arXiv subjects

A. A. Nugroho

Publications and source records attributed to A. A. Nugroho.

At least 19 recordsLinked to original sources

arXiv2026

Regression Model for Measurement of Wound Dimensions by Webcam Scanners and Time-of-Flight Sensors

One use of image processing is for medical equipment such as wound identification. This technology is carried out non-invasively by taking images so as to avoid direct touch with the wound thereby reducing the possibility of infection. The images obtained using the RGB camera will be used for color segmentation which will measure the wound dimensions. However, the image data is in the form of a raster, the distance will affect the pixel size. Therefore, it is necessary to consider the distance of the camera measurement to the object. The time-of-flight (ToF) method with a lidar sensor is used to calculate the distance of the camera to the object. It is necessary to calculate the ratio of the distance to the number of pixels obtained so that the value is always consistent. This study analyzed the use of appropriate ratios and regression systems on a webcam and a lidar sensor for measuring wound dimensions. The results of the study show that there is a regression model with a second-order polynomial relationship for the distance and number of pixels obtained consistently with an error value of less than 5% which shows very good results

physics.comp-ph↗

arXiv2023

Single crystal synthesis, structure, and magnetism of Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O

The recent claim of superconductivity above room temperature in Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O with 0.9 < $x$ < 1 (referred to as LK-99) has sparked considerable interest. To minimize the influence of structural defects and impurity phases on the physical properties, we have synthesized phase-pure single crystals with $x \sim 1$. We find that the crystals are highly insulating and optically transparent. X-ray analysis reveals an uneven distribution of the substituted Cu throughout the sample. Temperature ($T$) dependent magnetization measurements for $ 2 \leq T \leq 800$ K reveal the diamagnetic response characteristic of a non-magnetic insulator, as well as a small ferromagnetic component, possibly originating from frustrated exchange interactions in Cu-rich clusters in the Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O structure. No anomalies indicative of phase transitions are observed. We therefore rule out the presence of superconductivity in Pb$_{9}$Cu(PO$_4$)$_6$O crystals, and provide some considerations on the origin of anomalies previously reported in experiments on polycrystalline specimen.

cond-mat.supr-con↗

arXiv2023

Magnon dispersion in ferromagnetic SrRuO$_3$

The magnetic excitations in ferromagnetic SrRuO$_3$ were studied by inelastic neutron scattering combining experiments on triple-axis and time-of-flight spectrometers with and without polarization analysis. A quadratic spin-wave dispersion with an anisotropy gap describes the low-energy low-temperature response. The magnon dispersion extends to at least 35 meV and there is no direct evidence for a continuum of Stoner excitations below this energy. However, the magnon response is weakened at higher energy. In addition to the anomalous softening of the spin-wave stiffness and of the gap, which is induced by the topology of the Bloch states, the magnon excitations are broadened in energy and this effect increases upon heating.

cond-mat.str-el↗

arXiv2017

Evidence for Magnetic Weyl Fermions in a Correlated Metal

Recent discovery of both gapped and gapless topological phases in weakly correlated electron systems has introduced various relativistic particles and a number of exotic phenomena in condensed matter physics. The Weyl fermion is a prominent example of three dimensional (3D), gapless topological excitation, which has been experimentally identified in inversion symmetry breaking semimetals. However, their realization in spontaneously time reversal symmetry (TRS) breaking magnetically ordered states of correlated materials has so far remained hypothetical. Here, we report a set of experimental evidence for elusive magnetic Weyl fermions in Mn$_3$Sn, a non-collinear antiferromagnet that exhibits a large anomalous Hall effect even at room temperature. Detailed comparison between our angle resolved photoemission spectroscopy (ARPES) measurements and density functional theory (DFT) calculations reveals significant bandwidth renormalization and damping effects due to the strong correlation among Mn 3$d$ electrons. Moreover, our transport measurements have unveiled strong evidence for the chiral anomaly of Weyl fermions, namely, the emergence of positive magnetoconductance only in the presence of parallel electric and magnetic fields. The magnetic Weyl fermions of Mn$_3$Sn have a significant technological potential, since a weak field ($\sim$ 10 mT) is adequate for controlling the distribution of Weyl points and the large fictitious field ($\sim$ a few 100 T) in the momentum space. Our discovery thus lays the foundation for a new field of science and technology involving the magnetic Weyl excitations of strongly correlated electron systems.

cond-mat.str-el↗

arXiv2017

Electronic signature of the vacancy ordering in NbO (Nb3O3)

We investigated the electronic structure of the vacancy-ordered 4d-transition metal monoxide NbO (Nb3O3) using angle-integrated soft- and hard-x-ray photoelectron spectroscopy as well as ultra-violet angle-resolved photoelectron spectroscopy. We found that density-functional-based band structure calculations can describe the spectral features accurately provided that self-interaction effects are taken into account. In the angle-resolved spectra we were able to identify the so-called vacancy band that characterizes the ordering of the vacancies. This together with the band structure results indicates the important role of the very large inter-Nb-4d hybridization for the formation of the ordered vacancies and the high thermal stability of the ordered structure of niobium monoxide.

cond-mat.mtrl-sci↗

arXiv2017

Magnetic shape-memory effect in SrRuO$_3$

Like most perovskites, SrRuO$_3$ exhibits structural phase transitions associated with rotations of the RuO$_6$ octahedra. The application of moderate magnetic fields in the ferromagnetically ordered state allows one to fully control these structural distortions, although the ferromagnetic order occurs at six times lower temperature than the structural distortion. Our neutron diffraction and macroscopic measurements unambiguously show that magnetic fields rearrange structural domains, and that for the field along a cubic [110]$_c$ direction a fully detwinned crystal is obtained. Subsequent heating above the Curie temperature causes a magnetic shape-memory effect, where the initial structural domains recover.

cond-mat.mtrl-sci↗

arXiv2016

Magnetic anisotropy of large floating-zone-grown single-crystals of SrRuO3

SrRuO3 is a highly interesting material due to its anomalous-metal properties related with ferromagnetism and its relevance as conductive perovskite layer or substrate in heterostructure devices. We have used optical floating zone technique in an infrared image furnace to grow large single crystals of SrRuO3 with volumes attaining several hundred mm3. Crystals obtained for optimized growth parameters exhibit a high ferromagnetic Curie temperature of 165 K and a low-temperature magnetization of 1.6 muB at a magnetic field of 6 T. The high quality of the crystals is further documented by large residual resistance ratios of 75 and by crystal structure and chemical analyzes. With these crystals the magnetic anisotropy could be determined.

cond-mat.str-el↗

arXiv2015

Temperature-dependent and anisotropic optical response of layered Pr$_{0.5}$Ca$_{1.5}$MnO$_{4}$ probed by spectroscopic ellipsometry

We study the temperature dependence as well as anisotropy of optical conductivity ($σ_1$) in the pseudocubic single crystal Pr$_{0.5}$Ca$_{1.5}$MnO$_{4}$ using spectrocopic ellipsometry. Three transition temperatures are observed and can be linked to charge-orbital ($T_{\rm CO/OO}$ $\sim$ 320 K), two-dimensional-antiferromagnetic (2D-AFM) ($\sim$ 200 K), and three-dimensional AFM ($T_{\rm N} \sim$ 125 K) orderings. Below $T_{\rm CO/OO}$, $σ_1$ shows a charge ordering peak ($\sim$0.8 eV) with a significant blue shift as the temperature decreases. Calculations based on a model that incorporates a static Jahn-Teller distortion and assumes the existence of a local charge imbalance between two different sublattices support this assignment and explain the blue shift. This view is further supported by the partial spectral weight analysis showing the onset of optical anisotropy at $T_{\rm CO/OO}$ in the charge-ordering region ($0.5-2.5$ eV). Interestingly, in the charge-transfer region ($2.5-4$ eV), the spectral weight shows anomalies around the $T_{\rm 2D-AFM}$ that we attribute to the role of oxygen-$p$ orbitals in stabilizing the CE-type magnetic ordering. Our result shows the importance of spin, charge, and lattice degrees of freedom in this layered manganite.

cond-mat.str-el↗

arXiv2013

Spectroscopic evidence for giant orbital moment and magnetic anisotropy induced by local distortions in alpha-CoV2O6

We present a combined experimental and theoretical study on the local magnetism of the Co ions in the spin-chain compound CoV2O6, which crystallizes in two different allotropic phases, alpha- and gamma-CoV2O6. Using x-ray magnetic circular dichroism, we have found a very large and a moderate orbital contribution to the magnetism in alpha- and gamma-CoV2O6, respectively. Full-multiplet calculations indicate that the differences in the magnetic behavior of alpha- and gamma-CoV2O6 phases originate from different local distortions of the CoO6 octahedra. In particular, the strong compression of the CoO6 octahedra in alpha-CoV2O6 lead to a strong mixture of t2g and eg orbitals which, via the local atomic Coulomb and exchange interactions, results in an exceptionally large orbital moment.

cond-mat.str-el↗

arXiv2013

Orbital superexchange and crystal field simultaneously at play in YVO3: resonant inelastic x-ray scattering at the V L edge and the O K edge

We report on the observation of orbital excitations in YVO3 by means of resonant inelastic x-ray scattering (RIXS) at energies across the vanadium L3 and oxygen K absorption edges. Due to the excellent experimental resolution we are able to resolve the intra-t2g excitations at 0.1-0.2 eV, 1.07 eV, and 1.28 eV, the lowest excitations from the t2g into the eg levels at 1.86 eV, and further excitations above 2.2 eV. For the intra-t2g excitations at 0.1-0.2 eV, the RIXS peaks show small shifts of the order of 10-40 meV as a function of temperature and of about 13-20 meV as a function of the transferred momentum q||a. We argue that the latter reflects a finite dispersion of the orbital excitations. For incident energies tuned to the oxygen K edge, RIXS is more sensitive to intersite excitations. We observe excitations across the Mott-Hubbard gap and find an additional feature at 0.4 eV which we attribute to two-orbiton scattering, i.e., an exchange of orbitals between adjacent sites. Altogether, these results indicate that both superexchange interactions and the coupling to the lattice are important for a quantitative understanding of the orbital excitations in YVO3.

cond-mat.str-el↗

arXiv2012

Probing orbital fluctuations in RVO3 (R = Y, Gd, or Ce) by ellipsometry

We study optical excitations across the Mott gap in the multi-orbital Mott-Hubbard insulators RVO3. The multi-peak structure observed in the optical conductivity can be described consistently in terms of the different 3d^3 multiplets or upper Hubbard bands. The spectral weight is very sensitive to nearest-neighbor spin-spin and orbital-orbital correlations and thus shows a pronounced dependence on both temperature and polarization. Comparison with theoretical predictions based on either rigid orbital order or strong orbital fluctuations clearly rules out the latter. Both, the line shape and the temperature dependence give clear evidence for the importance of excitonic effects.

cond-mat.str-el↗

arXiv2012

Hubbard exciton revealed by time-domain optical spectroscopy

We use broadband ultra-fast pump-probe spectroscopy in the visible range to study the lowest excitations across the Mott-Hubbard gap in the orbitally ordered insulator YVO3. Separating thermal and non-thermal contributions to the optical transients, we show that the total spectral weight of the two lowest peaks is conserved, demonstrating that both excitations correspond to the same multiplet. The pump-induced transfer of spectral weight between the two peaks reveals that the low-energy one is a Hubbard exciton, i.e. a resonance or bound state between a doublon and a holon. Finally, we speculate that the pump-driven spin-disorder can be used to quantify the kinetic energy gain of the excitons in the ferromagnetic phase.

cond-mat.str-el↗

arXiv2011

Spin-wave excitations in the ferromagnetic-metallic and in the charge, orbital and spin ordered states in Nd$_{1-x}$Sr$_{x}$MnO$_{3}$ with x$\approx$0.5

Inelastic neutron scattering experiments have been performed on single crystals of Nd$_{1-x}$Sr$_{x}$MnO$_{3}$ with x$\approx$0.5. Colossal magnetoresistance (CMR) in the manganites arises from the interplay between a ferromagnetic metallic and antiferromagnetic charge and orbital ordered insulating state. Therefore, it appears important to compare these phases concerning their underlying magnetic interaction parameters. Our investigations of the spin-wave disperion in the AFM ordered state of Nd$_{0.5}$Sr$_{0.5}$MnO$_{3}$ exhibits a strongly anisotropic stiffness. The sign of the anisotropy is characteristic for the site-centered model for charge and orbital ordering in half-doped manganites. Within this model, linear spin-wave theory yields a perfect description of the experimental dispersion. Furthermore, magnetic excitations in the ferromagnetic metallic state of Nd$_{1-x}$Sr$_{x}$MnO$_{3}$ with x=0.49 and x=0.50 exhibit nearly the same magnon dispersion which can be described with a Heisenberg model including nearest-neighbor interactions.

cond-mat.str-el↗

arXiv2009

High-field recovery of the undistorted triangular lattice in the frustrated metamagnet CuFeO2

Pulsed field magnetization experiments extend the typical metamagnetic staircase of CuFeO2 up to 58 T to reveal an additional first order phase transition at high field for both the parallel and perpendicular field configuration. Virtually complete isotropic behavior is retrieved only above this transition, indicating the high-field recovery of the undistorted triangular lattice. A consistent phenomenological rationalization for the field dependence and metamagnetism crossover of the system is provided, demonstrating the importance of both spin-phonon coupling and a small field-dependent easy-axis anisotropy in accurately describing the magnetization process of CuFeO2.

cond-mat.str-el↗

arXiv2008

Anomaly in Nonlinear Magnetoelectric Response of YbMnO3

We observe a seemingly complex magnetic field dependence of dielectric constant of hexagonal YbMnO3 near the spin ordering temperature. After rescaling, the data taken at different temperatures and magnetic fields collapse on a single curve describing the sharp anomaly in nonlinear magnetoelectric response at the magnetic transition. We show that this anomaly is a result of the competition between two magnetic phases. The scaling and the shape of the anomaly are explained using the phenomenological Landau description of the competing phases in hexagonal manganites.

cond-mat.mtrl-sci↗

arXiv2008

Colossal dielectric constant up to GHz at room temperature

The search for new materials with extremely high ("colossal") dielectric constants, required for future electronics, is one of the most active fields of modern materials science. However, the applicability of the colossal-epsilon' materials, discovered so far, suffers from the fact that their dielectric constant, epsilon', only is huge in a limited frequency range below about 1 MHz. In the present report, we show that the dielectric properties of La15/8Sr1/8NiO4 surpass those of other materials. Especially, epsilon' retains its colossal magnitude of >10000 well into the GHz range. This material is prone to charge order and this spontaneous ordering process of the electronic subsystem can be assumed to play an important role in the generation of the observed unusual dielectric properties.

cond-mat.mtrl-sci↗

arXiv2008

Collective orbital excitations in orbitally ordered YVO3 and HoVO3

We study orbital excitations in the optical absorption spectra of YVO3 and HoVO3. We focus on an orbital absorption band observed at 0.4 eV for polarization E parallel c. This feature is only observed in the intermediate, monoclinic phase. By comparison with the local crystal-field excitations in VOCl and with recent theoretical predictions for the crystal-field levels we show that this absorption band cannot be interpreted in terms of a local crystal-field excitation. We discuss a microscopic model which attributes this absorption band to the exchange of two orbitals on adjacent sites, i.e., to the direct excitation of two orbitons. This model is strongly supported by the observed dependence on polarization and temperature. Moreover, the calculated spectral weight is in good agreement with the experimental result.

cond-mat.str-el↗

arXiv2006

How strongly correlated is MnSi?

We present an experimental study of the electronic structure of MnSi. Using X-ray Absorption Spectroscopy, X-ray photoemission and X-ray fluorescence we provide experimental evidence that MnSi has a mixed valence ground state. We show that self consistent LDA supercell calculations cannot replicate the XAS spectra of MnSi, while a good match is achieved within the atomic multiplet theory assuming a mixed valence ground state. We discuss the role of the electron-electron interactions in this compound and estimate that the valence fluctuations are suppressed by a factor of 2.5, which means that the Coulomb repulsion is not negligible.

cond-mat.str-el↗