angle. The shape of the anisotropy in the magnetoresistance remains when increasing temperature and Kohler's rule is obeyed. We associate the linear and nonsaturating magnetoresistance to a small Fermi surface with hot spots, possibly formed as a consequence of the structural transition. We discuss the relevance of electron-electron interactions under magnetic fields and aspects of the topologically nontrivial properties expected in Ru2Sn3This work was supported by the Spanish Research State Agency (FIS2017-84330-R, CEX2018-000805-M, RYC2014-15093, MAT2017-87134-C2-2-R), by the Comunidad de Madrid through the program NANOMAGCOST-CM
(Grant No. S2018/NMT-4321) and by the European Research
Council PNICTEYES project through Grant Agreement No 67908
Thermal creep emerging from cooling a tilted vortex lattice in uniaxial superconductor
A perturbed system relaxes towards an equilibrium given by a minimum in the
potential energy landscape. This often occurs by thermally activated jumps over
metastable states. The corresponding dynamics is named creep and follows
Arrhenius' law. Here we consider the situation where the equilibrium position
depends on temperature. We show that this effect occurs in the vortex lattice
of the anisotropic superconductor -
when the magnetic field is tilted away from the principal axes, and that it
leads to the peculiar appearance of creep when cooling the sample. Temperature
determines the system's ground state and at the same time brings the system
back to equilibrium, playing a dual and antagonistic role. We expect that
cooling induced creep occurs in correlated systems with many degrees of freedom
allowing to tune the equilibrium state via heat treatment.Comment: 7 pages, 4 figure
Andreev reflection under high magnetic fields in ferromagnet-superconductor nanocontacts
We study the magnetic-field dependence of the conductance in planar ferromagnet-superconductor nanocontacts created with focused-electron/ion-beam techniques. From the fits of the differential conductance curves in high magnetic fields, we obtain the magnetic field dependences of the superconducting gap and the broadening parameter. Orbital depairing is found to be linear with magnetic field. We evaluate the magnetic field dependence of the quasiparticle density of states, and we compare it with the value obtained by scanning tunneling spectroscopy experimentsThis work was supported by the Spanish Ministry of Science (through projects MAT2008-06567-C02, including FEDER funding) and the Arag´on Regional Government (project E26). S. Sangiao acknowledges financial support from Spanish ME
Superconducting gap and vortex lattice of the heavy fermion compound CeCu_2Si_2
The order parameter and pairing mechanism for superconductivity in heavy
fermion compounds are still poorly understood. Scanning tunneling microscopy
and spectroscopy at ultra-low temperatures can yield important information
about the superconducting order parameter and the gap structure. Here, we study
the first heavy fermion superconductor, CeCu_2Si_2. Our data show the
superconducting gap which is not fully formed and exhibits features that point
to a multi-gap order parameter. Spatial mapping of the zero bias conductance in
magnetic field reveals the vortex lattice, which allows us to unequivocally
link the observed conductance gap to superconductivity in CeCu_2Si_2. The
vortex lattice is found to be predominantly triangular with distortions at
fields close to \sim 0.7 H_{c2}.Comment: 6 pages, 4 figures, revised version accepted for publication in PR
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