115 research outputs found
Towards spin injection from silicon into topological insulators: Schottky barrier between Si and Bi2Se3
A scheme is proposed to electrically measure the spin-momentum coupling in
the topological insulator surface state by injection of spin polarized
electrons from silicon. As a first approach, devices were fabricated consisting
of thin (<100nm) exfoliated crystals of Bi2Se3 on n-type silicon with
independent electrical contacts to silicon and Bi2Se3. Analysis of the
temperature dependence of thermionic emission in reverse bias indicates a
barrier height of 0.34 eV at the Si-Bi2Se3 interface. This robust Schottky
barrier opens the possibility of novel device designs based on sub-band gap
internal photoemission from Bi2Se3 into Si
The Origin of Anomalous Low-Temperature Downturns in the Thermal Conductivity of Cuprates
We show that the anomalous decrease in the thermal conductivity of cuprates
below 300 mK, as has been observed recently in several cuprate materials
including PrCeCuO in the field-induced normal state,
is due to the thermal decoupling of phonons and electrons in the sample. Upon
lowering the temperature, the phonon-electron heat transfer rate decreases and,
as a result, a heat current bottleneck develops between the phonons, which can
in some cases be primarily responsible for heating the sample, and the
electrons. The contribution that the electrons make to the total low- heat
current is thus limited by the phonon-electron heat transfer rate, and falls
rapidly with decreasing temperature, resulting in the apparent low- downturn
of the thermal conductivity. We obtain the temperature and magnetic field
dependence of the low- thermal conductivity in the presence of
phonon-electron thermal decoupling and find good agreement with the data in
both the normal and superconducting states.Comment: 8 pages, 5 figure
Avoided Antiferromagnetic Order and Quantum Critical Point in CeCoIn
We measured specific heat and resistivity of heavy fermion CeCoIn5 between
the superconducting critical field and 9 T, with field in the
[001] direction, and at temperatures down to 50mK. At 5T the data show Non
Fermi Liquid behavior down to the lowest temperatures. At field above 8T the
data exhibit crossover from the Fermi liquid to a Non Fermi Liquid behavior. We
analyzed the scaling properties of the specific heat, and compared both
resistivity and the specific heat with the predictions of a spin-fluctuation
theory. Our analysis leads us to suggest that the NFL behavior is due to
incipient antiferromagnetism (AF) in CeCoIn5, with the quantum critical point
in the vicinity of the . Below the AF phase which competes
with the paramagnetic ground state is superseded by the superconducting
transition.Comment: 5 pages, 3 figure
Extreme magnetic field-boosted superconductivity
Applied magnetic fields underlie exotic quantum states, such as the
fractional quantum Hall effect and Bose-Einstein condensation of spin
excitations. Superconductivity, on the other hand, is inherently antagonistic
towards magnetic fields. Only in rare cases can these effects be mitigated over
limited fields, leading to reentrant superconductivity. Here, we report the
unprecedented coexistence of multiple high-field reentrant superconducting
phases in the spin-triplet superconductor UTe2. Strikingly, we observe
superconductivity in the highest magnetic field range identified for any
reentrant superconductor, beyond 65 T. These extreme properties reflect a new
kind of exotic superconductivity rooted in magnetic fluctuations and boosted by
a quantum dimensional crossover
Tuning a magnetic energy scale with pressure in UTe
A fragile ordered state can be easily tuned by various external parameters.
When the ordered state is suppressed to zero temperature, a quantum phase
transition occurs, which is often marked by the appearance of unconventional
superconductivity. While the quantum critical point can be hidden, the
influence of the quantum criticality extends to fairly high temperatures,
manifesting the non-Fermi liquid behavior in the wide range of the --
phase space. Here, we report the tuning of a magnetic energy scale in the
heavy-fermion superconductor UTe, previously identified as a peak in the
-axis electrical transport, with applied hydrostatic pressure and magnetic
field along the -axis as complementary (and opposing) tuning parameters.
Upon increasing pressure, the characteristic -axis peak moves to a lower
temperature before vanishing near the critical pressure of about 15 kbar. The
application of a magnetic field broadens the peak under all studied pressure
values. The observed Fermi-liquid behavior at ambient pressure is violated near
the critical pressure, exhibiting nearly linear resistivity in temperature and
an enhanced pre-factor. Our results provide a clear picture of energy scale
evolution relevant to magnetic quantum criticality in UTe
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