A high resolution, hard X-ray photoemission investigation of BaFe$_2$As$_2$: moderate influence of the surface and evidence for a low degree of Fe 3d - As 4p hybridization of the near-E$_F$ electronic states
S. de Jong, Y. Huang, R. Huisman, F. Massee, S. Thirupathaiah, M. Gorgoi, R. Follath, J. B. Goedkoop, M. S. Golden
Photoemission data taken with hard X-ray radiation on cleaved single crystals of the barium parent compound of the MFe$_2$As$_2$ pnictide high temperature superconductor family are presented. Making use of the increased bulk-sensitivity upon hard X-ray excitation, and comparing the results to data taken at conventional VUV photoemission excitation energies, it is shown that the BaFe$_2$As$_2$ cleavage surface provides an electrostatic environment that is slightly different to the bulk, most likely in the form of a modified Madelung potential. However, as the data argue against a different surface doping level, and the surface-related features in the spectra are by no means as dominating as seen in systems such as YBa$_2$Cu$_3$O$_x$, we can conclude that the itinerant, near-E$_F$ electronic states are almost unaffected by the existence of the cleavage surface. Furthermore, exploiting the strong changes in photoionisation cross section between the Fe and As states across the wide photon energy range employed, it is shown that the degree of energetic overlap between the iron 3d and arsenic 4p valence bands is particularly small at the Fermi level, which can only mean a very low degree of hybridization between the Fe 3d and As 4p states near and at E$_F$. Consequently, the itinerancy of the charge carriers in this group of materials involves mainly the Fe 3d - Fe 3d overlap integrals with at best a minor role for the Fe 3d - As 4p hopping parameters, and that the states which support superconductivity upon doping are essentially of Fe 3d character.
Using random-phase approximation spin-fluctuation theory, we study the influence of the hybridization between iron $d$-orbitals and pnictide $p$-orbitals on the superconducting pairing state in iron-based superconductors. The calculations are performed for a 16-orbital Hubbard-Hund tight-binding model of BaFe$_2$As$_2$ that includes the As-$p$ orbital degrees of freedom in addition to the Fe-$d$ orbitals and compared to calculations for a 10-orbital Fe-$d$ only model. In both models we find a leading $s^\pm$ pairing state and a subleading $d_ {x^2-y^2}$-wave state in the parent compound. Upon …
Transient single-particle spectral function of BaFe$_{2}$As$_{2}$, a parent compound of iron-based superconductors, has been studied by time- and angle-resolved photoemission spectroscopy with an extreme-ultraviolet laser generated by higher harmonics from Ar gas, which enables us to investigate the dynamics in the entire Brillouin zone. We observed electronic modifications from the spin-density-wave (SDW) ordered state within $\sim$ 1 ps after the arrival of a 1.5 eV pump pulse. We observed optically excited electrons at the zone center above $E_{F}$ at 0.12 ps, and their rapid decay. After t…
By means of one-step model calculations the strong in-plane anisotropy seen in angle-resolved photoemission of the well-known iron pnictide prototype compounds BaFe$_2$As$_2$ and Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ in their low-temperature antiferromagnetic phases is investigated. The fully-relativistic calculations are based on the Korringa-Kohn-Rostoker-Green function approach combined with the coherent potential approximation alloy theory to account for the disorder induced by Co substitution on Fe sites in a reliable way. The results of the calculations can be compared directly to experimental …
We performed polarization- and photon-energy-dependent angle-resolved photoemission spectroscopy of a slightly overdoped iron pnictide superconductor, BaFe$_{1.8}$Co$_{0.2}$As$_{2}$, to clarify the three-dimensional electronic structure including its orbital characters at the Brillouin zone center. Two hole Fermi surfaces (FSs) with $d_{xz/yz}$ and $d_{xy/x^2-y^2}$ orbitals were observed but $d_{z^2}$ hole FS, which has nodes according to a theory of the spin-fluctuation superconductivity mechanism, did not appear. These results suggest that no node will appear at hole FSs at the zone center.
From a combination of high resolution angle-resolved photoemission spectroscopy and density functional calculations, we show that BaFe2As2 possesses essentially two-dimensional electronic states, with a strong change of orbital character of two of the Gamma-centered Fermi surfaces as a function of kz. Upon Co doping, the electronic states in the vicinity of the Fermi level take on increasingly three-dimensional character. Both the orbital variation with kz and the more three-dimensional nature of the doped compounds have important consequences for the nesting conditions and thus possibly also …
In Fe-based superconductors, electron doping is often realized by the substitution of transition-metal atoms for Fe. In order to investigate how the electronic structure of the parent compound is influenced by Zn substitution, which supplies nominally four extra electrons per substituted atom but is expected to induce the strongest impurity potential among the transition-metal atoms, we have performed an angle-resolved photoemission spectroscopy measurements on Ba(Fe_{1-x}Zn_x)_2As_2 (Zn-122). In Zn-122, the temperature dependence of the resistivity shows a kink around T~135 K, indicating anti…
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 anti…
We report high resolution angle-resolved photoemission spectroscopy (ARPES) studies of the electronic structure of BaFe$_2$As$_2$, which is one of the parent compounds of the Fe-pnictide superconductors. ARPES measurements have been performed at 20 K and 300 K, corresponding to the orthorhombic antiferromagnetic phase and the tetragonal paramagnetic phase, respectively. Photon energies between 30 and 175 eV and polarizations parallel and perpendicular to the scattering plane have been used. Measurements of the Fermi surface yield two hole pockets at the $Γ$-point and an electron pocket at each…
We performed an angle-resolved photoemission spectroscopy study of BaFe2As2, which is the parent compound of the so-called 122 phase of the iron-pnictide high-temperature superconductors. We reveal the existence of a Dirac cone in the electronic structure of this material below the spin-density-wave temperature, which is responsible for small spots of high photoemission intensity at the Fermi level. Our analysis suggests that the cone is slightly anisotropic and its apex is located very near the Fermi level, leading to tiny Fermi surface pockets. Moreover, the bands forming the cone show an an…
We use high resolution angle-resolved photoemission spectroscopy to study the band structure and Fermi surface topology of the BaFe$_2$As$_2$ iron pnictides. We observe two electron bands and two hole bands near the X-point, $(π,π)$ of the Brillouin zone, in the paramagnetic state for different doping levels, including electron-doped Ba(Co$_{0.06}$Fe$_{0.94}$)$_2$As$_2$, undoped BaFe$_2$As$_2$, and hole-doped Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$. Among these four bands, only the electron bands cross the Fermi level, forming two electron pockets around X, while the hole bands approach but never reac…
Alkaline-earth iron arsenide (122) is one of the most studied families of iron-based superconductors, especially for angle-resolved photoemission spectroscopy. While extensive photoemission results have been obtained, the surface complexity of 122 caused by its charge-non-neutral surface is rarely considered. Here, we show that the surface of 122 can be neutralized by potassium deposition. In potassium-coated BaFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$, the surface-induced spectral broadening is strongly suppressed, and hence the coherent spectra that reflect the intrinsic bulk electronic state recover.…
Time- and angle-resolved extreme ultraviolet photoemission spectroscopy is used to study the electronic structure dynamics in BaFe$_2$As$_2$ around the high-symmetry points $Γ$ and $M$. A global oscillation of the Fermi level at the frequency of the $A_{1g}$(As) phonon mode is observed. It is argued that this behavior reflects a modulation of the effective chemical potential in the photoexcited surface region that arises from the high sensitivity of the band structure near the Fermi level to the $A_{1g}$ phonon mode combined with a low electron diffusivity perpendicular to the layers. The resu…
Nematicity plays an important role in the physics of iron-based superconductors (IBS). Its microscopic origin and in particular its importance for the mechanism of high-temperature superconductivity itself are highly debated. A crucial knowledge in this regard is the degree to which the nematic order influences the electronic structure of these materials. Earlier angle-resolved photoemission spectroscopy (ARPES) studies found that the effect is dramatic in three families of IBS including 11, 111 and 122 compounds: energy splitting reaches 70 meV and Fermi surface becomes noticeably distorted. …
We systemically investigate the nature of Ce 4f electrons in structurally layered heavy-fermion compounds CcmMnIn3m+2n (with M =Co, Rh, Ir, and Pt, m=l, 2, n=0 - 2), at low temperature using on-resonance angle-resolved photoemission spectroscopy. Three heavy quasiparticle bands f^0, f^1_7/2 and f^1_5/2 are observed in all compounds, but their intensities and energy locations vary greatly with materials. The strong f^0 states imply that the localized electron behavior dominates the Ce 4f states. The Ce 4f electrons are partially hybridized with the conduction electrons, making them have the dua…
We have investigated the low-energy electronic structure of the heavy fermion superconductor CeCoIn5 by angle-resolved photoemission. We focus on the dispersion and the peak width of the prominent quasi-two-dimensional Fermi surface sheet at the corner of the Brillouin zone as a function of temperature along certain k-directions with a photon energy of hn = 100 eV. We find slight changes of the Fermi vector and an anomalous broadening of the peak width when the Fermi energy is approached. Additionally we performed resonant ARPES experiments with hn = 121 eV. A flat f-derived band is observed w…
We determine the work functions of the iron arsenic compounds $A$Fe$_2$As$_2$ ($A=\mathrm{Ca, Ba, Cs}$) using photoemission spectroscopy to be 2.7 eV for CaFe$_2$As$_2$, 1.8 eV for BaFe$_2$As$_2$, and 1.3 eV for CsFe$_2$As$_2$. The work functions of these 122 iron-based superconductors track those of the elementary metal $A$ but are substantially smaller. The most likely explanation of this observation is that the cleaving surface exposes only half an $A$-layer. The low work function and good photoemission cross section of BaFe$_2$As$_2$ and CsFe$_2$As$_2$ enable photoemission even from a comm…
We use high resolution angle-resolved photoemission to study the electronic structure of the iron based high-temperature superconductors Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$ as a function of Ru concentration. We find that substitution of Ru for Fe is isoelectronic, i. e., it does not change the value of the chemical potential. More interestingly, there are no measured, significant changes in the shape of the Fermi surface or in the Fermi velocity over a wide range of substitution levels ($0<x<0.55$). Given that the suppression of the antiferromagnetic and structural phase has been associated with th…
We revisit the electronic structure of BaFe$_2$As$_2$, the archetypal parent compound of the Fe-based superconductors, using angle-resolved photoemission spectroscopy (ARPES). Our high-resolution measurements of samples detwinned by the application of a mechanical strain reveal a highly anisotropic 3D Fermi surface in the low temperature magnetic phase. By comparison of the observed dispersions with ab-initio calculations, we argue that overall it is magnetism, rather than orbital ordering, which is the dominant effect, reconstructing the electronic structure across the Fe 3d bandwidth. Finall…
The isovalent-substituted iron-pnictide superconductor SrFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ ($x$=0.35) has a slightly higher optimum critical temperature than the similar system BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$, and its parent compound SrFe$_{2}$As$_{2}$ has a much higher Néel temperature than BaFe$_{2}$As$_{2}$. We have studied the band structure and the Fermi surfaces of optimally-doped SrFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ by angle-resolved photoemission spectroscopy (ARPES). Three holelike Fermi surfaces (FSs) around (0,0) and two electronlike FSs around ($π$,$π$) have been observed as in …
We show that the Fermi surface (FS) in the antiferromagnetic phase of BaFe$_2$As$_2$ is composed of one hole and two electron pockets, all of which are three dimensional and closed, in sharp contrast to the FS observed by angle-resolved photoemission spectroscopy. Considerations on the carrier compensation and Sommerfeld coefficient rule out existence of unobserved FS pockets of significant sizes. A standard band structure calculation reasonably accounts for the observed FS, despite the overestimated ordered moment. The mass enhancement, the ratio of the effective mass to the band mass, is 2--…
We have performed an angle-resolved photoemission spectroscopy study of BaCr$_2$As$_2$, which has the same crystal structure as BaFe$_2$As$_2$, a parent compound of Fe-based superconductors. We determine the Fermi surface of this material and its band dispersion over 5 eV of binding energy. Very moderate band renormalization (1.35) is observed for only two bands. We attribute this small renormalization to enhanced direct exchange as compared to Fe in BaFe$_2$As$_2$, and to a larger contribution of the $e_g$ orbitals in the composition of the bands forming the Fermi surface, leading to an effec…
Single crystals of Ba$_{1-x}$Na$_x$Fe$_2$As$_2$ with $x$ = 0, 0.25, 0.35, 0.4 were grown using a self-flux high temperature solution growth technique. The superconducting and normal state properties were studied by temperature dependent magnetic susceptibility, electrical resistivity and specific heat revealing that the magnetic and structural transition is rapidly suppressed upon Na-substitution at the Ba-site in BaFe$_2$As$_2$, giving rise to superconductivity. A superconducting transition as high as 34 K is reached for a Na-content of $x$=0.4. The positive Hall coefficient confirms that the…
Low energy electron diffraction (LEED) experiments, LEED simulations and finite slab density functional calculations are combined to study the cleavage surface of Co doped BaFe_{2-x}Co_{x}As_{2} (x = 0.1, 0.17). We demonstrate that the energy dependence of the LEED data can only be understood from a terminating 1/2 Ba layer accompanied by distortions of the underlying As-Fe_2-As block. As a result, surface related Fe 3d states are present in the electronic structure, which we identify in angle resolved photoemission experiments. The close proximity of the surface-related states to the bulk ban…
We use angle-resolved photoemission spectroscopy and full-potential linearized augmented-plane-wave (FP-LAPW) calculations to study the electronic structure of BaCo2As2. The Fermi surface (FS) maps and the corresponding band dispersion data (at 90 K and 200 K) reveal a small electron pocket at the center and a large electron pocket at the corner of the Brillouin zone. Therefore the nesting between electron and hole FS pockets is absent in this compound, in contrast to the parent compounds of FeAs-based high-T_c superconductors. The electronic structure at about 500 meV binding energy is very s…
High resolution angle-resolved photoemission measurements have been carried out on BaFe2As2, a parent compound of the FeAs-based superconductors. In the magnetic ordering state, there is no gap opening observed on the Fermi surface. Instead, dramatic band structure reorganization occurs across the magnetic transition. The appearance of the singular Fermi spots near (pi,pi) is the most prominent signature of magnetic ordering. These observations provide direct evidence that the magnetic ordering state of BaFe2As2 is distinct from the conventional spin-density-wave state. They reflect the electr…
The effects of structural supermodulation with the period $λ\approx26$ Å\ along the $b$-axis of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ have been observed in photoemission studies from the early days as the presence of diffraction replicas of the intrinsic electronic structure. Although predicted to affect the electronic structure of the Cu-O plane, the influence of supermodulation potential on Cu-O electrons has never been observed in photoemission. In the present study, we clearly see, for the first time, the effects on the Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ electronic structure - we observe a hybridizatio…
We have investigated the electronic structure of $\mathrm{Sr}_{1-y}\mathrm{Ca}_{y}\mathrm{Fe_{2}}(\mathrm{As}_{1-x}\mathrm{P}_{x}\mathrm{)_{2}}$ ($x$ = 0.25, $y$ = 0.08) by means of angle-resolved photoemission spectroscopy. From the comparison with the results of $\mathrm{BaFe_{2}}(\mathrm{As}_{1-x}\mathrm{P}_{x}\mathrm{)_{2}}$, the effects of smaller structural anisotropy ($c/a$) on the Fermi surfaces (FSs) and the gap structures are discussed. The observed FSs have three dimensional shapes. One of the hole FSs is strongly warped between the $Γ$ and $Z$ points, and the innermost FS observed …
We have performed an angle-resolved photoemission spectroscopy (ARPES) study of the undoped and electron-doped iron pnictides BaFe2\_{-x}CoxAs2 (Ba122) (x=0, 0.14) and studied the Fermi surfaces (FSs) and band dispersions near the Fermi level. The FS sheets we observed are consistent with the shrinkage of the hole-like pockets around the Brillouin Zone (BZ) center and the expansion of the electron pockets around the BZ corner in the electron-doped compound as compared to the undoped parent compound. Band dispersions and FSs around the BZ center strongly depend on the photon energy, indicating …
We use microprobe Angle-Resolved Photoemission Spectroscopy to study the Fermi surface and band dispersion of the CuO2 planes in the high temperature superconductor, YBa2Cu4O8. We find a strong in-plane asymmetry of the electronic structure between directions along a and b axes. The saddle point of the antibonding band lies at a significantly higher energy in the a direction (pi,0) than the b direction (0,pi), whereas the bonding band displays the opposite behavior. We demonstrate that the abnormal band shape is due to a strong asymmetry of the bilayer band splitting, likely caused by a non-tr…
We use angle resolved photoemission spectroscopy (ARPES) to study the band structure of BaFe2As2 and CaFe2As2, two of the parent compounds of the iron arsenic high temperature superconductors. We find clear evidence for band back folding and hybridization demonstrating that conduction electrons are strongly affected by the emergence of magnetic order. Our high quality data revealed that although the Fermi surface is strongly three-dimensional, it does indeed have long parallel segments along the kz direction that can lead to the emergence of magnetic order. More interestingly, we find very unu…
We performed an angle-resolved photoemission spectroscopy study of BaMn$_2$As$_2$ and BaMn$_2$Sb$_2$, which are isostructural to the parent compound BaFe$_2$As$_2$ of the 122 family of ferropnictide superconductors. We show the existence of a strongly $k_z$-dependent band gap with a minimum at the Brillouin zone center, in agreement with their semiconducting properties. Despite the half-filling of the electronic 3$d$ shell, we show that the band structure in these materials is almost not renormalized from the Kohn-Sham bands of density functional theory. Our photon energy dependent study provi…
Chemical substitution is commonly used to explore new ground states in materials, yet the role of disorder is often overlooked. In Mn-substituted BaFe$_{2}$As$_{2}$ (MnBFA), superconductivity (SC) is absent, despite being observed for nominal hole-doped phases. Instead, a glassy magnetic phase emerges, associated with the $S=5/2$ Mn local spins. In this work, we present a comprehensive investigation of the electronic structure of MnBFA using angle-resolved photoemission spectroscopy (ARPES). We find that Mn causes a small and orbital-specific reduction of the electron pockets, only partially d…
Among numerous hypotheses, recently proposed to explain superconductivity in iron-based superconductors [1-9], many consider Fermi surface (FS) nesting [2, 4, 8, 10] and dimensionality [4, 9] as important contributors. Precise determination of the electronic spectrum and its modification by superconductivity, crucial for further theoretical advance, were hindered by a rich structure of the FS [11-17]. Here, using the angle-resolved photoemission spectroscopy (ARPES) with resolution of all three components of electron momentum and electronic states symmetry, we disentangle the electronic struct…
Hole doping and electronic correlations in Cr-substituted BaFe$_{2}$As$_{2}$
Universidade de São Paulo（圣保罗大学）；European Synchrotron Radiation Facility（欧洲同步辐射装置）；UNICAMP（坎皮纳斯州立大学）；Université de Fribourg（弗里堡大学）；Universidade Federal de Minas Gerais（米纳斯吉拉斯联邦大学）；Ames Laboratory, U.S. DOE（美国能源部艾姆斯实验室）
We have studied the electronic structure of Ba(Fe$_{1-x}$Mn$_{x}$)$_{2}$As$_{2}$ ($x$=0.08), which fails to become a superconductor in spite of the formal hole doping like Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$, by photoemission spectroscopy and X-ray absorption spectroscopy (XAS). With decreasing temperature, a transition from the paramagnetic phase to the antiferromagnetic phase was clearly observed by angle-resolved photoemission spectroscopy. XAS results indicated that the substituted Mn atoms form a strongly hybridized ground state. Resonance-photoemission spectra at the Mn $L_{3}$ edge reveal…
We use high-resolution angle-resolved photoemission spectroscopy to investigate the electronic structure of the antiferromagnetic heavy fermion compound CePt2In7, which is a member of the CeIn3-derived heavy fermion material family. Weak hybridization among 4f electron states and conduction bands was identified in CePt2In7 at low temperature much weaker than that in the other heavy fermion compounds like CeIrIn5 and CeRhIn5. The Ce 4f spectrum shows fine structures near the Fermi energy, reflecting the crystal electric field splitting of the 4f^1_5/2 and 4f^1_7/2 states. Also, we find that the…
Being homologue to the new, Fe-based type of high-temperature superconductors, CeFePO exhibits magnetism, Kondo and heavy-fermion phenomena. We experimentally studied the electronic structure of CeFePO by means of angle-resolved photoemission spectroscopy. In particular, contributions of the Ce 4f-derived states and their hybridization to the Fe 3d bands were explored using both symmetry selection rules for excitation and their photoionization cross-section variations as a function of photon energy. It was experimentally found - and later on confirmed by LDA as well as DMFT calculations - that…
The localized-to-itinerant transition of f electrons lies at the heart of heavy-fermion physics, but has only been directly observed in single-layer Ce-based materials. Here, we report a comprehensive study on the electronic structure and nature of the Ce 4f electrons in the heavy-fermion superconductor Ce2PdIn8, a typical n=2 CenMmIn3n+2m compound, using high-resolution and 4d-4f resonance photoemission spectroscopies. The electronic structure of this material has been studied over a wide temperature range, and hybridization between f and conduction electrons can be clearly observed to form a…
We report the high-resolution angle-resolved photoemission spectroscopy studies of electronic structure of EuFe2As2. The paramagnetic state data are found to be consistent with density-functional calculations. In the antiferromagnetic ordering state of Fe, our results show that the band splitting, folding, and hybridization evolve with temperature, which cannot be explained by a simple folding picture. Detailed measurements reveal that a tiny electron Fermi pocket and a tiny hole pocket are formed near (pi,pi) in the (0,0)-(pi,pi) direction, which qualitatively agree with the results of quantu…
We use angle-resolved photoemission spectroscopy (ARPES) to investigate the electronic properties of the newly discovered iron-arsenic superconductor, Ba(1-x)K(x)Fe2As2 and non-supercondcuting BaFe2As2. Our study indicates that the Fermi surface of the undoped, parent compound BaFe$_2$As$_2$ consists of hole pocket(s) at Gamma (0,0) and larger electron pocket(s) at X (1,0), in general agreement with full-potential linearized plane wave (FLAPW) calculations. Upon doping with potassium, the hole pocket expands and the electron pocket becomes smaller with its bottom approaching the chemical poten…
High-resolution laser-based angle-resolved photoemission measurements have been carried out on Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (Bi2212) and Bi$_2$Sr$_{2-x}$La$_x$CuO$_{6+δ}$ (Bi2201) superconductors. Unexpected hybridization between the main band and the superstructure band in Bi2212 is clearly revealed. In the momentum space where one main Fermi surface intersects with one superstructure Fermi surface, four bands are observed instead of two. The hybridization exists in both superconducting state and normal state, and in Bi2212 samples with different doping levels. Such a hybridization is not ob…
The discovery of infinite-layer nickelate superconductors has spurred enormous interest. While the Ni$^{1+}$ cations possess nominally the same 3$d^9$ configuration as Cu$^{2+}$ in cuprates, the electronic structure variances remain elusive. Here, we present a soft x-ray photoemission spectroscopy study on parent and doped infinite-layer Pr-nickelate thin films with a doped perovskite reference. By identifying the Ni character with resonant photoemission and comparison to density functional theory + U (on-site Coulomb repulsion energy) calculations, we estimate U ~5 eV, smaller than the charge…
We investigate the transient electronic structure of BaFe2As2, a parent compound of iron-based superconductors, by time- and angle-resolved photoemission spectroscopy. In order to probe the entire Brillouin zone, we utilize extreme ultraviolet photons and observe photoemission intensity oscillation with the frequency of the A1g phonon which is antiphase between the zone-centered hole Fermi surfaces (FSs) and zone-cornered electron FSs. We attribute the antiphase behavior to the warping in one of the zone-centered hole FSs accompanying the displacement of the pnictogen height, and find that thi…
Orbital Hybridization-Induced Ising-Type Superconductivity in a Confined Gallium Layer
The Pennsylvania State University（宾夕法尼亚州立大学）；Shanghai Jiao Tong University（上海交通大学）；University of Oxford（牛津大学）；Zhejiang University（浙江大学）；Diamond Light Source（钻石光源研究所）；University of North Texas（北德克萨斯大学）
Hybridization of Bogoliubov-quasiparticles between adjacent CuO$_2$ layers in the triple-layer cuprate Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+δ}$ studied by ARPES
Surface of quantum materials often exhibits significantly different behavior than the bulk due to changed topologies and symmetry protections. The outstanding problem is to find out if the exoticity of a material is linked to the changed topology at the surface or it is a bulk property. Hard x-ray photoemission spectroscopy (HAXPES) is a significantly bulk sensitive technique (escape depth of valence electrons is about 40 Å for 6 keV photon energy) and the probing depth can be tuned by changing the electron emission angle. Therefore, HAXPES is often used to reveal the surface-bulk differences …
