T. Dietl

University of Warsaw, Warszawa, Masovian Voivodeship, Poland

Are you T. Dietl?

Claim your profile

Publications (366)962.39 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Electronic and magnetic properties of Ga$_{1-x}$Mn$_{x}$As, obtained from first-principles calculations employing the hybrid HSE06 functional, are presented for $x=6.25\%$ and $12.5\%$ under pressures ranging from 0 to 15 GPa. In agreement with photoemission experiments at ambient pressure, we find for $x=6.25\%$ that non-hybridized Mn-3$d$ levels and Mn-induced states reside about 5 and 0.4 eV below the Fermi energy, respectively. For elevated pressures, the Mn-3$d$ levels, Mn-induced states, and the Fermi level shift towards higher energies, however, the position of the Mn-induced states relative to the Fermi energy remains constant due to hybridization of the Mn-3$d$ levels with the valence As-4$p$ orbitals. We also evaluate, employing Monte Carlo simulations, the Curie temperature ($T_{{\rm C}}$). At zero pressure, we obtain $T_{{\rm C}}=181$K, whereas the pressure-induced changes in $T_{{\rm C}}$ are d$T_{{\rm C}}$/d$p=+4.3$K/GPa for $x=12.5\%$ and an estimated value of d$T_{{\rm C}}$/d$p\approx+2.2$K/GPa for $x=6.25\%$ under pressures up to 6 GPa. The determined values of d$T_{{\rm C}}$/d$p$ compare favorably with d$T_{{\rm C}}$/d$p=+$(2-3) K/GPa at $p\leq1.2$GPa found experimentally and estimated within the $p$-$d$ Zener model for Ga$_{0.93}$Mn$_{0.07}$As in the regime where hole localization effects are of minor importance [M. Gryglas-Borysiewicz $et$ $al$., Phys. Rev. B 82, 153204 (2010)].
    Physical Review B 02/2015; 91(18). DOI:10.1103/PhysRevB.91.184409 · 3.74 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This review presents the recent progress in computational materials design, experimental realization, and control methods of spinodal nanodecomposition under three- and two-dimensional crystal-growth conditions in spintronic materials, such as magnetically doped semiconductors. The computational description of nanodecomposition, performed by combining first-principles calculations with kinetic Monte Carlo simulations, is discussed together with extensive electron microscopy, synchrotron radiation, scanning probe, and ion beam methods that have been employed to visualize binodal and spinodal nanodecomposition (chemical phase separation) as well as nanoprecipitation (crystallographic phase separation) in a range of semiconductor compounds with a concentration of transition metal (TM) impurities beyond the solubility limit. The role of growth conditions, co-doping by shallow impurities, kinetic barriers, and surface reactions in controlling the aggregation of magnetic cations is highlighted. According to theoretical simulations and experimental results the TM-rich regions appear either in the form of nanodots (the {\em dairiseki} phase) or nanocolumns (the {\em konbu} phase) buried in the host semiconductor. Particular attention is paid to Mn-doped group III arsenides and antimonides, TM-doped group III nitrides, Mn- and Fe-doped Ge, and Cr-doped group II chalcogenides, in which ferromagnetic features persisting up to above room temperature correlate with the presence of nanodecomposition and account for the application-relevant magneto-optical and magnetotransport properties of these compounds. Finally, it is pointed out that spinodal nanodecomposition can be viewed as a new class of bottom-up approach to nanofabrication.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A series of recent magnetooptical studies pointed to contradicting values of the s-d exchange energy N0{\alpha} in Mn-doped GaAs and GaN as well as in Fe-doped GaN. Here, a strong sensitivity of weak-localization phenomena to symmetry breaking perturbations (such as spin-splitting and spin-disorder scattering) is exploited to evaluate the magnitude of N0{\alpha} for n-type wurtzite (Ga,Mn)N:Si films grown by metalorganic vapor phase epitaxy. Millikelvin magnetoresistance studies and their quantitative interpretation point to N0{\alpha} < 40 meV, a value at least 5 times smaller than the one found with similar measurements on, e.g., $n$-(Zn,Mn)O. It is shown that this striking difference in the values of the s-d coupling between $n$-type III-V and II-VI dilute magnetic semiconductors can be explained by a theory that takes into account the acceptor character of Mn in III-V compounds.
    Physical Review B 12/2014; 91(20). DOI:10.1103/PhysRevB.91.205204 · 3.74 Impact Factor
  • Source
    Tomasz Dietl
    [Show abstract] [Hide abstract]
    ABSTRACT: A physically transparent and mathematically simple semiclassical model is employed to examine dynamics in the central-spin problem. The results reproduce a number of previous findings obtained by various quantum approaches and, at the same time, provide information on the electron spin dynamics and Berry's phase effects over a wider range of experimentally relevant parameters than available previously. This development is relevant to dynamics of bound magnetic polarons and spin dephasing of an electron trapped by an impurity or a quantum dot, and coupled by a contact interaction to neighboring localized magnetic impurities or nuclear spins. Furthermore, it substantiates the applicability of semiclassical models to simulate dynamic properties of spintronic nanostructures with a mesoscopic number of spins.
    Physical Review B 10/2014; 91(12). DOI:10.1103/PhysRevB.91.125204 · 3.74 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Millikelvin magnetotransport studies are carried out on heavily $n$-doped wurtzite GaN:Si films grown on semi-insulating GaN:Mn buffer layers by metal-organic vapor phase epitaxy. The dependency of the conductivity on magnetic field and temperature is interpreted in terms of theories that take into account disorder-induced quantum interference of one-electron and many-electron self-crossing trajectories. The Rashba parameter $\alpha_{\text{R}}\,=\,(4.5 \pm 1)$ meV{\AA} is determined, and it is shown that in the previous studies of electrons adjacent to GaN/(Al,Ga)N interfaces, bulk inversion asymmetry was dominant over structural inversion asymmetry. The comparison of experimental and theoretical values of $\alpha_{\text{R}}$ across a series of wurtzite semiconductors is presented as a test of current relativistic ab initio computation schemes. It is found that electron-electron scattering with small energy transfer accounts for low temperature decoherence in these systems.
    Physical Review B 02/2014; 89(20). DOI:10.1103/PhysRevB.89.205201 · 3.74 Impact Factor
  • Source
    Cezary Śliwa, Tomasz Dietl
    [Show abstract] [Hide abstract]
    ABSTRACT: The relationship between the modern and classical Landau's approaches to carrier orbital magnetization is theoretically studied within the k.p formalism, taking dilute ferromagnetic (Ga,Mn)As as an example. It is shown that while the evaluation of hole magnetization within the modern theory does not require information on the band structure in a magnetic field, the number of basis wave functions must be much larger than in the Landau approach to achieve the same quantitative accuracy. A numerically efficient method is proposed, which takes advantages of these two theoretical schemes. The computed orbital magnetization is in accord with experimental values obtained by x-ray magnetic circular dichroism in (III,Mn)V compounds. The direct effect of the magnetic field on the hole spectrum is studied too, and employed to interpret a dependence of the Coulomb blockade maxima on the magnetic field in a single electron transistor of (Ga,Mn)As.
    Physical Review B 02/2014; 90(4). DOI:10.1103/PhysRevB.90.045202 · 3.74 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Magnetic properties of Ga 1−x Mn x N are studied theoretically by employing a tight binding approach to determine exchange integrals J i j characterizing the coupling between Mn spin pairs located at distances R i j up to the 16th cation coordination sphere in zinc-blende GaN. It is shown that for a set of experimentally determined input parameters there are no itinerant carriers and the coupling between localized Mn 3+ spins in GaN proceeds via superexchange that is ferromagnetic for all explored R i j values. Extensive Monte Carlo simulations serve to evaluate the magnitudes of Curie temperature T C by the cumulant crossing method. The theoretical values of T C (x) are in quantitative agreement with the experimental data that are available for Ga 1−x Mn x N with randomly distributed Mn 3+ ions with the concentrations 0.01 ≤ x ≤ 0.1.
    JEMS 2013, Rhodes, Greece; 08/2013
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Magnetooptical properties of (Ga,Mn)N layers containing various concentrations of Fe-rich nanocrystals embedded in paramagnetic (Ga,Fe)N layers are reported. Previous studies of such samples demonstrated that magnetization consists of a paramagnetic contribution due to substitutional diluted Fe ions as well as of ferromagnetic and antiferromagnetic components originating from Fe-rich nanocrystals, whose relative abundance can be controlled by the grow conditions. The nanocrystals are found to broaden and to reduce the magnitude of the excitonic features. However, the ferromagnetic contribution, clearly seen in SQUID magnetometry, is not revealed by magnetic circular dichroism (MCD). Possible reasons for differences in magnetic response determined by MCD and SQUID measurements are discussed.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A series of (Zn,Co)O layers with Co contents x up to 40% grown by atomic layer deposition have been investigated. All structures deposited at 160 ∘C show magnetic properties specific to II-VI dilute magnetic semiconductors with localized spins S=3/2 coupled by strong but short-range antiferromagnetic interactions resulting in low-temperature spin-glass freezing for x=0.16 and 0.4. At higher growth temperature (200∘C) metallic Co nanocrystals precipitate in two locations giving rise to two different magnetic responses: (i) a superparamagnetic contribution coming from volume disperse nanocrystals; (ii) a ferromagneticlike behavior brought about by nanocrystals residing at the (Zn,Co)O/substrate interface. It is shown that the dipolar coupling within the interfacial two-dimensional dense dispersion of nanocrystals is responsible for the ferromagneticlike behavior.
    Physical Review B 08/2013; 88(8):085204. DOI:10.1103/PhysRevB.88.085204 · 3.74 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate experimentally transport in gated microsctructures containing a band-inverted HgTe/Hg_{0.3}Cd_{0.7}Te quantum well. Measurements of nonlocal resistances using many contacts prove that in the depletion regime the current is carried by the edge channels, as expected for a two-dimensional topological insulator. However, high and non-quantized values of channel resistances show that the topological protection length (i.e. the distance on which the carriers in helical edge channels propagate without backscattering) is much shorter than the channel length, which is ~100 micrometers. The weak temperature dependence of the resistance and the presence of temperature dependent reproducible quasi-periodic resistance fluctuations can be qualitatively explained by the presence of charge puddles in the well, to which the electrons from the edge channels are tunnel-coupled.
    Physical Review B 07/2013; 88(16). DOI:10.1103/PhysRevB.88.165309 · 3.74 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Nanometric inclusions filled with nitrogen, located adjacent to FenN (n¼3 or 4) nanocrystals within (Ga,Fe)N layers, are identified and characterized using scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). High-resolution STEM images reveal a truncation of the Fe-N nanocrystals at their boundaries with the nitrogen-containing inclusions. A controlled electron beam hole drilling experiment is used to release nitrogen gas from an inclusion in situ in the electron microscope. The density of nitrogen in an individual inclusion is measured to be 1.460.3 g/cm3. These observations provide an explanation for the location of surplus nitrogen in the (Ga,Fe)N layers, which is liberated by the nucleation of FenN (n>1) nanocrystals during growth.
    Journal of Applied Physics 07/2013; 114(3):033530. DOI:10.1063/1.4816049 · 2.19 Impact Factor
  • Source
    Tomasz Dietl, Hideo Ohno
    [Show abstract] [Hide abstract]
    ABSTRACT: This review compiles results of experimental and theoretical studies on thin films and quantum structures of semiconductors with randomly distributed Mn ions, which exhibit spintronic functionalities associated with collective ferromagnetic spin ordering. Properties of p-type Mn-containing III-V as well as II-VI, III-VI, IV-VI, I-II-V, and elemental group IV semiconductors are described paying particular attention to the most thoroughly investigated system (Ga,Mn)As that supports the hole-mediated ferromagnetic order up to 190 K for the net concentration of Mn spins below 10%. Multilayer structures showing efficient spin injection and spin-related magnetotransport properties as well as enabling magnetization manipulation by strain, light, electric fields, and spin currents are presented together with their impact on metal spintronics. The challenging interplay between magnetic and electronic properties in topologically trivial and non-trivial systems is described, emphasizing the entangled roles of disorder and correlation at the carrier localization boundary. Finally, the case of dilute magnetic insulators is considered, such as (Ga,Mn)N, where low temperature spin ordering is driven by short-ranged superexchange that is ferromagnetic for certain charge states of magnetic impurities.
    ChemInform 07/2013; 86(1). DOI:10.1103/RevModPhys.86.187
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Molecular beam epitaxy has been employed to obtain Ga1-xMnxN films with x up to 10% and Curie temperatures T_C up to 13 K. The magnitudes of T_C and their dependence on x, T_C(x) ~ x^m, where m = 2.2 +/- 0.2 are quantitatively described by a tight binding model of superexchange interactions and Monte Carlo simulations of T_C. The critical behavior of this dilute magnetic insulator shows strong deviations from the magnetically clean case (x = 1), in particular, (i) an apparent breakdown of the Harris criterion; (ii) a non-monotonic crossover in the values of the susceptibility critical exponent gamma_eff between the high temperature and critical regimes, and (iii) a smearing of the critical region, which can be explained either by the Griffiths effects or by macroscopic inhomogeneities in the spin distribution with a variance Delta x = (0.2 +/- 0.1)%.
    Physical review. B, Condensed matter 06/2013; 88(8). DOI:10.1103/PhysRevB.88.081201 · 3.66 Impact Factor
  • Source
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A simple fabrication method of silver (Ag) nanoislands on ZnO films is presented. Continuous wave and time-resolved photoluminescence and transmission are employed to investigate modifications of visible and UV emissions of ZnO brought about by coupling to localized surface plasmons residing on Ag nanoislands. The size of the nanoislands, determining their absorption and scattering efficiencies, is found to be an important factor governing plasmonic modification of optical response of ZnO films. The presence of the Ag nanoislands of appropriate dimensions causes a strong (threefold) increase in emission intensity and up to 1.5 times faster recombination. The experimental results are successfully described by model calculations within the Mie theory.
    Plasmonics 06/2013; 8(2):913-919. DOI:10.1007/s11468-013-9490-5 · 2.74 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The question of the correlation between magnetization, band splittings, and magnetic circular dichroism (MCD) in the fundamental gap region of dilute magnetic semiconductors is examined experimentally and theoretically taking the case of wurtzite Ga(1-x)FexN as an example. Magnetization and polarization-resolved reflectivity measurements have been performed down to 2K and up to 7T for x = 0.2%. Optical transitions originating from all three free excitons A, B and C, specific to the wurtzite structure, have been observed and their evolution with the magnetic field determined. It is demonstrated that the magnitude of the exciton splittings evaluated from reflectivity-MCD data can be overestimated by more than a factor of 2, as compared to the values obtained by describing the polarization-resolved reflectivity spectra with appropriate dielectric functions. A series of model calculations shows that the quantitative inaccuracy of MCD originates from a substantial influence of the magnetization-dependent exchange interactions not only on the spin splittings of excitons but also upon their linewidth and oscillator strength. At the same time, a method is proposed that allows to evaluate the field and temperature dependencies of the magnetization from MCD spectra. The accurate values of the excitonic splittings and of the magnetization reported here substantiate the magnitudes of the apparent $sp-d$ exchange integrals in (Ga,Fe)N previously determined.
    Physical review. B, Condensed matter 05/2013; 88(11). DOI:10.1103/PhysRevB.88.115208 · 3.66 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present an explanation of the long standing problem of the physical origin of uniaxial magnetic anisotropy energy (MAE) in epitaxially grown cubic (Ga,Mn)As. We prove that the uniaxial MAE originates from the energetic preference of the Mn ion dimers to incorporate along [-110] direction over the [110] one. This leads to lowering of the crystallographic symmetry of the epitaxially grown (Ga, Mn) As layers from cubic to C-2v, and in consequence, to the uniaxial magnetic anisotropy.
    31st International Conference on the Physics of Semiconductors (ICPS); 01/2013
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report on experiments allowing to set an upper limit on the magnitude of the spin Hall effect and the conductance by edge channels in quantum wells of PbTe embedded between PbEuTe barriers. We reexamine previous data obtained for epitaxial microstructures of n-type PbSe and PbTe, in which pronounced nonlocal effects and reproducible magnetoresistance oscillations were found. Here we show that these effects are brought about by a quasi-periodic network of threading dislocations adjacent to the BaF$_2$ substrate, which give rise to a p-type interfacial layer and an associated parasitic parallel conductance. We then present results of transport measurements on microstructures of modulation doped PbTe/(Pb,Eu)Te:Bi heterostructures for which the influence of parasitic parallel conductance is minimized, and for which quantum Hall transport had been observed, on similar samples, previously. These structures are of H-shaped geometry and they are patterned of 12 nm thick strained PbTe quantum wells embedded between Pb$_{0.92}$Eu$_{0.08}$Te barriers. The structures have different lateral sizes corresponding to both diffusive and ballistic electron transport in non-equivalent L valleys. For these structures no nonlocal resistance is detected confirming that PbTe is a trivial insulator. The magnitude of spin Hall angle gamma is estimated to be smaller than 0.02 for PbTe/PbEuTe microstructures in the diffusive regime.
    physica status solidi (b) 01/2013; 250(1). DOI:10.1002/pssb.201248431 · 1.61 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Owing to the variety of possible charge and spin states and to the different ways of coupling to the environment, paramagnetic centres in wide band-gap semiconductors and insulators exhibit a strikingly rich spectrum of properties and functionalities, exploited in commercial light emitters and proposed for applications in quantum information. Here we demonstrate, by combining synchrotron techniques with magnetic, optical and ab initio studies, that the codoping of GaN:Mn with Mg allows to control the Mn(n) (+) charge and spin state in the range 3≤n≤5 and 2≥S≥1. According to our results, this outstanding degree of tunability arises from the formation of hitherto concealed cation complexes Mn-Mg(k), where the number of ligands k is pre-defined by fabrication conditions. The properties of these complexes allow to extend towards the infrared the already remarkable optical capabilities of nitrides, open to solotronics functionalities, and generally represent a fresh perspective for magnetic semiconductors.
    Scientific Reports 10/2012; 2:722. DOI:10.1038/srep00722 · 5.58 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report on a monotonic reduction of Curie temperature in dilute ferromagnetic semiconductor (Ga,Mn)As upon a well controlled chemical-etching/oxidizing thinning from 15 nm down to complete removal of the ferromagnetic response. The effect already starts at the very beginning of the thinning process and is accompanied by the spin reorientation transition of the in-plane uniaxial anisotropy. We postulate that a negative gradient along the growth direction of self-compensating defects (Mn interstitial) and the presence of surface donor traps gives quantitative account on these effects within the p–d mean field Zener model with adequate modifications to take a nonuniform distribution of holes and Mn cations into account.
    Applied Physics Letters 06/2012; 100(26). DOI:10.1063/1.4731202 · 3.52 Impact Factor

Publication Stats

13k Citations
962.39 Total Impact Points

Institutions

  • 2002–2015
    • University of Warsaw
      • Institute of Theoretical Physics
      Warszawa, Masovian Voivodeship, Poland
  • 1999–2013
    • Tohoku University
      • • Institute for Materials Research
      • • Research Institute of Electrical Communication
      Japan
  • 1975–2013
    • Polish Academy of Sciences
      • Institute of Physics
      Warszawa, Masovian Voivodeship, Poland
  • 2005
    • University of Nottingham
      • School of Physics and Astronomy
      Nottingham, ENG, United Kingdom
  • 1996–2005
    • Institute of Physics of the Polish Academy of Sciences
      Warszawa, Masovian Voivodeship, Poland
    • Institute of Electron Technology
      Warszawa, Masovian Voivodeship, Poland
  • 2003
    • Weizmann Institute of Science
      Israel
    • Florida State University
      Tallahassee, Florida, United States
  • 1995–2002
    • University Joseph Fourier - Grenoble 1
      • Institut Néel
      Grenoble, Rhône-Alpes, France
    • University of Grenoble
      Grenoble, Rhône-Alpes, France
  • 1998
    • French National Centre for Scientific Research
      • Institut Néel
      Lutetia Parisorum, Île-de-France, France
  • 1992–1998
    • Johannes Kepler University Linz
      • Institute of Semiconductor and Solid State Physics
      Linz, Upper Austria, Austria
  • 1994
    • Montanuniversität Leoben
      Leoben, Styria, Austria