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Search Results: 1 - 10 of 462026 matches for " A. Golnik "
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Anomalies of the infrared-active phonons in underdoped YBCO as an evidence for the intra-bilayer Josephson effect
D. Munzar,C. Bernhard,A. Golnik,J. Humlicek,M. Cardona
Physics , 1999, DOI: 10.1016/S0038-1098(99)00377-4
Abstract: The spectra of the far-infrared c-axis conductivity of underdoped YBCO crystals exhibit dramatic changes of some of the phonon peaks when going from the normal to the superconducting state. We show that the most striking of these anomalies can be naturally explained by changes of the local fields acting on the ions arising from the onset of inter- and intra-bilayer Josephson effects.
Slowing hot carrier relaxation in graphene using a magnetic field
P. Plochocka,P. Kossacki,A. Golnik,T. Kazimierczuk,C. Berger,W. A. de Heer,M. Potemski
Physics , 2009, DOI: 10.1103/PhysRevB.80.245415
Abstract: A degenerate pump--probe technique is used to investigate the non equilibrium carrier dynamics in multi--layer graphene. Two distinctly different dynamics of the carrier relaxation are observed. A fast relaxation ($\sim 50$ fs) of the carriers after the initial effect of phase space filling followed by a slower relaxation ($\sim 4$ ps) due to thermalization. Both relaxation processes are less efficient when a magnetic field is applied at low temperatures which is attributed to the suppression of the electron-electron Auger scattering due to the non equidistant Landau level spacing of the Dirac fermions in graphene.
Optically induced energy and spin transfer in non-resonantly coupled pairs of self-assembled CdTe/ZnTe quantum dots
T. Kazimierczuk,J. Suffczynski,P. Wojnar,A. Golnik,J. A. Gaj,P. Kossacki
Physics , 2008, DOI: 10.1103/PhysRevB.79.153301
Abstract: Asymmetrical horizontal interdot coupling was demonstrated to exist in a system of a single plane of self-assembled CdTe/ZnTe quantum dots. Photoluminescence excitation (PLE), second order photon correlation and optical orientation were used as main experimental tools. Each individual absorbing dot was identified by a sharp PLE resonance, assigned to neutral exciton transition, while the corresponding emission contained several excitonic transitions of different charge states in another single quantum dot different from the absorbing one. Energy and spin transfer dynamics were studied. A high efficiency of spin transfer was found from optical orientation in a vertical magnetic field (70%) as well as without the magnetic field (40%), in spite of a significant anisotropic exchange splitting of the absorbing dot. Coherent mechanism of linear-to-circular polarization conversion was identified, with an efficiency (43%) close to the theoretical limit of 50%.
Single-photon emission from the natural quantum dots in the InAs/GaAs wetting layer
T. Kazimierczuk,A. Golnik,P. Kossacki,J. Gaj,Z. Wasilewski,A. Babinski
Physics , 2011, DOI: 10.1103/PhysRevB.84.115325
Abstract: Time-resolved microphotoluminescence study is presented for quantum dots which are formed in the InAs/GaAs wetting layer. These dots are due to fluctuations of In composition in the wetting layer. They show spectrally sharp luminescence lines with a low spatial density. We identify lines related to neutral exciton and biexciton as well as trions. Exciton emission antibunching (second order correlation value of g^2(0)=0.16) and biexciton-exciton emission cascade prove non-classical emission from the dots and confirm their potential as single photon sources.
The anomaly of the oxygen bond-bending mode at 320 cm$^{-1}$ and the additional absorption peak in the c-axis infrared conductivity of underdoped YBa$_{2}$Cu$_{3}$O$_{7-δ}$ single crystals revisited by ellipsometricmeasurements
C. Bernhard,D. Munzar,A. Golnik,C. T. Lin,A. Wittlin,J. Huml{í}?ek,M. Cardona
Physics , 1999, DOI: 10.1103/PhysRevB.61.618
Abstract: We have performed ellipsometric measurements of the far-infrared c-axis dielectric response of underdoped YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ single crystals. Here we report a detailed analysis of the temperature-dependent renormalization of the oxygen bending phonon mode at 320 cm$^{-1}$ and the formation of the additional absorption peak around 400-500 cm$^{-1}$. For a strongly underdoped YBa$_{2}$Cu$_{3}$O$_{6.5}$ crystal with T$_{c}$=52 K we find that, in agreement with previous reports based on conventional reflection measurements, the gradual onset of both features occurs well above T$_{c}$ at T*$\sim $150 K. Contrary to some of these reports, however, our data establish that the phonon anomaly and the formation of the additional peak exhibit very pronounced and steep changes right at T$_{c}$. For a less underdoped YBa$_{2}$Cu$_{3}$O$_{6.75}$ crystal with T$_{c}$=80 K, the onset temperature of the phonon anomaly almost coincides with T$_{c}$. Also in contrast to some previous reports, we find for both crystals that a sizeable fraction of the spectral weight of the additional absorption peak cannot be accounted for by the spectral-weight loss of the phonon modes but instead arises from a redistribution of the electronic continuum. Our ellipsometric data are consistent with a model where the bilayer cuprate compounds are treated as a superlattice of intra- and inter-bilayer Josephson-junctions.
Introducing single Mn2+ ions into spontaneously coupled quantum dot pairs
M. Koperski,M. Goryca,T. Kazimierczuk,T. Smoleński,A. Golnik,P. Wojnar,P. Kossacki
Physics , 2013, DOI: 10.1103/PhysRevB.89.075311
Abstract: We present the photoluminescence excitation study of the self-assembled CdTe/ZnTe quantum dots doped with manganese ions. We demonstrate the identification method of spontaneously coupled quantum dots pairs containing single Mn2+ ions. As the result of the coupling, the resonant absorption of the photon in one quantum dot is followed by the exciton transfer into a neighboring dot. It is shown that the Mn2+ ion might be present in the absorbing, emitting or both quantum dots. The magnetic properties of the Mn2+ spin are revealed by a characteristic sixfold splitting of the excitonic line. The statistics of the value of this splitting is analyzed for the large number of the dots and gives the information on the maximum density of the neutral exciton wave function.
Anomalous peak in the superconducting condensate density of cuprate high T_{c} superconductors at a unique critical doping state
C. Bernhard,J. L. Tallon,Th. Blasius,A. Golnik,Ch. Niedermayer
Physics , 2000, DOI: 10.1103/PhysRevLett.86.1614
Abstract: The doping dependence of the superconducting condensate density, n_{s}^{o}, has been studied by muon-spin-rotation for Y_{0.8}Ca_{0.2}Ba_{2}(Cu_{1-z}Zn_{z})_{3}O_{7-\delta} and Tl_{0.5-y}Pb_{0.5+y}Sr_{2}Ca_{1-x}Y_{x}Cu_{2}O_{7}. We find that n_{s}^{o} exhibits a pronounced peak at a unique doping state in the slightly overdoped regime. Its position coincides with the critical doping state where the normal state pseudogap first appears depleting the electronic density of states. A surprising correlation between n_{s}^{o} and the condensation energy U_{o} is observed which suggests unconventional behavior even in the overdoped region.
Far-infrared c-axis conductivity of flux-grown Y$_{1-x}$Pr$_{x}$Ba$_{2}$Cu$_{3}$O$_{7}$ single crystals studied by spectral ellipsometry
C. Bernhard,T. Holden,A. Golnik,C. T. Lin,M. Cardona
Physics , 2000, DOI: 10.1103/PhysRevB.62.9138
Abstract: The far-infrared c-axis conductivity of flux-grown Y$_{1-x}$Pr$_{x}$Ba$_{2}$Cu$_{3}$O$_{7}$ single crystals with 0.2$\leq $x$\leq $0.5 has been studied by sepectral ellipsometry. We find that the c-axis response exhibits spectral features similar to deoxygenated underdoped YBa$_{2}$Cu$_{3}$O$_{7-\delta}$, i.e., a pseudogap develops in the normal state, the phonon mode at 320 cm$^{-1}$ exhibits an anomalous T-dependence and an additional absorption peak forms at T. This suggests that the T$_{c}$ suppression in flux grown Pr-substituted crystals is caused by a decrease of the hole content and/or by carrier localization rather than by pair breaking.
Coherent precession of an individual 5/2 spin
M. Goryca,M. Koperski,P. Wojnar,T. Smoleński,T. Kazimierczuk,A. Golnik,P. Kossacki
Physics , 2014, DOI: 10.1103/PhysRevLett.113.227202
Abstract: We present a direct observation of a coherent spin precession of an individual Mn$^{2+}$ ion, having both electronic and nuclear spins equal to 5/2, embedded in a CdTe quantum dot and placed in magnetic field. The spin state evolution is probed in a time-resolved pump-probe measurement of absorption of the single dot. The experiment reveals subtle details of the large-spin coherent dynamics, such as non-sinusoidal evolution of states occupation, and beatings caused by the strain-induced differences in energy levels separation. Sensitivity of the large-spin impurity on the crystal strain opens the possibility of using it as a local strain probe.
Efficient injection of spin-polarized excitons and optical spin orientation of a single Mn2+ ion in a CdSe/ZnSe quantum dot
T. Smoleński,W. Pacuski,M. Goryca,M. Nawrocki,A. Golnik,P. Kossacki
Physics , 2014,
Abstract: Circularly polarized optical excitation is used to demonstrate the efficient injection of spin-polarized excitons to individual self-assembled CdSe quantum dots in ZnSe barrier. The exciton spin-transfer is studied by means of polarization-resolved single dot spectroscopy performed in magnetic field applied in Faraday configuration. Detailed analysis of the neutral exciton photoluminescence spectra reveals the presence of exciton spin relaxation during its lifetime in a quantum dot. This process is seen for both nonmagnetic dots and those containing single Mn$^{2+}$ ions. Taking this into account we determine the spin-polarization degree of excitons injected to a dot under circularly polarized below-the-barrier optical excitation at 488 nm. It is found to be close to 40% in the entire range of the applied magnetic field. Exploiting the established spin-conserving excitation channel we demonstrate the optical spin orientation of a single Mn$^{2+}$ ion embedded in a CdSe/ZnSe quantum dot.
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