Electron Pockets Research Articles

Anisotropic magnetoresistance and electronic features of the candidate topological compound praseodymium monobismuthide.

PrBi, a sister member of the rare-earth monopnictide family, is an excellent candidate for studying extreme magnetoresistance and nontrivial topological electronic states. In this study, we perform angular magnetoresistance measurements as well as bulk and surface band structure calculations on this compound. PrBi's magnetoresistance is revealed to be significantly angle-dependent and shows a fourfold symmetry as always observed in the nonmagnetic isostructural counterparts, including LaSb, LaBi, and LuBi. Its angular magnetoresistance can be reproduced well using the semiclassical two-band model. The deduced parameters suggest that PrBi hosts an elongated electron pocket with a mobility anisotropy of ∼3.13 and is slightly uncompensated in its carrier concentration. Our bulk and surface band structure calculations confirm the anisotropic electronic features. Moreover, we reveal that a nodal-line-shaped surface state appears at the X̄ point, and is associated with the quadratic dispersion along the -X̄ direction, and the linear type-I Dirac dispersion along the X̄-M̄ direction. Owing to the type-I Dirac dispersion feature, PrBi could serve as a promising material platform for studying many unexpected physical properties, such as the highly anisotropic transport and valley polarization of electrons.

Enhancement of the Magnetoresistance in the Mobility‐Engineered Compensated Metal Pt5P2

AbstractThe magnetoresistance (MR) in nonmagnetic materials continues to be a fertile research area in materials science. The search for giant, positive MR has been limited to a rather small window of materials such as high‐mobility semimetals in single‐crystalline form. Here, the observation of a very large positive MR in metallic Pt5P2 in polycrystalline form is reported. The observations reveal that improvement of the crystallinity results in a significant enhancement of the positive MR, exceeding 10 000% at 9 T, comparable to high‐mobility semimetals. Based on first‐principles calculations combined with magnetotransport and thermoelectric measurements, the Fermi surface of Pt5P2 is found to consist of a collection of multiple electron and hole pockets compensating one another, along with a characteristic pocket continuously connected to the adjacent Brillouin zone, together with possible topologically protected band crossings. This work extends the landscape of high MR candidate materials to polycrystalline metals, which demonstrates the importance of crystallinity and purity of the samples for the optimization of the MR.

Common Topological Features in Band Structure of RNiSb and RSb Compounds for R = Tb, Dy, Ho.

The electronic and band structures of ternary RNiSb and binary RSb compounds for R = Tb, Dy, Ho, have been investigated using an ab initio method accounting for strong electron correlations in the 4f shell of the rare-earth metals. These ternary compounds are found to be semiconductors with the indirect gap of 0.21, 0.21, and 0.26 eV for Tb, Dy, and Ho(NiSb), respectively. In contrast, in all binary RSb compounds, bands near the Fermi energy at the Г and X points are shifted relatively to RNiSb and form hole and electron pockets, so the energy gap is closed in RSb. The band structure typical for semimetals is formed in all RSb compounds for R = Tb, Dy, Ho. For the first time, we identify similar features near the Fermi level in the considered binary semimetals, namely, the presence of the hole and electron pockets in the vicinity of the Г and X points, the nonsymmetric electron pocket along Γ-X-W direction and hole pockets along the L-Γ-X direction, which were previously found experimentally in the other compound of this series GdSb. The magnetic moment of all considered compounds is fully determined by magnetic moments of the rare earth elements, the calculated effective magnetic moments of these ions have values close to the experimental values for all ternary compounds.

Shift of the superconducting dome induced by a conduction band of small occupancy: Enhanced d -wave pairing in the overdoped regime

Motivated by the presence of an extremely small electron pocket in the electronic band structure of infinite-layer nickelate superconductors, we systematically explore the superconducting (SC) properties of a two-dimensional Hubbard model influenced by an additional conduction band with small occupancy (dry Fermi sea). Our dynamic cluster quantum Monte Carlo calculations demonstrated the unusual impact of this additional dry metallic layer, which shifts the SC dome of the correlated Hubbard layer towards the overdoped regime, namely the $d$-wave SC can be enhanced (suppressed) in the overdoped (underdoped) regime. Simultaneously, the pseudogap crossover line shifts to the same higher doping regime as well. Our analysis revealed the interplay of the effective pairing interaction, pair-field susceptibility, and antiferromagnetic spin fluctuation in the underlying nonmonotonic physics. We postulate on the physical picture of the SC dome shift in terms of the Kondo-type electron-hole binding in the case of a dry additional conduction band. Our investigation provided valuable insights on tuning the SC properties via external dry bands.

Plasmonic gain in current biased tilted Dirac nodes

Surface plasmons, which allow tight confinement of light, suffer from high intrinsic electronic losses. It has been shown that stimulated emission from excited electrons can transfer energy to plasmons and compensate for the high intrinsic losses. To-date, these realizations have relied on introducing an external gain media coupled to the surface plasmon. Here, we propose that plasmons in two-dimensional materials with closely located electron and hole Fermi pockets can be amplified, when an electrical current bias is applied along the displaced electron-hole pockets, without the need for an external gain media. As a prototypical example, we consider WTe2 from the family of 1T{}^{{prime} }-MX2 materials, whose electronic structure can be described within a type-II tilted massive Dirac model. We find that the nonlocal plasmonic response experiences prominent gain for experimentally accessible currents on the order of mAμm−1. Furthermore, the group velocity of the plasmon found from the isofrequency curves imply that the amplified plasmons are highly collimated along a direction perpendicular to the Dirac node tilt when the electrical current is applied along it.

Two-dimensional multiband superconductivity of the optimally and uniformly Li-intercalated FeSe nanoflakes

We investigated the electrical transport properties of optimally Li+-intercalated FeSe nanoflakes. Using solid electrolyte gating, we obtained high and uniform electron doping up to ∼0.55 electrons per Fe sites in the FeSe nanoflakes, which exhibit a sharp superconducting transition at Tc ∼45.0 K. The temperature and magnetic-field dependent current-voltage characteristics clearly revealed the two-dimensional nature of the superconductivity in the intercalated FeSe nanoflakes. From the self-field critical current measurements, we found two distinct isotropic superconducting gaps with different gap ratios. These findings suggest that the highly electron-doped FeSe hosts two interband pairing channels between the hybridized electron pockets, in contrast to the case of pristine FeSe with electron and hole pockets.

Correlation-driven electronic nematicity in the Dirac semimetal BaNiS2

In BaNiS2, a Dirac nodal line band structure exists within a two-dimensional Ni square lattice system, in which significant electronic correlation effects are anticipated. Using scanning tunneling microscopy (STM), we discover signs of correlated-electron behavior, namely electronic nematicity appearing as a pair of C2-symmetry striped patterns in the local density-of-states at ∼60 meV above the Fermi energy. In observations of quasiparticle interference, as well as identifying scattering between Dirac cones, we find that the striped patterns in real space stem from a lifting of degeneracy among electron pockets at the Brillouin zone boundary. We infer a momentum-dependent energy shift with d-form factor, which we model numerically within a density wave (DW) equation framework that considers spin-fluctuation-driven nematicity. This suggests an unusual mechanism driving the nematic instability, stemming from only a small perturbation to the Fermi surface, in a system with very low density of states at the Fermi energy. The Dirac points lie at nodes of the d-form factor and are almost unaffected by it. These results highlight BaNiS2 as a unique material in which Dirac electrons and symmetry-breaking electronic correlations coexist.

Anisotropic Gap Structure and Sign Reversal Symmetry in Monolayer Fe(Se,Te).

The iron-based superconductors are an ideal platform to reveal the enigma of the unconventional superconductivity and potential topological superconductivity. Among them, the monolayer Fe(Se,Te)/SrTiO3(001), which is proposed to be topological nontrivial, shows interface-enhanced high-temperature superconductivity in the two-dimensional limit. However, the experimental studies on the superconducting pairing mechanism of monolayer Fe(Se,Te) films are still limited. Here, by measuring the quasiparticle interference in monolayer Fe(Se,Te)/SrTiO3(001), we report the observation of the anisotropic structure of the large superconducting gap and the sign change of the superconducting gap on different electron pockets. The results are well consistent with the "bonding-antibonding" s±-wave pairing symmetry driven by spin fluctuations in conjunction with spin-orbit coupling. Our work is of basic significance not only for a unified superconducting formalism in the iron-based superconductors, but also for understanding of topological superconductivity in high-temperature superconductors.

InBi: A Ferroelastic Monolayer with Strain Tunable Spin-Orbit Dirac Points and Carrier Self-Doping Effect.

Semimetallic two-dimensional (2D) Dirac materials beyond graphene, especially 2D materials with robust Dirac points against the spin-orbit coupling (SOC), are still highly sought. Herein, we theoretically demonstrate the InBi monolayer as a long-sought 2D Dirac material whose exotic Dirac Fermionic states cannot be gapped out by SOC. The InBi monolayer with the litharge crystal structure possesses not only 4-fold band degeneracy, linear energy dispersion, and ultrahigh Fermi velocity in the order of 105 m/s, but also spontaneous ferroelasticity that can lead to the orthorhombic lattice deformation and semimetallic electronic structure. Specifically, the symmetry protected spin-orbit Dirac points in 2D InBi are located at the Brillouin Zone (BZ) boundary and near the Fermi level in energy. More importantly, with coexisting spin-orbit Dirac points and spontaneous ferroelasticity, the InBi monolayer exhibits an additional advantage for engineering Dirac Fermionic states by ferroelastic (FE) strain. Energy levels of Dirac points are strongly coupled to FE strain, and the semimetallic electronic structure of the InBi monolayer is also susceptible to the FE strain induced carrier self-doping effect. Depending on the strain orientation within the InBi monolayer, electron and hole Fermi pockets will develop along the two planar directions, leading to the characteristic transport coefficients (as evidenced by our transport simulations based on Boltzmann formalism) for future experimental detection. FE strain tunable Dirac Fermionic states together with the carrier self-doping effect will benefit future development of ultrathin electronic devices with both high carrier mobility and controllable charge conductivities.

Development of Electronic Pocket Books For Immune System Material To Increase Students' Learning Motivation

The teaching and learning process certainly requires interesting media and does not tend to be boring. For this reason, it is necessary to use media that can attract students' interest by using electronic pocket book media. This study aims to determine the quality of electronic pocket books and determine the effectiveness of electronic pocket book media. This development research uses the ADDIE (Analysis, Design, Development, Implementation, and Evaluation) model. The analysis stage is an analysis of the needs of students. The design stage is the making of an electronic pocket book media design. The Development stage is an assessment of the feasibility of experts, namely material experts, media experts and teachers at SMA PGRI 1 Bogor. The Implementation stage is an assessment of the feasibility of the media and the Evaluation stage is a measurement of development achievement. The results showed the feasibility level of electronic pocketbook media, according to material experts, electronic pocketbooks were included in the appropriate category, while according to high school biology teachers and students, electronic pocketbooks were included in the very feasible category. The results of the analysis of student learning motivation before and after using the media were obtained, this showed a significant difference between before and after using the media, so it can be concluded that the electronic pocket book learning media can increase students' learning motivation.

Phase-transition-induced thermal hysteresis in Type-II weyl semimetals [formula omitted] and [formula omitted

The resistivity versus temperature measurement is commonly used for identifying temperature-induced phase change and the resulting hysteresis loop. While the resistance is influenced by both the density of states and the carrier lifetimes, the Seebeck coefficient is influenced predominantly by the density of states, and hence is a better probe of the phase of the material. Here, 1T′−Td temperature-induced phase transition in MoTe2 is studied using temperature-dependent X-ray diffraction, resistivity, and Seebeck coefficient measurements. A more distinct hysteresis is observed when measuring the Seebeck coefficient which is consistent with direct measurements of the crystallographic angle using the temperature-dependent X-ray diffraction. The Seebeck and electrical resistivity measurements indicate a competing contribution of the electrons and holes. The contribution of electron pockets becomes more dominant when molybdenum atoms are replaced by tungsten. In MoTe2, a topologically induced enhancement of the Nernst coefficient is observed at low temperatures, and a relatively large phase-transition induced Thomson coefficient of 111 μV⋅K−1 is measured at 254 K which is larger than the Seebeck coefficient measured in the entire temperature range.

Fine details of sixfold Dirac fermions in pyrite-structured PdSb2

We report detailed angle-resolved photoemission measurements on the electronic structure of an unconventional multifold Dirac fermionic semimetal ${\mathrm{PdSb}}_{2}$ with a pyrite structure. By exploiting the photon energy and polarization dependence of the matrix element in photoemission intensity and by comparing photoemission data with ab initio band calculations, we experimentally identify the exact electronic structure, including the orbital characters of the electron pockets at the $R$ point in the Brillouin zone of ${\mathrm{PdSb}}_{2}$. Each electron pocket and hole-pocket-like structure consists of three doubly degenerate parabolic bands, respectively, which cross one another at the $R$ point, forming a sixfold Dirac fermion. The overall electronic structure is consistent with the band calculations, but the gap size between two sextuple points is very sensitive to the Wyckoff position of Sb atoms, which is a result of the competition between the band energies and crystal symmetries.

Efektifitas Penggunaan E-Bekal Sebagai Uang Saku Elektronik di Pesantren

E-bekal is electronic pocket money used in the Nurul Jadid Islamic boarding school environment. The emergence of e-bekal is the answer to several problems. Many students from out of town and even abroad have difficulty receiving pocket money from their parents, uncontrolled student pocket money, and many cases of losing money. The emergence of e-bekal as an answer to the problem certainly has a practical value because in solving the problem, there must be some obstacles that will be faced so that researchers feel the need to conduct research related to the effectiveness of using e-supply as electronic pocket money in Islamic boarding schools. This study wants to examine how effective the presence of e-bekal among students as direct users of e-bekal is. The method used in this research is descriptive and quantitative with the type of case study. The results of this study conclude that the use of e-Bekal is still less effective because there are still many students who have not felt the benefits that can be supposed in using e-bekal, even though they tend to be less inclined to use e-bekal as a medium of payment because there are still many obstacles in its use, so that need a lot of system improvements and also upgrade the e-stock software it self.

Fermiology and Origin of T_{c} Enhancement in a Kagome Superconductor Cs(V_{1-x}Nb_{x})_{3}Sb_{5}.

Kagome metals AV_{3}Sb_{5} (A=K, Rb, and Cs) exhibit a characteristic superconducting ground state coexisting with a charge density wave (CDW), whereas the mechanisms of the superconductivity and CDW have yet to be clarified. Here we report a systematic angle-resolved photoemission spectroscopy (ARPES) study of Cs(V_{1-x}Nb_{x})_{3}Sb_{5} as a function of Nb content x, where isovalent Nb substitution causes an enhancement of superconducting transition temperature (T_{c}) and the reduction of CDW temperature (T_{CDW}). We found that the Nb substitution shifts the Sb-derived electron band at the Γ point downward and simultaneously moves the V-derived band around the M point upward to lift up the saddle point (SP) away from the Fermi level, leading to the reduction of the CDW-gap magnitude and T_{CDW}. This indicates a primary role of the SP density of states to stabilize the CDW. The present result also suggests that the enhancement of superconductivity by Nb substitution is caused by the cooperation between the expansion of the Sb-derived electron pocket and the recovery of the V-derived density of states at the Fermi level.

Fermiology of a topological line-nodal compound CaSb2 and its implication to superconductivity: Angle-resolved photoemission study

We performed angle-resolved photoemission spectroscopy with micro-focused beam on a topological line-nodal compound CaSb2 which undergoes a superconducting transition at the onset Tc~1.8 K, to clarify the Fermi-surface topology relevant to the occurrence of superconductivity. We found that a three-dimensional hole pocket at the G point is commonly seen for two types of single-crystalline samples fabricated by different growth conditions. On the other hand, the carrier-doping level estimated from the position of the chemical potential was found to be sensitive to the sample fabrication condition. The cylindrical electron pocket at the Y(C) point predicted by the calculations is absent in one of the two samples, despite the fact that both samples commonly show superconductivity with similar Ts's. This suggests a key role of the three-dimensional hole pocket to the occurrence of superconductivity, and further points to an intriguing possibility to control the topological nature of superconductivity by carrier tuning in CaSb2.

Strong modulation of carrier effective mass in WTe2 via coherent lattice manipulation

The layered transition-metal dichalcogenide WTe2 is characterized by distinctive transport and topological properties. These properties are largely determined by electronic states close to the Fermi level, specifically to electron and hole pockets in the Fermi sea. In principle, these states can be manipulated by changes to the crystal structure. The precise impact of particular structural changes on the electronic properties is a strong function of the specific nature of the atomic displacements. Here, we report on time-resolved X-ray diffraction and infrared reflectivity measurements of the coherent structural dynamics in WTe2 induced by femtosecond laser pulses excitation (central wavelength 800 nm), with emphasis on a quantitative description of both in-plane and out-of-plane vibrational modes. We estimate the magnitude of these motions, and calculate via density functional theory their effect on the electronic structure. Based on these results, we predict that phonons periodically modulate the effective mass of carriers in the electron and hole pockets up to 20%. This work opens up new opportunities for modulating the peculiar transport properties of WTe2 on short time scales.

Field-induced quasi-particle tunneling in the nodal-line semimetal HfSiS revealed by de Haas-van Alphen quantum oscillations

We present a de Haas--van Alphen quantum oscillation study of the Dirac nodal-line semimetal HfSiS up to 32 T to unravel the structure of the high-frequency magnetic breakdown spectrum that was previously obscured in transport experiments. Despite a threefold enhanced gap between adjacent electron and hole pockets relative to the sister compound ZrSiS, a large number of large-area magnetic breakdown orbits enclosing the nodal-loop are identified. All breakdown orbits are assigned by extracting their cyclotron masses. Moreover, one additional low-frequency magnetic breakdown orbit, previously absent in ZrSiS, is observed and attributed to the larger spin-orbit interaction in HfSiS.

VALIDITY OF ELECTRONIC POCKETBOOK CONTAINING DIVERSITY OF ANURA IN TANIPAH, SOUTH KALIMANTAN

Study of Anura can be used as material for enriching learning resources in school, as well as being a material for developing local potential, development is carried out in the form of an electronic pocket book. One of biology subject matter that can be applied with local potential is biodiversity. The purpose of this study was to describe validity of electronic pocket book containing study of Anura diversity in Tanipah, South Kalimantan. This book has been prepared as additional reading material on biodiversity. This development research use Borg and Gall model, but only on step (1) research and data collection, (2) planning, (3) initial product development, (4) initial field trial, and (5) major revision. Data collection is carried out directly in the field, then the data is integrated to electronic pocket book. The result of pocket book validity test is 94%, mean very valid. Based on the assessment, the book can be used as material for enriching concept of biodiversity.

ELECTRONIC POCKET BOOK ON DIVERSITY OF WATER PLANTS IN RIVER IRRIGATION RAWA VILLAGE TANIPAH DISTRICT MANDASTANA

Plant diversity can be used as learning enrichment material in schools. Likewise, the types of aquatic plants used as enrichment materials in electronic pocket books. This study aims to describe the validity of the electronic pocket book of aquatic plants in the Rawa Irrigation River, Tanipah Village, Mandastana Regency. Research using a descriptive approach with the development of formative evaluation Tessmer (1998) is limited to the stages of development which include self-evaluation, expert review, and content practicality tests. The test results on this product are very valid and very practical. So that it can be used as material to enrich the concept of biodiversity in secondary schools.

Interband scattering across the Lifshitz transition in WTe2

In this paper, we investigate the resistance fluctuations near the Lifshitz transition in ${\mathrm{WTe}}_{2}$ devices. We identify the Lifshitz transition from electrical and thermal transport studies. The band structure obtained at low temperatures using quantum oscillation measurements consists of two hole pockets and two electron pockets at the Fermi energy, the hole pockets vanish above the Lifshitz transition temperature. The electrical noise shows a conspicuous peak near the Lifshitz transition temperature; we establish this noise to be arising from charge carrier scattering between the Weyl nodes and proximate areas of the bands. Our comparative study of the noise on ${\mathrm{WTe}}_{2}$ devices fabricated on substrates with different scattering mechanisms elucidates the effect of interband scattering on the physics of Weyl semimetals.