Search results

1

Metal-Insulator Transition in Doped Semiconductors

100%

Jaroszyński J.

Acta Physica Polonica A

|

1991

|

vol. 80

|

issue 2

255-265

EN

A survey is given of different kinds of metal-insulator transitions (MIT) in doped semiconductors. The role of electron-electron Coulomb interactions and of disorder is discussed vis-a-vis millikelvin experimental results for semimagnetic semiconductors (SMSC) in the vicinity of MIT. Critical behavior of conductivity tensor components and dielectric susceptibility at the magnetic field-induced 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 certain a concentration of local electron moments, 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.

2

Electromagnetic Properties of Mesoscopic Cylinder

63%

Zipper E., Stebelski M., Lisowski M.

Acta Physica Polonica A

|

1997

|

vol. 92

|

issue 5

1087-1091

EN

The electromagnetic response of a mesoscopic cylinder made of a normal metal or a semiconductor is studied. The relation between the induced current J(q,w) and the electric field E(q,w) is derived. It is shown that the kernel K(q,w) which determines the properties of the system has a finite limit which implies infinite conductivity. The mesoscopic cylinder by virtue of its topology and small dimensions can support a persistent current. If the coherence of currents from different channels is strong enough a novel effect - the self-sustaining current can be obtained. We show that a mesoscopic multichannel system exhibits some features which bear resemblance to the superconductor.

3

Phase Diagram of Metal-Insulator Transition in System with Anderson-Hubbard Centers

63%

Skorenkyy Y., Didukh L., Kramar O., Dovhopyaty Y.

Acta Physica Polonica A

|

2012

|

vol. 122

|

issue 3

532-534

EN

The model of a strongly correlated system in which periodically spaced Anderson-Hubbard centers are introduced into narrow-band metal is considered. Besides the interactions between localized magnetic moments and strong on-site Coulomb interaction, the model takes into account the hybridization of localized and band states. To study the effect of the lattice deformation on the electrical properties of the system, the phonon term and elastic energy have been taken into account. Green functions for band and localized electrons have been found. On this base, the energy spectrum has been investigated as a function of model parameters, temperature and external pressure. The criterion of the metal-insulator transition for an integer value of electron concentration has been derived and the phase diagram of the metal-insulator transition has been built.

4

Conductivity Near the Metal-to-Insulator Transition in Cd_{1-x}Mn_{x}Se:Sc

63%

Głód P., Sawicki M., Lenard A., Dietl T., Plesiewicz W.

Acta Physica Polonica A

|

1991

|

vol. 79

|

issue 2-3

389-392

EN

Earlier studies of transition metal impurities in II-VI compounds suggest that Sc acts as a resonant donor. We performed Hall effect and conductivity measurements of CdSe:Sc and Cd_{0.95}Mn_{0.05}Se:Sc. The results, particularly the critical concentration of the metal-to-insulator transition, turned out to be similar to those obtained previously for Cd_{1-x}Mn_{x}Se doped with hydrogenic-like impurities, such as In and Ga. Therefore, if the ground state of Sc impurity is indeed located above the bottom of the conduction band, our data demonstrate that the metal-to-insulator transition is primarily driven by the scattering, i.e. it corresponds to the Anderson localization.

5

Global Structure of the Falicov-Kimball Model Ground State Phase Diagram

63%

Lach J., Łyżwa R., Jędrzejewski J.

Acta Physica Polonica A

|

1993

|

vol. 84

|

issue 2

327-344

EN

The two-state spinless Falicov-Kimball model on a one-dimensional lattice is studied by means of well-controlled numerical procedures. Restricted phase diagrams in the grand-canonical ensemble and at zero temperature are constructed. The evolution of these phase diagrams, as the interaction parameter U is varied, including the band structures corresponding to configurations of localized particles (ions) and densities of mobile particles (electrons), is monitored. The changes observed enable us to draw conclusions for the global structure of the phase diagram and to make a qualitative plot of such a diagram. Particular attention is paid to the possibility of conductor-insulator transitions. The results obtained suggest that the system is an insulator for all U only if the electron and ion densities ρ_{e},ρ_{i} satisfy the conditions: ρ_{e} + ρ_{i} = 1, |ρ_{i} - 1/2| ≤ δ < 1/2. For all other pairs (ρ_{e},ρ_{i}) there is a critical U at which the system undergoes a conductor-insulator transition.

6

Investigation of Quantum Effects in Carbonaceous Materials Near the Metal-Insulator Transition by Means of THz Photoconductivity

63%

Dorosinets V., Ksenevich V., Seliuta D., Martūnas Z., Valušis G.

Acta Physica Polonica A

|

2008

|

vol. 113

|

issue 3

875-878

EN

A series of carbonaceous fibers with conductivity tuned to the metal-insulator transition were prepared by heat treatment of chemically modified polymer precursors. Peculiar behaviour of the resistivity versus temperature dependence R(T) at low temperatures suggests quantum corrections to the Drude conductivity due to weak localization and electron-electron interaction dominating in the conductivity. The THz conductivity method is employed to study the modification of the density of states and provides evidence for a strong change in density of states at the Fermi level caused by the quantum effects.

7

Correlation between Magnetic Phases and Insulator-Metal Transition in La_{1/3}Nd_{1/3}Ca_{1/3}MnO_{3} Perovskite

63%

Baszyński J., Idzikowski B., Toliński T., Hoser A.

Acta Physica Polonica A

|

2000

|

vol. 97

|

issue 5

779-782

EN

The La_{1/3}Nd_{1/3}Ca_{1/3}MnO_{3} ceramic perovskites are investigated using the neutron diffraction technique and resistance measurements in the temperature range from 260 K down to 5 K. We have found that the integrated intensity of the antiferromagnetic peaks was growing with decreasing temperature and reached the maximum at a temperature about 20 K lower than that of the semiconductor-metal transition and did not vanish at 5 K. The semiconductor-metal transition is correlated with the temperature of the maximum of the lattice c-parameter and the percolation of ferromagnetic domains. Our results suggest that although the ferromagnetic long-range order is established through the semiconductor-metal transition induced percolation network, locally the antiferromagnetic correlation can remain.

8

Infrared Reflection of MnTe_2 under High Pressure

63%

Mita Y., Ishida Y., Kobayashi M., Endo S.

Acta Physica Polonica A

|

2008

|

vol. 113

|

issue 1

617-620

EN

The IR reflection measurements of MnTe_2 were performed at room temperature under various pressures. It is observed that the reflectivity increases at the pressure range of 8-25 GPa and becomes almost constant at the higher pressure. The carrier concentrations obtained from the reflectivity spectra at the highest pressure region are the order of 10^{22} cm^{-3}. Therefore it is concluded that pressure-induced semiconductor-metal transition occurs at the pressure range of 8-25 GPa.

9

Neutron Diffraction Study of Ferromagnetic Ordering in La_{1/3}Nd_{1/3}Ca_{1/3}MnO_{3} Induced by Electric Field

63%

Baszyński J., Idzikowski B., Toliński T., Hoser A.

Acta Physica Polonica A

|

2000

|

vol. 97

|

issue 5

831-834

EN

We used the neutron diffraction technique to study the ferromagnetic ordering process in La_{1/3}Nd_{1/3}Ca_{1/3}MnO_{3} induced by the short impulse of the external electric field E=4 V/cm at a magnetic field H=1.5 T. Our sample was prepared by the standard solid-state reaction. The diffraction measurements at 4 K, carried out for the neutron wavelength λ=0.2442 nm, have revealed the orthorhombic perovskite structure with the unit-cell parameters: a=0.5480 nm, b=0.5550 nm and c=0.7737 nm. We observed that a short impulse of the electric field develops the ferromagnetic ordering in a similar way as the magnetic field up to 4 T. We assume that the increased ferromagnetic ordering induced by the external electric field at a given magnetic field has the same physical origin as in the case of the Zener double exchange. The effect is confirmed by magnetic moment measurements using vibrating sample magnetometer.

10

Transport and Magnetic Studies of New Mixed-Valence Compounds: K_{3}Cu_{8}Se_{6}, KCu_{3}Se_{2}, K_{3}Cu_{8}Te_{6} and BaCuS_{3-x}

63%

Jacyna-Onyszkiewicz I., Sidowski M., Starodub W., Ratuszna A., Robaszkiewicz S.

Acta Physica Polonica A

|

1997

|

vol. 91

|

issue 2

405-408

EN

New mixed-valent copper chalcogenides BaCuS_{3-x} and K_{3}Cu_{8}X_{6} with X=Se or Te and KCu_{3}Se_{2}, with chemical patterns corresponding to the recently investigated K_{3}Cu_{8}S_{6} and KCu_{3}S_{2}, were synthesized. For these new samples the results of resistivity and magnetic susceptibility measurements are presented. For BaCuS_{3-x}, K_{3}Cu_{8}Se_{6} and KCu_{3}Se_{2} the metal-insulator transition is observed with the low temperature phase being metallic, which is untypical, whereas K_{3}Cu_{8}Te_{6} is a metal in the investigated temperature range. The temperature dependence of magnetic susceptibility of the studied samples testifies to their diamagnetic or weakly paramagnetic behaviour.

11

Electronic Phase Transition in Layered Materials 1T-TaS_{x}Se_{2-x} Probed by Cryogenic STM/STS

63%

Hasegawa T., Shiino O., Yamaguchi W., Endo T., Sugawara H., Kitazawa K.

Acta Physica Polonica A

|

1998

|

vol. 93

|

issue 2

297-305

EN

A metal-insulator transition, Mott transition, in layered materials 1T-TaS_{x}Se_{2-x} was investigated by cryogenic scanning tunneling microscopy/ spectroscopy. At 77 K, tunneling spectra in the insulating phase showed a conduction band with almost half filling, which becomes narrower as x decreases. Around the transition point x≈1.4 at 77 K, we observed a sign of gap opening without an overshooting peak at zero bias, supporting the Mott localization picture in which a carrier number vanishes at the transition point. From the site-specified scanning tunneling spectroscopy measurements, furthermore, electrons were found to localize at the charge density wave crest positions. In 1T-TaS_{2}, we have also found that both metallic and insulating phases coexist in a nanometer scale just above the transition temperature, 180 K. >From the minimum size of the insulating region, the coherence length of Mott insulating state was evaluated to be≈5 nm.

12

Correlation-Driven Metal-Insulator Transitions

63%

Honig J.

Acta Physica Polonica A

|

2000

|

vol. 97

|

issue 1

141-156

EN

The effect of correlation-driven electronic transitions are described for the V_{2}O_{3}, NiS_{2-x}Se_{x}, and Fe_{3}O_{4} systems. The various tranformations can all be rationalized in terms of elementary concepts pertaining to the Mott-Hubbard intraatomic electronic interactions or in terms of an order-disorder formalism involving Coulomb interactions among electrons on adjacent sites. Attention is directed to some outstanding issues that require further resolution.

13

Scanning Tunneling Spectra and Low Energy Ion Scattering Studies of the Verwey Transition in MBE Fe_3O_4 (100) Thin Film

51%

Kim-Ngan N., Soszka W., Hietschold M.

Acta Physica Polonica A

|

2001

|

vol. 99

|

issue 2

267-276

EN

The (100) surface of magnetite Fe_3O_4 thin film was studied by a UHV low-temperature scanning tunneling microscope and by an ion scattering spectroscopy. The tunneling spectra revealed a widening of the gap with decreasing temperature, which may be related to the metal-insulator phase transition in this material. A strong effect of this phase transition on ion scattering from such a surface was observed. The temperature dependence of the scattered ion yield, R^+(T), revealed two minima at around 100 K and at 125 K under Ne^+ bombardment with the primary energy up to 6 keV. The disappearance of the high-temperature minimum at a bombarding energy of 6.5 keV gave a further evidence for the ion velocity dependence of the character of the R^+(T) curve, which has been first observed for a MBE Fe_3O_4 (111) film surface.

14

Non-Fermi Liquid Behavior of Correlated Fermions in Applied Field

51%

Korbel P., Spałek J., Wójcik W.

Acta Physica Polonica A

|

1997

|

vol. 92

|

issue 2

323-326

EN

We have determined an instability of the Fermi-liquid state of almost localized fermions in an applied magnetic field. It is proposed that a transition to a strongly correlated fermions (statistical-spin-liquid) state takes place at that point. The resultant magnetization curve and the field dependence of the specific heat are calculated and compared with those for CeRu_{2}Si_{2}.

15

Lieb-Wu Solution, Gutzwiller-Wave-Function, and Gutzwiller-Ansatz Approximations with Adjustable Single-Particle Wave Function for the Hubbard Chain

51%

Kurzyk J., Spałek J., Wójcik W.

Acta Physica Polonica A

|

2007

|

vol. 111

|

issue 4

603-618

EN

The optimized single-particle wave functions contained in the parameters of the Hubbard model (t and U) were determined for an infinite atomic chain. In effect, the electronic properties of the chain as a function of interatomic distance R were obtained and compared for the Lieb-Wu exact solution, the Gutzwiller-wave-function approximation, and the Gutzwiller-ansatz case. The ground state energy and other characteristics for the infinite chain were also compared with those obtained earlier for a nanoscopic chain within the exact diagonalization combined with an ab initio adjustment of the single-particle wave functions in the correlated state (exact diagonalization combined with an ab initio method). For the sake of completeness, we briefly characterize also each of the solutions. Our approach completes the Lieb-Wu solution, as it provides the system electronic properties evolution as a function of physically controlable parameter - the interatomic distance.

16

Surprises in Correlated Electron Physics

51%

Byczuk K., Hofstetter W., Kollar M., Vollhardt D.

Acta Physica Polonica A

|

2007

|

vol. 111

|

issue 4

549-561

EN

Strong electronic correlations and especially the interplay between correlations and disorder lead to many interesting and quite unexpected phenomena. A short summary of our recent investigations into the properties of strongly correlated electron systems with and without disorder using the dynamical mean-field theory is presented.

17

Study of the Mott Transition in the Three-Dimensional Hubbard Model

51%

Mancini F., Turkowski V.

Acta Physica Polonica A

|

2002

|

vol. 101

|

issue 4

505-523

EN

The Mott-Hubbard transition in the three-dimensional Hubbard model is studied by means of the composite operator method. Analytical and numerical calculations show the existence of a critical value U_c of the Coulomb interaction which separates paramagnetic insulating and metallic phases. In the composite operator method the ratio U_c/W, where W is the band width, has the same value as in the two-dimensional case. The ground state of the Mott insulator is characterized by a local antiferromagnetic order where the electrons keep some mobility, but this latter must be compatible with the local ordering. By analyzing the intersite hopping it is possible to establish that some correlation functions behave as order parameters in the insulating phase.

18

Influence of Bound Magnetic Polarons on Magnetic and Electrical Properties in Metallic n-Cd_{0.95}Mn_{0.05}Se

51%

Głód P., Sawicki M., Dietl T., Skośkiewicz T., Lenard A., Plesiewicz W.

Acta Physica Polonica A

|

1995

|

vol. 87

|

issue 1

173-175

EN

Doping-induced contribution to the millikelvin magnetic susceptibility of Cd_{0.95}Mn_{0.05}Se:In has been found to undergo a maximum at n ≈ 2n_{c}, and to vanish for n ≥ 8n_{c}, where n_{c} is the electron concentration corresponding to the metal-insulator transition. This confirms the presence, also in the metallic phase, of bound magnetic polarons. Their slow dynamics may account for hysteresis visible in our magnetoresistance data.

19

Some Electronic Properties of Sr_{1-x}A_{x}CuO_{2+δ} where A=La, K, and Ca

51%

Onyszkiewicz I., Czarnecki P., Poltoracky Y., Zimpel M.

Acta Physica Polonica A

|

1994

|

vol. 85

|

issue 2

303-306

EN

The electronic properties of Sr_{1-x}A_{x}CuO_{2+δ} (A = La, K, Ca) were examined. The crystal structure of the synthesized compounds was identified as orthorhombic with some admixture of tetragonal phase. For Sr_{1-x}La_{x}CuO_{2+δ} the insulator-metal like transition was observed with increasing La content. The d_{x²-y²} ground state of Cu ions was deduced from electron spin resonance measurements. The electronic state of Cu ions and their surrounding local symmetry was also found to be La and oxygen content dependent.

20

Hole Transport in Impurity Band and Valence Bands Studied in Moderately Doped GaAs:Mn Single Crystals

51%

Słupiński T., Caban J., Moskalik K.

Acta Physica Polonica A

|

2007

|

vol. 112

|

issue 2

325-330

EN

We report on a simple experiment on temperature-dependent Hall effect measurements in GaMnAs single crystalline samples with Mn composition estimated at 0.05-0.3 at.% which is slightly below the onset of ferromagnetism. Impurity band transport is visible for Mn compositions of ≈0.3 at.% as a clear metallic behaviour. The results show an interesting situation that the metal-insulator transition in GaAs:Mn occurs within the impurity band which is separated from the valence bands for Mn concentrations studied here. We also discuss on the equilibrium high temperature solubility limit of Mn in GaAs, unknown precisely in the literature.

Refine search results

Metal-Insulator Transition in Doped Semiconductors

Electromagnetic Properties of Mesoscopic Cylinder

Phase Diagram of Metal-Insulator Transition in System with Anderson-Hubbard Centers

Conductivity Near the Metal-to-Insulator Transition in Cd_{1-x}Mn_{x}Se:Sc

Global Structure of the Falicov-Kimball Model Ground State Phase Diagram

Investigation of Quantum Effects in Carbonaceous Materials Near the Metal-Insulator Transition by Means of THz Photoconductivity

Correlation between Magnetic Phases and Insulator-Metal Transition in La_{1/3}Nd_{1/3}Ca_{1/3}MnO_{3} Perovskite

Infrared Reflection of MnTe_2 under High Pressure

Neutron Diffraction Study of Ferromagnetic Ordering in La_{1/3}Nd_{1/3}Ca_{1/3}MnO_{3} Induced by Electric Field

Transport and Magnetic Studies of New Mixed-Valence Compounds: K_{3}Cu_{8}Se_{6}, KCu_{3}Se_{2}, K_{3}Cu_{8}Te_{6} and BaCuS_{3-x}

Electronic Phase Transition in Layered Materials 1T-TaS_{x}Se_{2-x} Probed by Cryogenic STM/STS

Correlation-Driven Metal-Insulator Transitions

Scanning Tunneling Spectra and Low Energy Ion Scattering Studies of the Verwey Transition in MBE Fe_3O_4 (100) Thin Film

Non-Fermi Liquid Behavior of Correlated Fermions in Applied Field

Lieb-Wu Solution, Gutzwiller-Wave-Function, and Gutzwiller-Ansatz Approximations with Adjustable Single-Particle Wave Function for the Hubbard Chain

Surprises in Correlated Electron Physics

Study of the Mott Transition in the Three-Dimensional Hubbard Model

Influence of Bound Magnetic Polarons on Magnetic and Electrical Properties in Metallic n-Cd_{0.95}Mn_{0.05}Se

Some Electronic Properties of Sr_{1-x}A_{x}CuO_{2+δ} where A=La, K, and Ca

Hole Transport in Impurity Band and Valence Bands Studied in Moderately Doped GaAs:Mn Single Crystals