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With a surge of interest in spintronics, the manipulation and detection of colossal magnetoresistance in quasi-two-dimensional layered magnetic materials have become a key focus, driven by their relatively scarce occurrence compared to giant magnetoresistance and tunneling magnetoresistance. This study presents an investigation into the desired colossal magnetoresistance, achieved by introducing magnetic frustration through Te doping in quasi-two-dimensional antiferromagnet Cr2Se3 matrix. The resulting Cr0.98SeTe0.27 exhibits cluster glass-like behavior with a freezing temperature of 28 K. Magnetotransport studies reveal a significant negative magnetoresistance of up to 32%. Additionally, angle-dependent transport measurements demonstrate a magnetic field-induced transition from positive to negative resistance anisotropy, suggesting a magnetic field-driven alteration in the electronic structure of this narrow band gap semiconductor, a characteristic feature of the colossal magnetoresistance effect. This behavior is further corroborated by density functional theory calculations. This systematic investigation provides a crucial understanding of the control of colossal magnetoresistan

We measure the colossal permittivity in single crystal Fe$_2$TiO$_5$ using broadband spectroscopy in the frequency range 20 Hz - 1 MHz. The relaxation response is analyzed using a Debye-like model with Arrhenius activation in two different ways and yields an energy barrier of 286.1 $\pm$ 2.8 meV. DC transport yields an activation energy of 288.8 $\pm$ 2.8 meV. These results strongly imply that the energy barrier for localized dipole motion and itinerant charge transport originate from the same atom-level forces. A further implication is that colossal dielectric behavior is a microscopic bulk phenomenon arising from a system on brink of metallicity.

Negative permittivity metamaterial is a scientifically rich avenue due to its tremendous application in several arena of materials research including novel superlens, band-gap materials, invisibility cloaks, antenna and filter design. Traditionally, epsilon negative (ENG) behaviour is achieved in multi-phase composites with the addition of conducting metal fillers. However, this study reports colossal ENG feature in a single phase Calcium Ferrite for a particular nano hollow spherical (NHS) morphology, without the use of any filler. On the contrary, the same material synthesized in a different morphology, namely, nano solid sphere (NSS) shows conventional dielectric behaviour. Occurrence of ENG is successfully interpreted with the phase inversion of dominant polarization within the hollow cavity of NHS. This report marks a significant step in realizing colossal ENG in a single phase material just by restructuring the nanoscale morphology.

Colloidal quantum dots (QDs) are an attractive medium for nonlinear optics and deterministic heterogeneous integration with photonic devices. Their intrinsic nonlinearities can be strengthened further by coupling QDs to low mode-volume photonic nanocavities, enabling low-power, on-chip nonlinear optics. In this paper, we demonstrated cavity-enhanced second harmonic generation via integration of colossal QDs with a silicon nitride nanobeam cavity. By pumping the cavity-QD system with an ultrafast pulsed laser, we observed a strong second harmonic generation from the cavity-coupled QD, and we estimate an enhancement factor of ~3,040. Our work, coupled with previously reported deterministic positioning of colossal QDs, can enable a scalable QD-cavity platform for low-power nonlinear optics.

Recently colossal Seebeck coefficient ($S$) has found in the several thermoelectric (TE) materials. We present colossal $S$ and large thermal electron motivate force (EMF) reproduced by space charge (SC) model, introducing multi-Debye lengths within grain boundaries (GBs) of TE materials with phonon drag (PD) effect accompanying with electron by electron-phonon interaction. In addition to $S$, the polarity reversal was also reproduced by transfer process with inner bias around SP generated from thermal EMF. Colossal $S$ and EMF for TE material were reproduced by inner SC model as a functions of averaged multi-Debye length within GBs.

We argue that colossal magnetoresistance is a critical phenomenon and propose a mechanism to describe it. The mechanism relies on the halfmetallic behavior of the materials showing colossal magnetoresistance, and yields a correlated percolation model that, we argue, captures all qualitative features of colossal magnetoresistance, above as well as below the Curie temperature. The model only serves for revealing the underlying mechanism of colossal magnetoresistance, and does not aim to reproduce precise, numerical results.

We report the detailed study of dielectric response of Pr(0.6)Ca(0.4)MnO(3) (PCMO), member of manganite family showing colossal magnetoresistance. Measurements have been performed on four polycrystalline samples and four single crystals, allowing us to compare and extract the essence of dielectric response in the material. High frequency dielectric function is found to be 30, as expected for the perovskite material. Dielectric relaxation is found in frequency window of 20Hz-1MHz at temperatures of 50-200K that yields to colossal low-frequency dielectric function, i.e. static dielectric constant. Static dielectric constant is always colossal, but varies considerably in different samples from 1000 until 100000. The measured data can be simulated very well by blocking (surface barrier) capacitance in series with sample resistance. This indicates that the large dielectric constant in PCMO arises from the Schottky barriers at electrical contacts. Measurements in magnetic field and with d.c. bias support this interpretation. Weak anomaly at the charge ordering temperature can also be attributed to interplay of sample and contact resistance. We comment our results in the framework of rela

Comments on "Giant Dielectric Response in the One-Dimensional Charge-Ordered Semiconductor (NbSe_{4})_{3}I" (D. Staresinic et al., Phys. Rev. Lett. 96, 046402 (2006)) and "Colossal Magnetocapacitance and Colossal Magnetoresistance in HgCr_{2}S_{4}" (S. Weber et al., Phys. Rev. Lett. 96, 157202 (2006))

Colossal magnetoresistance (CMR) refers to a large change in electrical conductivity induced by a magnetic field in the vicinity of a metal-insulator transition and has inspired extensive studies for decades\cite{Ramirez1997, Tokura2006}. Here we demonstrate an analogous spin effect near the Néel temperature $T_{\rm{N}}$=296 K of the antiferromagnetic insulator \CrO. Using a yttrium iron garnet \YIG/\CrO/Pt trilayer, we injected a spin current from the YIG into the \CrO layer, and collected via the inverse spin Hall effect the signal transmitted in the heavy metal Pt. We observed a change by two orders of magnitude in the transmitted spin current within 14 K of the Néel temperature. This transition between spin conducting and nonconducting states could be also modulated by a magnetic field in isothermal conditions. This effect, that we term spin colossal magnetoresistance (SCMR), has the potential to simplify the design of fundamental spintronics components, for instance enabling the realization of spin current switches or spin-current based memories.

Ba7Ir3O13+δ in thin film form is discovered. These films are characterized by colossal permittivity (CP) ~104 at room temperature, attributable to the colossal internal barrier layer capacitance effect at atomically thin domain boundaries. These findings suggest a new route to seeking novel CP materials through designing atomically thin domain boundaries.

A recent vast experimental and theoretical effort in manganites has shown that the colossal magnetoresistance effect can be understood based on the competition of charge-ordered and ferromagnetic phases. The general aspects of the theoretical description appear to be valid for any compound with intrinsic phase competition. In high temperature superconductors, recent experiments have shown the existence of intrinsic inhomogeneities in many materials, revealing a phenomenology quite similar to that of manganese oxides. Here, the results for manganites are briefly reviewed with emphasis on the general aspects. In addition, theoretical speculations are formulated in the context of Cu-oxides by mere analogy with manganites. This includes a tentative explanation of the spin-glass regime as a mixture of antiferromagnetic and superconducting islands, the rationalization of the pseudogap temperature T* as a Griffiths temperature where clusters start forming upon cooling, the prediction of "colossal" effects in cuprates, and the observation that quenched disorder may be far more relevant in Cu-oxides than previously anticipated.

Many transition-metal oxides show very large ("colossal") magnitudes of the dielectric constant and thus have immense potential for applications in modern microelectronics and for the development of new capacitance-based energy-storage devices. In the present work, we thoroughly discuss the mechanisms that can lead to colossal values of the dielectric constant, especially emphasising effects generated by external and internal interfaces, including electronic phase separation. In addition, we provide a detailed overview and discussion of the dielectric properties of CaCu3Ti4O12 and related systems, which is today's most investigated material with colossal dielectric constant. Also a variety of further transition-metal oxides with large dielectric constants are treated in detail, among them the system La2-xSrxNiO4 where electronic phase separation may play a role in the generation of a colossal dielectric constant.

Piezoresistance, the change of a material's electrical resistance ($R$) in response to an applied mechanical stress ($σ$), is the driving principle of electromechanical devices such as strain gauges, accelerometers, and cantilever force sensors. Enhanced piezoresistance has been traditionally observed in two classes of uncorrelated materials: nonmagnetic semiconductors and composite structures. We report the discovery of a remarkably large piezoresistance in Eu$_5$In$_2$Sb$_6$ single crystals, wherein anisotropic metallic clusters naturally form within a semiconducting matrix due to electronic interactions. Eu$_5$In$_2$Sb$_6$ shows a highly anisotropic piezoresistance, and uniaxial pressure along [001] of only 0.4~GPa leads to a resistivity drop of more than 99.95\% that results in a colossal piezoresistance factor of $5000\times10^{-11}$Pa$^{-1}$. Our result not only reveals the role of interactions and phase separation in the realization of colossal piezoresistance, but it also highlights a novel route to multi-functional devices with large responses to both pressure and magnetic field.

The temperature-dependent effective potential (TDEP) method for anharmonic phonon dispersion is generalized to the full potential case by combining with path integral formalism. This extension naturally resolves the intrinsic difficulty in the original TDEP at low temperature. The new method is applied to solid metallic hydrogen at high pressure. A colossal nuclear quantum effect (NQE) and subsequent anharmonicity are discovered, which not only leads to unexpectedly large drift of protons, but also slows down the convergence rate substantially when computing the phonon dispersions. By employing direct ab initio path integral molecular dynamics simulations as the benchmark, a possible breakdown of phonon picture in metallic hydrogen due to colossal NQE is indicated, implying novel lattice dynamical phenomena might exist. Inspired by this observation, a general theoretical formalism for quantum lattice dynamics beyond phonon is sketched, with the main features being discussed.

We report magnetic and inter-plane transport properties of Ca3Ru2O7 at high magnetic fields and low temperatures. Ca3Ru2O7 with a bilayered orthorhombic structure is a Mott-like system with a narrow charge gap of 0.1eV. Of a host of unusual physical phenomena revealed in this study, a few are particularly intriguing: (1) a collapse of the c-axis lattice parameter at a metal-nonmetal transition, TMI (=48 K), and a rapid increase of TMI with low uniaxial pressure applied along the c-axis; (2) quantum oscillations in the gapped, nonmetallic state for 20 mK<T<6.5 K; (3) tunneling colossal magnetoresistance, which yields a precipitate drop in resistivity by as much as three orders of magnitude; (4) different in-plane anisotropies of the colossal magnetoresistance and magnetization. All results appear to indicate a highly anisotropic ground state and a critical role of coupling between lattice and magnetism. The implication of these phenomena is discussed.

A colossal electroresistance effect is observed around room temperature in a transition metal oxide LuFe2O4. The measurements of resistance under various applied voltages as well as the highly nonlinear current-voltage characteristics reveal that a small electric field is able to drive the material from the insulating state to a metallic state. The threshold field at which the insulating-metallic transition occurs, decreases exponentially with increasing temperature. We interpret this transition as a consequence of the breakdown of the charge-ordered state triggered by applied electric field, which is supported by the dramatic dielectric response in a small electric field. This colossal electroresistance effect as well as the high dielectric tunability around room temperature in low applied fields makes LuFe2O4 a very promising material for many applications.

Colossal electroresistance (CER) in manganites, i.e., a large change in electrical resistance under the influence of either an applied electric field or an applied electric current, has often been described as complimentary to the colossal magnetoresistance (CMR) effect. Mixed valent vanadates with active t2g and empty eg orbitals, unlike manganites, have not naturally been discussed in this context, as double exchange based CMR is not realizable in them. However, presence of coupled spin and orbital degrees of freedom, metal-insulator transition (MIT) accompanied by orbital order-disorder transition, etc., anyway make the vanadates an exciting group of materials. Here we probe a Fe-doped hollandite lead vanadate PbFe1.75V4.25O11 (PFVO), which exhibits a clear MIT as a function of temperature. Most importantly, a giant fall in the resistivity, indicative of a CER, as well as a systematic shift in the MIT towards higher temperature are observed as a function of applied electric current. Detailed structural, magnetic, thermodynamic and transport studies point towards a complex interplay between orbital order/disorder effect, MIT and double exchange in this system.

In the present work, we address the question of an impurity-related origin of the colossal magnetocapacitive effect in the spinel system CdCr2S4. We demonstrate that a strong variation in the dielectric constant below the magnetic transition temperature or in external magnetic fields also arises in crystals prepared without chlorine. This excludes that an inhomogeneous distribution of chlorine impurities at the surface or in the bulk material gives rise to the unusual effects in the spinel multiferroics. In addition, we show that colossal magnetocapacitive effects can be also generated in chlorine-free ceramic samples of CdCr2S4, doped with indium.

In addition to mechanisms already proposed to account for the formation in manganites of a small-polaron superlattice above the Curie temperature Tc and to a metallic-like sea of large polarons below Tc, we now consider other observed colossal-resistance inducing fields, such as magnetic, electric, photon, or strain fields. We attribute the charge-ordered phase formation to the occurrence of strong dipolar binding of vibronic small polarons arising from the phonon coupling of highly polarizable two-level orbital systems. These species having associated inherent electric and magnetic off-center dipoles, they couple to the external fields leading to the observed colossal effects. The random phase appears due to polaron band widening in the external field.