1,865 research outputs found
Probing the pairing symmetry in the over-doped Fe-based superconductor Ba_0.35Rb_0.65Fe_2As_2 as a function of hydrostatic pressure
We report muon spin rotation experiments on the magnetic penetration depth
lambda and the temperature dependence of lambda^{-2} in the over-doped Fe-based
high-temperature superconductor (Fe-HTS) Ba_{1-x}Rb_ xFe_2As_2 (x = 0.65)
studied at ambient and under hydrostatic pressures up to p = 2.3 GPa. We find
that in this system lambda^{-2}(T) is best described by d-wave scenario. This
is in contrast to the case of the optimally doped x = 0.35 system which is
known to be a nodeless s^{+-}-wave superconductor. This suggests that the
doping induces the change of the pairing symmetry from s^{+-} to d-wave in
Ba_{1-x}Rb_{x}Fe_{2}As_{2}. In addition, we find that the d-wave order
parameter is robust against pressure, suggesting that d is the common and
dominant pairing symmetry in over-doped Ba_{1-x}Rb_{x}Fe_{2}As_{2}. Application
of pressure of p = 2.3 GPa causes a decrease of lambda(0) by less than 5 %,
while at optimal doping x = 0.35 a significant decrease of lambda(0) was
reported. The superconducting transition temperature T_c as well as the gap to
T_c ratio 2Delta/k_BT_c show only a modest decrease with pressure. By combining
the present data with those previously obtained for optimally doped system x =
0.35 and for the end member x = 1 we conclude that the SC gap symmetry as well
as the pressure effects on the SC quantities strongly depend on the Rb doping
level. These results are discussed in the light of the putative Lifshitz
transition, i.e., a disappearance of the electron pockets in the Fermi surface
of Ba_{1-x}Rb_{x}Fe_{2}As_{2} upon hole doping.Comment: Accepted for publication in Physical Review
Evidence for strong lattice effects as revealed from huge unconventional oxygen isotope effects on the pseudogap temperature in LaSrCuO
The oxygen isotope (O/O) effect (OIE) on the pseudogap
(charge-stripe ordering) temperature is investigated for the cuprate
superconductor LaSrCuO as a function of doping by means
of x-ray absorption near edge structure (XANES) studies. A strong dependent
and sign reversed OIE on is observed. The OIE exponent
systematically decreases from for to for ,
corresponding to increasing and decreasing superconducting
transition temperature . Both and
exhibit a linear doping dependence with different
slopes and critical end points (where and
fall to zero) at and
, indicating a large positive OIE of
with an exponent of . The remarkably large and
strongly doping dependent OIE on signals a substantial involvement
of the lattice in the formation of the pseudogap, consistent with a polaronic
approach to cuprate superconductivity and the vibronic character of its ground
state
Low-temperature magnetic fluctuations in the Kondo insulator SmB6
We present the results of a systematic investigation of the magnetic
properties of the three-dimensional Kondo topological insulator SmB6 using
magnetization and muon-spin relaxation/rotation (muSR) measurements. The muSR
measurements exhibit magnetic field fluctuations in SmB6 below 15 K due to
electronic moments present in the system. However, no evidence for magnetic
ordering is found down to 19 mK. The observed magnetism in SmB6 is homogeneous
in nature throughout the full volume of the sample. Bulk magnetization
measurements on the same sample show consistent behavior. The agreement between
muSR, magnetization, and NMR results strongly indicate the appearance of
intrinsic bulk magnetic in-gap states associated with fluctuating magnetic
fields in SmB6 at low temperature.Comment: 5 pages, 5 figure
Superconductivity and magnetism in RbxFe2-ySe2: Impact of thermal treatment on mesoscopic phase separation
An extended study of the superconducting and normal-state properties of
various as-grown and post-annealed RbxFe2-ySe2 single crystals is presented.
Magnetization experiments evidence that annealing of RbxFe2-ySe2 at 413 K, well
below the onset of phase separation Tp=489 K, neither changes the magnetic nor
the superconducting properties of the crystals. In addition, annealing at 563
K, well above Tp, suppresses the superconducting transition temperature Tc and
leads to an increase of the antiferromagnetic susceptibility accompanied by the
creation of ferromagnetic impurity phases, which are developing with annealing
time. However, annealing at T=488K=Tp increases Tc up to 33.3 K, sharpens the
superconducting transition, increases the lower critical field, and strengthens
the screening efficiency of the applied magnetic field. Resistivity
measurements of the as-grown and optimally annealed samples reveal an increase
of the upper critical field along both crystallographic directions as well as
its anisotropy. Muon spin rotation and scanning transmission electron
microscopy experiments suggest the coexistence of two phases below Tp: a
magnetic majority phase of Rb2Fe4Se5 and a non-magnetic minority phase of
Rb0.5Fe2Se2. Both microscopic techniques indicate that annealing the specimens
just at Tp does not affect the volume fraction of the two phases, although the
magnetic field distribution in the samples changes substantially. This suggests
that the microstructure of the sample, caused by mesoscopic phase separation,
is modified by annealing just at Tp, leading to an improvement of the
superconducting properties of RbxFe2-ySe2 and an enhancement of Tc.Comment: 13 pages, 12 figure
Growth, Crystal Structure and Magnetic Characterization of Zn-Stabilized CePtIn4
The growth and characterization of CePtIn4, stabilized by 10% Zn substitution
for In, is reported. The new material is orthorhombic, space group Cmcm (No.
63), with lattice parameters a = 4.51751(4) {\AA}, b = 16.7570(2) {\AA}, and c
= 7.36682(8) {\AA}, and the refined crystal composition has 10% of Zn
substituted for In, i.e. the crystals are CePt(In3.6Zn0.1)4. Crystals were
grown using a self-flux method: only growths containing Zn yielded CePtIn4
crystals, while Ce3Pt4In13 crystals formed when Zn was not present. Anisotropic
temperature-dependent magnetic susceptibilities for single crystals show that
Zn-stabilized CePtIn4 orders magnetically at ~1.9 K. High-temperature
Curie-Weiss fits indicate an effective moment of ~2.30 muB/ Ce and a
directionally averaged Weiss-temperature of approximately - 9 K. Specific heat
data shows a peak consistent with the ordering temperature seen in the magnetic
susceptibility data. Zn-stabilized CePtIn4 is metallic and displays no
superconducting transition down to 0.14 K.Comment: 8 pages, 5 figures, 1 tabl
2-Chlorodeoxyadenosine (2-CDA) therapy in previously untreated patients with follicular stage III-IV non-Hodgkin's lymphoma
Examining the surface phase diagram of IrTe with photoemission
In the transition metal dichalcogenide IrTe, low-temperature
charge-ordered phase transitions involving Ir dimers lead to the occurrence of
stripe phases of different periodicities, and nearly degenerate energies.
Bulk-sensitive measurements have shown that, upon cooling, IrTe undergoes
two such first-order transitions to and
reconstructed phases at ~K and ~K,
respectively. Here, using surface sensitive probes of the electronic structure
of IrTe, we reveal the first-order phase transition at ~K to
the stripes phase, previously proposed to be the surface ground
state. This is achieved by combining x-ray photoemission spectroscopy and
angle-resolved photoemission spectroscopy, which give access to the evolution
of stripe domains and a particular surface state, the energy of which is
dependent on the Ir dimer length. By performing measurements over a full
thermal cycle, we also report the complete hysteresis of all these phases
Uniaxial strain-induced phase transition in the 2D topological semimetal IrTe2
Strain is ubiquitous in solid-state materials, but despite its fundamental importance and technological relevance, leveraging externally applied strain to gain control over material properties is still in its infancy. In particular, strain control over the diverse phase transitions and topological states in two-dimensional transition metal dichalcogenides remains an open challenge. Here, we exploit uniaxial strain to stabilize the long-debated structural ground state of the 2D topological semimetal IrTe, which is hidden in unstrained samples. Combined angle-resolved photoemission spectroscopy and scanning tunneling microscopy data reveal the strain-stabilized phase has a 6 × 1 periodicity and undergoes a Lifshitz transition, granting unprecedented spectroscopic access to previously inaccessible type-II topological Dirac states that dominate the modified inter-layer hopping. Supported by density functional theory calculations, we show that strain induces an Ir to Te charge transfer resulting in strongly weakened inter-layer Te bonds and a reshaped energetic landscape favoring the 6×1 phase. Our results highlight the potential to exploit strain-engineered properties in layered materials, particularly in the context of tuning inter-layer behavior
Anomalous Shubnikov-de Haas effect and observation of the Bloch-Gr\"uneisen temperature in the Dirac semimetal ZrTe5
Appearance of quantum oscillations (QO) in both thermodynamic and transport
properties of metals at low temperatures is the most striking experimental
consequence of the existence of a Fermi surface (FS). The frequency of these
oscillations and the temperature dependence of their amplitude provides
essential information about the FS topology and fermionic quasiparticle
properties. Here, we report the observation of an anomalous suppression of the
QO amplitude seen in resistivity (Shubnikov de-Haas effect) at sub-kelvin
temperatures in ZrTe5 samples with a single small FS sheet comprising less than
5% of the first Brillouin zone. By comparing these results with measurements of
the magneto-acoustic QO and the recovery of the usual Lifshitz-Kosevich
behavior of the Shubnikov de-Haas (SdH) effect in ZrTe samples with a
multi-sheet FS, we show that the suppression of the SdH effect originates from
a decoupling of the electron liquid from the lattice. On crossing the so-called
Bloch-Gr\"uneisen temperature, T, electron-phonon scattering becomes
strongly suppressed and in the absence of Umklapp scattering the electronic
liquid regains Galilean invariance. In addition, we show, using a combination
of zero-field electrical conductivity and ultrasonic-absorption measurements,
that entering this regime leads to an abrupt increase of electronic viscosity
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