13 research outputs found
Coherent modulation of the electron temperature and electron-phonon couplings in a 2D material
Ultrashort light pulses can selectively excite charges, spins and phonons in
materials, providing a powerful approach for manipulating their properties.
Here we use femtosecond laser pulses to coherently manipulate the electron and
phonon distributions, and their couplings, in the charge density wave (CDW)
material 1T-TaSe. After exciting the material with a short light pulse,
spatial smearing of the electrons launches a coherent lattice breathing mode,
which in turn modulates the electron temperature. This indicates a
bi-directional energy exchange between the electrons and the strongly-coupled
phonons. By tuning the laser excitation fluence, we can control the magnitude
of the electron temperature modulation, from ~ 200 K in the case of weak
excitation, to ~ 1000 K for strong laser excitation. This is accompanied by a
switching of the dominant mechanism from anharmonic phonon-phonon coupling to
coherent electron-phonon coupling, as manifested by a phase change of in
the electron temperature modulation. Our approach thus opens up possibilities
for coherently manipulating the interactions and properties of quasi-2D and
other quantum materials using light.Comment: 15 pages, 4 figure
Evolution of the strange-metal scattering in momentum space of electron-doped
The linear-in-temperature resistivity is one of the important mysteries in
the strange metal state of high-temperature cuprate superconductors. To uncover
this anomalous property, the energy-momentum-dependent imaginary part of the
self-energy Im holds the key information. Here we
perform systematic doping, momentum, and temperature-dependent angle-resolved
photoemission spectroscopy measurements of electron-doped cuprate and extract the evolution of the strange metal
scattering in momentum space. At low doping levels and low temperatures, Im
dependence dominates the whole momentum space. For
high doping levels and high temperatures, Im
shows up, starting from the antinodal region. By comparing with the hole-doped
cuprates and , we find a dichotomy of the scattering rate exists along the
nodal and antinodal direction, which is ubiquitous in the cuprate family. Our
work provides new insight into the strange metal state in cuprates
Testing Electron-phonon Coupling for the Superconductivity in Kagome Metal
In crystalline materials, electron-phonon coupling (EPC) is a ubiquitous
many-body interaction that drives conventional Bardeen-Cooper-Schrieffer
superconductivity. Recently, in a new kagome metal ,
superconductivity that possibly intertwines with time-reversal and spatial
symmetry-breaking orders is observed. Density functional theory calculations
predicted weak EPC strength,, supporting an unconventional pairing
mechanism in . However, experimental determination of
is still missing, hindering a microscopic understanding of the intertwined
ground state of . Here, using 7-eV laser-based angle-resolved
photoemission spectroscopy and Eliashberg function analysis, we determine an
intermediate =0.45~0.6 at T=6 K for both Sb 5p and V 3d electronic
bands, which can support a conventional superconducting transition temperature
on the same magnitude of experimental value in . Remarkably,
the EPC on the V 3d-band enhances to ~0.75 as the superconducting
transition temperature elevated to 4.4 K in .
Our results provide an important clue to understand the pairing mechanism in
the Kagome superconductor .Comment: To appear in Nature Communication
Creation of a novel inverted charge density wave state
Charge density wave (CDW) order is an emergent quantum phase that is characterized by periodic lattice distortion and charge density modulation, often present near superconducting transitions. Here, we uncover a novel inverted CDW state by using a femtosecond laser to coherently reverse the star-of-David lattice distortion in 1T-TaSe2. We track the signature of this novel CDW state using time- and angle-resolved photoemission spectroscopy and the time-dependent density functional theory to validate that it is associated with a unique lattice and charge arrangement never before realized. The dynamic electronic structure further reveals its novel properties that are characterized by an increased density of states near the Fermi level, high metallicity, and altered electron–phonon couplings. Our results demonstrate how ultrafast lasers can be used to create unique states in materials by manipulating charge-lattice orders and couplings.INTRODUCTIO
Testing electron–phonon coupling for the superconductivity in kagome metal CsV3Sb5
Electron-phonon coupling is thought to be too weak to be responsible for the superconducting Cooper pairing of the kagome metals AV3Sb5, but an experimental measurement is lacking. Here, the authors use ARPES measurements to find that electron-phonon coupling in CsV3Sb5 is strong enough to support the experimental superconducting transition
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Coexistence of Bulk-Nodal and Surface-Nodeless Cooper Pairings in a Superconducting Dirac Semimetal
The interplay of nontrivial topology and superconductivity in condensed matter physics gives rise to exotic phenomena. However, materials are extremely rare where it is possible to explore the full details of the superconducting pairing. Here, we investigate the momentum dependence of the superconducting gap distribution in a novel Dirac material PdTe. Using high resolution, low temperature photoemission spectroscopy, we establish it as a spin-orbit coupled Dirac semimetal with the topological Fermi arc crossing the Fermi level on the (010) surface. This spin-textured surface state exhibits a fully gapped superconducting Cooper pairing structure below T_{c}∼4.5 K. Moreover, we find a node in the bulk near the Brillouin zone boundary, away from the topological Fermi arc. These observations not only demonstrate the band resolved electronic correlation between topological Fermi arc states and the way it induces Cooper pairing in PdTe, but also provide a rare case where surface and bulk states host a coexistence of nodeless and nodal gap structures enforced by spin-orbit coupling