Magnetic Field Induced Metal Insulator Transition Research Articles

Quantum linear magnetoresistance and magnetic-field-induced metal–insulator transition in the Weyl semimetal candidate HgSe

In ultrapure single HgSe crystal, a large linear magnetoresistance with a record magnitude of 15 000% in mercury chalcogenides was discovered in a quantum limit at the magnetic field of 12 T in the temperature range of 20–40 K. The effect was described in terms of Abrikosov's theory of quantum linear magnetoresistance, thus providing its first experimental confirmation. In the temperature range of 0.4–4.2 K, a magnetic field-induced metal–insulator transition appeared in the ultrapure HgSe. Estimates show that the critical magnetic field of this transition of 6.8 T satisfies the criterion for stabilization of a condensed Wigner phase in the quantum limit.

Grain-Size-Induced Collapse of Variable Range Hopping and Promotion of Ferromagnetism in Manganite La0.5Ca0.5MnO3

Among transition metal oxides, manganites have attracted significant attention because of colossal magnetoresistance (CMR)—a magnetic field-induced metal–insulator transition close to the Curie temperature. CMR is closely related to the ferromagnetic (FM) metallic phase which strongly competes with the antiferromagnetic (AFM) charge ordered (CO) phase, where conducting electrons localize and create a long range order giving rise to insulator-like behavior. One of the major open questions in manganites is the exact origin of this insulating behavior. Here we report a dc resistivity and magnetization study on manganite La1−xCaxMnO3 ceramic samples with different grain size, at the very boundary between CO/AFM insulating and FM metallic phases x=0.5. Clear signatures of variable range hopping (VRH) are discerned in resistivity, implying the disorder-induced (Anderson) localization of conducting electrons. A significant increase of disorder associated with the reduction in grain size, however, pushes the system in the opposite direction from the Anderson localization scenario, resulting in a drastic decrease of resistivity, collapse of the VRH, suppression of the CO/AFM phase and growth of an FM contribution. These contradictory results are interpreted within the standard core-shell model and recent theories of Anderson localization of interacting particles.

Magnetic field induced metal–insulator transition in single nodal ring topological semimetals

Our theoretical investigation indicates that an applied magnetic field can open a gap between the conduction and valence bands of a nodal line semimetal (NLSM), though it is a kind of gapless material in the absence of a magnetic field. The emerging bandgap depends sensitively on the strength and orientation of the magnetic field which implies a tunable and large anisotropy of magnetoresistance in such kinds of topological materials. Following such a theoretical finding, we predict that in some candidates of NSLMs with a single nodal ring, such as the materials of CaP3 family, a transition between metallic and insulating states driven by a magnetic field is possibly observed experimentally. Consequently, a magnetic field can be viewed as a novel mechanism for metal–insulator transition of solid materials, in additional to the well-known conventional ones such as the Anderson and Mott transitions.

Magnetic Field Induced Metal-Insulator Transition and Reentrant Metallic Behaviors in Kish Graphite

The metal-insulator transition on electronic transport properties and the extraordinarily large magnetoresistances (MR) at low temperature had been found in Kish graphite under low magnetic field. Along with the large ordinary magnetoresistances (MR), Kish graphite had clearly shown the reentrant metallic behavior at low temperature under 600 and 900 Oe applied magnetic fields. Besides a dominating ordinary MR (OMR) mechanism in the free-electron mode, the Coulomb interacting quasiparticles within graphite sheet play some role to extraordinarily large OMR.

Magnetic field induced metal–insulator transition in semiconductors

Metal–insulator transition in doped semiconductors is investigated in the presence of intense magnetic fields. Using Thomas–Fermi screening function and a screened coulomb potential in the Hamiltonian, a two-parameter varitional calculation leads to metallization. The correlation effect among the electrons is considered through an effectivemass that depends on the spatial seperation between impurities. Results are provided for a many valley semiconductor (Si) and two single valley semiconductors (GaAs and CdTe). Our results show that in a magnetic field the critical concentration at which metallization occurs increases. The correlation effects bring out one order change in the critical concentration values, in intense magnetic fields.

Magnetoresistance and magnetic field induced metal–insulator transition in intercalated amorphous carbon

In this work, we discuss the preparation of iodine and sulfur incorporated amorphous carbon (a-C) films by vapor phase pyrolysis technique. Iodine incorporated a-C films depict an unusual resistivity behavior at low temperatures, where a clear positive temperature coefficient (PTCR) is witnessed, which also depicts a pyrolysis temperature and iodine incorporation induced metal–insulator (M–I) transition. Magnetic field induced M–I transition is also observed in iodinated samples. Magnetoresistance measurements performed on these films from 1.3–10 K in the presence of magnetic field (0–7 T) account for a positive magnetoresistance irrespective of the regimes they fall in. Universal scaling of magnetoconductance observed in intercalated a-C system depicts the dominance of electron–electron interaction.

Magnetization, thermoelectric, and pressure studies of the magnetic-field-induced metal-insulator transition inτ-phase organic conductors

We have investigated the magnetic field-induced metal-insulator transition in the tau-phase organic conductors, which occurs in fields above 35 T, and below 14 K, by magnetization, thermoelectric, and pressure dependent transport methods. Our results show that the transition is a bulk thermodynamic process where a magnetic field-dependent gap opens upon entry into the insulating state. We argue that the transition involves a magnetic field-induced change in the electronic structure.

Magnetic freeze-out and impurity band conduction in n-InSb

Non-ohmic conduction of n-InSb with different donor concentrations ( N d=2×10 14– 1×10 15 cm −3 ) in perpendicular magnetic fields has been measured at low temperatures, in order to infer the impurity band mobility μ i with the aid of the two-band analysis. The decrease of μ i with increasing magnetic fields has been found to reflect exactly the shrinkage of donor wave functions due to magnetic field and the magnetic-field induced metal–insulator transition is an event in the impurity band. The temperature dependence of μ i in moderate magnetic fields above the transition field B c appears to obey the Mott variable-range hopping law as μ i =μ 0 exp[−(T 0/T) x] with x=1/4.

Localisation and interaction effects in metallic n-type InP

We present results on the magnetic field induced metal–insulator transition (MIT) in compensated InP. The experiments were carried out at low temperatures in the range 4.2–0.066 K and in magnetic fields up to 11 T. Not too close to the MIT the electrical conductivity σ was found to obey σ= σ( T=0)+ mT 1/2 where both the inelastic diffusion length L I∼( σ( T=0)) 3/2/ T 1/2 and the interaction length L T∼( σ( T=0)) 1/2/ T 1/2 contribute to a T 1/2 term in σ. It is convenient to develop a criterion to distinguish their contribution. It is based on the relation between the magnitude m and the zero temperature conductivity σ( T=0).

A novel transport model for the metal-to-insulator transition in quasi-three-dimensional wide quantum wells

We present a systematic study of the magnetic field induced metal–insulator transition in quasi-three-dimensional wide quantum wells by numerical calculations. Depending on carrier density and carrier mobility we observe both a change from metal to insulator-like temperature dependence as well as a magnetic field dependent transition between both regimes.

Magnetic field induced metal-to-insulator transition in wide quantum wells

We present a systematic experimental study of the magnetic field induced metal–insulator transition in high mobility quasi-3D wide quantum wells. Depending on carrier density and carrier mobility we observe both a metal-like and insulator-like temperature dependence as well as a magnetic field induced transition between both regimes.

Interaction effects at the magnetic-field induced metal—insulator transition in Si/SiGe superlattices

A metal-insulator transition was induced by in-plane magnetic fields up to 27 T in homogeneously Sb-doped Si/SiGe superlattice structures. The localisation is not observed for perpendicular magnetic fields. A comparison with magnetoconductivity investigations in the weakly localised regime shows that the delocalising effect originates from the interaction-induced spin-triplet term in the particle-hole diffusion channel. It is expected that this term, possibly together with the singlet particle-particle contribution, is of general importance in disordered n-type Si bulk and heterostructures.

Magneto-quantum oscillations in the Hall constant of three-dimensional metallic semiconductors

Magneto-quantum oscillations of the Hall constant have been observed in metallically doped three-dimensional semiconductors in a magnetic field far below the magnetic-field-induced metal-insulator (MI) transition. Especially around the magnetic field where all the electrons enter the lowest Landau level, a strong increase of the Hall constant is observed. This phenomenon is explained in terms of a field-induced MI transition in the tails of the spin-split Landau levels which can be understood in analogy to the well known MI transition in metallic semiconductors.

MAGNETIC-FIELD-INDUCED METAL-INSULATOR TRANSITION AND THERMALLY ACTIVATED ELECTRONIC TRANSPORT IN LOW COMPENSATED n-Hg1-xCdxTe

报道了ｘ＝０．２１４组份、低补偿度（Ｋ《１）ｎ－Ｈｇ1-xＣｄxＴｅ晶体在０．３─３０Ｋ温度范围，０─７Ｔ强磁场下的横向磁阻、电子霍耳迁移率、霍耳系数测量结果，观测到了磁致金属－绝缘体相变和相变后的温度激活输运行为。分析实验数据，提出：低补偿度、组份：ｘ＝０．２附近的ｎ－Ｈｇ1-xＣｄxＴｅ，磁致金属－绝缘体相变（ＭＩＴ）发生的机理是载流子在浅施主杂质态上的磁冻结；发生磁冻结的前提是热冻出（ｔｈｅｒｍａｌ ｆｒｅｅｚｅ

Magnetic field-induced metal-insulator transition in diluted magnetic semiconductors

The role of electron-electron Coulomb interactions and disorder is discussed vis-a-vis millikelvin experimental results for diluted magnetic semiconductors (DMS) in the vicinity of a metal-insulator transition (MIT) induced by a magnetic field. The critical behavior of conductivity tensor components and the dielectric susceptibility at the MIT in p-type Hg 1− x Mn x Te is compatible with the model in which the MIT is a result of quantum localization driven by disorder-modified electron-electron interactions. At the same time the critical behavior of the Hall coefficient suggests that, in addition to electrons forming the Fermi liquid (FL) and undergoing localization at the MIT, there is a concentration of local electron s-spins, even on the metallic side of the MIT. The formation of these moments can presumably be described in terms of a disordered Hubbard-Mott model.

Magnetic field-induced metal-insulator transition in InP: new result at very low temperatures

The metal-insulator transition in compensated n-type indium phosphide, with an impurity concentration just above the critical concentration obtained from the Mott criterion has been induced by a magnetic field. First-order phenomena are considered, corrections to the conductivity due to electron-electron interaction or quantum interferences in the metallic regime will be described elsewhere. Two aspects of the MI transition (Anderson and Mott transitions) are observed by increasing the magnetic field at temperatures down to 50 mK. The Mott minimum metallic conductivity, whose existence has been shown earlier at higher temperatures, is still found down to the lowest attainable temperatures, and its value remains in agreement with the first Mott estimation. For a sample near the MI transition, arguments are given for conduction mechanisms occurring in the impurity band rather than in a tail of the conduction band.