arXiv subjects

H. F. Yang

Publications and source records attributed to H. F. Yang.

23 records · Page 2Linked to original sources

arXiv2016

Origin of the kink in the band dispersion of the ferromagnetic perovskite SrRuO3: Electron-phonon coupling

Perovskite SrRuO3, a prototypical conductive ferromagnetic oxide, exhibits a kink in its band dispersion signalling the unusual electron dynamics therein. However, the origin of this kink remains elusive. By taking advantage of the combo of reactive molecular beam epitaxy and in situ angle-resolved photoemission spectroscopy, we systematically studied the evolution of the low-energy electronic structure of SrRuO3 films with thickness thinning down to nearly two-dimensional limit in a well-controlled way. The kink structure persists even in the 4-unit-cell-thick film. Moreover, through quantitative self-energy analysis, we observed the negligible thickness dependence of the binding energy of the kink, which is in sharp contrast to the downward trend of the Curie temperature with reducing the film thickness. Together with previously reported transport and Raman studies, this finding suggests that the kink of perovskite SrRuO3 should originate from the electron-phonon coupling rather than magnetic collective modes, and the in-plane phonons may play a dominant role. Considering such a kink structure of SrRuO3 is similar to these of many other correlated oxides, we suggest the possible ubiquity of the coupling of electrons to oxygen-related phonons in correlated oxides.

cond-mat.str-el↗

arXiv2015

Tuning the electronic structure of Sr2IrO4 thin films by bulk electronic doping using molecular beam epitaxy

By means of oxide molecular beam epitaxy with shutter-growth mode, we have fabricated a series of electron-doped (Sr1-xLax)2IrO4(001)(x = 0, 0.05, 0.1 and 0.15) single crystalline thin films and then investigated the doping dependence of electronic structure utilizing in-situ angle-resolved photoemission spectroscopy. We find that with increasing doping proportion, the Fermi levels of samples progressively shift upward. Prominently, an extra electron pocket crossing the Fermi level around the M point has been evidently observed in 15 % nominal doping sample. Moreover, bulk-sensitive transport measurements confirm that doping effectively suppresses the insulating state with respect to the as-grown Sr2IrO4, though doped samples still remain insulating at low temperatures due to the localization effect possibly stemming from disorders including oxygen deficiencies. Our work provides another feasible doping method to tune electronic structure of Sr2IrO4.

cond-mat.str-el↗

arXiv2015

Signature of strong spin-orbital coupling in the large non-saturating magnetoresistance material WTe2

We report the detailed electronic structure of WTe$_2$ by high resolution angle-resolved photoemission spectroscopy. Unlike the simple one electron plus one hole pocket type of Fermi surface topology reported before, we resolved a rather complicated Fermi surface of WTe$_2$. Specifically, there are totally nine Fermi pockets, including one hole pocket at the Brillouin zone center $Γ$, and two hole pockets and two electron pockets on each side of $Γ$ along the $Γ$-$X$ direction. Remarkably, we have observed circular dichroism in our photoemission spectra, which suggests that the orbital angular momentum exhibits a rich texture at various sections of the Fermi surface. As reported previously for topological insulators and Rashiba systems, such a circular dichroism is a signature for spin-orbital coupling (SOC). This is further confirmed by our density functional theory calculations, where the spin texture is qualitatively reproduced as the conjugate consequence of SOC. Since the backscattering processes are directly involved with the resistivity, our data suggest that the SOC and the related spin and orbital angular momentum textures may be considered in the understanding of the anomalous magnetoresistance of WTe$_2$.

cond-mat.str-el↗

arXiv2014

Significant contribution of As 4p orbitals to the low-lying electronic structure of 112-type iron-based superconductor Ca0.9La0.1FeAs2

We report a systematic polarization-dependent angle-resolved photoemission spectroscopy study of the three-dimensional electronic structure of the recently discovered 112-type iron-based superconductor Ca1-xLaxFeAs2 (x = 0.1). Besides the commonly reported three hole-like and two electron-like bands in iron-based superconductors, we resolve one additional hole-like band around the zone center and one more fast-dispersing band near the X point in the vicinity of Fermi level. By tuning the polarization and the energy of incident photons,we are able to identify the specific orbital characters and the kz dependence of all bands. Combining with band calculations, we find As 4pz and 4px (4py) orbitals contribute significantly to the additional three-dimensional hole-like band and the narrow band, respectively. Also, there are considerable hybridization between the As 4p zand Fe 3d orbitals in the additional hole-like band, which suggests the strong coupling between the unique arsenic zigzag bond layers and the FeAs layers therein. Our findings provide a comprehensive picture of the orbital characters of the low-lying band structure of 112-type iron-based superconductors, which can be a starting point for the further understanding of their unconventional superconductivity.

cond-mat.supr-con↗

arXiv2014

Electronic Structure of Single Crystalline NdO$_{0.5}$F$_{0.5}$BiS$_{2}$ Studied by Angle-resolved Photoemission Spectroscopy

NdO$_{0.5}$F$_{0.5}$BiS$_{2}$ is a new layered superconductor. We have studied the low-lying electronic structure of a single crystalline NdO$_{0.5}$F$_{0.5}$BiS$_{2}$ superconductor, whose superconducting transition temperature is 4.87K, with angle-resolved photoemission spectroscopy. The Fermi surface consists of two small electron pockets around the X point and shows little warping along the $k_z$ direction. Our results demonstrate the multi-band and two-dimensional nature of the electronic structure. The good agreement between the photoemission data and the band calculations gives the renormalization factor of 1, indicating the rather weak electron correlations in this material. Moreover, we found that the actual electron doping level and Fermi surface size are much smaller than what are expected from the nominal composition, which could be largely explained by the bismuth dificiency. The small Fermi pocket size and the weak electron correlations found here put strong constraints on theory, and suggest that the BiS$_2$-based superconductors could be conventional BCS superconductors mediated by the electron-phonon coupling.

cond-mat.supr-con↗