35 research outputs found
Origin of the anomalous mass renormalization in metallic quantum well states of correlated oxide SrVO
angle-resolved photoemission spectroscopy (ARPES) has been
performed on SrVO ultrathin films, which show metallic quantum well (QW)
states, to unveil the origin of the anomalous mass enhancement in the QW
subbands. The line-shape analysis of the ARPES spectra reveals that the
strength of the electron correlation increases as the subband bottom energy
approaches the Fermi level. These results indicate that the anomalous
subband-dependent mass enhancement mainly arises from the quasi-one-dimensional
character of confined V states as a result of their orbital-selective
quantization.Comment: 6 pages, 3 figure
Emergence of quantum critical behavior in metallic quantum-well states of strongly correlated oxides
Controlling quantum critical phenomena in strongly correlated electron
systems, which emerge in the neighborhood of a quantum phase transition, is a
major challenge in modern condensed matter physics. Quantum critical phenomena
are generated from the delicate balance between long-range order and its
quantum fluctuation. So far, the nature of quantum phase transitions has been
investigated by changing a limited number of external parameters such as
pressure and magnetic field. We propose a new approach for investigating
quantum criticality by changing the strength of quantum fluctuation that is
controlled by the dimensional crossover in metallic quantum well (QW)
structures of strongly correlated oxides. With reducing layer thickness to the
critical thickness of metal-insulator transition, crossover from a Fermi liquid
to a non-Fermi liquid has clearly been observed in the metallic QW of SrVO
by \textit{in situ} angle-resolved photoemission spectroscopy. Non-Fermi liquid
behavior with the critical exponent is found to emerge in the
two-dimensional limit of the metallic QW states, indicating that a quantum
critical point exists in the neighborhood of the thickness-dependent Mott
transition. These results suggest that artificial QW structures provide a
unique platform for investigating novel quantum phenomena in strongly
correlated oxides in a controllable fashion.Comment: 6 pages, 3 figure
Temperature evolution of magnetic phases near the thickness-dependent metal-insulator transition in LaSrMnO thin films observed by XMCD
Perovskite-type manganites, which are well-known for their intriguing
physical properties such as colossal magnetoresistance (CMR) and half
metalicity, have been considered as candidate materials for spintronics.
However, their ferromagnetic (FM) properties are often suppressed in thin films
when the thickness is reduced down to several monolayers (MLs). In order to
investigate how the magnetic phases evolve near the paramagnetic (PM)-to-FM
phase transition boundary, we have performed temperature-dependent x-ray
magnetic circular dichroism (XMCD) experiments on a LaSrMnO
(LSMO, ) thin film, whose thickness (8 ML) is close to the boundary
between the FM-metallic and the PM-insulating phases. By utilizing the
element-selectiveness of XMCD, we have quantitatively estimated the fractions
of the PM and superparamagnetic (SPM) phases as well as the FM one as a
function of temperature. The results can be reasonably described based on a
microscopic phase-separation model.Comment: 6 pages, 3 figure
Relationship between charge redistribution and ferromagnetism at the heterointerface between perovskite oxides LaNiO3 and LaMnO
To investigate the relationship between the charge redistribution and
ferromagnetism at the heterointerface between perovskite transition-metal
oxides LaNiO (LNO) and LaMnO (LMO), we performed x-ray absorption
spectroscopy and x-ray magnetic circular dichroism (XMCD) measurements. In the
LNO/LMO heterostructures with asymmetric charge redistribution, the electrons
donated from Mn to Ni ions are confined within one monolayer (ML) of LNO at the
interface, whereas holes are distributed over 3-4 ML on the LMO side. A
detailed analysis of the Ni- and Mn- XMCD spectra reveals
that Ni magnetization is induced only by the Ni ions in the 1 ML LNO
adjacent to the interface, while the magnetization of Mn ions is increased in
the 3-4 ML LMO of the interfacial region. The characteristic length scale of
the emergent (increased) interfacial ferromagnetism of the LNO (LMO) layers is
in good agreement with that of the charge distribution across the interface,
indicating a close relationship between the charge redistribution due to the
interfacial charge transfer and the ferromagnetism of the LNO/LMO interface.
Furthermore, the XMCD spectra clearly demonstrate that the vectors of induced
magnetization of both ions are aligned ferromagnetically, suggesting that the
delicate balance between the exchange interactions occurring inside each layer
and across the interface may induce the canted ferromagnetism of Ni
ions, resulting in weak magnetization in the 1 ML LNO adjacent to the
interface.Comment: 22 pages, 4 figure