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$μ$SR study on noncentrosymmetric superconductor NbGe$_{\mathbf{2}}$
Authors:
J. C. Jiao,
K. W. Chen,
A. D. Hillier,
T. U. Ito,
W. Higemoto,
Z. Li,
B. J. Lv,
Z. -A. Xu,
L. Shu
Abstract:
We report a muon spin relaxation ($μ$SR) study on polycrystalline noncentrosymmetric superconductor NbGe$_2$~with the superconducting transition temperature $T_c=2.0\sim2.1$~K. Zero-field $μ$SR~experiment indicates the absence of spontaneous magnetic field in the superconducting state, showing the preservation of time-reversal symmetry in the superconducting state. Transverse-field $μ$SR~experimen…
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We report a muon spin relaxation ($μ$SR) study on polycrystalline noncentrosymmetric superconductor NbGe$_2$~with the superconducting transition temperature $T_c=2.0\sim2.1$~K. Zero-field $μ$SR~experiment indicates the absence of spontaneous magnetic field in the superconducting state, showing the preservation of time-reversal symmetry in the superconducting state. Transverse-field $μ$SR~experiment is performed to map the phase diagram of NbGe$_2$, from which clear evidence of both type-I and type-II superconductivity is obtained. More importantly, we clearly delineate the region in the phase diagram where type-I and type-II superconductivity coexist.
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Submitted 12 December, 2024;
originally announced December 2024.
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Bulk and surface electronic structure of trigonal structured PtBi2 studied by angle-resolved photoemission spectroscopy
Authors:
Q. Yao,
Y. P. Du,
X. J. Yang,
Y. Zheng,
D. F. Xu,
X. H. Niu,
H. F. Yang,
P. Dudin,
T. K. Kim,
M. Hoesch,
I. Vobornik,
Z. -A. Xu,
X. G. Wan,
D. L. Feng,
D. W. Shen
Abstract:
PtBi2 with a layered trigonal crystal structure was recently reported to exhibit an unconventional large linear magnetoresistance, while the mechanism involved is still elusive. Using high resolution angle-resolved photoemission spectroscopy, we present a systematic study on its bulk and surface electronic structure. Through careful comparison with first-principle calculations, our experiment dist…
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PtBi2 with a layered trigonal crystal structure was recently reported to exhibit an unconventional large linear magnetoresistance, while the mechanism involved is still elusive. Using high resolution angle-resolved photoemission spectroscopy, we present a systematic study on its bulk and surface electronic structure. Through careful comparison with first-principle calculations, our experiment distinguishes the low-lying bulk bands from entangled surface states, allowing the estimation of the real stoichiometry of samples. We find significant electron doping in PtBi2, implying a substantial Bi deficiency induced disorder therein. We discover a Dirac-cone-like surface state on the boundary of the Brillouin zone, which is identified as an accidental Dirac band without topological protection. Our findings exclude quantum-limit-induced linear band dispersion as the cause of the unconventional large linear magnetoresistance.
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Submitted 20 July, 2016; v1 submitted 12 July, 2016;
originally announced July 2016.
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Observation of Fermi Arcs in non-Centrosymmetric Weyl Semi-metal Candidate NbP
Authors:
D. F. Xu,
Y. P. Du,
Z. Wang,
Y. P. Li,
X. H. Niu,
Q. Yao,
P. Dudin,
Z. -A. Xu,
X. G. Wan,
D. L. Feng
Abstract:
We report the surface electronic structure of niobium phosphide NbP single crystal on (001) surface by vacuum ultraviolet angle-resolved photoemission spectroscopy. Combining with our first principle calculations, we identify the existence of the Fermi arcs originated from topological surface states. Furthermore, the surface states exhibit circular dichroism pattern, which may correlate with its n…
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We report the surface electronic structure of niobium phosphide NbP single crystal on (001) surface by vacuum ultraviolet angle-resolved photoemission spectroscopy. Combining with our first principle calculations, we identify the existence of the Fermi arcs originated from topological surface states. Furthermore, the surface states exhibit circular dichroism pattern, which may correlate with its non-trivial spin texture. Our results provide critical evidence for the existence of the Weyl Fermions in NbP, which lays the foundation for further investigations.
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Submitted 13 September, 2015;
originally announced September 2015.
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Evolution from incoherent to coherent electronic states and its implications to superconductivity in FeTe1-xSex
Authors:
E. Ieki,
K. Nakayama,
Y. Miyata,
T. Sato,
H. Miao,
N. Xu,
X. -P. Wang,
P. Zhang,
T. Qian,
P. Richard,
Z. -J. Xu,
J. S. Wen,
G. D. Gu,
H. Q. Luo,
H. -H. Wen,
H. Ding,
T. Takahashi
Abstract:
We have performed systematic angle-resolved photoemission spectroscopy (ARPES) of iron-chalcogenide superconductor FeTe1-xSex to elucidate the electronic states relevant to the superconductivity. While the Fermi-surface shape is nearly independent of x, we found that the ARPES spectral line shape shows prominent x dependence. A broad ARPES spectrum characterized by a small quasiparticle weight at…
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We have performed systematic angle-resolved photoemission spectroscopy (ARPES) of iron-chalcogenide superconductor FeTe1-xSex to elucidate the electronic states relevant to the superconductivity. While the Fermi-surface shape is nearly independent of x, we found that the ARPES spectral line shape shows prominent x dependence. A broad ARPES spectrum characterized by a small quasiparticle weight at x = 0, indicative of incoherent electronic states, becomes progressively sharper with increasing x, and a well-defined quasiparticle peak appears around x = 0.45 where bulk superconductivity is realized. The present result suggests the evolution from incoherent to coherent electronic states and its close relationship to the emergence of superconductivity.
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Submitted 6 May, 2014;
originally announced May 2014.
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Possible observation of parametrically amplified coherent phasons in K0.3MoO3 using time-resolved extreme-ultraviolet ARPES
Authors:
H. Y. Liu,
I. Gierz,
J. C. Petersen,
S. Kaiser,
A. Simoncig,
A. L. Cavalieri,
C. Cacho,
I. C. E. Turcu,
E. Springate,
F. Frassetto,
L. Poletto,
S. S. Dhesi,
Z. -A. Xu,
T. Cuk,
R. Merlin,
A. Cavalleri
Abstract:
We use time- and angle-resolved photoemission spectroscopy (tr-ARPES) in the Extreme Ultraviolet (EUV) to measure the time- and momentum-dependent electronic structure of photo-excited K0.3MoO3. Prompt depletion of the Charge Density Wave (CDW) condensate launches coherent oscillations of the amplitude mode, observed as a 1.7-THz-frequency modulation of the bonding band position. In contrast, the…
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We use time- and angle-resolved photoemission spectroscopy (tr-ARPES) in the Extreme Ultraviolet (EUV) to measure the time- and momentum-dependent electronic structure of photo-excited K0.3MoO3. Prompt depletion of the Charge Density Wave (CDW) condensate launches coherent oscillations of the amplitude mode, observed as a 1.7-THz-frequency modulation of the bonding band position. In contrast, the anti-bonding band oscillates at about half this frequency. We attribute these oscillations to coherent excitation of phasons via parametric amplification of phase fluctuations.
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Submitted 11 April, 2013; v1 submitted 25 June, 2012;
originally announced June 2012.
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Effects of Ru Substitution on Dimensionality and Electron Correlations in Ba(Fe_{1-x}Ru_x)_2As_2
Authors:
N. Xu,
T. Qian,
P. Richard,
Y. -B. Shi,
X. -P. Wang,
P. Zhang,
Y. -B. Huang,
Y. -M. Xu,
H. Miao,
G. Xu,
G. -F. Xuan,
W. -H. Jiao,
Z. -A. Xu,
G. -H. Cao,
H. Ding
Abstract:
We report a systematic angle-resolved photoemission spectroscopy study on Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$ for a wide range of Ru concentrations (0.15 $\leq$ \emph{x} $\leq$ 0.74). We observed a crossover from two-dimension to three-dimension for some of the hole-like Fermi surfaces with Ru substitution and a large reduction in the mass renormalization close to optimal doping. These results suggest…
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We report a systematic angle-resolved photoemission spectroscopy study on Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$ for a wide range of Ru concentrations (0.15 $\leq$ \emph{x} $\leq$ 0.74). We observed a crossover from two-dimension to three-dimension for some of the hole-like Fermi surfaces with Ru substitution and a large reduction in the mass renormalization close to optimal doping. These results suggest that isovalent Ru substitution has remarkable effects on the low-energy electron excitations, which are important for the evolution of superconductivity and antiferromagnetism in this system.
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Submitted 21 March, 2012;
originally announced March 2012.
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Order parameter fluctuations at a buried quantum critical point
Authors:
Yejun Feng,
Jiyang Wang,
R. Jaramillo,
Jasper van Wezel,
S. Haravifard,
G. Srajer,
Y. Liu,
Z. -A. Xu,
P. B. Littlewood,
T. F. Rosenbaum
Abstract:
Quantum criticality is a central concept in condensed matter physics, but the direct observation of quantum critical fluctuations has remained elusive. Here we present an x-ray diffraction study of the charge density wave (CDW) in 2H-NbSe2 at high pressure and low temperature, where we observe a broad regime of order parameter fluctuations that are controlled by proximity to a quantum critical poi…
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Quantum criticality is a central concept in condensed matter physics, but the direct observation of quantum critical fluctuations has remained elusive. Here we present an x-ray diffraction study of the charge density wave (CDW) in 2H-NbSe2 at high pressure and low temperature, where we observe a broad regime of order parameter fluctuations that are controlled by proximity to a quantum critical point. X-rays can track the CDW despite the fact that the quantum critical regime is shrouded inside a superconducting phase, and, in contrast to transport probes, allow direct measurement of the critical fluctuations of the charge order. Concurrent measurements of the crystal lattice point to a critical transition that is continuous in nature. Our results confirm the longstanding expectations of enhanced quantum fluctuations in low dimensional systems, and may help to constrain theories of the quantum critical Fermi surface.
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Submitted 12 March, 2012; v1 submitted 1 September, 2011;
originally announced September 2011.
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Isotropic superconducting gaps with enhanced pairing on electron Fermi surfaces in FeTe0.55Se0.45
Authors:
H. Miao,
P. Richard,
Y. Tanaka,
K. Nakayama,
T. Qian,
K. Umezawa,
T. Sato,
Y. -M. Xu,
Y. -B. Shi,
N. Xu,
X. -P. Wang,
P. Zhang,
H. -B. Yang,
Z. -J. Xu,
J. S. Wen,
G. -D. Gu,
X. Dai,
J. -P. Hu,
T. Takahashi,
H. Ding
Abstract:
The momentum distribution of the energy gap opening at the Fermi level of superconductors is a direct fingerprint of the pairing mechanism. While the phase diagram of the iron-based superconductors promotes antiferromagnetic fluctuations as a natural candidate for electron pairing, the precise origin of the interaction is highly debated. We used angle-resolved photoemission spectroscopy to reveal…
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The momentum distribution of the energy gap opening at the Fermi level of superconductors is a direct fingerprint of the pairing mechanism. While the phase diagram of the iron-based superconductors promotes antiferromagnetic fluctuations as a natural candidate for electron pairing, the precise origin of the interaction is highly debated. We used angle-resolved photoemission spectroscopy to reveal directly the momentum distribution of the superconducting gap in FeTe1-xSex, which has the simplest structure of all iron-based superconductors. We found isotropic superconducting gaps on all Fermi surfaces whose sizes can be fitted by a single gap function derived from a strong coupling approach, strongly suggesting local antiferromagnetic exchange interactions as the pairing origin.
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Submitted 5 July, 2011;
originally announced July 2011.
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Electronic structure of heavily electron-doped BaFe$_{1.7}$Co$_{0.3}$As$_2$ studied by angle-resolved photoemission
Authors:
Y. Sekiba,
T. Sato,
K. Nakayama,
K. Terashima,
P. Richard,
J. H. Bowen,
H. Ding,
Y. -M. Xu,
L. J. Li,
G. H. Cao,
Z. -A. Xu,
T. Takahashi
Abstract:
We have performed high-resolution angle-resolved photoemission spectroscopy on heavily electron-doped non-superconducting (SC) BaFe$_{1.7}$Co$_{0.3}$As$_2$. We find that the two hole Fermi surface pockets at the zone center observed in the hole-doped superconducting Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ are absent or very small in this compound, while the two electron pockets at the M point significan…
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We have performed high-resolution angle-resolved photoemission spectroscopy on heavily electron-doped non-superconducting (SC) BaFe$_{1.7}$Co$_{0.3}$As$_2$. We find that the two hole Fermi surface pockets at the zone center observed in the hole-doped superconducting Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ are absent or very small in this compound, while the two electron pockets at the M point significantly expand due to electron doping by the Co substitution. Comparison of the Fermi surface between non-SC and SC samples indicates that the coexistence of hole and electron pockets connected via the antiferromagnetic wave vector is essential in realizing the mechanism of superconductivity in the iron-based superconductors.
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Submitted 5 March, 2009; v1 submitted 22 December, 2008;
originally announced December 2008.
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Fermi surface nesting induced strong pairing in iron-based superconductors
Authors:
K. Terashima,
Y. Sekiba,
J. H. Bowen,
K. Nakayama,
T. Kawahara,
T. Sato,
P. Richard,
Y. -M. Xu,
L. J. Li,
G. H. Cao,
Z. -A. Xu,
H. Ding,
T. Takahashi
Abstract:
The discovery of high-temperature superconductivity in iron pnictides raised the possibility of an unconventional superconducting mechanism in multiband materials. The observation of Fermi-surface(FS)-dependent nodeless superconducting gaps suggested that inter-FS interactions may play a crucial role in superconducting pairing. In the optimally hole-doped Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$, the pai…
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The discovery of high-temperature superconductivity in iron pnictides raised the possibility of an unconventional superconducting mechanism in multiband materials. The observation of Fermi-surface(FS)-dependent nodeless superconducting gaps suggested that inter-FS interactions may play a crucial role in superconducting pairing. In the optimally hole-doped Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$, the pairing strength is enhanced simultaneously (2$Δ$/Tc$\sim$7) on the nearly nested FS pockets, i.e. the inner holelike ($α$) FS and the two hybridized electronlike FSs, while the pairing remains weak (2$Δ$/Tc$\sim$3.6) in the poorly-nested outer hole-like ($β$) FS. Here we report that in the electron-doped BaFe$_{1.85}$Co$_{0.15}$As$_2$ the FS nesting condition switches from the $α$ to the $β$ FS due to the opposite size changes for hole- and electron-like FSs upon electron doping. The strong pairing strength (2$Δ$/Tc$\sim$6) is also found to switch to the nested $β$ FS, indicating an intimate connection between FS nesting and superconducting pairing, and strongly supporting the inter-FS pairing mechanism in the iron-based superconductors.
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Submitted 8 June, 2009; v1 submitted 18 December, 2008;
originally announced December 2008.