12 research outputs found
Advances in Complex Oxide Quantum Materials Through New Approaches to Molecular Beam Epitaxy
Molecular beam epitaxy (MBE), a workhorse of the semiconductor industry, has
progressed rapidly in the last few decades in the development of novel
materials. Recent developments in condensed matter and materials physics have
seen the rise of many novel quantum materials that require ultra-clean and
high-quality samples for fundamental studies and applications. Novel
oxide-based quantum materials synthesized using MBE have advanced the
development of the field and materials. In this review, we discuss the recent
progress in new MBE techniques that have enabled synthesis of complex oxides
that exhibit "quantum" phenomena, including superconductivity and topological
electronic states. We show how these techniques have produced breakthroughs in
the synthesis of 4d and 5d oxide films and heterostructures that are of
particular interest as quantum materials. These new techniques in MBE offer a
bright future for the synthesis of ultra-high quality oxide quantum materials.Comment: 29 pages, 7 figure
Thickness-dependent, tunable anomalous Hall effect in hydrogen-reduced PdCoO thin films
It was recently reported that hydrogen-reduced PdCoO films exhibit strong
perpendicular magnetic anisotropy (PMA) with sign tunable anomalous Hall effect
(AHE). Here, we provide extensive thickness-dependent study of this system, and
show that the electronic and magnetic properties are strongly dependent on the
thickness and annealing conditions. Below a critical thickness of 25 nm, AHE
shows clear PMA with hysteresis, and its sign changes from positive to
negative, and back to positive as the annealing temperature increases from 100
C to 400 C. Beyond the critical thickness, both PMA and AHE
hysteresis disappear and the AHE sign remains positive regardless of the
annealing parameters. Our results show that PMA may have a large role on AHE
sign-tunability and that below the critical thickness, competition between
different AHE mechanisms drives this sign change
Diffusion-assisted molecular beam epitaxy of CuCrO thin films
Using molecular beam epitaxy (MBE) to grow multi-elemental oxides (MEO) is
generally challenging, partly due to difficulty in stoichiometry control.
Occasionally, if one of the elements is volatile at the growth temperature,
stoichiometry control can be greatly simplified using adsorption-controlled
growth mode. Otherwise, stoichiometry control remains one of the main hurdles
to achieving high quality MEO film growths. Here, we report another kind of
self-limited growth mode, dubbed diffusion-assisted epitaxy, in which excess
species diffuses into the substrate and leads to the desired stoichiometry, in
a manner similar to the conventional adsorption-controlled epitaxy.
Specifically, we demonstrate that using diffusion-assisted epitaxy,
high-quality epitaxial CuCrO films can be grown over a wide growth window
without precise flux control using MBE.Comment: Accepted to the special edition of JVSTA on Thin Film Deposition for
Materials Discover
Interaction of in-plane Drude carrier with c-axis phonon in
We performed polarized reflection and transmission measurements on the
layered conducting oxide thin films. For the ab-plane, an optical
peak near 750 cm drives the scattering rate
and effective mass of the Drude carrier to
increase and decrease respectively for . For the
c-axis, a longitudinal optical phonon (LO) is present at as evidenced
by a peak in the loss function Im[]. Further
polarized measurements in different light propagation (q) and electric field
(E) configurations indicate that the Peak at results from an
electron-phonon coupling of the ab-plane carrier with the c-LO phonon, which
leads to the frequency-dependent and . This
unusual interaction was previously reported in high-temperature superconductors
(HTSC) between a non-Drude, mid-infrared band and a c-LO. On the contrary, it
is the Drude carrier that couples in . The coupling between the
ab-plane Drude carrier and c-LO suggests that the c-LO phonon may play a
significant role in the characteristic ab-plane electronic properties of including the ultra-high dc-conductivity, phonon-drag, and
hydrodynamic electron transport.Comment: 4 figure
Interaction of in-plane Drude carrier with c -axis phonon in PdCoO2
Funding: E.C. was supported by the NRF-2021R1A2C1009073 of Korea funded by the Ministry of Education. D.S. was partially supported by MOLIT as an Innovative Talent Education Program for Smart City. The work at Rutgers University is supported by the National Science Foundation’s DMR2004125 and the Army Research Office’s W911NF2010108. S.B.C. was supported by the National Research Foundation of Korea (NRF) grants funded by the Korean government (MSIT)(NRF-2023R1A2C1006144, NRF-2020R1A2C1007554, and NRF-2018R1A6A1A06024977). Research in Dresden benefits from the environment provided by the DFG Cluster of Excellence ct.qmat (EXC 2147, project ID 390858490). The work at HYU was supported by the NRF grant funded by the Korean government (MSIT) (2022R1F1A1072865), the BrainLink program funded by MSIT (2022H1D3A3A01077468), and the Quantum Simulator Development Project for Materials Innovation through the NRF funded by MSIT (2023M3K5A1094813).We performed polarized reflection and transmission measurements on the layered conducting oxide PdCoO2 thin films. For the ab-plane, an optical peak near Ω ≈ 750 cm−1 drives the scattering rate 1/τ(ω) and effective mass m*(ω) of the Drude carrier to increase and decrease respectively for ω ≧ Ω. For the c-axis, a longitudinal optical phonon (LO) is present at Ω as evidenced by a peak in the loss function Im[−1/εc(ω)]. Further polarized measurements in different light propagation (q) and electric field (E) configurations indicate that the Peak at Ω results from an electron-phonon coupling of the ab-plane carrier with the c-LO phonon, which leads to the frequency-dependent 1/τ(ω) and m*(ω). This unusual interaction was previously reported in high-temperature superconductors (HTSC) between a non-Drude, mid-infrared (IR) band and a c-LO. On the contrary, it is the Drude carrier that couples in PdCoO2. The coupling between the ab-plane Drude carrier and c-LO suggests that the c-LO phonon may play a significant role in the characteristic ab-plane electronic properties of PdCoO2, including the ultra-high dc-conductivity, phonon-drag, and hydrodynamic electron transport.Publisher PDFPeer reviewe
Disorder-enhanced effective masses and deviations from Matthiessen's rule in PdCoO thin films
The observation of hydrodynamic transport in the metallic delafossite
PdCoO has increased interest in this family of highly conductive oxides,
but experimental studies so far have mostly been confined to bulk crystals. In
this work, the development of high-quality thin films of PdCoO has enabled
a thorough study of the conductivity as a function of film thickness using both
dc transport and time-domain THz spectroscopy. With increasing film thickness
from 12 nm to 102 nm, the residual resistivity decreases and we observe a large
deviation from Matthiessen's rule (DMR) in the temperature dependence of the
resistivity. We find that the complex THz conductivity is well fit by a single
Drude term. We fit the data to extract the spectral weight and scattering rate
simultaneously. The temperature dependence of the Drude scattering rate is
found to be nearly independent of the residual resistivity and cannot be the
primary mechanism for the observed DMR. Rather, we observe large changes in the
spectral weight as a function of disorder, changing by a factor of 1.5 from the
most disordered to least disordered films. We believe this corresponds to a
mass enhancement of times the value of the bulk effective mass which
increases with residual disorder. This suggests that the mechanism behind the
DMR observed in dc resistivity is primarily driven by changes in the electron
mass. We discuss the possible origins of this behavior including the
possibility of disorder-enhanced electron-phonon scattering, which can be
systematically tuned by film thickness.Comment: 10 pages, 8 figure
Influence of the Cation on the Surface Electronic Band Structure and Magnetic Properties of Mn:ZnS and Mn:CdS Quantum Dot Thin Films
Infrared plasmons in ultrahigh conductive PdCoO2 metallic oxide
PdCoO2 layered delafossite is the most conductive compound among metallic oxides, with a room-temperature resistivity of nearly 2 mu Omega cm, corresponding to a mean free path of about 600 angstrom. These values represent a record considering that the charge density of PdCoO2 is three times lower than copper. Although its notable electronic transport properties, PdCoO2 collective charge density modes (i.e. surface plasmons) have never been investigated, at least to our knowledge. In this paper, we study surface plasmons in high-quality PdCoO2 thin films, patterned in the form of micro-ribbon arrays. By changing their width W and period 2W, we select suitable values of the plasmon wavevector q, experimentally sampling the surface plasmon dispersion in the mid-infrared electromagnetic region. Near the ribbon edge, we observe a strong field enhancement due to the plasmon confinement, indicating PdCoO2 as a promising infrared plasmonic material