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A. Koitzsch

Publications and source records attributed to A. Koitzsch.

42 records · Page 3Linked to original sources
arXiv2003

Low-energy excitations around (π/2, π/2) points in the pseudogap phase of Nd_1.85Ce_0.15CuO_4

Polarized electronic Raman scattering from the NCCO superconductor at optimal electron doping (T_c=22 K) reveals the formation of an anisotropic pseudogap below a characteristic temperature T* ~ 220 K and energy E*_g = 850 cm-1. Below T* a pronounced suppression of the incoherent spectral weight below E*_g in the nodal directions of k-space is observed. This is concomitant with the emergence of long-lived excitations in the vicinity of the (π/2, π/2) points that do not contribute to the optical conductivity.

cond-mat.str-el↗
arXiv2003

Doping dependence of the mass enhancement in (Pb,Bi)_2 Sr_2 Ca Cu_2 O_8 at the antinodal point in the superconducting and normal state

Angle-resolved photoemission spectroscopy (ARPES) is used to study the mass renormalization of the charge carriers in the high-T_c superconductor (Pb,Bi)_2Sr_2CaCu_2O_8 in the vicinity of the (pi,0) point in the superconducting and the normal state. Using matrix element effects at different photon energies and due to a high momentum and energy resolution the bonding and the antibonding bands could be separated in the whole dopant range. A huge anisotropic coupling to a bosonic collective mode is observed below T_c for both bands in particular for the underdoped case. Above T_c, the more isotropic coupling to a continuum or a mode at much higher energy is significantly weaker.

cond-mat.supr-con↗
arXiv2002

What the resonance peak does

High-resolution angle-resolved photoemission with variable excitation energies is used to disentangle bilayer splitting effects and intrinsic (self-energy) effects in the electronic spectral function near the ($π$,0)-point of differently doped (Pb,Bi)$_2$Sr$_2$CaCu$_2$O$_{8+δ}$. In contrast to overdoped samples, where intrinsic effects at the ($π$,0)point are virtually absent, we find in underdoped samples \textit{intrinsic} effects in the superconducting-state ($π$,0) spectra of the antibonding band. This intrinsic effect is present only below the critical temperature and weakens considerably with doping. Our results give strong support for models which involve a strong coupling of electronic excitations with the resonance mode seen in inelastic neutron scattering experiments.

cond-mat.supr-con↗
arXiv2002

Nonmonotonic d_{x^2-y^2} Superconducting Order Parameter in Nd_{2-x}Ce_xCuO_4

Low energy polarized electronic Raman scattering of the electron doped superconductor Nd_1.85Ce_0.15CuO_4 (T_c=22 K) has revealed a nonmonotonic d_{x^2-y^2} superconducting order parameter. It has a maximum gap of 4.4 k_BT_c at Fermi surface intersections with antiferromagnetic Brillouin zone (the ``hot spots'') and a smaller gap of 3.3 k_BT_c at fermionic Brillouin zone boundaries. The gap enhancement in the vicinity of the ``hot spots'' emphasizes role of antiferromagnetic fluctuations and similarity in the origin of superconductivity for electron- and hole-doped cuprates.

cond-mat.supr-con↗
arXiv2001

Antiferromagnetism in CaCu$_{3}$Ti$_{4}$O$_{12}$ studied by magnetic Raman spectroscopy

For CaCu$_{3}$Ti$_{4}$O$_{12}$ -- an insulator that exhibits a giant dielectric response above 100 K -- Cu$^{2+}$ antiferromagnetic spin ordering has been investigated by magnetic Raman scattering and magnetization measurements. Below the Néel temperature, T$_{N} = 25$ K, magnetic excitations have been identified. Above T$_{N}$ Raman spectra reveal short-range antiferromagnetic fluctuations that increase with cooling like T$^{-1}$. No deviations from Curie-Weiss law have been observed above T$_{N}$.

cond-mat.str-el↗