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Zhuojin Xie,
Shaolong He,
Chaoyu Chen,
Ya Feng,
Hemian Yi,
Aiji Liang,
Lin Zhao,
Daixiang Mou,
Junfeng He,
Yingying Peng, [......],
Xiaoli Dong,
Jun Zhang,
Xiaoyang Wang,
Qinjun Peng,
Zhimin Wang,
Shenjin Zhang,
Feng Yang,
Chuangtian Chen,
Zuyan Xu, X. J. Zhou
[show abstract]
[hide abstract]
ABSTRACT: Topological insulators represent a new quantum state of matter that are
insulating in the bulk but metallic on the surface possessing unique electronic
structure and spin texture. They all share the same total angular momentum
texture in the Dirac surface state with the electron spin locked with the
crystal momentum. Here we report direct observation of the spin texture locking
with the orbital texture in a topological insulator Bi2Se3. The spin texture of
the Bi2Se3 surface state has been directly measured by high resolution spin-
and angle-resolved photoemission spectroscopy. Different orbitals in Bi2Se3
have been selectively probed by using variable polarization of the incident
light. We have revealed distinct spin textures in different light polarization
geometries that constitute strong evidence of the orbital-dependent spin
texture in Bi2Se3. As different topological compounds may have very different
orbital characters for the surface states, our observations provide a new
orbital degree of freedom in controlling the spin structure in the topological
insulators. We also demonstrate light manipulation of the orbital-selective
spin texture in Bi2Se3 that is important for the future applications of
topological insulators in spin-related technologies.
03/2013;
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[show abstract]
[hide abstract]
ABSTRACT: The detailed structural properties of La-doped Bi2Sr2-xLaxCuO6 (La-Bi2201,
0<=x<=1.1) have been studied by transmission electron microscopy (TEM). The
well-known incommensurate supermodulation q1 in the Bi-based cuprates evolves
from a monoclinic superstructure in the pristine Bi2201 phase to an orthogonal
one in La-Bi2201(x=0.73) phase. The b-component of the modulation vector (q1)
for x=0.25 sample is about 0.24b* and increases slightly to 0.246b* in x=0.84
sample, while it increases significantly to 0.286b* for x=1.10 sample. We have
revealed a new anti-phase stripe superstructure in all the La-doped Bi2201
samples, giving rise to a new modulation with a vector q2. This q2 modulation
is directly evolved from the orthogonal modulation q1 through an addition of
the anti-phase structure so that its vector q2 equals to q1b/2. We also
discussed the implication of these structural studies on the electronic
structure by angle-resolved photoemission spectroscopy (ARPES) experiments in
La-Bi2201.
03/2013;
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Yingying Peng,
Jianqiao Meng,
Daixiang Mou,
Junfeng He,
Lin Zhao,
Yue Wu,
Guodong Liu,
Xiaoli Dong,
Shaolong He,
Jun Zhang,
Xiaoyang Wang,
Qinjun Peng,
Zhimin Wang,
Shenjin Zhang,
Feng Yang,
Chuangtian Chen,
Zuyan Xu,
T. K. Lee, X. J. Zhou
[show abstract]
[hide abstract]
ABSTRACT: The parent compound of the copper-oxide high temperature superconductors is a
Mott insulator. Superconductivity is realized by doping an appropriate amount
of charge carriers. How a Mott insulator transforms into a superconductor is
crucial in understanding the unusual physical properties of high temperature
superconductors and the superconductivity mechanism. Systematic investigations
of the electronic structure in the lightly-doped region, especially across the
insulator-superconductor transition are necessary but so far have not reached a
consistent picture. In this paper, we report high resolution angle-resolved
photoemission measurement on heavily underdoped Bi2Sr2-xLax}CuO6+d system. The
electronic structure of the lightly-doped samples exhibit a number of
characteristics: existence of an energy gap along the (0,0)-(pi,pi) nodal
direction, d-wave-like anisotropic energy gap along the underlying Fermi
surface, and coexistence of coherence peak and a broad hump in the
photoemission spectra. Our results reveal a clear insulator-superconductor
transition at a critical doping level of ~0.10 where the nodal energy gap
approaches zero, the three-dimensional antiferromagnetic order disappears, and
superconductivity starts to emerge. These observations clearly signal a close
connection between the nodal gap, antiferromagnetic insulating phase, and high
temperature superconductivity. They point to the importance of combining the
electron correlation, antiferromagnetism and strong electron-phonon coupling in
understanding high temperature superconductors in the very underdoped region.
02/2013;
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Chaoyu Chen,
Zhuojin Xie,
Ya Feng,
Hemian Yi,
Aiji Liang,
Shaolong He,
Daixiang Mou,
Junfeng He,
Yingying Peng,
Xu Liu, [......],
Jun Zhang,
Li Yu,
Xiaoyang Wang,
Qinjun Peng,
Zhimin Wang,
Shenjin Zhang,
Feng Yang,
Chuangtian Chen,
Zuyan Xu, X. J. Zhou
[show abstract]
[hide abstract]
ABSTRACT: Three-dimensional topological insulators are characterized by insulating bulk
state and metallic surface state involving Dirac fermions that behave as
massless relativistic particles. These Dirac fermions are responsible for
achieving a number of novel and exotic quantum phenomena in the topological
insulators and for their potential applications in spintronics and quantum
computations. It is thus essential to understand the electron dynamics of the
Dirac fermions, i.e., how they interact with other electrons, phonons and
disorders. Here we report super-high resolution angle-resolved photoemission
studies on the Dirac fermion dynamics in the prototypical Bi2(Te,Se)3
topological insulators. We have directly revealed signatures of the
electron-phonon coupling in these topological insulators and found that the
electron-disorder interaction is the dominant factor in the scattering process.
The Dirac fermion dynamics in Bi2(Te3-xSex) topological insulators can be tuned
by varying the composition, x, or by controlling the charge carriers. Our
findings provide crucial information in understanding the electron dynamics of
the Dirac fermions in topological insulators and in engineering their surface
state for fundamental studies and potential applications.
02/2013;
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Junfeng He,
Wentao Zhang,
Jin Mo Bok,
Daixiang Mou,
Lin Zhao,
Yingying Peng,
Shaolong He,
Guodong Liu,
Xiaoli Dong,
Jun Zhang, [......],
Xiaoyang Wang,
Qinjun Peng,
Zhimin Wang,
Shenjin Zhang,
Feng Yang,
Chuangtian Chen,
Zuyan Xu,
H. -Y. Choi,
C. M. Varma, X. J. Zhou
[show abstract]
[hide abstract]
ABSTRACT: Super-high resolution laser-based angle-resolved photoemission measurements
have been carried out on Bi2Sr2CaCu2O8+d (Bi2212) superconductors to
investigate momentum dependence of electron coupling with collective
excitations (modes). Two coexisting energy scales are clearly revealed over a
large momentum space for the first time in the superconducting state of an
overdoped Bi2212 superconductor. These two energy scales exhibit distinct
momentum dependence: one keeps its energy near 78 meV over a large momentum
space while the other changes its energy from $\sim$40 meV near the antinodal
region to $\sim$70 meV near the nodal region. These observations provide a new
picture on momentum evolution of electron-boson coupling in Bi2212 that
electrons are coupled with two sharp modes simultaneously over a large momentum
space in the superconducting states. Their unusual momentum dependence poses a
challenge to our current understanding of electron-mode-coupling and its role
for high temperature superconductivity in cuprate superconductors.
10/2012;
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Shaolong He,
Junfeng He,
Wenhao Zhang,
Lin Zhao,
Defa Liu,
Xu Liu,
Daixiang Mou,
Yun-Bo Ou,
Qing-Yan Wang,
Zhi Li, [......],
Li Yu,
Guodong Liu,
Xiaoli Dong,
Jun Zhang,
Chuangtian Chen,
Zuyan Xu,
Xi Chen,
Xucun Ma,
Qikun Xue, X. J. Zhou
[show abstract]
[hide abstract]
ABSTRACT: Superconductivity in the cuprate superconductors and the Fe-based
superconductors is realized by doping the parent compound with charge carriers,
or by application of high pressure, to suppress the antiferromagnetic state.
Such a rich phase diagram is important in understanding superconductivity
mechanism and other physics in the Cu- and Fe-based high temperature
superconductors. In this paper, we report a phase diagram in the single-layer
FeSe films grown on SrTiO3 substrate by an annealing procedure to tune the
charge carrier concentration over a wide range. A dramatic change of the band
structure and Fermi surface is observed, with two distinct phases identified
that are competing during the annealing process. Superconductivity with a
record high transition temperature (Tc) at ~65 K is realized by optimizing the
annealing process. The wide tunability of the system across different phases,
and its high-Tc, make the single-layer FeSe film ideal not only to investigate
the superconductivity physics and mechanism, but also to study novel quantum
phenomena and for potential applications.
07/2012;
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Shanyu Liu,
Wentao Zhang,
Hongming Weng,
Lin Zhao,
Haiyun Liu,
Xiaowen Jia,
Guodong Liu,
Xiaoli Dong,
Jun Zhang,
Z. Q. Mao,
Chuangtian Chen,
Zuyan Xu,
Xi Dai,
Zhong Fang, X. J. Zhou
[show abstract]
[hide abstract]
ABSTRACT: High resolution angle-resolved photoemission measurements are carried out to
systematically investigate the effect of cleaving temperature on the electronic
structure and Fermi surface of Sr$_2$RuO$_4$. Different from previous reports
that high cleaving temperature can suppress surface Fermi surface, we find that
the surface Fermi surface remains obvious and strong in Sr$_2$RuO$_4$ cleaved
at high temperature, even at room temperature. This indicates that cleaving
temperature is not a key effective factor in suppressing the surface bands. On
the other hand, in the aged surface of Sr$_2$RuO$_4$ that is cleaved and held
for a long time, the bulk bands can be enhanced. We have also carried out laser
ARPES measurements on Sr$_2$RuO$_4$ by using vacuum ultra-violet laser (photon
energy at 6.994 eV) and found an obvious enhancement of bulk bands even for
samples cleaved at low temperature. These information are important in
realizing an effective approach in manipulating and detecting the surface and
bulk electronic structure of Sr$_2$RuO$_4$. In particular, the enhancement of
bulk sensitivity, together with its super-high instrumental resolution of VUV
laser ARPES, will be advantageous in investigating fine electronic structure
and superconducting properties of Sr$_2$RuO$_4$ in the future.
05/2012;
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Shanyu Liu,
Hongming Weng,
Daixiang Mou,
Wentao Zhang,
Quansheng Wu,
Junfeng He,
Guodong Liu,
Lin Zhao,
Haiyun Liu,
Xiaowen Jia,
Yingying Peng,
Shaolong He,
Xiaoli Dong,
Jun Zhang,
Z. Q. Mao,
Chuangtian Chen,
Zuyan Xu,
Xi Dai,
Zhong Fang, X. J. Zhou
[show abstract]
[hide abstract]
ABSTRACT: High resolution angle-resolved photoemission measurements have been carried
out on Sr2RuO4. We observe clearly two sets of Fermi surface sheets near the
(\pi,0)-(0,\pi) line which are most likely attributed to the surface and bulk
Fermi surface splitting of the \beta band. This is in strong contrast to the
nearly null surface and bulk Fermi surface splitting of the \alpha band
although both have identical orbital components. Extensive band structure
calculations are performed by considering various scenarios, including
structural distortion, spin-orbit coupling and surface ferromagnetism. However,
none of them can explain such a qualitative difference of the surface and bulk
Fermi surface splitting between the \alpha and \beta sheets. This unusual
behavior points to an unknown order on the surface of Sr2RuO4 that remains to
be uncovered. Its revelation will be important for studying and utilizing novel
quantum phenomena associated with the surface of Sr2RuO4 as a result of its
being a possible p-wave chiral superconductor and a topological superconductor.
05/2012;
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Chaoyu Chen,
Shaolong He,
Hongming Weng,
Wentao Zhang,
Lin Zhao,
Haiyun Liu,
Xiaowen Jia,
Daixiang Mou,
Shanyu Liu,
Junfeng He, [......],
Xiaoyang Wang,
Qinjun Peng,
Zhimin Wang,
Shenjin Zhang,
Feng Yang,
Chuangtian Chen,
Zuyan Xu,
Xi Dai,
Zhong Fang, X J Zhou
[show abstract]
[hide abstract]
ABSTRACT: The physical property investigation (like transport measurements) and ultimate application of the topological insulators usually involve surfaces that are exposed to ambient environment (1 atm and room temperature). One critical issue is how the topological surface state will behave under such ambient conditions. We report high resolution angle-resolved photoemission measurements to directly probe the surface state of the prototypical topological insulators, Bi(2)Se(3) and Bi(2)Te(3), upon exposing to various environments. We find that the topological order is robust even when the surface is exposed to air at room temperature. However, the surface state is strongly modified after such an exposure. Particularly, we have observed the formation of two-dimensional quantum well states near the exposed surface of the topological insulators. These findings provide key information in understanding the surface properties of the topological insulators under ambient environment and in engineering the topological surface state for applications.
Proceedings of the National Academy of Sciences 03/2012; 109(10):3694-8. · 9.68 Impact Factor
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Defa Liu,
Wenhao Zhang,
Daixiang Mou,
Junfeng He,
Yun-Bo Ou,
Qing-Yan Wang,
Zhi Li,
Lili Wang,
Lin Zhao,
Shaolong He, [......],
Guodong Liu,
Xiaoli Dong,
Jun Zhang,
Chuangtian Chen,
Zuyan Xu,
Jiangping Hu,
Xi Chen,
Xucun Ma,
Qikun Xue, X. J. Zhou
[show abstract]
[hide abstract]
ABSTRACT: The latest discovery of high temperature superconductivity signature in
single-layer FeSe is significant because it is possible to break the
superconducting critical temperature ceiling (maximum Tc~55 K) that has been
stagnant since the discovery of Fe-based superconductivity in 2008. It also
blows the superconductivity community by surprise because such a high Tc is
unexpected in FeSe system with the bulk FeSe exhibiting a Tc at only 8 K at
ambient pressure which can be enhanced to 38 K under high pressure. The Tc is
still unusually high even considering the newly-discovered intercalated FeSe
system A_xFe_{2-y}Se_2 (A=K, Cs, Rb and Tl) with a Tc at 32 K at ambient
pressure and possible Tc near 48 K under high pressure. Particularly
interesting is that such a high temperature superconductivity occurs in a
single-layer FeSe system that is considered as a key building block of the
Fe-based superconductors. Understanding the origin of high temperature
superconductivity in such a strictly two-dimensional FeSe system is crucial to
understanding the superconductivity mechanism in Fe-based superconductors in
particular, and providing key insights on how to achieve high temperature
superconductivity in general. Here we report distinct electronic structure
associated with the single-layer FeSe superconductor. Its Fermi surface
topology is different from other Fe-based superconductors; it consists only of
electron pockets near the zone corner without indication of any Fermi surface
around the zone center. Our observation of large and nearly isotropic
superconducting gap in this strictly two-dimensional system rules out existence
of node in the superconducting gap. These results have provided an unambiguous
case that such a unique electronic structure is favorable for realizing high
temperature superconductivity.
02/2012;
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Defa Liu,
Wenhao Zhang,
Daixiang Mou,
Junfeng He,
Yun-Bo Ou,
Qing-Yan Wang,
Zhi Li,
Lili Wang,
Lin Zhao,
Shaolong He, [......],
Guodong Liu,
Xiaoli Dong,
Jun Zhang,
Chuangtian Chen,
Zuyan Xu,
Jiangping Hu,
Xi Chen,
Xucun Ma,
Qikun Xue, X J Zhou
[show abstract]
[hide abstract]
ABSTRACT: The recent discovery of high-temperature superconductivity in iron-based compounds has attracted much attention. How to further increase the superconducting transition temperature (T(c)) and how to understand the superconductivity mechanism are two prominent issues facing the current study of iron-based superconductors. The latest report of high-T(c) superconductivity in a single-layer FeSe is therefore both surprising and significant. Here we present investigations of the electronic structure and superconducting gap of the single-layer FeSe superconductor. Its Fermi surface is distinct from other iron-based superconductors, consisting only of electron-like pockets near the zone corner without indication of any Fermi surface around the zone centre. Nearly isotropic superconducting gap is observed in this strictly two-dimensional system. The temperature dependence of the superconducting gap gives a transition temperature T(c)~ 55 K. These results have established a clear case that such a simple electronic structure is compatible with high-T(c) superconductivity in iron-based superconductors.
Nature Communications 01/2012; 3:931. · 7.40 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We present a combined study of the angle-resolved-photoemission spectroscopy
(ARPES) and quantum Monte Carlo simulations to propose a novel polaronic
metallic state in underdoped cuprates. An approximation scheme is proposed to
represent underdoped cuprates away from 1/2 filling, replacing the many-body
Hamiltonian by that of a single polaron with effective electron-phonon
interaction (EPI), that successfully explains many puzzles such as a large
momentum-dependent dichotomy between nodal and anti-nodal directions, and an
unconventional doping dependence of ARPES in the underdoped region.
09/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We analyze the ultra high resolution laser angle resolved photo-emission
spectroscopy (ARPES) intensity from the slightly underdoped
Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ in the superconductive (SC) state. The
momentum distribution curves (MDC) were fitted at each energy $\w$ employing
the SC Green's function along several cuts perpendicular to the Fermi surface
with the tilt angle $\theta$ with respect to the nodal cut. The clear
observation of particle-hole mixing was utilized such that the complex
self-energy as a function of $\omega$ is directly obtained from the fitting.
The obtained angle resolved self-energy is then used to deduce the Eliashberg
function $\alpha^2 F^{(+)}(\th,\w)$ in the diagonal channel by inverting the
d-wave Eliashberg equation using the maximum entropy method. Besides a broad
featureless spectrum up to the cutoff energy $\omega_c$, the deduced $\alpha^2
F$ exhibits two peaks around 0.05 eV and 0.015 eV. The former and the broad
feature are already present in the normal state, while the latter emerges only
below $T_c$. Both peaks become enhanced as $T$ is lowered or the angle $\th$
moves away from the nodal direction. The implication of these findings are
discussed.
08/2011;
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Chaoyu Chen,
Shaolong He,
Hongming Weng,
Wentao Zhang,
Lin Zhao,
Haiyun Liu,
Xiaowen Jia,
Daixiang Mou,
Shanyu Liu,
Junfeng He, [......],
Xiaoyang Wang,
Qinjun Peng,
Zhimin Wang,
Shenjin Zhang,
Feng Yang,
Chuangtian Chen,
Zuyan Xu,
Xi Dai,
Zhong Fang, X. J. Zhou
[show abstract]
[hide abstract]
ABSTRACT: The topological insulators represent a unique state of matter where the bulk
is insulating with an energy gap while the surface is metallic with a Dirac
cone protected by the time reversal symmetry. These characteristics provide a
venue to explore novel quantum phenomena in fundamental physics and show
potential applications in spintronics and quantum computing. One critical issue
directly related with the applications as well as the fundamental studies is
how the topological surface state will behave under ambient conditions (1
atmosphere air and room temperature). In this paper, we report high resolution
angle-resolved photoemission measurements on the surface state of the
prototypical topological insulators, Bi2Se3, Bi2Te3 and Bi2(Se0.4Te2.6), upon
exposing to ambient conditions. We find that the topological order persists
even when the surface is exposed to air at room temperature. However, the
surface state is strongly modified after such an exposure. Particularly, we
have observed the formation of two-dimensional quantum well states near the
surface of the topological insulators after the exposure which depends
sensitively on the original composition, x, in Bi2(Se3-xTex). These rich
information are crucial in utilizing the surface state and in probing its
physical properties under ambient conditions.
07/2011;
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Xiaowen Jia,
Yan Liu,
Li Yu,
Junfeng He,
Lin Zhao,
Wentao Zhang,
Haiyun Liu,
Guodong Liu,
Shaolong He,
Jun Zhang, [......],
Guiling Wang,
Yong Zhu,
Xiaoyang Wang,
Qinjun Peng,
Zhimin Wang,
Shenjin Zhang,
Feng Yang,
Zuyan Xu,
Chuangtian Chen, X. J. Zhou
[show abstract]
[hide abstract]
ABSTRACT: High quality single crystals of heavy Fermion CeCoIn5 superconductor have
been grown by flux method with a typical size of (1~2)mm x (1~2)mm x ~0.1 mm.
The single crystals are characterized by structural analysis from X-ray
diffraction and Laue diffraction, as well as compositional analysis. Magnetic
and electrical measurements on the single crystals show a sharp superconducting
transition with a transition temperature at Tc(onset) ~ 2.3 K and a transition
width of ~0.15 K. The resistivity of the CeCoIn5 crystal exhibits a hump at ~45
K which is typical of a heavy Fermion system. High resolution angle-resolved
photoemission spectroscopy (ARPES) measurements of CeCoIn5 reveal clear Fermi
surface sheets that are consistent with the band structure calculations when
assuming itinerant Ce 4f electrons at low temperature. This work provides
important information on the electronic structure of heavy Fermion CeCoIn5
superconductor. It also lays a foundation for further studies on the physical
properties and superconducting mechanism of the heavy Fermion superconductors.
04/2011;
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Wentao Zhang,
Jin Mo Bok,
Jae Hyun Yun,
Junfeng He,
Guodong Liu,
Lin Zhao,
Haiyun Liu,
Jianqiao Meng,
Xiaowen Jia,
Yingying Peng, [......],
Xiaoyang Wang,
Qinjun Peng,
Zhimin Wang,
Shenjin Zhang,
Feng Yang,
Chuangtian Chen,
Zuyan Xu,
H. -Y. Choi,
C. M. Varma, X. J. Zhou
[show abstract]
[hide abstract]
ABSTRACT: Super-high resolution laser-based angle-resolved photoemission measurements
have been performed on a high temperature superconductor Bi_2Sr_2CaCu_2O_8. The
band back-bending characteristic of the Bogoliubov-like quasiparticle
dispersion is clearly revealed at low temperature in the superconducting state.
This makes it possible for the first time to experimentally extract the complex
electron self-energy and the complex gap function in the superconducting state.
The resultant electron self-energy and gap function exhibit features at ~54 meV
and ~40 meV, in addition to the superconducting gap-induced structure at lower
binding energy and a broad featureless structure at higher binding energy.
These information will provide key insight and constraints on the origin of
electron pairing in high temperature superconductors.
03/2011;
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Daixiang Mou,
Shanyu Liu,
Xiaowen Jia,
Junfeng He,
Yingying Peng,
Lin Zhao,
Li Yu,
Guodong Liu,
Shaolong He,
Xiaoli Dong, [......],
Chiheng Dong,
Minghu Fang,
Xiaoyang Wang,
Qinjun Peng,
Zhimin Wang,
Shenjin Zhang,
Feng Yang,
Zuyan Xu,
Chuangtian Chen, X J Zhou
[show abstract]
[hide abstract]
ABSTRACT: High resolution angle-resolved photoemission measurements have been carried out to study the electronic structure and superconducting gap of the (Tl0.58Rb0.42)Fe1.72Se2 superconductor with a T(c) = 32  K. The Fermi surface topology consists of two electronlike Fermi surface sheets around the Γ point which is distinct from that in all other iron-based superconductors reported so far. The Fermi surface around the M point shows a nearly isotropic superconducting gap of ∼12  meV. The large Fermi surface near the Γ point also shows a nearly isotropic superconducting gap of ∼15  meV, while no superconducting gap opening is clearly observed for the inner tiny Fermi surface. Our observed new Fermi surface topology and its associated superconducting gap will provide key insights and constraints into the understanding of the superconductivity mechanism in iron-based superconductors.
Physical Review Letters 03/2011; 106(10):107001. · 7.37 Impact Factor
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Lin Zhao,
Daixiang Mou,
Shanyu Liu,
Xiaowen Jia,
Junfeng He,
Yingying Peng,
Li Yu,
Xu Liu,
Guodong Liu,
Shaolong He, [......],
J. G. Guo,
X-L Chen,
Xiaoyang Wang,
Qinjun Peng,
Zhimin Wang,
Shenjin Zhang,
Feng Yang,
Zuyan Xu,
Chuangtian Chen, X. J. Zhou
[show abstract]
[hide abstract]
ABSTRACT: We carried out high resolution angle-resolved photoemission measurements on
the electronic structure and superconducting gap of K_0.68Fe_1.79Se_2 (T_c=32
K) and (Tl_0.45K_0.34)Fe_1.84Se_2 (T_c=28 K) superconductors. In addition to
the electron-like Fermi surface near M(\pi,\pi), two electron-like Fermi
pockets are revealed around the zone center \Gamma(0,0) in K0.68Fe1.79Se_2.
This observation makes the Fermi surface topology of K_0.68Fe_1.79Se_2
consistent with that of (Tl,Rb)_xFe_{2-y}Se_2 and (Tl,K)_xFe_{2-y}Se_2
compounds. A nearly isotropic superconducting gap (\Delta) is observed along
the electron-like Fermi pocket near the M point in K_0.68Fe_1.79Se_2
(\Delta\sim 9 meV) and (Tl_0.45K_0.34)Fe_1.84Se_2 (\Delta\sim 8 meV). The
establishment of a universal picture on the Fermi surface topology and
superconducting gap in the A_xFe_2-ySe_2 (A=K, Tl, Cs, Rb and etc.)
superconductors will provide important information in understanding the
superconductivity mechanism of the iron-based superconductors.
02/2011;
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[show abstract]
[hide abstract]
ABSTRACT: In our Nature paper, we reported observation of Fermi pocket in Bi_2(Sr_{2-x}La_x)CuO_{6+\delta} (La-Bi2201) by angle-resolved photoemission (ARPES) measurements. King et al. tried to assign the Fermi pocket we observed as due to an additional q2 superstructure. In the process, it creates a number of serious inconsistencies and flaws in their interpretation. Any one of these inconsistencies goes strongly against King et al.'s proposal, making their proposed structural origin highly unlikely as the cause of the observed Fermi pocket. In our Nature paper, we already pointed out that this structural origin is unlikely based on the absence of additional q2-induced first-order superstructure bands of the main band MB. This conclusion remains valid and gains even stronger support by considering King et al's data.
12/2010;
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Haiyun Liu,
G F Chen,
Wentao Zhang,
Lin Zhao,
Guodong Liu,
T-L Xia,
Xiaowen Jia,
Daixiang Mu,
Shanyu Liu,
Shaolong He,
Yingying Peng,
Junfeng He,
Zhaoyu Chen,
Xiaoli Dong,
Jun Zhang,
Guiling Wang,
Yong Zhu,
Zuyan Xu,
Chuangtian Chen, X J Zhou
[show abstract]
[hide abstract]
ABSTRACT: We report the first comprehensive high-resolution angle-resolved photoemission measurements on CeFeAsO, a parent compound of FeAs-based high temperature superconductors with a magnetic-structural transition at ∼150 K. In the magnetic-ordering state, four holelike Fermi surface sheets are observed near Γ(0,0), and the Fermi surface near M(±π,±π) shows a tiny electronlike pocket at M surrounded by four strong spots. The unusual Fermi surface topology deviates strongly from the band structure calculations. The electronic signature of the magnetic-structural transition shows up in the dramatic change of the quasiparticle scattering rate. A dispersion kink at ∼25 meV is observed for the first time in the parent compound of Fe-based superconductors.
Physical Review Letters 07/2010; 105(2):027001. · 7.37 Impact Factor
