Abstract
The 2-dimensional layered oxide material SrCu
2
(BO
3
)
2
, long studied as a realization of the Shastry-Sutherland spin topology, exhibits a range of intriguing physics as a function of ...both hydrostatic pressure and magnetic field, with a still debated intermediate plaquette phase appearing at approximately 20 kbar and a possible deconfined critical point at higher pressure. Here, we employ a tunnel diode oscillator (TDO) technique to probe the behavior in the combined extreme conditions of high pressure, high magnetic field, and low temperature. We reveal an extensive phase space consisting of multiple magnetic analogs of the elusive supersolid phase and a magnetization plateau. In particular, a 10 × 2 supersolid and a 1/5 plateau, identified by infinite Projected Entangled Pair States (iPEPS) calculations, are found to rely on the presence of both magnetic and non-magnetic particles in the sea of dimer singlets. These states are best understood as descendants of the full-plaquette phase, the leading candidate for the intermediate phase of SrCu
2
(BO
3
)
2
.
In underdoped cuprates, the interplay of the pseudogap, superconductivity, and charge and spin ordering can give rise to exotic quantum states, including the pair density wave (PDW), in which the ...superconducting (SC) order parameter is oscillatory in space. However, the evidence for a PDW state remains inconclusive and its broader relevance to cuprate physics is an open question. To test the interlayer frustration, the crucial component of the PDW picture, we perform transport measurements on charge- and spin-stripe-ordered La
Eu
Sr
CuO
and La
Nd
Sr
CuO
in perpendicular magnetic fields (H
), and also with an additional field applied parallel to CuO
layers (H
). We detect several phenomena predicted to arise from the existence of a PDW, including an enhancement of interlayer SC phase coherence with increasing H
. These data also provide much-needed transport signatures of the PDW in the regime where superconductivity is destroyed by quantum phase fluctuations.
Abstract
The origin of the weak insulating behavior of the resistivity, i.e.
$${\rho }_{xx}\propto {\mathrm{ln}}\,(1/T)$$
ρ
x
x
∝
ln
(
1
/
T
)
, revealed when magnetic fields (
H
) suppress ...superconductivity in underdoped cuprates has been a longtime mystery. Surprisingly, the high-field behavior of the resistivity observed recently in charge- and spin-stripe-ordered La-214 cuprates suggests a metallic, as opposed to insulating, high-field normal state. Here we report the vanishing of the Hall coefficient in this field-revealed normal state for all
$$T\ <\ (2-6){T}_{{\rm{c}}}^{0}$$
T
<
(
2
−
6
)
T
c
0
, where
$${T}_{{\rm{c}}}^{0}$$
T
c
0
is the zero-field superconducting transition temperature. Our measurements demonstrate that this is a robust fundamental property of the normal state of cuprates with intertwined orders, exhibited in the previously unexplored regime of
T
and
H
. The behavior of the high-field Hall coefficient is fundamentally different from that in other cuprates such as YBa
2
Cu
3
O
6+
x
and YBa
2
Cu
4
O
8
, and may imply an approximate particle-hole symmetry that is unique to stripe-ordered cuprates. Our results highlight the important role of the competing orders in determining the normal state of cuprates.
Human calcium-sensing receptor (CaSR) is a G-protein-coupled receptor that maintains Ca
2+
homeostasis in serum. Here, we present the cryo-electron microscopy structures of the CaSR in the inactive ...and agonist+PAM bound states. Complemented with previously reported structures of CaSR, we show that in addition to the full inactive and active states, there are multiple intermediate states during the activation of CaSR. We used a negative allosteric nanobody to stabilize the CaSR in the fully inactive state and found a new binding site for Ca
2+
ion that acts as a composite agonist with L-amino acid to stabilize the closure of active Venus flytraps. Our data show that agonist binding leads to compaction of the dimer, proximity of the cysteine-rich domains, large-scale transitions of seven-transmembrane domains, and inter- and intrasubunit conformational changes of seven-transmembrane domains to accommodate downstream transducers. Our results reveal the structural basis for activation mechanisms of CaSR and clarify the mode of action of Ca
2+
ions and L-amino acid leading to the activation of the receptor.
Impurities often play a defining role in the ground states of frustrated quantum magnets. Studies of their effects are crucial in understanding of the phase diagram in these materials. SrCu
(BO
)
, ...an experimental realization of the Shastry-Sutherland (SS) lattice, provides a unique model system for such studies using both experimental and numerical approaches. Here we report effects of impurities on the crystals of bound states, and doping-induced emergent ground states in Mg-doped SrCu
(BO
)
, which remain stable in high magnetic fields. Using four complementary magnetometry techniques and theoretical simulations, a rich impurity-induced phenomenology at high fields is discovered. The results demonstrate a rare example in which even a small doping concentration interacts strongly with both triplets and bound states of triplets, and thus plays a significant role in the magnetization process even at high magnetic fields. Our findings provide insights into the study of impurity effects in geometrically frustrated quantum magnets.
SignificanceThe coronavirus main protease (M
) is required for viral replication. Here, we obtained the extended conformation of the native monomer of severe acute respiratory syndrome coronavirus 2 ...(SARS-CoV-2) M
by trapping it with nanobodies and found that the catalytic domain and the helix domain dissociate, revealing allosteric targets. Another monomeric state is termed compact conformation and is similar to one protomer of the dimeric form. We designed a Nanoluc Binary Techonology (NanoBiT)-based high-throughput allosteric inhibitor assay based on structural conformational change. Our results provide insight into the maturation, dimerization, and catalysis of the coronavirus M
and pave a way to develop an anticoronaviral drug through targeting the maturation process to inhibit the autocleavage of M
.
Abstract Assembling graphene sheets into macroscopic fibers with graphitic layers uniaxially aligned along the fiber axis is of both fundamental and technological importance. However, the optimal ...performance of graphene-based fibers has been far lower than what is expected based on the properties of individual graphene. Here we show that both mechanical properties and electrical conductivity of graphene-based fibers can be significantly improved if bridges are created between graphene edges through covalent conjugating aromatic amide bonds. The improved electrical conductivity is likely due to extended electron conjugation over the aromatic amide bridged graphene sheets. The larger sheets also result in improved π-π stacking, which, along with the robust aromatic amide linkage, provides high mechanical strength. In our experiments, graphene edges were bridged using the established wet-spinning technique in the presence of an aromatic amine linker, which selectively reacts to carboxyl groups at the graphene edge sites. This technique is already industrial and can be easily upscaled. Our methodology thus paves the way to the fabrication of high-performance macroscopic graphene fibers under optimal techno-economic and ecological conditions.
In order to determine the matching relationship of polymer molecular weight and reservoir permeability in ASP (alkaline/surfactant/polymer) flooding, a number of core flooding experiments with ...different polymer molecular weights are performed. Two types of curves for the relationship between the pressure difference and the injection pore volume multiples are obtained. One describes the characteristics of the core plugging; the other describes the characteristics of the injection well. The relationship between the polymer molecular cyclotron radius and the pore throat radius used to describe the relationship between the polymer molecular weight and the core permeability. The results indicate that when the ratio of the pore throat radius (rh) to the polymer molecular cyclotron radius (rp) is greater than 7, the injection of ASP system with a variety of molecular weights will not be blocked; on contrary, when the ratio is less than 7, the core will be blocked. The range of water permeability of the core is determined by the value of the polymer molecular weight. The ratio between the pore throat radius (rh) to the polymer molecular cyclotron radius (rp) for the ASP system is greater than that of polymer system (rh/rp = 5). A scanning electron microscope (SEM) is used to compare the morphology of polymer molecules in polymer solution and ASP solution, and shows that the dimension of polymer molecular coils in ASP solution is smaller than that in polymer solution, which is caused by the double effect of alkali and surfactant.
Abstract
Recently, Yb-based triangular-lattice antiferromagnets have garnered significant interest as possible quantum spin-liquid candidates. One example is YbMgGaO
4
, which showed many promising ...spin-liquid features, but also possesses a high degree of disorder owing to site-mixing between the non-magnetic cations. To further elucidate the role of chemical disorder and to explore the phase diagram of these materials in applied field, we present neutron scattering and sensitive magnetometry measurements of the closely related compound, YbZnGaO
4
. Our results suggest a difference in magnetic anisotropy between the two compounds, and we use key observations of the magnetic phase crossover to motivate an exploration of the field- and exchange parameter-dependent phase diagram, providing an expanded view of the available magnetic states in applied field. This enriched map of the phase space serves as a basis to restrict the values of parameters describing the magnetic Hamiltonian with broad application to recently discovered related materials.
Abstract
Ba
3
Yb
2
Zn
5
O
11
is exceptional among breathing pyrochlore compounds for being in the nearly-decoupled limit where inter-tetrahedron interactions are weak, hosting isolated clusters or ...molecular magnet-like tetrahedra of magnetic ytterbium (Yb
3+
) ions. In this work, we present the study carried out on single-crystal samples of the breathing pyrochlore Ba
3
Yb
2
Zn
5
O
11
, using a variety of magnetometry and neutron scattering techniques along with theoretical modeling. We employ inelastic neutron scattering to investigate the magnetic dynamics as a function of applied field (with respect to both magnitude and direction) down to a temperature of 70 mK, where inelastic scattering reveals dispersionless bands of excitations as found in earlier powder sample studies, in good agreement with a single-tetrahedron model. However, diffuse neutron scattering at zero field and dc-susceptibility at finite field exhibit features suggesting the presence of excitations at low-energy that are not captured by the single tetrahedron model. Analysis of the local structure down to 2 K via pair distribution function analysis finds no evidence of structural disorder. We conclude that effects beyond the single tetrahedron model are important in describing the low-energy, low-temperature physics of Ba
3
Yb
2
Zn
5
O
11
, but their nature remains undetermined.
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