2,760 research outputs found
Correlated normal state fermiology and topological superconductivity in UTe2
UTe2 is a promising candidate for spin-triplet superconductors, in which a
paramagnetic normal state becomes superconducting due to spin fluctuations. The
subsequent discovery of various unusual superconducting properties has promoted
the use of UTe2 as an exciting playground to study unconventional
superconductivity, but fathoming the normal state fermiology and its influence
on the superconductivity still requires further investigation. Here, we
theoretically show that electron correlation induces a dramatic change in the
normal state fermiology with an emergent correlated Fermi surface (FS) driven
by Kondo resonance at low temperatures. This emergent correlated FS can account
for various unconventional superconducting properties in a unified way. In
particular, the geometry of the correlated FS can naturally host topological
superconductivity in the presence of odd-parity pairings, which become the
leading instability due to strong ferromagnetic spin fluctuations. Moreover,
two pairs of odd-parity channels appear as accidentally degenerate solutions,
which can naturally explain the multicomponent superconductivity with broken
time-reversal symmetry. Interestingly, the resulting time-reversal breaking
superconducting state is a Weyl superconductor in which Weyl points migrate
along the correlated FS as the relative magnitude of nearly degenerate pairing
solutions varies. We believe that the correlated normal state fermiology we
discovered provides a unified platform to describe the unconventional
superconductivity in UTe2.Comment: 13 pages, 4 figures and 1 table in the main text, and 10 figures and
1 table in the Supplementary Informatio
Topological acoustic triple point
Acoustic phonon in a crystalline solid is a well-known and ubiquitous example
of elementary excitation with a triple degeneracy in the band structure.
Because of the Nambu-Goldstone theorem, this triple degeneracy is always
present in the phonon band structure. Here, we show that the triple degeneracy
of acoustic phonons can be characterized by a topological charge
that is a property of three-band systems with symmetry, where
and are the inversion and the time-reversal
symmetries, respectively. We therefore call triple points with nontrivial
the topological acoustic triple point (TATP). The topological
charge can equivalently be characterized by the skyrmion number
of the longitudinal mode, or by the Euler number of the transverse modes, and
this strongly constrains the nodal structure around the TATP. The TATP can also
be symmetry-protected at high-symmetry momenta in the band structure of phonons
and spinless electrons by the and the groups. The nontrivial
wavefunction texture around the TATP can induce anomalous thermal transport in
phononic systems and orbital Hall effect in electronic systems. Our theory
demonstrates that the gapless points associated with the Nambu-Goldstone
theorem are an avenue for discovering new classes of degeneracy points with
distinct topological characteristics.Comment: 7+15 pages, 5+6 figure
Two-Dimensional Dirac Fermions Protected by Space-Time Inversion Symmetry in Black Phosphorus
We report the realization of novel symmetry-protected Dirac fermions in a
surface-doped two-dimensional (2D) semiconductor, black phosphorus. The widely
tunable band gap of black phosphorus by the surface Stark effect is employed to
achieve a surprisingly large band inversion up to ~0.6 eV. High-resolution
angle-resolved photoemission spectra directly reveal the pair creation of Dirac
points and their moving along the axis of the glide-mirror symmetry. Unlike
graphene, the Dirac point of black phosphorus is stable, as protected by
spacetime inversion symmetry, even in the presence of spin-orbit coupling. Our
results establish black phosphorus in the inverted regime as a simple model
system of 2D symmetry-protected (topological) Dirac semimetals, offering an
unprecedented opportunity for the discovery of 2D Weyl semimetals
On the environmental decoherence and spin interference in mesoscopic loop structures
Mechanisms of 'environmental decoherence' such as surface scattering,
Elliot-Yafet process and precession mechanisms, as well as their influence on
the spin phase relaxation are considered and compared. It is shown that the
'spin ballistic' regime is possible, when the phase relaxation length for the
spin part of the wave function (WF)is much greater than the phase relaxation
length for the 'orbital part'. In the presence of an additional magnetic field,
the spin part of the electron's WF acquires a phase shift due to additional
spin precession about that field. If the structure length is chosen to be
greater than the phase relaxation length for the 'orbital part' and less than
the phase relaxation length for the spin part of WF, it is possible to 'wash
out' the quantum interference related to the phase coherence of the 'orbital
part' of the WF, retaining at the same time that related to the phase coherence
of the spin part and, hence, to reveal corresponding conductance oscillations
Magnetic wallpaper Dirac fermions and topological magnetic Dirac insulators
Topological crystalline insulators (TCIs) can host anomalous surface states
which inherits the characteristics of crystalline symmetry that protects the
bulk topology. Especially, the diversity of magnetic crystalline symmetries
indicates the potential for novel magnetic TCIs with distinct surface
characteristics. Here, we propose a topological magnetic Dirac insulator
(TMDI), whose two-dimensional surface hosts fourfold-degenerate Dirac fermions
protected by either the or magnetic wallpaper group. The
bulk topology of TMDIs is protected by diagonal mirror symmetries, which give
chiral dispersion of surface Dirac fermions and mirror-protected hinge modes.
We propose candidate materials for TMDIs including NdTeClO
and DyB based on first-principles calculations, and construct a general
scheme for searching TMDIs using the space group of paramagnetic parent states.
Our theoretical discovery of TMDIs will facilitate future research on magnetic
TCIs and illustrate a distinct way to achieve anomalous surface states in
magnetic crystals.Comment: 10+36 pages, 4+23 figures, published versio
FK506-binding protein-like and FK506-binding protein 8 regulate dual leucine zipper kinase degradation and neuronal responses to axon injury
The dual leucine zipper kinase (DLK) is a key regulator of axon regeneration and degeneration in response to neuronal injury; however, regulatory mechanisms of the DLK function via its interacting proteins are largely unknown. To better understand the molecular mechanism of DLK function, we performed yeast two-hybrid screening analysis and identified FK506-binding protein-like (FKBPL, also known as WAF-1/CIP1 stabilizing protein 39) as a DLK-binding protein. FKBPL binds to the kinase domain of DLK and inhibits its kinase activity. In addition, FKBPL induces DLK protein degradation through ubiquitin-dependent pathways. We further assessed other members in the FKBP protein family and found that FK506-binding protein 8 (FKBP8) also induced DLK degradation. We identified the lysine 271 residue in the kinase domain as a major site of DLK ubiquitination and SUMO3 conjugation and was thus responsible for regulating FKBP8-mediated proteasomal degradation that was inhibited by the substitution of the lysine 271 to arginine. FKBP8-mediated degradation of DLK is mediated by autophagy pathway because knockdown of Atg5 inhibited DLK destabilization. We show that in vivo overexpression of FKBP8 delayed the progression of axon degeneration and suppressed neuronal death after axotomy in sciatic and optic nerves. Taken together, this study identified FKBPL and FKBP8 as novel DLK-interacting proteins that regulate DLK stability via the ubiquitin-proteasome and lysosomal protein degradation pathways
Desorption of alkali atoms from 4He nanodroplets
The dynamics following the photoexcitation of Na and Li atoms located on the
surface of helium nanodroplets has been investigated in a joint experimental
and theoretical study. Photoelectron spectroscopy has revealed that excitation
of the alkali atoms via the (n+1) -> ns transition leads to the desorption of
these atoms. The mean kinetic energy of the desorbed atoms, as determined by
ion imaging, shows a linear dependence on excitation frequency. These
experimental findings are analyzed within a three-dimensional, time-dependent
density functional approach for the helium droplet combined with a Bohmian
dynamics description of the desorbing atom. This hybrid method reproduces well
the key experimental observables. The dependence of the observables on the
impurity mass is discussed by comparing the results obtained for the 6Li and
7Li isotopes. The calculations show that the desorption of the excited alkali
atom is accompanied by the creation of highly non-linear density waves in the
helium droplet that propagate at supersonic velocities
Current-Carrying Ground States in Mesoscopic and Macroscopic Systems
We extend a theorem of Bloch, which concerns the net orbital current carried
by an interacting electron system in equilibrium, to include mesoscopic
effects. We obtain a rigorous upper bound to the allowed ground-state current
in a ring or disc, for an interacting electron system in the presence of static
but otherwise arbitrary electric and magnetic fields. We also investigate the
effects of spin-orbit and current-current interactions on the upper bound.
Current-current interactions, caused by the magnetic field produced at a point
r by a moving electron at r, are found to reduce the upper bound by an amount
that is determined by the self-inductance of the system. A solvable model of an
electron system that includes current-current interactions is shown to realize
our upper bound, and the upper bound is compared with measurements of the
persistent current in a single ring.Comment: 7 pager, Revtex, 1 figure available from [email protected]
Causal categories: relativistically interacting processes
A symmetric monoidal category naturally arises as the mathematical structure
that organizes physical systems, processes, and composition thereof, both
sequentially and in parallel. This structure admits a purely graphical
calculus. This paper is concerned with the encoding of a fixed causal structure
within a symmetric monoidal category: causal dependencies will correspond to
topological connectedness in the graphical language. We show that correlations,
either classical or quantum, force terminality of the tensor unit. We also show
that well-definedness of the concept of a global state forces the monoidal
product to be only partially defined, which in turn results in a relativistic
covariance theorem. Except for these assumptions, at no stage do we assume
anything more than purely compositional symmetric-monoidal categorical
structure. We cast these two structural results in terms of a mathematical
entity, which we call a `causal category'. We provide methods of constructing
causal categories, and we study the consequences of these methods for the
general framework of categorical quantum mechanics.Comment: 43 pages, lots of figure
Titanium Oxide Nanotube Surface Topography and MicroRNA-488 Contribute to Modulating Osteogenesis
Understanding the biocomplexity of cell behavior in relation to the topographical characteristics of implants is essential for successful osseointegration with good longevity and minimum failure. Here, we investigated whether culture on titanium oxide (TiO2) nanotubes of various diameters could affect the behavior and differentiation of MC3T3-E1 cells. Among the tested nanotubes, those of 50 nm in diameter were found to trigger the expression of the osteoblast-specific transcription factors, sp7 and Dlx5, and upregulate the expression of alkaline phosphatase (ALP). Here, we report that miR-488 was significantly induced in osteoblasts cultured on 50 nm nanotubes and continued to increase with the progression of osteoblast differentiation. Furthermore, downregulation of miR-488 suppressed the expression levels of ALP and matrix metalloprotease-2 (MMP-2). This suppression of ALP transcription was overcome by treatment with the MMP-2 activator, bafilomycin A1. Collectively, these results suggest that 50 nm is the optimum TiO2 nanotube diameter for implants, and that modulation of miR-488 can change the differentiation activity of cells on TiO2 nanotubes. This emphasizes that we must fully understand the physicochemical properties of TiO2 nanotubes and the endogenous biomolecules that interact with such surfaces, in order to fully support their clinical application
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