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result(s) for
"Cheng, J"
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Dome-shaped magnetic order competing with high-temperature superconductivity at high pressures in FeSe
The coexistence and competition between superconductivity and electronic orders, such as spin or charge density waves, have been a central issue in high transition-temperature (
T
c
) superconductors. Unlike other iron-based superconductors, FeSe exhibits nematic ordering without magnetism whose relationship with its superconductivity remains unclear. Moreover, a pressure-induced fourfold increase of
T
c
has been reported, which poses a profound mystery. Here we report high-pressure magnetotransport measurements in FeSe up to ∼15 GPa, which uncover the dome shape of magnetic phase superseding the nematic order. Above ∼6 GPa the sudden enhancement of superconductivity (
T
c
≤38.3 K) accompanies a suppression of magnetic order, demonstrating their competing nature with very similar energy scales. Above the magnetic dome, we find anomalous transport properties suggesting a possible pseudogap formation, whereas linear-in-temperature resistivity is observed in the normal states of the high-
T
c
phase above 6 GPa. The obtained phase diagram highlights unique features of FeSe among iron-based superconductors, but bears some resemblance to that of high-
T
c
cuprates.
The relationship between electronic ordering and superconductivity, crucial to understand high-
T
c
superconductors, remains elusive. Here, Sun
et al
. report the pressure-induced dome shape of a magnetic phase superceding the nematic order in FeSe, suggesting competing nature between magnetism and superconductivity.
Journal Article
Discovery of conjoined charge density waves in the kagome superconductor CsV3Sb5
The electronic instabilities in CsV
3
Sb
5
are believed to originate from the V 3
d
-electrons on the kagome plane, however the role of Sb 5
p
-electrons for 3-dimensional orders is largely unexplored. Here, using resonant tender X-ray scattering and high-pressure X-ray scattering, we report a rare realization of conjoined charge density waves (CDWs) in CsV
3
Sb
5
, where a 2 × 2 × 1 CDW in the kagome sublattice and a Sb 5
p
-electron assisted 2 × 2 × 2 CDW coexist. At ambient pressure, we discover a resonant enhancement on Sb
L
1
-edge (2
s
→5
p
) at the 2 × 2 × 2 CDW wavevectors. The resonance, however, is absent at the 2 × 2 × 1 CDW wavevectors. Applying hydrostatic pressure, CDW transition temperatures are separated, where the 2 × 2 × 2 CDW emerges 4 K above the 2 × 2 × 1 CDW at 1 GPa. These observations demonstrate that symmetry-breaking phases in CsV
3
Sb
5
go beyond the minimal framework of kagome electronic bands near van Hove filling.
The nature of unconventional charge density wave in kagome metals is currently under intense debate. Here the authors report the coexistence of the 2 × 2 × 1 charge density wave in the kagome sublattice and the Sb 5p-electron assisted 2 × 2 × 2 charge density waves in CsV
3
Sb
5
.
Journal Article
Survival of itinerant excitations and quantum spin state transitions in YbMgGaO4 with chemical disorder
A recent focus of quantum spin liquid (QSL) studies is how disorder/randomness in a QSL candidate affects its true magnetic ground state. The ultimate question is whether the QSL survives disorder or the disorder leads to a “spin-liquid-like” state, such as the proposed random-singlet (RS) state. Since disorder is a standard feature of most QSL candidates, this question represents a major challenge for QSL candidates. YbMgGaO
4
, a triangular lattice antiferromagnet with effective spin-1/2 Yb
3+
ions, is an ideal system to address this question, since it shows no long-range magnetic ordering with Mg/Ga site disorder. Despite the intensive study, it remains unresolved as to whether YbMgGaO
4
is a QSL or in the RS state. Here, through ultralow-temperature thermal conductivity and magnetic torque measurements, plus specific heat and DC magnetization data, we observed a residual
κ
0
/
T
term and series of quantum spin state transitions in the zero temperature limit for YbMgGaO
4
. These observations strongly suggest that a QSL state with itinerant excitations and quantum spin fluctuations survives disorder in YbMgGaO
4
.
It remains an open question as to whether the quantum spin liquid state survives material disorder, or is replaced by some spin-liquid like state. Here, Rao et al succeed in resolving a resolving a
κ
0
/T residual in the thermal conductivity of YbMgGaO
4
strongly suggesting the survival of the quantum spin liquid state.
Journal Article
Third order optical nonlinearity of graphene
We perform a perturbative calculation of the third order optical conductivities of doped graphene, using approximations valid around the Dirac points and neglecting effects due to scattering and electron-electron interactions. In this limit analytic formulas can be constructed for the conductivities. We discuss in detail the results for third harmonic generation, the Kerr effect and two-photon carrier injection, parametric frequency conversion, and two-color coherent current injection. We find a complicated dependence on the chemical potential and photon energies. The linear dispersion causes resonances over a wide range of photon energies, and it is possible to obtain large optical nonlinearities by tuning the chemical potential.
Journal Article
Factors Influencing STEM Career Aspirations of Underrepresented High School Students
A shortage of female and minority students pursuing science, technology, engineering, and mathematics (STEM) careers has prompted researchers and policy makers to examine the current STEM supply pipeline. This study examined factors influencing STEM career aspirations of a nationally representative sample of 9th‐grade students (N = 21,444). Characteristics of students who aspired to STEM careers and non‐STEM careers were examined. Guided by the career aspirations model (Mau & Bikos, ), the authors conducted logistic regression analyses to investigate variables predicting STEM career aspirations. Results indicated that race, gender, socioeconomic status, math interest, and science self‐efficacy were the most important predictors of STEM career aspirations. Counselors in school and related career services contexts are encouraged to consider these important factors in identifying high school students who are interested in STEM career choices, as well as in planning career interventions to facilitate their career paths. Future researchers could test the applicability of this model with middle school students or adults.
Journal Article
Manipulating exchange bias in 2D magnetic heterojunction for high-performance robust memory applications
The exchange bias (EB) effect plays an undisputed role in the development of highly sensitive, robust, and high-density spintronic devices in magnetic data storage. However, the weak EB field, low blocking temperature, as well as the lack of modulation methods, seriously limit the application of EB in van der Waals (vdW) spintronic devices. Here, we utilized pressure engineering to tune the vdW spacing of the two-dimensional (2D) FePSe
3
/Fe
3
GeTe
2
heterostructures. The EB field (
H
EB
, from 29.2 mT to 111.2 mT) and blocking temperature (
T
b
, from 20 K to 110 K) are significantly enhanced, and a highly sensitive and robust spin valve is demonstrated. Interestingly, this enhancement of the EB effect was extended to exposed Fe
3
GeTe
2
, due to the single-domain nature of Fe
3
GeTe
2
. Our findings provide opportunities for the producing, exploring, and tuning of magnetic vdW heterostructures with strong interlayer coupling, thereby enabling customized 2D spintronic devices in the future.
When an antiferromagnet is in close proximity to a ferromagnet, the antiferromagnet pins the spins of the ferromagnet, resulting in an exchange bias effect. This effect has been instrumental in the development of a variety of spintronic devices. Here, Haung et al. u
s
e pressure to tune the exchange bias effect in all van der Waals heterostructure composed of FePSe
3
/Fe
3
GeTe
2
.
Journal Article
Talin1 phosphorylation activates β1 integrins: a novel mechanism to promote prostate cancer bone metastasis
Talins are adaptor proteins that regulate focal adhesion signaling by conjugating integrins to the cytoskeleton. Talins directly bind integrins and are essential for integrin activation. We previously showed that β1 integrins are activated in metastatic prostate cancer (PCa) cells, increasing PCa metastasis to lymph nodes and bone. However, how β1 integrins are activated in PCa cells is unknown. In this study, we identified a novel mechanism of β1 integrin activation. Using knockdown experiments, we first demonstrated that talin1, but not talin2, is important in β1 integrin activation. We next showed that talin1 S425 phosphorylation, but not total talin1 expression, correlates with metastatic potential of PCa cells. Expressing a non-phosphorylatable mutant, talin1
S425A
, in talin1-silenced PC3-MM2 and C4-2B4 PCa cells, decreased activation of β1 integrins, integrin-mediated adhesion, motility and increased the sensitivity of the cells to anoikis. In contrast, reexpression of the phosphorylation-mimicking mutant talin1
S425D
led to increased β1 integrin activation and generated biologic effects opposite to talin1
S425A
expression. In the highly metastatic PC3-MM2 cells, expression of a non-phosphorylatable mutant, talin1
S425A
, in talin1-silenced PC3-MM2 cells, abolished their ability to colonize in the bone following intracardiac injection, while reexpression of phosphorylation-mimicking mutant talin1
S425D
restored their ability to metastasize to bone. Immunohistochemical staining demonstrated that talin S425 phosphorylation is significantly increased in human bone metastases when compared with normal tissues, primary tumors or lymph node metastases. We further showed that p35 expression, an activator of Cdk5, and Cdk5 activity were increased in metastatic tumor cells, and that Cdk5 kinase activity is responsible for talin1 phosphorylation and subsequent β1 integrin activation. Together, our study reveals Cdk5-mediated phosphorylation of talin1 leading to β1 integrin activation is a novel mechanism that increases metastatic potential of PCa cells.
Journal Article
Maximizing T c by tuning nematicity and magnetism in FeSe1−x S x superconductors
A fundamental issue concerning iron-based superconductivity is the roles of electronic nematicity and magnetism in realising high transition temperature ( T c ). To address this issue, FeSe is a key material, as it exhibits a unique pressure phase diagram involving non-magnetic nematic and pressure-induced antiferromagnetic ordered phases. However, as these two phases in FeSe have considerable overlap, how each order affects superconductivity remains perplexing. Here we construct the three-dimensional electronic phase diagram, temperature ( T ) against pressure ( P ) and isovalent S-substitution ( x ), for FeSe 1− x S x . By simultaneously tuning chemical and physical pressures, against which the chalcogen height shows a contrasting variation, we achieve a complete separation of nematic and antiferromagnetic phases. In between, an extended non-magnetic tetragonal phase emerges, where T c shows a striking enhancement. The completed phase diagram uncovers that high- T c superconductivity lies near both ends of the dome-shaped antiferromagnetic phase, whereas T c remains low near the nematic critical point.
Journal Article
Properties and Energetics of Magnetic Reconnection: I. Evolution of Flare Ribbons
In this article, we measure the mean magnetic shear from the morphological evolution of flare ribbons, and examine the evolution of flare thermal and nonthermal X-ray emissions during the progress of flare reconnection. We analyze three eruptive flares and three confined flares ranging from GOES class C8.0 to M7.0. They exhibit two well-defined ribbons along the magnetic polarity-inversion line (PIL), and have been observed by the Atmospheric Imaging Assembly and the Ramaty High Energy Solar Spectroscopic Imager from the onset of the flare throughout the impulsive phase. The analysis confirms the strong-to-weak shear evolution in the core region of the flare, and the flare hard X-ray emission rises as the shear decreases. In eruptive flares, in this sample, significant nonthermal hard X-ray emission lags the ultraviolet emission from flare ribbons, and rises rapidly when the shear is modest. In all flares, we observe that the plasma temperature rises in the early phase when the flare ribbons rapidly spread along the PIL and the shear is high. We compare these results with prior studies, and discuss their implications, as well as complications, related to the physical mechanisms governing energy partition during flare reconnection.
Journal Article