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M Windt

Publications and source records attributed to M Windt.

3 recordsLinked to original sources
PubMed2002

Experimental quest for orbital waves.

One challenge in condensed-matter physics is the experimental confirmation of a new kind of elementary excitation orbital waves, or orbitons, which are predicted to exist in an orbitally ordered state. Saitoh et al. have observed three peaks at 160, 144 and 126 meV in the Raman scattering of orbitally ordered lanthanum manganate (LaMnO(3)), and interpret these as evidence of orbitons. However, we find similar peaks in the optical conductivity, sigma(omega), of LaMnO(3) and point out that the direct observation of orbitons in sigma(omega) is prohibited by a selection rule. This suggests that the Raman peaks observed by Saitoh et al. arise from multiphonons, and that the existence of orbitons has yet to be experimentally confirmed.

Journal Article↗
PubMed2001

Observation of two-magnon bound states in the two-leg ladders of (Ca,La)(14)Cu(24)O(41).

Phonon-assisted two-magnon absorption is studied in the spin- 1/2 two-leg ladders of (Ca,La)(14)Cu(24)O(41) for E parallel c (legs) and E parallel a (rungs). We verify the theoretically predicted existence of two-magnon singlet bound states, which give rise to peaks at approximately equal to 2140 and 2800 cm(-1). The two-magnon continuum is observed at approximately equal to 4000 cm(-1). Two different theoretical approaches (Jordan-Wigner fermions and perturbation theory) describe the data very well for J parallel approximately equal to 1020-1100 cm(-1), J parallel/J perpendicular approximately equal to 1-1.2. At high energies, the magnetic contribution to sigma(omega) is strikingly similar in the ladders and in the undoped high-T(c) cuprates, which emphasizes the importance of strong quantum fluctuations in the latter.

Journal Article↗