10 research outputs found
Observability of Higgs Mode in a system without Lorentz invariance
We study the observability of the Higgs mode in BEC-BCS crossover. The
observability of Higgs mode is investigated by calculating the spectral weight
functions of the amplitude fluctuation below the critical transition
temperature. At zero temperature, we find that there are two sharp peaks on the
spectral function of the amplitude fluctuation attributed to Goldstone and
Higgs modes respectively. As the system goes from BCS to BEC side, there is
strong enhancement of spectral weight transfer from the Higgs to Goldstone
mode. However, even at the unitary regime where the Lorentz invariance is lost,
the sharp feature of Higgs mode still exists. We specifically calculate the
finite temperature spectral function of amplitude fluctuation at the unitary
regime and show that the Higgs mode is observable at the temperature that
present experiments can reach.Comment: 5 pages, 2 figure
Crossover from Non-Fermi-Liquid to Pseudogap Behavior in the Spectral of Local Impurity in Power-Law Diverging Multichannel Kondo Model
Motivated by the emergence of higher-order van Hove singularities (VHS) with
power-law divergent density of states (DOS)
(, ) in materials, we investigate a
multichannel Kondo model involving conduction electrons near the higher-order
van Hove filling. This model considers channel and spin degrees of
freedom. Employing a renormalization group analysis and dynamical large-
approach, our results reveal a crossover from a non-Fermi liquid to pseudogap
behavior in the spectral properties of the local impurity at the overscreened
fixed point. At this critical fixed point, we precisely determine the
conditions under which the crossover occurs, either by tuning the exponent
or the ratio to a critical value. The results of this study
provide novel insights into the non-Fermi liquid and pseudogap behaviors
observed in strongly correlated systems, shedding light on the intriguing
interplay between higher-order van Hove singularities and multichannel Kondo
physics.Comment: 5 pages, 5 fugure
Coexistence of Tri-Hexagonal and Star-of-David Pattern in the Charge Density Wave of the Kagome Superconductor AVSb
The recently discovered layered kagome metals AVSb(A=K, Rb, Cs) have
attracted much attention because of their unique combination of
superconductivity, charge density wave (CDW) order, and nontrivial band
topology. The CDW order with an in-plane 2x2 reconstruction is found to exhibit
exotic properties, such as time-reversal symmetry breaking and rotational
symmetry breaking. However, the nature of the CDW, including its
dimensionality, structural pattern, and effect on electronic structure, remains
elusive despite intense research efforts. Here, using angle-resolved
photoemission spectroscopy, we unveil for the first time characteristic
double-band splittings and band reconstructions, as well as the band gap
resulting from band folding, in the CDW phase. Supported by density functional
theory calculations, we unambiguously show that the CDW in AVSb
originates from the intrinsic coexistence of Star-of-David and Tri-Hexagonal
distortions. The alternating stacking of these two distortions naturally leads
to three-dimensional 2x2x2 or 2x2x4 CDW order. Our results provide crucial
insights into the nature and distortion pattern of the CDW order, thereby
laying down the basis for a substantiated understanding of the exotic
properties in the family of AVSb kagome metals
Spectroscopic Evidence for a Three-Dimensional Charge Density Wave in Kagome Superconductor CsVSb
The recently discovered AV3Sb5 (A=K, Rb, Cs) family, possessing V kagome
nets, has received considerable attention due to the topological electronic
structure and intriguing correlated phenomena, including an exotic charge
density wave (CDW) and superconductivity. Detailed electronic structure studies
are essential to unravel the characteristics and origin of the CDW as well as
its interplay with superconductivity. Here, we present angle-resolved
photoemission spectroscopy (ARPES) measurements for CsV3Sb5 at multiple
temperatures and photon energies to reveal the nature of the CDW from an
electronic structure perspective. We present evidence for a three-dimensional
(3D) CDW order. In the process we also pinpoint a surface state attributed to a
Cs terminated surface. This state was previously attributed to band folding
band due to a CDW along the c direction or a quantum well state from quantum
confinement. The CDW expected 2-fold lattice reconstruction along c axis is
observed to be a quadrupling of the unit cell, thus for the first time directly
demonstrating the 3D nature of the CDW from the electronic structure
perspective. Moreover, this 3D CDW configuration originates from two distinct
types of distortions in adjacent kagome layers. These present results not only
provide key insights into the nature of the unconventional CDW in CsV3Sb5 but
also provides an important reference for further studies on the relationship
between the CDW and superconductivity.Comment: 19 pages, 4 figure
Phonon promoted charge density wave in topological kagome metal ScVSn
Charge density wave (CDW) orders in vanadium-based kagome metals have
recently received tremendous attention due to their unique properties and
intricate interplay with exotic correlated phenomena, topological and
symmetry-breaking states. However, the origin of the CDW order remains a topic
of debate. The discovery of ScVSn, a vanadium-based bilayer kagome
metal exhibiting an in-plane x 30
CDW order with time-reversal symmetry breaking, provides a novel platform to
explore the underlying mechanism behind the unconventional CDW. Here, we
combine high-resolution angle-resolved photoemission spectroscopy, Raman
scattering measurements and density functional theory to investigate the
electronic structures and phonon modes of ScVSn and their evolution
with temperature. We identify topologically nontrivial Dirac surface states and
multiple van Hove singularities (VHSs) in the vicinity of the Fermi level, with
one VHS near the K point exhibiting nesting wave vectors in proximity to the
x 30 CDW wave vector. Additionally,
Raman measurements indicate a strong intrinsic electron-phonon coupling in
ScVSn, as evidenced by the presence of a two-phonon mode and a
large frequency amplitude mode. Our findings highlight the fundamental role of
lattice degrees of freedom in promoting the CDW in ScVSn and
provide important insights into the fascinating correlation phenomena observed
in kagome metals
Phonon promoted charge density wave in topological kagome metal ScV<sub>6</sub>Sn<sub>6</sub>
Charge density wave (CDW) orders in vanadium-based kagome metals have recently received tremendous attention, yet their origin remains a topic of debate. The discovery of ScV 6 Sn 6 , a bilayer kagome metal featuring an intriguing 3 × 3 × 3 CDW order, offers a novel platform to explore the underlying mechanism behind the unconventional CDW. Here, we combine high-resolution angle-resolved photoemission spectroscopy, Raman scattering and density functional theory to investigate the electronic structure and phonon modes of ScV 6 Sn 6 . We identify topologically nontrivial surface states and multiple van Hove singularities (VHSs) in the vicinity of the Fermi level, with one VHS aligning with the in-plane component of the CDW vector near the K ¯ point. Additionally, Raman measurements indicate a strong electron-phonon coupling, as evidenced by a two-phonon mode and new emergent modes. Our findings highlight the fundamental role of lattice degrees of freedom in promoting the CDW in ScV 6 Sn 6