arXiv subjects

M. H. Jung

Publications and source records attributed to M. H. Jung.

17 recordsLinked to original sources

arXiv2023

Light-field-driven non-Ohmic current and Keldysh crossover in a Weyl semimetal

In recent years, coherent electrons driven by light fields have attracted significant interest in exploring novel material phases and functionalities. However, observing coherent light-field-driven electron dynamics in solids is challenging because the electrons are scattered within several ten femtoseconds in ordinary materials, and the coherence between light and electrons is disturbed. However, when we use Weyl semimetals, the electron scattering becomes relatively long (several hundred femtoseconds - several picoseconds), owing to the suppression of the back-scattering process. This study presents the light-field-driven dynamics by the THz pulse to Weyl semimetal Co3Sn2S2, where the intense THz pulse of a monocycle electric field nonlinearly generates direct current (DC) via coherent acceleration without scattering and non-adiabatic excitation (Landau-Zener Transition). In other words, the non-Ohmic current appears in the Weyl semimetal with a combination of the long relaxation time and an intense THz pulse. This nonlinear DC generation also demonstrates a Keldysh crossover from a photon picture to a light-field picture by increasing the electric field strength.

cond-mat.mtrl-sci↗

arXiv2009

Large 1/f noise of unipolar resistance switching and its percolating nature

We investigated the 1/f noise of Pt/NiO/Pt capacitors that show unipolar resistance switching. When they were switched from the low to high resistance states, the power spectral density of the voltage fluctuation was increased by approximately five orders of magnitude. At 100 K, the relative resistance fluctuation, SR/R2, in the low resistance state displayed a power law dependence on the resistance R with exponent w = 1.6. This behavior can be explained by percolation theory; however, at higher temperatures or near the switching voltage, SR/R2 becomes enhanced further. This large 1/f noise can be therefore an important problem in the development of resistance random access memory devices.

cond-mat.mtrl-sci↗

arXiv2009

Nonlinear Dynamics of Domain Wall Propagation in Epitaxial Ferroelectric Thin Films

We investigated the ferroelectric domain wall propagation in epitaxial Pb(Zr,Ti)O3 thin films over a wide temperature range (3 - 300 K). We measured the domain wall velocity under various electric fields and found that the velocity data is strongly nonlinear with electric fields, especially at low temperature. We found that, as one of surface growth problems, our domain wall velocity data from ferroelectric epitaxial film could be classified into the creep, depinning, and flow regimes due to competition between disorder and elasticity. The measured values of velocity and dynamical exponents indicate that the ferroelectric domain walls in the epitaxial films are fractal and pinned by a disorder-induced local field.

cond-mat.mtrl-sci↗

arXiv2007

Probing the Band Structure of LaTe_2 Using Angle Resolved Photoemission Spectroscopy

With the current interest in the rare-earth tellurides as high temperature charge density wave materials, a greater understanding of the physics of these systems is needed, particularly in the case of the ditellurides. We report a detailed study of the band structure of LaTe_2 in the charge density wave state using high-resolution angle resolved photoemission spectroscopy (ARPES). From this work we hope to provide insights into the successes and weaknesses of past theoretical study as well as helping to clear up prior ambiguities by providing an experimental basis for future work in the tellurides.

cond-mat.str-el↗

arXiv2007

Revealing Charge Density Wave Formation in the LaTe_2 System by Angle Resolved Photoemission Spectroscopy

We present the first direct study of charge density wave (CDW) formation in quasi-2D single layer LaTe_2 using high-resolution angle resolved photoemission spectroscopy (ARPES) and low energy electron diffraction (LEED). CDW formation is driven by Fermi surface (FS) nesting, however characterized by a surprisingly smaller gap (50meV) than seen in the double layer RTe_3 compounds, extending over the entire FS. This establishes LaTe_2 as the first reported semiconducting 2D CDW system where the CDW phase is FS nesting driven. In addition, the layer dependence of this phase in the tellurides and the possible transition from a stripe to a checkerboard phase is discussed.

cond-mat.str-el↗

arXiv2003

Formation of mid-gap states and ferromagnetism in semiconducting CaB$_6$

We present a consistent overall picture of the electronic structure and ferromagnetic interaction in CaB$_6$, based on our joint transport, optical, and tunneling measurements on high-quality {\em defect-controlled} single crystals. Pure CaB$_6$ single crystals, synthesized with 99.9999 %-pure boron, exhibited fully {\em semiconducting} characteristics, such as monotonic resistance for 2--300 K, a tunneling conductance gap, and an optical absorption threshold at 1.0 eV. {\em Boron-related defects} formed in CaB$_6$ single crystals synthesized with 99.9 %-pure boron induced {\em mid-gap states} 0.18 eV below the conduction band and extra free charge carriers, with the transport, optical, and tunneling properties substantially modified. Remarkably, no ferromagnetic signals were detected from single crystals made with 99.9999 %-pure boron, regardless of stoichiometry, whereas those made with 99.9 %-boron exhibited ferromagnetism within a finite range of carrier density. The possible surmise between the electronic state and magnetization will be discussed.

cond-mat.str-el↗

arXiv2003

Pressure effect on magnetism in CeTe$_{1.82}$

We report the normal-state transport and magnetic properties of a pressure-induced superconductor CeTe$_{1.82}$. We found that the applied pressure is required to increase the Kondo temperature scale ($T^*_{\rm K} \sim$ 170 K), associated with the two-dimensional motion of the carriers confined within the Te plane. Both the short-range ferromagnetic ordering temperature ($T_{\rm SRF} \sim$ 6 K) and the long-range antiferromagnetic transition temperature ($T_{\rm N} \sim$ 4.3 K) are slightly increased with pressure. We suggest that the application of pressure enhances a coupling between the 4$f$ and conduction electrons. We also found that the field effect on the transport under pressure is analogous to that at ambient pressure, where a large magnetoresistance is observed in the vicinity of $T_{\rm SRF}$.

cond-mat.str-el↗

arXiv2003

Magnetic field and pressure effects on charge density wave, superconducting, and magnetic states in Lu$_5$Ir$_4$Si$_{10}$ and Er$_5$Ir$_4$Si$_{10}$

We have studied the charge-density-wave (CDW) state for the superconducting Lu$_5$Ir$_4$Si$_{10}$ and the antiferromagnetic Er$_5$Ir$_4$Si$_{10}$ as variables of temperature, magnetic field, and hydrostatic pressure. For Lu$_5$Ir$_4$Si$_{10}$, the application of pressure strongly suppresses the CDW phase but weakly enhances the superconducting phase. For Er$_5$Ir$_4$Si$_{10}$, the incommensurate CDW state is pressure independent and the commensurate CDW state strongly depends on the pressure, whereas the antiferromagnetic ordering is slightly depressed by applying pressure. In addition, Er$_5$Ir$_4$Si$_{10}$ shows negative magnetoresistance at low temperatures, compared with the positive magnetoresistance of Lu$_5$Ir$_4$Si$_{10}$.

cond-mat.str-el↗

arXiv2003

First Investiation of magnetic ground states in the rare-earth intermetallic compounds RAl$_{0.9}$Si$_{1.1}$ (R = Ce, Pr, Gd)

We report the magnetic properties strongly varying with the rare-earth elements in the newly found ternary compounds $R$Al$_{0.9}$Si$_{1.1}$, which crystallize in the tetragonal $α$-ThSi$_2$-type structure. For $R$ = Ce the alloy has a weak ferromagnetism below 11 K and for $R$ = Pr it orders ferromagnetically at 17 K, while for $R$ = Gd it is antiferromagnetic with $T_{\rm N}$ = 30.5 K. In addition, we find no field effect on $T_{\rm N}$ of $R$ = Gd because of the large internal mean field, but significant changes in the magnetic properties of $R$ = Ce and Pr.

cond-mat.str-el↗

arXiv2002

Anderson lattice in CeNiSi$_2$ intermediate valence compound

We present experimental results of electrical resistivity, Hall coefficient, magnetic susceptibility, and specific heat for single crystals of Ce-based intervalent compound CeNiSi$_2$. The results show similar behaviors observed in Yb-based intervalent compounds and support recent thoery of the Anderson lattice, in which the Fermi-liquid coherence is gloval over the whole lattice. There is a low-temperature scale $T_{coh} \sim$ 50 K for the onset of Fermi-liquid coherence, in addition to a high-temperature scale $T_K^* \sim$ 150 K for the Kondo-lattice condensation. Therefore, we conclude that two energy scales are generic in intermediate valence compounds based on Ce where the orbital degeneracy is smaller and where the size of the $4f$ orbital is larger than those based on Yb.

cond-mat.str-el↗

arXiv2002

Superconductivity in Magnetically Ordered CeTe$_{1.82}$

We report the discovery of pressure-induced superconductivity in a semimetallic magnetic material CeTe$_{1.82}$. The superconducting transition temperature $T_{SC}$ = 2.7 K (well below the magnetic ordering temperatures) under pressure ($>$ 2 kbar) is remarkably high, considering the relatively low carrier density due to a charge-density-wave transition associated with lattice modulation. The coexisting magnetic structure of a mixed ferromagnetism and antiferromagnetism can provide a clue for this high $T_{SC}$. We discuss a theoretical model for its possible pairing symmetry and pairing mechanism.

cond-mat.str-el↗

arXiv2002

Electrical and magnetic properties of the new Kondo-lattice compound Ce3Pd4Ge4

We have measured the electric resistivity, magnetoresistance, magnetic susceptibility and magnetization of the new Kondo-lattice compound Ce3Pd4Ge4. The electrical resistivity exhibits a rapid drop at temperatures below 6 K, while the magnetic susceptibility does not show any corresponding anomaly at that temperature. This phenomenon is similar to that of Ce3Pd20Ge6 which shows quadrupolar interation. We suggest that there is the possibility of quadrupolar interaction in the orthorhombic 4f-electron system Ce3Pd4Ge4. In addition, it is realized that the spin-dependent scattering effect is responsible for the magnetotransport.

cond-mat.str-el↗

arXiv2002

High-Field Properties of Single-Crystalline Cavo3

The magnetic properties of perovskite CaVO3 single crystals have been studied by means of magnetoresistance r(T, H) and magnetization M(H) measurements in fields to 18T. At 2 K, the magnetoresistance is positive and a maximum value of Dr(18T)/r(0) = 16.5% is found for H//a. The magnetization exhibits a smooth increase at 2 K, reaching values of M(18T) = 0.03, 0.05, 0.17 mB/f.u. for H//a, H//b, and H//c, respectively. This anisotropy found in M(H) is consistent with that observed for Dr(H//a) > Dr(H//b) > Dr(H//c). These results can be interpreted in terms of the field-dependent scattering mechanism of CaVO3.

cond-mat.str-el↗

arXiv2002

Magnetocrystalline Anisotropy in a Single Crystal of CeNiGe2

We report measurements on single crystals of orthorhombic CeNiGe2, which is found to exhibit highly anisotropic magnetic and transport properties. The magnetization ratio M(H//b)/M(H^b) at 2 K is observed to be about 18 at 4 T and the electrical resistivity ratio r//b/r^b is about 70 at room temperature. It is confirmed that CeNiGe2 undergoes two-step antiferromagnetic transition at 4 and 3 K, as reported for polycrystalline samples. The application of magnetic field along the b axis (the easy magnetization axis) stabilizes a ferromagnetic correlation between the Ce ions and enhances the hopping of carriers. This results in large negative magnetoresistance along the b axis.

cond-mat.str-el↗

arXiv2001

Magnetic and transport properties of the new antiferromagnetic Kondo-lattice CeNiBi2

We report results of the first studies on the magnetic and transport properties of a new material CeNiBi_2. The magnetic susceptibility exhibits a sharp peak at T_N = 6K, indicating an antiferromagnetic phase transition. This antiferromagnetic order below T_N is confirmed by magnetization measurement, which displays a metamagnetic-like transition at H_m = 5 T. Both low-temperature susceptibility and high-field magnetization are suggestive of strong crystalline-electric-field effect in CeNiBi_2. The electrical resistivity shows the presence of Kondo and crystal-field effects with a sharp drop below TN due to the antiferromagnetic ordering. This sharp drop below T_N in the electrical resistivity is suppressed slightly to higher temperatures by an applied magnetic field to 18 T. With increasing magnetic field, the slope of magnetoresistance changes from positive to negative, being indicative of the transition to a ferromagnetic state.

cond-mat.str-el↗

arXiv2001

Two energy scales and slow crossover in YbAl3

Experimental results for the susceptibility, specific heat, 4f occupation number, Hall effect and magnetoresistance for single crystals of YbAl$_{3}$ show that, in addition to the Kondo energy scale $k_{B}T_{K}$ $% \sim $ 670K, there is a low temperature scale $T_{coh}<50$K for the onset of coherence. Furthermore the crossover from the low temperature Fermi liquid regime to the high temperature local moment regime is slower than predicted by the Anderson impurity model. These effects may reflect the behavior of the Anderson Lattice in the limit of low conduction electron density.

cond-mat.str-el↗

arXiv2001

Anisotropic Superconductivity in Epitaxial MgB2 Films

High-quality epitaxial MgB2 thin films prepared by pulsed laser deposition with Tc = 39 K offer the opportunity to study the anisotropy and robustness of the superconducting state in magnetic fields. We measure the in-plane electrical resistivity of the films in magnetic fields to 60T and estimate the superconducting upper critical field Hc(0) = 24 +- 3 T for field oriented along the c-axis, and Hab(0) = 30 +- 2 T for field in the plane of the film. We find the zero-temperature coherence lengths xi_c(0) = 30 A and xi_ab(0) = 37 A to be shorter than the calculated electronic mean free path l = 100 +- 50 A, which places our films in the clean limit. The observation of such large upper critical fields from clean limit samples, coupled with the relatively small anisotropy, provides strong evidence of the viability of MgB2 as a technologically important superconductor.

cond-mat.supr-con↗