60 research outputs found
Distinct Fermi-Momentum Dependent Energy Gaps in Deeply Underdoped Bi2212
We use angle-resolved photoemission spectroscopy applied to deeply underdoped
cuprate superconductors Bi2Sr2(Ca,Y)Cu2O8 (Bi2212) to reveal the presence of
two distinct energy gaps exhibiting different doping dependence. One gap,
associated with the antinodal region where no coherent peak is observed,
increases with underdoping - a behavior known for more than a decade and
considered as the general gap behavior in the underdoped regime. The other gap,
associated with the near nodal regime where a coherent peak in the spectrum can
be observed, does not increase with less doping - a behavior not observed in
the single particle spectra before. We propose a two-gap scenario in momentum
space that is consistent with other experiments and may contain important
information on the mechanism of high-Tc superconductivity.Comment: 12 pages, 3 figures, submitted to Scienc
Perpendicular magnetic anisotropy at Fe/Au(111) interface studied by M\"{o}ssbauer, x-ray absorption, and photoemission spectroscopies
The origin of the interfacial perpendicular magnetic anisotropy (PMA) induced
in the ultrathin Fe layer on the Au(111) surface was examined using
synchrotron-radiation-based M\"{o}ssbauer spectroscopy (MS), X-ray magnetic
circular dichroism (XMCD), and angle-resolved photoemission spectroscopy
(ARPES). To probe the detailed interfacial electronic structure of orbital
hybridization between the Fe 3 and Au 6 bands, we detected the
interfacial proximity effect, which modulates the valence-band electronic
structure of Fe, resulting in PMA. MS and XMCD measurements were used to detect
the interfacial magnetic structure and anisotropy in orbital magnetic moments,
respectively. - ARPES also confirms the initial growth of Fe on large
spin-orbit coupled surface Shockley states under Au(111) modulated electronic
states in the vicinity of the Fermi level. This suggests that PMA in the
Fe/Au(111) interface originates from the cooperation effects among the spin,
orbital magnetic moments in Fe, and large spin-orbit coupling in Au. These
findings pave the way to develop interfacial PMA using - hybridization
with a large spin-orbit interaction
Two-dimensional heavy fermion in a monoatomic-layer Kondo lattice YbCu2
Nakamura T., Sugihara H., Chen Y., et al. Two-dimensional heavy fermion in a monoatomic-layer Kondo lattice YbCu2. Nature Communications 14, 7850 (2023); https://doi.org/10.1038/s41467-023-43662-9.The Kondo effect between localized f-electrons and conductive carriers leads to exotic physical phenomena. Among them, heavy-fermion (HF) systems, in which massive effective carriers appear due to the Kondo effect, have fascinated many researchers. Dimensionality is also an important characteristic of the HF system, especially because it is strongly related to quantum criticality. However, the realization of the perfect two-dimensional (2D) HF materials is still a challenging topic. Here, we report the surface electronic structure of the monoatomic-layer Kondo lattice YbCu2 on a Cu(111) surface observed by synchrotron-based angle-resolved photoemission spectroscopy. The 2D conducting band and the Yb 4f state, located very close to the Fermi level, are observed. These bands are hybridized at low-temperature, forming the 2D HF state, with an evaluated coherence temperature of about 30 K. The effective mass of the 2D state is enhanced by a factor of 100 by the development of the HF state. Furthermore, clear evidence of the hybridization gap formation in the temperature dependence of the Kondo-resonance peak has been observed below the coherence temperature. Our study provides a new candidate as an ideal 2D HF material for understanding the Kondo effect at low dimensions
Semiconducting Electronic Structure of the Ferromagnetic Spinel Revealed by Soft-X-Ray Angle-Resolved Photoemission Spectroscopy
We study the electronic structure of the ferromagnetic spinel
by soft-x-ray angle-resolved
photoemission spectroscopy (SX-ARPES) and first-principles calculations. While
a theoretical study has predicted that this material is a magnetic Weyl
semimetal, SX-ARPES measurements give direct evidence for a semiconducting
state in the ferromagnetic phase. Band calculations based on the density
functional theory with hybrid functionals reproduce the experimentally
determined band gap value, and the calculated band dispersion matches well with
ARPES experiments. We conclude that the theoretical prediction of a Weyl
semimetal state in underestimates the
band gap, and this material is a ferromagnetic semiconductor.Comment: 6+13 pages, 4+13 figure
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