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Robust spin order and fragile charge order in Na0.5CoO2 as revealed by time-resolved terahertz spectroscopy
Authors:
X. Y. Zhou,
S. J. Zhang,
D. Wu,
H. Wang,
B. H. Li,
S. F. Wu,
Q. M. Liu,
T. C. Hu,
R. S. Li,
J. Y. Yuan,
S. X. Xu,
Q. Wu,
L. Yue,
T. Dong,
N. L. Wang
Abstract:
Near-infrared (NIR) pump-terahertz (THz) probe spectroscopy is used to investigate the charge and spin exciations in a strongly correlated electron compound Na0.5CoO2. This compound exhibits a coexistence of various charge and spin orders arising from intricate interactions among charge, spin, and orbital degrees of freedom. NIR pulses create significantly diverse effects on the charge and spin or…
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Near-infrared (NIR) pump-terahertz (THz) probe spectroscopy is used to investigate the charge and spin exciations in a strongly correlated electron compound Na0.5CoO2. This compound exhibits a coexistence of various charge and spin orders arising from intricate interactions among charge, spin, and orbital degrees of freedom. NIR pulses create significantly diverse effects on the charge and spin orders; while the charge order is easily melted,coherent magnon excitations are present in all fluences examined. Furthermore, a novel π phase shift of the coherent magnon oscillations is observed in the pump-induced change of the terahertz electric field between regions of increasing and decreasing field change. These results unequivocally illustrate that ultrashort laser pulses enable the disentanglement of different interactions within complex systems characterized by multiple orders, providing a fresh perspective on the interplay between itinerant and localized electrons within the Co 3d t2g multiplets.
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Submitted 14 April, 2024;
originally announced April 2024.
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Orbital-differentiated coherence-incoherence crossover identified by photoemission spectroscopy in LiFeAs
Authors:
H. Miao,
Z. P. Yin,
S. F. Wu,
J. M. Li,
J. Ma,
B. -Q. Lv,
X. P. Wang,
T. Qian,
P. Richard,
L. -Y. Xing,
X. -C. Wang,
C. Q. Jin,
K. Haule,
G. Kotliar,
H. Ding
Abstract:
In the iron-based superconductors (FeSCs), orbital differentiation is an important phenomenon, whereby correlations stronger on the dxy orbital than on the dxz/yz orbital yield quasi-particles with dxy} orbital character having larger mass renormalization and abnormal temperature evolution. However, the physical origin of this orbital differentiation is debated between the Hund's coupling induced…
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In the iron-based superconductors (FeSCs), orbital differentiation is an important phenomenon, whereby correlations stronger on the dxy orbital than on the dxz/yz orbital yield quasi-particles with dxy} orbital character having larger mass renormalization and abnormal temperature evolution. However, the physical origin of this orbital differentiation is debated between the Hund's coupling induced unbinding of spin and orbital degrees of freedom and the Hubbard interaction instigated orbital selective Mott transition. Here we use angle-resolved photoemission spectroscopy to identify an orbital-dependent correlation-induced quasi-particle (QP) anomaly in LiFeAs. The excellent agreement between our photoemission measurements and first-principles many-body theory calculations shows that the orbital-differentiated QP lifetime anomalies in LiFeAs are controlled by the Hund's coupling.
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Submitted 11 July, 2016;
originally announced July 2016.
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Ultrafast Carrier Dynamics in the Large Magnetoresistance Material WTe$_{2}$
Authors:
Y. M. Dai,
J. Bowlan,
H. Li,
H. Miao,
S. F. Wu,
W. D. Kong,
Y. G. Shi,
S. A. Trugman,
J. -X. Zhu,
H. Ding,
A. J. Taylor,
D. A. Yarotski,
R. P. Prasankumar
Abstract:
Ultrafast optical pump-probe spectroscopy is used to track carrier dynamics in the large magnetoresistance material WTe$_{2}$. Our experiments reveal a fast relaxation process occurring on a sub-picosecond time scale that is caused by electron-phonon thermalization, allowing us to extract the electron-phonon coupling constant. An additional slower relaxation process, occurring on a time scale of…
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Ultrafast optical pump-probe spectroscopy is used to track carrier dynamics in the large magnetoresistance material WTe$_{2}$. Our experiments reveal a fast relaxation process occurring on a sub-picosecond time scale that is caused by electron-phonon thermalization, allowing us to extract the electron-phonon coupling constant. An additional slower relaxation process, occurring on a time scale of $\sim$5-15 picoseconds, is attributed to phonon-assisted electron-hole recombination. As the temperature decreases from 300 K, the timescale governing this process increases due to the reduction of the phonon population. However, below $\sim$50 K, an unusual decrease of the recombination time sets in, most likely due to a change in the electronic structure that has been linked to the large magnetoresistance observed in this material.
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Submitted 7 October, 2015; v1 submitted 24 June, 2015;
originally announced June 2015.
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Direct spectroscopic evidence for completely filled Cu $3d$ shell in BaCu$_2$As$_2$ and $α$-BaCu$_2$Sb$_2$
Authors:
S. F. Wu,
P. Richard,
A. van Roekeghem,
S. M. Nie,
H. Miao,
N. Xu,
T. Qian,
B. Saparov,
Z. Fang,
S. Biermann,
Athena S. Sefat,
H. Ding
Abstract:
We use angle-resolved photoemission spectroscopy to extract the band dispersion and the Fermi surface of BaCu$_2$As$_2$ and $α$-BaCu$_2$Sb$_2$. While the Cu $3d$ bands in both materials are located around 3.5 eV below the Fermi level, the low-energy photoemission intensity mainly comes from As $4p$ states, suggesting a completely filled Cu $3d$ shell. The splitting of the As $3d$ core levels and t…
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We use angle-resolved photoemission spectroscopy to extract the band dispersion and the Fermi surface of BaCu$_2$As$_2$ and $α$-BaCu$_2$Sb$_2$. While the Cu $3d$ bands in both materials are located around 3.5 eV below the Fermi level, the low-energy photoemission intensity mainly comes from As $4p$ states, suggesting a completely filled Cu $3d$ shell. The splitting of the As $3d$ core levels and the lack of pronounced three-dimensionality in the measured band structure of BaCu$_2$As$_2$ indicate a surface state likely induced by the cleavage of this material in the collapsed tetragonal phase, which is consistent with our observation of a Cu$^{+1}$ oxydation state. However, the observation of Cu states at similar energy in $α$-BaCu$_2$Sb$_2$ without the pnictide-pnictide interlayer bonding characteristic of the collapsed tetragonal phase suggests that the short interlayer distance in BaCu$_2$As$_2$ follows from the stability of the Cu$^{+1}$ rather than the other way around. Our results confirm the prediction that BaCu$_2$As$_2$ is an $sp$ metal with weak electronic correlations.
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Submitted 1 April, 2015;
originally announced April 2015.
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Raman scattering investigation of the electron-phonon coupling in superconducting Nd(O,F)BiS$_2$
Authors:
S. F. Wu,
P. Richard,
X. B. Wang,
C. S. Lian,
S. M. Nie,
J. T. Wang,
N. L. Wang,
H. Ding
Abstract:
We have performed polarized Raman scattering measurements on the newly discovered superconductor Nd(O,F)BiS$_2$ ($T_c = 4$ K). We observe 2 Raman active modes, with frequencies in accordance with first-principles calculations. One A$_{1g}$ phonon mode at 112.4 cm$^{-1}$ exhibits a Fano line shape due to electron-phonon coupling. We find a resonance for this mode at 2.45 eV excitation energy. We es…
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We have performed polarized Raman scattering measurements on the newly discovered superconductor Nd(O,F)BiS$_2$ ($T_c = 4$ K). We observe 2 Raman active modes, with frequencies in accordance with first-principles calculations. One A$_{1g}$ phonon mode at 112.4 cm$^{-1}$ exhibits a Fano line shape due to electron-phonon coupling. We find a resonance for this mode at 2.45 eV excitation energy. We estimate a 0.68 contribution of this mode to the electron-phonon coupling constant $λ$. Our Raman results suggest that the BiS$_2$-based superconductors are possibly phonon-mediated BCS superconductors.
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Submitted 24 July, 2014;
originally announced July 2014.